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Biodiversity within dry forests of the interior of British Columbia : the role of aspen and stand structure Oaten, Dustin Kyle 2007

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B I O D I V E R S I T Y W I T H I N D R Y F O R E S T S OF T H E I N T E R I O R OF B R I T I S H C O L U M B I A : T H E R O L E OF A S P E N A N D S T A N D S T R U C T U R E by D U S T I N K Y L E O A T E N B N R S . , Thompson Rivers University, 2003 A THESIS S U B M I T T E D I N P A R T I A L F U L F I L M E N T OF T H E R E Q U I R E M E N T S F O R T H E D E G R E E OF M A S T E R OF S C I E N C E in T H E F A C U L T Y OF G R A D U A T E S T U D I E S (Forestry) T H E U N I V E R S I T Y OF B R I T I S H C O L U M B I A A P R I L 2007 © Dustin Ky le Oaten, 2007 A B S T R A C T The dry interior forests of British Columbia are composed of contiguous coniferous forests dominated by Douglas-fir (Pseudotsuga menziesii), with a small portion consisting of trembling aspen (Populus tremuloides). These aspen trees are of particular interest as there is evidence that they may support a relatively abundant and diverse faunal community. However, this potential has not been extensively explored within these forests. Two bioindicator taxa, small mammals and cavity-nesting birds, were investigated within aspen stands near Kamloops, British Columbia, Canada during 2005 and 2006, and were compared to neighbouring Douglas-fir and mixedwood stands. Seven thousand ninety seven captures of 12 small mammal species were made during 15,761 trap nights, with 48% of captures within aspen stands. Seven species were numerically dominant within these stands including the deer mice (Peromyscus maniculatus), southern red-backed vole (Clethrionomys gapperi), long-tailed vole (Microtus longicaudus), montane vole (Microtus montanus), meadow vole (Microtus pennsylvanicus), and the northwestern chipmunk (Tamias amoenus). Eight stand level attribute variables were highly correlated with total small mammal abundance: percent aspen, total plant cover, number of grass species, snag density (stems/ha), C W D volume (m3/ha), plant richness, and shrub and herb cover. Fourteen cavity-nesting bird species were detected 1541 times during 288 point count surveys, with 48% of detections within aspen stands. Four species dominated the counts: three weak secondary cavity excavators and a single primary cavity excavator. The total abundance of cavity-nesting bird species was correlated with total volume of C W D (m /ha), snag volume (m /ha), snag density (stems/ha), downed C W D volume (m /ha) and percent aspen. Overall, the pure stands of aspen supported the largest numbers and diversity of small mammals and birds; these results highlight the importance of aspen stands as they may serve as biodiversity 'hotspots' within dry interior British Columbia forests. Forest managers should incorporate the maintenance of these stands into their long-term management plans. i i T A B L E O F C O N T E N T S A B S T R A C T ... ' . . i i T A B L E O F C O N T E N T S .- i i i LIST O F T A B L E S v i i A C K N O W L E D G E M E N T S , xi i D E D I C A T I O N '. : ; x i i i 1.0 C H A P T E R O N E - B I O D I V E R S I T Y , I N D I C A T O R S A N D A S P E N 1 1.1 I N D I C A T O R SPECIES A N D B I O D I V E R S I T Y 1 1.2 H A B I T A T S E L E C T I O N A N D H O M E R A N G E 2 1.3 S T A N D A T T R I B U T E S . . . 3 1.4 F O R E S T M A N A G E M E N T A N D B I O D I V E R S I T Y : 3 1.5 A S P E N A N D D R Y I N T E R I O R F O R E S T S 4 1.6 O B J E C T I V E S 5 1.7 S T U D Y A R E A S 6 1.8 L I T E R A T U R E C I T E D 10 2.0 C H A P T E R T W O - S T A N D C H A R A C T E R I S T I C S W I T H I N A S P E N , M I X E D W O O D A N D D O U G L A S - F I R F O R E S T S I N T H E I N T E R I O R O F B R I T I S H C O L U M B I A , C A N A D A 15 2.1 I N T R O D U C T I O N 15 2.2 M E T H O D S ..... '. 17 2.2.1 S T U D Y A R E A S 17 2.2.2 S T A N D S T R U C T U R E 17 2.2.3 U N D E R S T O R Y V E G E T A T I O N 18 2.2.4 D A T A A N A L Y S I S : 18 i i i 2.3 R E S U L T S 19 2.3.1 S T A N D S T R U C T U R E 19 2.3.2 C O A R S E W O O D Y D E B R I S 19 2.4 D I S C U S S I O N 27 2.5 C O N C L U S I O N 29 2.6 L I T E R A T U R E C I T E D 31 3.0 C H A P T E R T H R E E - S M A L L M A M M A L C O M M U N I T I E S W I T H I N T H R E E S T A N D T Y P E S W I T H I N T H E D R Y I N T E R I O R F O R E S T S OF B R I T I S H C O L U M B I A , C A N A D A 3.1 I N T R O D U C T I O N 36 3.2 M E T H O D S 39 3.2.1 S T U D Y A R E A S 39 3.2.2 S M A L L M A M M A L T R A P P I N G 39 3.2.3 D A T A A N A L Y S I S 40 3.3 R E S U L T S 42 3.3.1 D E N S I T Y E S T I M A T E S 43 3.3.2 T O T A L A B U N D A N C E OF A L L SPECIES 48 3.3.3 T R A P P I N G S U C C E S S 49 3.3.4 I N D I V I D U A L C H I P M U N K A N D S O R E X C A P T U R E S 50 3.3.5 P I N A N T A N L A K E C O M P A R I S O N 52 3.3.6 C O R R E L A T I O N A N A L Y S I S OF A B U N D A N C E A N D A T T R I B U T E S 53 3.3.7 H A B I T A T Q U A L I T Y 56 3.3.8 C L U S T E R A N A L Y S I S 57 3.3.9 SPECIES D I V E R S I T Y 58 iv 3.4 D I S C U S S I O N 63 3.5 C O N C L U S I O N 69 3.6 L I T E R A T U R E C I T E D 70 4.0 C H A P T E R F O U R - C A V I T Y - N E S T I N G B I R D C O M M U N I T I E S W I T H I N T H E D R Y I N T E R I O R F O R E S T S OF B R I T I S H C O L U M B I A , C A N A D A : T H E R O L E OF A S P E N 77 4.1 I N T R O D U C T I O N 77 4.2 M E T H O D S 79 4.2.1 S T U D Y A R E A S 79 4.2.2 C A V I T Y - N E S T I N G B I R D S U R V E Y S 80 4.2.3 D A T A A N A L Y S I S 80 4.3 R E S U L T S 83 4.3.1 T O T A L D E T E C T I O N S 83 4.3.2 T O T A L SPECIES D E T E C T I O N S 84 4.3.3 M E A N N U M B E R OF D E T E C T I O N S 85 4.3.4 W E A K A N D P R I M A R Y C A V I T Y - E X C A V A T I N G C O M P A R I S O N 87 4.3.5 C O R R E L A T I O N 90 4.3.6 C L U S T E R A N A L Y S I S 91 4.3.7 SPECIES D I V E R S I T Y 96 4.4 D I S C U S S I O N 99 4.5 C O N C L U S I O N 103 4.6 L I T E R A T U R E C I T E D 104 5.0 C H A P T E R F I V E - M A N A G E M E N T C O N S I D E R A T I O N S A N D C O N C L U S I O N S . . 109 5.1 O V E R V I E W OF R E S U L T S 109 5.2 I M P L I C A T I O N S F O R A S P E N M A N A G E M E N T 109 5.2.1 A S P E N E C O S Y S T E M M A N A G E M E N T 109 5.2.2 S T A N D M A N A G E M E N T 111 5.3 F U T U R E W O R K A N D C O N S I D E R A T I O N S 112 5.3.1 S M A L L M A M M A L L I M I T A T I O N S A N D F U T U R E W O R K 112 5.3.2 C A V I T Y - N E S T I N G B I R D L I M I T A T I O N S A N F U T U R E W O R K 113 5.3.3 S T A N D A T T R I B U T E L I M I T A T I O N S A N D F U T U R E W O R K 113 5.4 C O N C L U S I O N 114 5.5 L I T E R A T U R E C I T E D 116 A P P E N D I X 1 - U B C R E S E A R C H E T H I C S B O A R D ' S C E R T I F I C A T E OF A P P R O V A L 120 A P P E N D I X 2 - V E G E T A T I O N T A B L E S . . 122 A P P E N D I X 3 - T R A P P I N G D A T E S 130 A P P E N D I X 4 - 2005 S M A L L M A M M A L C A P T U R E O V E R V I E W 131 A P P E N D I X 5 - 2006 S M A L L M A M M A L C A P T U R E O V E R V I E W 132 A P P E N D I X 6 - M E A N N U M B E R OF D E T E C T I O N S P E R P O I N T - C O U N T S T A T I O N 133 vi LIST OF T A B L E S Table 2.1 Stand structure attributes and results of A N O V A s 20 Table 2.2. Summary of characteristics of D C W D (volume and number o f pieces of debris in diameter and decay classes) within aspen, mixedwood, and Douglas-fir stands and results of A N O V A s exploring differences in these characteristics 22 Table 2.3 Summary of characteristics of S C W D (volume, snag density and number of pieces of debris in diameter and decay classes) within aspen, mixedwood, and Douglas-fir stands and results of A N O V A ' s exploring differences in these characteristics 23 Table 3.1 Total numbers of individuals captured of each small mammal species within aspen (AT) , mixedwood (Mix) , and Douglas-fir (FD) stands during 2005 and 2006. Bold type indicates highest value 43 Table 3.2 Spearman's rank correlation matrix of the relationship between stand attributes and mean abundance of each small mammal species. Only correlation values > 0.50 are included and the numbers in bold represent the highest positive or negative correlation values, r > 0.50. P M = (P. maniculatus), C G = (C. gapperi), M M = (M. montanus), M P = (M. pennsylvanicus), M L = (M. longicaudus), Z P = ( Z princeps), and T A = (T. amoenus) 54 Table 3.3 Spearman's rank correlation matrix of the relationship between the mean abundance of each small mammal species. Numbers in bold represent significant correlation values where r > 0.50 55 Table 3.4 Small mammal diversity indices for 2005 and each study site. Rank is based on the average rank of all diversity values 61 Table 3.5 Small mammal diversity indices for 2006 and each study site. Rank is based on the average rank of all diversity values 62 Table 4.1 Cavity-nesting birds sampled during study as well as playback order and guild association 81 Table 4.2 Mean number of detections per point count station for all cavity-nesting bird species recorded in aspen (AT) , mixedwood ( M I X ) , and Douglas-fir (FD) stands for both sampling years, and results of A N O V A analysis, t-tests conducted at a = 0.017, examining differences in the number of detections of each species. Bo ld type indicates stand type with highest mean value. See Appendix 6 for exact test statistical values 86 Table 4.3 Results of Spearman's rank correlation analysis of the total abundance of cavity-nesting birds and the total abundance of primary cavity-excavating (PCE) and weak cavity-excavating (WCE) species with various stand level attributes. Bold values represent correlation coefficients and values in parantheses are significance values 92 Table 4.4 Results of Spearman's rank correlation analysis between the respective abundance (mean number per point count station) of the cavity-nesting bird species. Bold values represent correlation coefficients and values in parantheses are significance values. Note: bird codes are available in Table 4.1 93 Table 4.5 2005 cavity-nesting bird diversity indices and stand rank, overall diversity, together with results of A N O V A s and post-hoc tests analyzing differences in these indices between stand types 97 Table 4.6 2006 cavity-nesting bird diversity indices and stand rank, overall diversity, together with results of A N O V A s and post-hoc tests analyzing differences in these indices between stand types 98 Table 5.1 Overview of results showing measurement, pattern and significance for each focal taxa/attribute measured. Note: A = highest in aspen, M = highest in mixedwood, and D F = highest in Douglas-fir 110 LIST OF F I G U R E S Figure 1 ; 1 Schematic overview of study region (A) and extent of the interior Douglas-fir B E C zone in British Columbia, Canada (B) as well as the relative location of the study area (circle) 7 Figure 1.2 Relative study block location near Kamloops, British Columbia, Canada. Note: (A) aspen, (O) mixedwood and ( • ) Douglas-fir sites. Badger Lake (A3, M 3 , F3) and Pinantan Lake (A4, M 4 , F4) study blocks contained single replicates and the Monte Lake ( A l , A 2 , M l , M 2 , F l , F2) study block contained two replicates each of aspen (A), mixedwood (M) and Douglas-fir (F) stands 8 Figure 1.3 Photographs of typical (A) aspen (Populus tremuloides), (B) mixedwood, and (C) Douglas-fir (Pseudotsuga menziesii) stands 9 Figure 2.1 Total coarse woody debris in aspen (AT) , mixedwood (M) and Douglas-fir (FD) stands within the dry forests of the interior of British Columbia, Canada 21 Figure 2.2 Snag densities at each study site as well as the relative proportion of each of four size classes 21 Figure 2.3 Total species richness of herbs, shrubs and grasses for each study site 24 Figure 2.4 Plant richness and total plant cover (%) for each study site. Note: aspen stands had values consistently higher than either of the other stand types for both variables 25 Figure 2.5 Total percent cover of herbs, shrubs and grasses for each study site. Note: all aspen stands have values consistently higher for both shrub and herb cover but differences in grass cover are more variable 27 Figure 3.1 Total number of captures of small mammals within each stand type and each trapping session 44 Figure 3.2 Population density and standard error for C. gapperi within all three stand types and all six trapping periods 45 Figure 3.3 Population density and standard error for P. maniculatus within all three stand types and all six trapping periods 45 Figure 3.4 Population density and standard error for M. montanus within all three stand types and all six trapping periods 46 Figure 3.5 Population density and standard error for M. longicaudus within all three stand types and all six trapping periods 47 ix Figure 3.6 Population density and standard error for M. pennsylvanicus within all three stand types and all six trapping periods 48 Figure 3.7 Trapping success (animals/trap night), an index of overall abundance, for each stand type and trapping session 49 Figure 3.8 Total number of captures of northwestern chipmunks for each stand type and each trapping session 51 Figure 3.9 Number of Sorex spp. captures for each stand type and each trapping session 51 Figure 3.10 Comparison of trapping success (animals/trap night) for the aspen (AT) , mixedwood ( M I X ) and Douglas-fir (DF) sites at Pinantan Lake for each year, with the average for each stand type (n = 4). The aspen site at Pinantan Lake had similar values to the overall aspen stand averages but large differences can be seen with the mixedwood and Douglas-fir averages and these overall stand averages 52 Figure 3.11 Ratio of adults to juveniles within the small mammal communities of aspen, mixedwood and Douglas-fir stands 56 Figure 3.12 Proportion of reproductive adult females within the small mammal populations within aspen, mixedwood and Douglas-fir stands. Data points represent proportions along with standard error 57 Figure 3.13 Dendrogram showing results of a cluster analysis used to group study sites on the basis of similarities in small mammal communities 59 Figure 3.14 Dendrogram showing results of a cluster analysis used to group study sites on the basis of similarities in stand attributes (total plant cover, aspen cover, shrub cover, herb cover, snag density (stems/ha), snag volume (m3/ha), total C W D volume (m3/ha), grass species, stand age, and C W D volume (m3/ha) 60 Figure 4.1 Total number of cavity-nesting bird species detections for each year (2005 and 2006). Note: A T refers to aspen, M I X to mixedwood, and F D to Douglas-fir 84 Figure 4.2 Total number of cavity-nesting bird detections by species and stand type. See Table 4.1 for species codes 85 Figure 4.3 Comparison of total number of detections by stand type and year (2005 and 2006) for primary cavity-excavating (PCE) and weak cavity-excavating (WCE) birds. Note: A T refers to aspen, M I X to mixedwood, and F D to Douglas-fir and 05 and 06 correspond to 2005 and 2006 87 Figure 4.4 The relative abundance of primary cavity-excavating and weak cavity-excavating species within each study site 89 x Figure 4.5 Number of detections per point count station for the five species that showed a marked change during the two-years of sampling. Four weak cavity-excavating species increased in abundance while one primary cavity-excavating species ( H A W O ) decreased in abundance. A l l other species were slightly more abundant in the second year or showed no change 90 Figure 4.6 Dendrogram showing results of a cluster analysis used to group study sites on the basis of similarities in the abundance of each cavity-nesting bird species 94 Figure 4.7 Dendrogram showing results of a cluster analysis used to group study sites on the basis of similarities in the abundance of the communities of primary cavity-excavating and weak cavity-excavating birds 95 xi A C K N O W L E D G E M E N T S I would like to thank those who provided me with support during this work. This includes Dr. Kar l Larsen for his supervision and support during all phases of this thesis. Dr. Larsen also provided me with insight and was instrumental in the completion of this thesis. I would also like to thank Dr. John Nelson for his understanding and support while at U B C . I am also indebted to Dr. Tom Sullivan (small mammals) and Dr. Peter Marshall (coarse woody debris) for helping me with these portions of the thesis. Dr. Walt Klenner from the B C Ministry of Forests also was generous enough to lend me a large number of small mammal traps, for which 1 am thankful. I would also like to thank those that helped me with field work: Steve Symes, Helen Kerr, Mike Epp, Beckie Rozander, and Tiffany Cobb - their hard work and commitment made this project possible. Last, but not least, I would like to thank my wife Leanne, for her patience and support and for taking care of our kids. I also owe gratitude to my kids, Joe, Madison, and Kait l in , for their enthusiasm, imagination, and energy, which were infectious and fueled my commitment to this work. This work was generously supported by the Sustainable Forest Management Network, the National Science and Engineering Research Council of Canada, the Forest Sciences Program, Tolko Industries Ltd. , B C Ministry of Forests, and Thompson Rivers University. A l l research was conducted with the approval of the University of British Columbia Research Ethics Board (Appendix 1.0) and Thompson Rivers University Research Ethics - Animal Subjects Committee. x i i D E D I C A T I O N For my wife Leanne, and our kids, Joe, Madison and Kaitlin xi i i 1.0 C H A P T E R O N E - B I O D I V E R S I T Y , I N D I C A T O R S A N D A S P E N 1.1 I N D I C A T O R SPECIES A N D B I O D I V E R S I T Y Biodiversity may be defined as the variety and variability among living organisms and the ecological complexes in which they occur (Office of Technology Assessment 1987). The spatial pattern of biodiversity has frequently been measured at different levels including alpha (a), beta (P), and gamma (y) diversity (Whitaker 1960). Alpha diversity may be defined as the number of species within a sampling unit (Anderson et al. 2006) while beta diversity can be defined as the variation in species composition among sites (Legendre et al. 2005). Gamma diversity refers to the overall number of species within a defined geographic area (Anderson et al. 2006). Ecologists frequently attempt to measure beta diversity as it may play a central role in the functioning of ecosystems (Loreau et al. 2001), in the conservation of biodiversity, and in ecosystem management (Legendre et al. 2005). A reduction in beta diversity may cause a reduction in ecosystem-level processes (Srivastra and Vellend 2005) as well as in the potential resilience of a particular ecosystem to external pressures such as forest management (Fischer et al. 2006). As such, the measurement and management of beta diversity has become a central issue in ecosystem management (Thompson 2006). Biodiversity encompasses two different concepts of variety and variability: richness and evenness (Burton et al. 1992). When comparing the relative diversity of one area to another, indices of diversity are commonly used. Common indices include: species richness (the number of species present in a particular area), Simpson's D (Simpson 1949), Shannon-Wiener H ' (Pielou 1966) and MacArthur's (MacArthur and MacArthur 1961) diversity indices. These diversity indices include elements of richness and evenness in their calculations (Burton et al. 1992). These indices, along with indicator species, are commonly used for studies examining beta diversity (Thompson 2006). A n indicator species is a species or a taxonomic group that reflects the biotic or abiotic state of the environment, represents the impact of environmental change on a habitat, community or ecosystem, and/or indicates the diversity of other species (McGeoch 1998, and Rainio and Niemela 2003). Indicator species commonly are used for such studies, as it is normally impossible to measure all of the components of biodiversity; in addition, it often 1 becomes necessary to measure the diversity of a limited number of taxonomically-related species as a means of assessing overall species diversity - bioindicators (Holloway and Jardine 1968, Caro and O'Doherty 1999, and Mikusinski et al. 2001). Bioindicators can be defined as a species, taxonomic group or functional group that is indicative of the diversity of a subset of taxa, or of wholesale diversity, within an area (McGeoch 1998, and Rainio and Niemela 2003). Lindenmayer et al. (2000) further classify bioindicators as: (1) species whose presence or absence indicates presence or absence of some other species, (2) species whose addition or loss leads to major changes in abundance or occurrence of at least one other species, or (3) dominant species that provide a major part of the biomass or number of individuals. McGeoch (1998) and Noss (1990) also suggest that studies using bioindicators may be more effective i f groups of taxonomically related species are used to assess biodiversity. Several taxonomic groups have been suggested as having potential value for assessing regional biodiversity as bioindicators including small mammals and cavity-nesting birds (Mikusinski et al. 2001, and Pearce and Venier 2005). 1.2 H A B I T A T S E L E C T I O N A N D H O M E R A N G E Habitat selection is a strong factor influencing population dynamics and community organization (Pulliam and Danielson 1991). Two scales of habitat selection are likely to influence patterns of animal density in heterogeneous landscapes: foraging locations, and home range and dispersal ability (Morris 1992). Dispersal among patches, habitats, and populations represents a major component of a species' life history. Dispersal is crucial for the persistence of any species and has major ramifications on population and community dynamics (Morris 1992, and Morris et al. 2004). Habitat choice during foraging often is a product of an individual's home range size (Morris 1992) and the initial selection of this home range may be a driving force behind an individual's survival and reproductive success (Morris 1987). A s such, the scale of home range size and dispersal ability should be considered when selecting individual taxa as bioindicators. Small mammals and cavity-nesting birds display a range of dispersal ability and home range sizes (Sutherland et al. 2000, and Bowman et al. 2002). They also have been identified as potential bioindicators for assessing biodiversity (see Steele et al. 1984, 2 Croonquist and Brooks 1991, Bowers and Matter 1997, Carey and Harrington 2001, Sullivan and Sullivan 2001, Klenner and Sullivan 2003, and McShea et al. 2003 for small mammals, and Jarvinen and Vaisanen 1979, Croonquist and Brooks 1991, Bradford et al. 1998, Mikusinski et al. 2001, and Venier and Pearce 2004 for cavity-nesting birds). B y using a suite of bioindicators having a range of home range size and dispersal ability, as well as representing a variety of taxa, the estimate of biodiversity should be more inclusive of other species. 1.3 S T A N D A T T R I B U T E S A l l forest dwelling species, including bioindicators, potentially can be linked to forest structure at some scale. The amount, distribution and diversity of habitat elements such as standing coarse woody debris (SCWD) , downed coarse woody debris ( D C W D ) , as well as stand attributes and understory plant structure and diversity play vital roles in the life history of small mammals and cavity-nesting birds (see Hoyt and Hannon 2002 for birds, and Bowman et al. 2000 for small mammals). The amount, structure, and dynamics of S C W D and D C W D also can influence species composition, nutrient cycling and site productivity (Spies et al. 1988). A s such, it is important to examine the dynamics of these attributes within and between study sites to quantify the relationship between these variables and the presence, abundance and diversity of cavity-nesting birds and small mammals. 1.4 F O R E S T M A N A G E M E N T A N D B I O D I V E R S I T Y Patterns of species richness and community assemblages should be a major consideration when tailoring timber harvesting across landscapes composed of different forest types. Within British Columbia (BC), it has been suggested that the Interior Douglas-fir (IDF) biogeoclimatic (BEC) zone should be given a relatively high conservation priority due to a high degree of species richness as compared to other forest types (Hebert 2005). In fact, IDF B E C zone forests support the highest richness of vertebrate species of all other forested zones in B C (Bunnell 1995). To this end, current forest retention practices have focused on maintaining this forest type. However, the IDF zone is far from being a 3 homogenous forest type: most patches are dominated by Douglas-fir (Pseudotsuga menziesn), but a smaller amount may be composed primarily of aspen (Populus tremuloides), or a mixture of these and other tree species. Understanding the relative importance of these different habitats within the IDF is one of the next crucial steps in the overall forest management process. Selecting sites that are important for conservation requires that priority assignment is based partly on the contribution the area can make to representing overall biodiversity (Faith and Walker 1996). Traditionally, the identification of areas deserving high priority for protection has been guided by a number of different conservation criteria (Margules 1986). This includes the area's potential contribution to overall representation of biodiversity (Garson et al. 2002). Additionally, to begin to prioritize areas for conservation, biologists and managers need information on beta diversity patterns (Kerr 1997). A full assessment of the biodiversity of any habitat type is an extremely large i f not impossible undertaking. Surrogates or indicators for biodiversity, such as individual taxa or species assemblages have been used in priority site selection (Freemark et al. 2006). 1.5 A S P E N A N D D R Y I N T E R I O R F O R E S T S The aspen component of IDF forests is of particular interest as this stand type has generally been shown to have relatively high biotic diversity (Stelfox 1995, White et al. 1998, Griffiths-Kyle and Beier 2003, and Sheppard et al. 2006). Generally, the relatively large amount of structural diversity within aspen stands appears to play a strong role in this pattern (Stelfox 1995). This pattern has been studied mainly in boreal forest ecosystems (Gustafsson and Eriksson 1995, and Stelfox 1995) and the western United States (DeByle and Winokur 1985, Kay 1997, White et al. 1998, Bartos 2001, and Sheppard et al. 2006). Within dry interior B C forests, aspen usually is a minor forest type surrounded by, or included within, drier coniferous forests. A s such, there is a potential that these stands may serve as "oases" of plant and animal diversity (Sheppard et al. 2006). However, this potential pattern of diversity has not been closely explored. Within western North America, aspen may be a keystone species whose ecological importance to the landscape and biodiversity may only be bested by riparian areas (Campbell 4 and Bartos 2001). Aspen also may be an excellent indicator of ecological integrity because the species seldom grows from seed due to its demanding seed bed requirements (Kay 1997). There also is significant evidence that the aspen component within North American forests is being significantly reduced by fire exclusion, poor seedbed conditions and increased herbivory from ungulates and cattle (Kay 1997, White et al. 1998, and Bartos 2001). Because of the rarity of these stands, their potential importance to ecological integrity, and because remaining stands appear threatened by anthropogenic influence, it is important that we further our understanding of their contribution to biodiversity across the landscape. 1.6 O B J E C T I V E S The purpose of this thesis is to examine and compare the communities and relative diversity of cavity-nesting birds and small mammals within aspen, mixedwood, and Douglas-fir stands within the dry, interior forests of British Columbia. Several objectives were set in order to accomplish this. The first objective was to quantify.the degree to which aspen stands contribute to biodiversity within IDF forests as compared to mixedwood and Douglas-fir stands. I accomplished this by comparing and contrasting the community dynamics of cavity-nesting birds and small mammals within these three stand types. I also accomplished this by examining differences in species richness and diversity indices for small mammals and cavity-nesting birds. M y second objective was to examine the role of habitat attributes in influencing the dynamics and diversity of the focal taxa within these stands. This was accomplished by quantifying and comparing the plant communities, D C W D , S C W D and stand attributes within each of the stand types. I also used correlation and regression analysis to identify important predictor habitat attributes for each focal group. M y objective for Chapter 2 was to compare and contrast the stand attributes associated with each stand type. In Chapter 3, I examined the small mammal communities within each stand type and identify which stand type supports the most diverse and abundant communities of these animals. I also attempted to elicit how specific stand attributes may influence the richness and composition of small mammal communities. M y objective for Chapter 4 was to compare and contrast the communities of cavity-nesting birds within each stand type and to identify which stand type supports the most diverse and abundant 5 community of these birds. I also attempted to identify how specific stand attributes may influence the richness and composition of cavity-nesting bird communities. In my final chapter, I draw overall conclusions based on my research, and identify the potential management implications of my work. 1.7 S T U D Y A R E A S This study was located near Kamloops, British Columbia, Canada (50°43 ' N ; 120°25' W). A l l study sites were located within the Interior Douglas-fir (IDF) biogeoclimatic zone (Meidinger and Pojar 1991) (Figure 1.1). These sites are characterized by a warm, dry climatic regime with a relatively long growing season in which moisture deficits are common (Lloyd et al. 1990). Mature climax forests are dominated by Douglas-fir and a smaller component of lodgepole pine (Pinus contorta var. latifolia) or hybrid spruce (Picea glauca x engelmannii). Some mixedwood sites contain a component of Douglas-fir as well as aspen, but relatively few sites are dominated by the latter (Lloyd et al. 1990). The herb-dominated community includes pinegrass {Calamagrostis rubescens), birch-leaved spirea (Spiraea betufolia), soopolallie (Sheperdia canadensis), twinflower (Linnaea borealis), and kinnikinnick (Arctostaphylos uva-ursi) (Lloyd et al. 1990). Study sites ranged in elevation from 858-1137 m. Four replicate stands of aspen (A), mixedwood (M) and Douglas-fir (F) were selected within three geographically-distinct areas (blocks), Monte Lake ( A l , A 2 , M l , M 2 , F I , F2), Badger Lake (A3, M 3 , F3) and Pinantan Lake (A4, M 4 , F4), within the IDF dki (Thompson Dry Cool Interior Douglas-fir Variant) B E C zone (see Figure 1.2 for study site location and Figure 1.3 for photographs of typical study sites). The scarcity of aspen stands in the IDFdki, coupled with a required minimum stand size of 5 ha (to permit placement of sampling grids - see Chapters 3 and 4), reduced the number of potential aspen study sites to a small number. From there, logistical constraints were used to select the actual study sites. Corresponding mixedwood and Douglas-fir stands were selected based on proximity to the aspen stands and the same minimum stand size requirements. 6 Figure 1.1 Schematic overview of study region (A) and extent of the interior Douglas-fir B E C zone in British Columbia, Canada (B) as well as the relative location of the study area (circle). 7 Figure 1.2 Relative study block location near Kamloops, British Columbia, Canada. Note: (A) aspen, (O) mixedwood and ( • ) Douglas-fir sites. Badger Lake (A3, M 3 , F3) and Pinantan Lake (A4, M 4 , F4) study blocks contained single replicates and the Monte Lake ( A l , A 2 , M l , M 2 , F l , F2) study block contained two replicates each of aspen (A), mixedwood (M) and Douglas-fir (F) stands. 8 Figure 1.3 Photographs of typical (A) aspen (Populus tremuloides), (B) mixedwood, and (C) Douglas-fir (Pseudotsuga menziesu) stands. 9 1.8 L I T E R A T U R E C I T E D Anderson, M . J . , K . E . Ellingsen., and B . H . McArd le . 2006. 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Wildlife Society Bulletin. 26(3): 449-462. 14 2.0 C H A P T E R T W O - S T A N D C H A R A C T E R I S T I C S W I T H I N A S P E N , M I X E D W O O D A N D D O U G L A S - F I R F O R E S T S IN T H E I N T E R I O R OF B R I T I S H C O L U M B I A , C A N A D A 1 2.1 I N T R O D U C T I O N During the past decade, forest management generally has shifted to coarse-filter ecosystem management (Armstrong et al. 2003), with the conservation of biological richness recognized as an important ecological criterion of forest sustainability (Canadian Council of Forest Ministers 1995). This shift has occurred with the understanding that ecosystems are composed of plants, animals, microbes, and the physical environment that coexist as interdependent, functional units within climatically, geologically, and geographically defined boundaries (Welsh and Droege 2001). It also has recognized that traditional ecosystem management has a direct influence on the structure and dynamics of plants, snags, coarse woody debris and stand level attributes and that dynamics of these attributes directly affect biological diversity (Voller and Harrison 1998). The amount, distribution and diversity of habitat attributes such as standing coarse woody debris (SCWD) , downed coarse woody debris ( D C W D ) , as well as stand attributes and understory plant structure and diversity all play vital roles in the life history of many species (e.g. Robson and Holmes 1984, Ohmann et al. 1994, Hagan and Grove 1999, Bowman et al. 2000, Carey and Harrington 2001, Lohr et al. 2002, Hoyt and Hannon 2002, and Uyshen et al. 2004,). Cavities and loose bark of S C W D provide nesting and roosting sites, and D C W D provide cover, moist microclimate, nest and burrow sites, and travel routes (Loeb 1999) and food such as fungi, plants, and invertebrates (Bowman et al. 2000 and Harmon et al. 1986). The amount, structure, and dynamics of S C W D and D C W D also can influence species composition, nutrient cycling and site productivity (Spies et al. 1988). Descriptions of the characteristics and dynamics of S C W D , D C W D and plant communities within forest ecosystems are crucial to guiding managers in maintaining biodiversity and ecosystem productivity (Clark et al. 1998). Understanding the different roles of coarse woody debris ( C W D ) is very important to the effective management of forests, A version of this chapter wi l l be submitted for publication. 15 because removal of C W D can lead to unexpected alterations within ecosystems (Harmon et al. 1986, and Graham et al. 1994). Knowledge of the dynamics of C W D and plant communities is important for understanding stand dynamics and variation in wildlife habitat quality among stands. In temperate-zone landscapes dominated by coniferous forests, the amount of S C W D and D C W D as well as the density of deciduous trees (aspen, Populus and birch, Betula) have been found to influence the composition and species richness of forest faunal communities (Angelstam and Mikuskinski 1994). Although managers are increasingly aware that S C W D and D C W D are important components of forest ecosystems, they frequently lack information on what biomass and volume of this material is naturally present, and in what sizes, stem densities, and decay states (Clark et al. 1998). Within western North America, trembling aspen (Populus tremuloides) may be a keystone species whose ecological importance to the landscape and biodiversity may only be bested by riparian areas (Campbell and Bartos 2001). Generally, the relatively large amount of structural diversity within aspen stands appears to play a strong role in this pattern (Stelfox 1995). This pattern has been studied mainly in boreal forest ecosystems (Gustafsson and Eriksson 1995, and Stelfox 1995), and the western United States (Kay 1997, White et al. 1998, and Bartos 2001). It is unclear, however, as to the structural diversity of aspen forests within dry interior British Columbia forests. Plant diversity within aspen stands in the interior of British Columbia also has received little attention (but see description in L loyd et al. 1990). This pattern may be potentially important as the complex dynamics of these stands may allow for high species diversity as several microhabitats are likely available for different plant species (Lee and Sturgess 2001). There also is significant evidence that the aspen component within North American forests is being significantly reduced by historical forest management, fire suppression, poor seedbed conditions, and increased herbivory from ungulates and cattle (Kay 1997, White et al. 1998, and Bartos 2001). Because of the rarity of these stands, their potential importance to ecological integrity, and because remaining stands appear threatened by anthropogenic influences, it is important that we further our understanding as to the structural dynamics within these forests. A n understanding of these dynamics wi l l aid in our ability to manage these stands at the site and landscape level. 16 2.2 M E T H O D S 2.2.1 S T U D Y A R E A S This study is part of a larger study examining the biodiversity of aspen stands within the dry, interior forests of British Columbia, which also included an examination of cavity-nesting bird and small mammal communities (Chapters 3 and 4). The field work was conducted near Kamloops, British Columbia, Canada (50°43 ' N ; 120°25' W). A l l study sites were located within the Interior Douglas-fir, Thompson dry cool (IDFdki; dry precipitation regime; cool temperature regime) biogeoclimatic zone (Meidinger and Pojar 1991). Four replicate stands of aspen (A), mixedwood (M) and Douglas-fir (F) were selected within three geographically distinct areas (blocks), Monte Lake ( A l , A 2 , M l , M 2 , F I , F2), Badger Lake (A3, M 3 , F3) and Pinantan Lake (A4, M 4 , F4) (see Figure 1.2 - Chapter 1). The scarcity of aspen stands in the IDFdki, coupled with a required minimum stand size of 5 ha (to permit placement of sampling grids - see Chapters 3 and 4), reduced the number of potential aspen study sites to a small number. From there, logistical constraints were used to select the actual study sites. Corresponding mixedwood and Douglas-fir stands were selected based on proximity to the aspen stands and the same minimum stand size requirements. 2.2.2 S T A N D S T R U C T U R E Stand structure attribute sampling was carried out using three randomly-located 0.04 ha plots (20 x 20 m) (Mclntire and Fortin 2006). A l l live trees within these plots were identified to species and measured for height with the use of a clinometer and measuring tape. A diameter at breast height (DBH) tape was used to measure tree diameter. Tree ages were determined for mature trees within each site by increment boring (Spies et al. 1988) Douglas-fir and aspen trees at 1.3 m. A s aspen trees are susceptible to heart rot (Martin and Eadie 1999), the assessment of age of these trees was augmented by cutting a cross section from recently-fallen trees. Coring of aspen and Douglas-fir trees occurred during the late autumn as tree morphology had changed such that increment boring would be more successful (DeByle and Winokur 1985). A l l ages were determined in the lab using a compound microscope and no age correction factor was applied. 17 Five 0.1 hectare plots were randomly established within each study site to measure and quantify S C W D (Spies et al. 1988, and Bowman et al. 2000). Each dead tree (> 0.1 m in height) was identified to species and measured for D B H , height and decay class. The Maser decay class scale (Maser 1979) was used to assign a decay class to each tree (1 = sound to 5 = highly decayed). Standard species specific volume equations were used to calculate overall S C W D volume (Schlaegel 1975 and Hann et al. 1987). Five 0.05 ha plots also were established within each study site to sample for downed coarse woody debris ( D C W D ) (Spies et al. 1988). A l l logs £7.5 cm diameter (large end) that projected into the plots were measured. These logs were identified by species, measured for length (within the plot) and D B H at both ends. They also were given a decay-class rating based on the scale developed by Hautala et al. (2004). This scale allows for a simple identification of decay class for logs based on the hardness of the log and the amount of decay present. The volume of each piece was calculated from overall length and upper- and lower-end D B H using Smalian's formula for cubic volume (Wenger 1984). 2.2.3 U N D E R S T O R Y V E G E T A T I O N The line intercept method was used to examine the percent cover and diversity of plant species within each study site. Line intercept sampling is a method of sampling vegetation based on measurement of all plants intercepted by the vertical plane of randomly located lines of equal length (Canfield 1941). This line has length and vertical dimensions only. Three replicate 15m transects were sampled in each study site. The line locations were randomly, as was their associated azimuth. Plant species were identified in accordance with Hitchcock and Croonquist (1973) and Parish et al. (1996). 2.2.4 D A T A A N A L Y S I S Data for plants and stand structure were analyzed with a randomized-block A N O V A using the function P R O C G L M in S A S 9.1 (SAS Institute 2006). I tested for differences in the number of, and total cover of mosses, herbs, and shrubs as well as total species richness and cover between stand types. The volume of D C W D and S C W D as well as the overall volume of C W D (m3/ha) were calculated (Siitonen et al. 2000) and differences in these values were examined. Differences in all other stand attributes also were examined using 18 randomized-block A N O V A . Pairwise t-tests were used for all post-hoc tests with an associated significance level of 0.017 (0.05/number of replicate blocks). A l l data not conforming to normality or equal variance were subject to various transformations (Zar 1999). Percentage data were arcsine transformed to meet requirements of normality and equal variance (Zar 1999) and all mean data is reported with standard error. 2.3 R E S U L T S 2.3.1 S T A N D S T R U C T U R E There was no significant difference in tree density among the three stand types (F<\j = 3.83; P = 0.075): aspen stands averaged 427 ± 11.44 stems/ha, mixedwood 339 ± 39.94 stems/ha and Douglas-fir stands 261 ± 4.85 stems/ha (Table 2.1).. Mean D B H and height also were not significantly different within the stand types. Diameter at breast height and height in aspen stands averaged 24.88 ± 1.01 and 21.75 ± 0.76, mixedwood averaged 26.28 ± 1.40 and 20.98 ± 0.82 Douglas-fir stands averaged 29.98 ± 0.45 and 21.88 ± 0.53 respectively. Tree ages were significantly different (F^j = 6.22; P = 0.029) within the three stand types with aspen stands being significantly older than the mixedwood stands (fy.o 17,11 = 3.51; P = 0.010). There was no difference in stand age between aspen and Douglas-fir stands (fo.017,11 ~ 2.07; P = 0.077) and mixedwood and Douglas-fir stands C^o.017,11 = -1.43; P = 0.195). Tree age in aspen stands averaged 100.53 ± 0.67, mixedwood averaged 88.90 ± 1.59 and Douglas-fir stands averaged 93.98 ±1.59. 2.3.2 C O A R S E W O O D Y D E B R I S The mean volume of downed coarse woody debris (Figure 2.1) was also significantly different between stand types (Table 2.2). Aspen stands had an average volume of 66.67 ± 14.04 m 3/ha, the mixedwood stands, 24.42 ± 3.03 m 3/ha, and the Douglas-fir stands, 20.67 ± 4.48m 3/ha. Aspen stands also had significantly more (^4,7 = 13.69; P = 0.004) large (>25 cm) pieces than the mixedwood (/0.017,11 = 4.24; P = 0.004) or the Douglas-fir stands (fo.017,11 = 4.77; P = 0.002). In terms of decay classes, aspen stands had significantly more pieces in classes 2 and 4 ( F 4 l 7 = 8.33; P = 0.012 and F4j = 11.34; P = 0.009) than the mixedwood stands (fo.017,11 = 3.44; P = 0.011 and r 0 .oi7,n = 3.25; P = 0.015) (Figure 2.1). 19 Table 2.1 Stand structure attributes and results of A N O V A s . Site Tree Age D B H (cm) Height (m) % A T % F D Density (stems/ha) A l 96.8 ± 1.61 19.0 ± 0 . 7 5 17.2 ± 0 . 5 4 95.80 2.80 477 A 2 100.7 ± 1.49 25.5 ± 1.51 23.3 ± 1.74 72.00 0.00 434 A3 103.2 ± 1.96 27.0 ± 1.33 2 2 . 9 ± 1.18 71.90 15.60 430 A 4 101.4 ± 1.95 2 8 . 0 ± 1.10 23.6 ± 1.30 70.70 24.30 366 M l 86.9 ± 5 . 8 0 23.7 ± 1.05 21.6 ± 0 . 7 2 36.10 62.20 360 M 2 91.7 ± 2.33 20.7 ± 0 . 8 6 19.7 ± 0 . 5 0 23.50 72.80 553 M 3 88.1 ± 2 . 2 1 33.8 ± 2.10 25.2 ± 1.39 36.20 59.60 254 M 4 88.9 ± 2 . 2 4 26.9 ± 1.61 17.4 ± 1.06 34.20 65.80 187 FI 1 0 1 . 2 ± 5.21 32.0 ± 1.50 21.2 ± 0 . 7 0 0 95.40 284 F2 97.4 ± 6 . 4 3 29.9 ± 2 . 4 0 23.1 ± 1.10 0 96.70 243 F3 88.1 ± 10.12 30.4 ± 1.60 24.0 ± 0.90 0 100.00 270 F4 89.2 ± 4 . 6 1 27.6 ± 1.69 19.2 ± 0 . 9 9 0 100.00 247 ^ ( 4 , 7 ) ; P **6.22; 0.029 1.99; 0.206 0.14; 0.871 - _ 3.83; 0.075 ^0.017,11 a2.07; 0.077 ^0.017,11 b3.51; 0.010 ^0.017,11 c-1.43; 0.195 Note: Tree age, D B H and height data are mean values ± 1 SE. Statistical difference between aspen and Douglas-fir; bbetween aspen and mixedwood; cbetween Douglas-fir and mixedwood at a = 0.017. The mean volume of S C W D was significantly different between the three stand types ( F 4 / 7 = 12.97; P = 0.004) (Table 2.2). Aspen stands had greater volume than either the mixedwood (fo.017,11 = 2.68; P = 0.008) or the Douglas-fir stands (fo.017,11 = 4.89; P = 0.002). Aspen stands also had significantly higher snag density (F^i = 29.72; P = O.001) than either the mixedwood (/o.on.n = 7.02; P = <0.001) or the Douglas-fir stands ( /0 .017,11 = 6.27; P -<0.001). Aspen stands also had more small (<10 cm) and large (>25 cm) snags than the other stand types. There also were more pieces within decay Class 1 in aspen stands (F4J = 24.67; P = O.001) than the mixedwood (fo.017,11 = 4.35; P = O .001) or the Douglas-fir stands (to.017,11 = 6.95; P = O.001) . Figure 2.2 graphically displays the distribution of D C W D and S C W D within four size categories. 20 Figure 2.1 Total coarse woody debris in aspen (AT) , mixedwood (M) and Douglas-fir (FD) stands within the dry forests of the interior of British Columbia, Canada. 400 A l A2 A3 A4 M l M2 M3 M4 F l F2 F3 F4 ASPEN MIXEDWOOD DOUGLAS-FIR Figure 2.2 Snag densities at each study site as well as the relative proportion of each of four size classes. 21 Table 2.2 Summary of characteristics of D C W D (volume and number of pieces of debris in diameter and decay classes) within aspen, mixedwood, and Douglas-fir stands and results of A N O V A s exploring differences in these characteristics. Stands Aspen Mixedwood Douglas-fir Variable (n = 4) (n = 4) (n = 4) P ^0.017,11 P Volume (m /ha) 66.67 ± 14.04 24.41 ± 3 . 0 3 20.67 ± 4.48 *8.29 0.012 a3.44 0.011 b3.16 0.016 No. of wood pieces < 10 cm 26.50 ± 7 . 0 8 15.25 ± 2 . 1 7 6.25 ± 1.78 4.08 0.067 10-25 cm 48.50 ± 13.21 24.75 ± 4.32 16.75 ± 1.65 3.86 0.074 >25 cm 9.50 ± 0 . 5 5 2.75 ± 0.24 3.50 ± 0 . 8 5 *13.69 0.004 a4.24 b4.77 0.004 0.002 Decay classes 1 4.75 ± 3 . 5 5 2.00 ± 0.40 1.00 ± 0 . 4 1 0.76 0.505 2 46.50 ± 17.24 25.75 ± 2 . 6 9 11.00 ± 1.40 *7.33 0.016 b3.44 0.011 3 23.00 ± 9 . 0 3 9.50 ± 3 . 1 1 5.00 ± 1.59 1.69 0.252 4 8.50 ± 1.33 3.75 ± 2.17 4.00 ± 0.72 *11.34 0.009 b3.25 0.015 5 4.00 ± 0 . 8 2 1.73 ± 1.03 3.50 ± 2 . 3 6 0.62 0.565 Note: Data are means ± 1 SE. * refers to a significant difference by stand type where P ^ 0.05. arefers to a significantly higher value within aspen versus Douglas-fir and brefers to a significantly higher value in aspen versus mixedwood stands. There was no difference in any test for a difference between mixedwood and Douglas-fir stands (all P > 0.020). Table 2.3 Summary of characteristics of S C W D (volume, snag density and number of pieces of debris in diameter and decay classes) within aspen, mixedwood, and Douglas-fir stands and results of A N O V A s exploring differences in these characteristics. Stands Aspen Mixedwood Douglas-fir Variable (n = 4) (n = 4) (n = 4) P 7o.017,ll P Volume (m /ha) 51.02 ± 10.69 15.43 ± 5 . 8 3 3.46 ± 0 . 7 2 *12.97 <0.001 a4.89 0.002 b2.68 0.008 Snag Density 250.00 ± 4 2 . 3 2 99.17 ± 16.35 60.00 ± 15.33 *24.67 O.001 a6.95 O.001 b4.35 0.003 No . of wood pieces Diameter classes < 10 cm 4.25 ± 0.63 4.00 ± 1.96 3.75 ± 1.80 *9.02 0.012 a4.03 0.005 b3.18 0.016 10-25 cm 53.50 ± 8 . 7 4 19.25 ± 4 . 5 9 13.00 ± 2 . 4 8 >25 cm 19.25 ± 4 . 2 1 4.75 ± 1 . 3 1 3 .50± 1.55 *9.35 0.011 a3.89 0.006 b3.58 0.009 Decay classes 1 44.50 ± 6 . 8 0 11.25 ± 1 . 1 1 7.25 ± 1.93 *29.72 <0.001 a7.02 O.001 b6.27 <0.001 2 24.00 ± 15.20 13.00 ± 3 . 4 9 7.75 ± 2 . 1 7 0.79 0.492 3 5.25 ± 2 . 6 9 3.00 ± 2 . 0 4 3.00 ± 2 . 0 4 0.38 0.700 4 0.50 ± 0 . 5 0 0.75 ± 0.75 O.001 <0.001 <0.001 5 O.001 O.001 <0.001 <0.001 <0.001 Note: Data are means ± 1 SE. * refers to a significant difference by stand type where P < 0.05. arefers to a significantly higher value within aspen versus Douglas-fir and brefers to a significantly higher value in aspen versus mixedwood stands. There was no difference in any test for a difference between mixedwood and Douglas-fir stands. 2.3.3 U N D E R S T O R Y V E G E T A T I O N Mean plant species richness, total number of species identified, was significantly different between the three stand types (F^j = 6.87; P = 0.022) (Figure 2.3). Aspen stands had significantly higher mean species richness than mixedwood (fo.017,11 ~ 3.18; P = 0.014) and Douglas-fir stands (^0.017,11 = 3.18; P = 0.0154) but was similar for mixedwood and Douglas-fir stands (ro.017,11 = 0.05; P = 0.959). Mean species richness for herb species was different between the two of the three stand types (F4,7 = 5.12; P = 0.043). Aspen stands had significantly higher mean herb species richness than the Douglas-fir stands (/o.oi7,n = 3.14; P - 0.016) but this measurement was similar for aspen and mixedwood stands (fo.017,11 = 2.10; P = 0.074) and mixedwood and Douglas-fir stands (fo.017,11 = 1-05; P = 0.330). Mean species richness for moss and lichens was not significantly different between stand types (Fnj= 0.01; P = 0.991). Mean species richness for grass species was similar between the three stand types (F4/7 = 0.61; P = 0.568). Mean species richness for shrub species was similar between the three stand types (F 4 , 7 = 1.85; P = 0.230) (Figure 2.3). 36 —•— Herb richness O Shrub richness — T — Grass richness 4 0 8 A l A2 A3 A4 M l M2 M3 M4 Fl F2 F3 F4 ASPEN MIXEDWOOD DOUGLAS-FIR Figure 2.3 Total species richness of herbs, shrubs and grasses for each study site. 24 Mean total percent cover for all plant species (Figure 2.4) was significantly different within the three stand types ( F 4 i 7 = 34.37; P = <0.001) with aspen stands having significantly higher mean total percent cover than the Douglas-fir (?o.o 17,11 = 7.79; P = <0.001) and mixedwood stands ( /0 .017.11 = 6.35; P = O.001) . The mixedwood and Douglas-fir stands had similar mean total percent cover (fo.017,11 - 1.45; P = 0.191). There also was a significant difference in the mean percent cover of bare ground between the three stand types (F^ 7 = 16.85; P = 0.002). Aspen stands had significantly lower percent bare ground cover than the Douglas-fir (fo.017,11 = 3.77; P = 0.007) and mixedwood stands (fo.017.11 = 5.71; P = O.001) . The mixedwood and Douglas-fir stands had similar mean percent cover of bare ground (fo.oi7,n= 1-93; P = 0.095). 60 55 H 50 45 H 40 I H I 30 H 1 25 -\ 20 15 10 5 0 *~^\ Plant richness -•— Total plant cover i———1———1———1———1———r A l A2 A3 A4 M l M2 M3 M4 F l F2 F3 F4 j 150 - 140 - 130 - 120 - 110 - 100 ;over 1 - 90 c _w - 80 "E. 13 - 70 0 - 60 - 50 - 40 -- 30 A S P E N M I X E D W O O D DOUGLAS-FIR Figure 2.4 Plant richness and total plant cover (%) for each study site. Note: aspen stands had values consistently higher than either of the other stand types for both variables. 25 Mean total percent cover of herbs was different among the stand types (F$p - 7.32; P = 0.016) and significantly higher within aspen stands than Douglas-fir (/o.oi7,n = 3.13; P -0.016) and mixedwood stands (fo.017,11 = 3.47; P = 0.010) (Figure 2.5). Prominent herb species (those present in 8 or more study sites) in these stands included heart-leaved arnica (Arnica cordifolia), showy aster (Aster conspicuous), wi ld strawberry (Fragaria virginiana), mountain sweet-cicely (Osmorhiza chilensis), false Solomon ' s seal (Smilacina racemosa), common dandelion (Taraxacum officinale), western meadowrue (Thalictrum occidentale), and American vetch (Vicia americanum). For total herbaceous species, eleven species occurred in aspen stands only, five species occurred only in the mixedwood stands and two herbaceous species were unique to Dougias-fir stands. Mean percent cover of shrubs/deciduous trees was different among the stand types (F^j = 7.21; P = 0.015) and significantly higher within aspen stands than Douglas-fir (^0.017,11 = 3.32; P = 0.013) and mixedwood stands (^0.017,11 = 3.26; P = 0.014) (Figure 2.5). Douglas-fir and mixedwood stands were similar in terms of shrub/deciduous tree percent cover (?o.oi7,n = 0.057; P = 0.956). Prominent shrub species in these stands included saskatoon (Amelanchier alnifolia), twinflower (Linnaea borealis), tall Oregon-grape (Mahonia aquifolium), falsebox (Pachistima myrsinites), aspen (Populus tremuloides), prickly rose (Rosa acicidaris), birch-leaved spirea (Spiraea betulifolia), and common snowberry (Symphoricarpos albus). Eight shrub species occurred only within aspen stands and one species was unique to mixedwood stands. Mean total percent cover of moss and lichen was similar among the stand types (Ftj = 1.61; P = 0.266). Prominent species included common lawn moss (Bracythecium albicans), step moss (Hylocomium splendens), dog pelt (Peltigera canina), redstem feathermoss (Pleurozium schreberi), and electrified cat's tail moss (Rhytidiadelphus triquetrus). Six shrub species occurred only within aspen stands, six were unique to mixedwood stands, and three species were only found in mixedwood stands. Mean total percent cover for grasses was similar between all three stand types (F^j = 2.00; P - 0.205) (Figure 2.5). Prominent grass species included pinegrass (Calamagrostis rubescens), blue wildrye (Elymus glaucus), western fescue (Festuca occidentalis), and Kentucky bluegrass (Poa pratensis). No grass species was unique to any one stand type. See Appendix 2 for an overview of plant species occurrences within each stand type. 26 A l A 2 A3 A 4 M l M 2 M 3 M 4 FI F2 F3 F4 A S P E N M I X E D W O O D D O U G L A S - F I R Figure 2.5 Total percent cover of herbs, shrubs and grasses for each study site. Note: all aspen stands have values consistently higher for both shrub and herb cover but differences in grass cover are more variable. 2.4 D I S C U S S I O N Results of this study show that aspen stands had significantly higher snag density and volume, coarse woody debris volume, plant diversity, and total shrub and plant cover than mixedwood and Douglas-fir stands. This is potentially important as these attributes may directly affect biological diversity (Voller and Harrison 1998) and ecosystem function (Spies et al. 1988, and Loreau et al. 2001). Many forest-dwelling species are dependent on these features for all or part of their life history and the abundance and diversity of these features may lead to increased species diversity (Van Home 1983). The amount and distribution of D C W D within a particular stand is heavily influenced by the dominant tree species, disturbance history, successional stage (Keddy and Drummond 1996), and the structural characteristics of tree species (Harmon et al. 1986). As such, 27 coniferous forests may be expected to have greater D C W D volumes than deciduous forests (Stelfox 1995). This is due to lower rates of decay in coniferous forests, caused by potentially larger average tree sizes (Abbott and Crossley 1982) as well as differences in wood structure (Wilcox 1973). However, aspen stands here had significantly higher volumes of D C W D than either the mixedwood or the Douglas-fir stands. These forests were not different in terms of size or density of trees; as such, this is most likely a factor of tree morphology (Debyle and Winokur 1985). Aspen trees are more susceptible to heart rot and other decay agents than coniferous trees and aspen snags fall over much more quickly than coniferous snags (DeByle and Winokur 1985). A s such, current D C W D recruitment is higher within these aspen stands than the mixedwood or Douglas-fir forests. These stands also have a large component of dead trees that wi l l continue to contribute to D C W D . The age of a forest stand often is correlated with the abundance of coarse woody debris, with older stands generally having higher volumes (Sturtevant et al. 1997). Here, stand age did not play a role in these patterns as Douglas-fir stands were similar in age to the aspen stands but had significantly lower volumes of coarse woody debris. The likely cause of higher debris volumes within aspen stands is probably due to tree morphology. Douglas-fir trees often live longer than aspen trees (Parish et al. 1996) and the rate of decay also is much slower for these trees (Debyle and Winokur 1985). The aspen stands here are likely to be classified as old-growth stands (Lee et al. 1997) while the Douglas-fir stands as mature (Spies et al. 1988). This is likely a strong factor in the difference in coarse woody debris. A s expected, aspen stands had significantly higher density and volume of snags than either the mixedwood or the Douglas-fir stands. Snag recruitment is more likely to occur in aspen trees versus coniferous trees due to their higher susceptibility to heart rot and other decay agents (DeByle and Winokur 1985). The aspen stands here also contained a high density and proportion of snags (47-85% dead trees). Healthy aspen stands commonly have between 6 and 20% dead standing trees (DeByle and Winokur 1985) and Lee et al. (1997) reported snag densities of 12 stems/ha for old aspen-dominated mixedwood forests in Alberta. These high snag densities suggest that these stands are in an advanced successional stage. The volume of coarse woody debris measured here is comparable to those reported in other studies. For example, Pedlar et al. (2002) found that mixedwood and deciduous forests 28 had significantly higher coarse woody debris volumes that were five to eight times higher than coniferous forests. However, their work showed that mixedwood stands had the highest volumes (160.80 m 3/ha). In my work, coarse woody debris volumes in mixedwood stands were three times lower than aspen stands and only slightly higher than Douglas-fir stands. This was unexpected as mixedwood stands contained a large proportion of aspen trees within them. This may have been related to stand age, as these mixedwood stands were significantly younger than the other stand types. Lee et al. (1997) reported a value of 101.4 m 3/ha for D C W D in aspen-dominated mixedwood forests in Alberta. This value is higher than those reported here for D C W D , but is comparable to total coarse woody debris volume. Deciduous forests often contain an abundant community of coarse woody debris. Aspen stands elsewhere have been shown to contain a rich community of plants (e.g. Sheppard et al. 2006); this pattern also was seen in this study. Aspen stands in my study had a significantly more diverse community of plants than either the mixedwood or the Douglas-fir stands. This is important because a diversity of plants may increase animal diversity (Siemann et al. 1996) and may be related to several community and ecosystem processes (Tilman et al. 1996). The complex dynamics of these stands has probably contributed to this diversity as several microhabitats are likely available for different plant species (Lee and Sturgess 2001). These stands also had a significantly higher percent cover of shrubs and total plants. The cover of plants and shrubs may help to facilitate the survival and microhabitat selection of some species (Dueser and Shugart 1978). A diversity and abundance of plants and shrubs may provide a diversity of food for many species and potentially help support a diverse faunal community. The potential for this association is examined in Chapter 3 and Chapter 4. 2.5 C O N C L U S I O N Aspen stands in this study contain an abundance of snags and coarse woody debris and a diversity of plant species. As such, these stands may serve as an integral part of the dry interior B C forest ecosystems and may be areas of high biological diversity (see Chapters 3 and 4 for evidence of this). 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Ecological Applications. 7(2): 702-712. Tilman, D. , C . L . Lehman., and K T . Thomson. 1997. Plant diversity and ecosystem productivity: theoretical considerations. Ecology. 94: 1857-1861. Ulyshen, M . D . , J .L. Hanula, S. Horn, J.C. Ki lgo . , and C E . Moorman. 2004. Spatial and temporal patterns of beetles associated with coarse woody debris in managed bottomland hardwood forests. Forest Ecology and Management. 199: 259-272. Van Home, B . 1983. Density as a misleading indicator of habitat quality. Journal of Wildlife Management. 47(4): 893-901. Voller, J., and S. Harrison (editors). 1998. Conservation Biology Principles for Forested Landscapes. U B C Press, Vancouver, British Columbia. 243 pp. Welsh, Jr. H . H . , and S. Droege. 2001. A case for using plethodontid salamanders for monitoring biodiversity and ecosystem integrity of North American forests. Conservation Biology. 15(3): 558-569. Wenger, K . F . 1984. Forestry Handbook. 2 n d Edition. John Wiley and Sons, New York, N Y . White, C . A . , C E . Olmsted., and C E . Kay. 1998. Aspen, elk, and fire in the Rocky Mountain national parks of North America. Wildlife Society Bulletin. 26(3): 449-462. 34 Wilcox, W . W . 1973. Degradation in relation to wood structure. Pages 107-147. in Nichols, D . D . (editor). Wood deterioration and its preservative treatments. Syracuse University Press, Syracuse, New York, U S A . Zar, J .H. 1999. Biostatistical analysis. Prentice Hal l , Upper Saddle River, N . J . 718 pp. 35 3.0 C H A P T E R T H R E E - S M A L L M A M M A L C O M M U N I T I E S W I T H I N T H R E E S T A N D T Y P E S W I T H I N T H E D R Y I N T E R I O R F O R E S T S OF B R I T I S H C O L U M B I A , C A N A D A 1 3.1 I N T R O D U C T I O N Small mammals contribute to the biodiversity of North American temperate forests, both the diversity of species and to the functional diversity of the forest ecosystem (Carey and Johnson 1995). Further, small mammals are an important component of forest ecosystems because of their roles as prey for terrestrial and avian predators (Carey and Harrington 2001), distributors of mycorrhizal fungi, (Maser et al. 1979) seeds, spores and propagules of vascular plants, bryophytes, fungi, and lichens (Carey and Harrington 2001), and as consumers of invertebrates (Elkinton et al. 1996) and plants (Sullivan et al. 2000). The activity of small mammals also works to mix soil and decompose organic matter and litter (Bowman et al. 2000). Small mammal species composition thus may relate information as to the functioning of a particular ecosystem (Pearce and Venier 2005). As such, many authors have suggested that they are useful bioindicator taxa for assessing regional biodiversity (Steele et al. 1984, Croonquist and Brooks 1991, Bowers and Matter 1997, Carey and Harrington 2001, Sullivan and Sullivan 2001, Klenner and Sullivan 2003, and McShea et al. 2003). The diversity and abundance of small mammals may be heavily influenced by competition for limited resources. For example, many small mammal species compete for commonly used resources (Kelt et al. 1995) such as nesting sites, and food resources and space (Lambin 1994). This competition often influences the species distribution patterns within forested landscapes. Alternatively, many rodent species co-occur with one or more similar species (M'Closkey and Fieldwick 1975) and microhabitat selection (Morris 1996) often is used as a means of avoiding competition (Abramsky et al. 1979). Potentially, habitats that have adequate resources for ecological separation and niche requirements to the degree that interspecific competition is minimized, may be able to support diverse and abundant communities of small mammals. Alternatively, competitive exclusion may occur and some habitats may be dominated by a single species (Anderson et al. 2002). Interspecific A version of this chapter wi l l be submitted for publication. 36 interactions also are common within small mammal species and these interactions can influence the distribution, population levels, and movements of small mammals (Douglass 1976). Some small mammal species such as the deer mouse (Peromyscus maniculatus) and southern red-backed vole (Clethrionomys gapperi) (Banfield 1974), the long-tailed (Microtus longicaudus) and montane vole (Microtus montanus) (Randall and Johnson 1979), and the deer mouse and meadow vole (Microtus pennsylvanicus) (Douglass 1976) may exhibit strong habitat segregation. Forest stand dynamics play a large role in the diversity and abundance of many species. A s such, it is important to examine the dynamics of these attributes within study sites to quantify the relationship between these variables and the diversity and abundance of many species. The amount, distribution and diversity of habitat attributes such as standing coarse woody debris (SCWD) , downed coarse woody debris ( D C W D ) , as well as stand attributes and understory plant structure and diversity play vital roles in the life history of small mammals (Hagan and Grove 1999, Bowman et al. 2000, and Carey and Harrington 2001). For example, cavities and loose bark of S C W D provide nesting sites and D C W D provide cover and travel routes (Loeb 1999). The amount, structure, and dynamics of S C W D and D C W D also can influence species composition, nutrient cycling and site productivity (Spies et al. 1988). Stand structure and understory vegetation also are key factors that affect populations of small mammals (Carey and Johnston 1995). In landscapes dominated by coniferous forests, the amount of dead wood and the density of deciduous trees (aspen, Populus and birch, Betuld) also have been found to influence the composition and species richness of some species (Angelstam and Mikuskinski 1994). Habitat selection by small mammals is strongly dependent on factors that ensure the provision of cover and the availability of food sources (Beaudoin et al. 2004) such as specific habitat attributes. Previous work (Chapter 2) has identified that aspen stands within the dry interior forests of British Columbia have significantly more snags, coarse woody debris, plant diversity and shrub cover - all potentially important features for small mammals. Therefore, one would predict that these stands would support an abundant and diverse community of small mammals. Several authors have noted that trembling aspen (Populus tremuloides) stands may support a relatively high biotic diversity as compared to other forest types (Kay 1997, White 37 et al. 1998, and Griffi ths-Kyle and Beier 2003). Generally, the relatively large amount of structural diversity within aspen stands appears to play a strong role in this pattern (Stelfox 1995). However, this pattern has been studied mainly in boreal forest ecosystems (Gustafsson and Eriksson 1995, and Stelfox 1995) and the western United States (Kay 1997, White et al. 1998, and Bartos 2001). It is unclear as to how aspen contributes to overall diversity within dry interior British Columbia forest. There also is considerable evidence that the aspen component within North American forests is being significantly reduced by fire exclusion, poor seedbed conditions and increased herbivory from ungulates and cattle (White et al. 1998, and Bartos 2001). Because of the rarity of these stands, and potential and realized threats by anthropogenic factors, it is important that we further our understanding of their contribution to biodiversity across the landscape. Bioindicator species often are used to serve as a surrogate or indicator of the diversity of other species occurring within the same geographical area (McGeoch 1998, and Rainio and Niemela 2003). There are several reasons for using bioindicator species including the cost-effectiveness of sampling a few species or species groups, and being able to assess overall biotic diversity using these same assemblages (Carignan and Vi l la rd 2002, and Rainio and Niemela 2003). While several authors have outlined the problems associated with using bioindicator species for ecological studies (Landres et al. 1988, Temple and Wiens 1989, Noss 1990, Noss 1999, and Carignan and Vil lard 2001) they also have realized that the benefits of their use may outweigh these problems (Landres et al. 1988, Noss 1990, Noss 1999, Carignan and Vi l la rd 2001, and Venier and Pearce 2004) i f these indicators are selected and applied carefully (Lindenmayer 1999, and Rainio and Niemela 2003). A s it is impossible to measure all components of biodiversity, it becomes necessary to measure the diversity of a limited number of taxonomic related species as a means of assessing the overall assemblage of species (Holloway and Jardine 1968, Caro and O'Doherty 1999, and Mikusinski et al. 2001). Here I explore the small mammal community dynamics within three stand types within the dry interior forests of British Columbia. Specifically, I explore how diversity and abundance vary within three stand types: aspen, mixedwood, and Douglas-fir. I also explore which stand attributes may be used to best explain both the diversity of and abundance of small mammals within a particular stand type. 38 3.2 M E T H O D S 3.2.1 S T U D Y A R E A S This work is part of a larger study examining the biodiversity of aspen stands within the dry, interior forests of British Columbia, which also included an examination of cavity-nesting communities and stand attributes (Chapters 2 and 4). The field work was conducted near Kamloops, British Columbia, Canada (50°43 ' N ; 120°25' W). A l l study sites were located within the Interior Douglas-fir, Thompson dry cool (IDFdki; dry precipitation regime; cool temperature regime) biogeoclimatic zone (Meidinger and Pojar 1991). Four replicate stands of aspen (A), mixedwood (M) and Douglas-fir (F) were selected within three geographically distinct areas (blocks), Monte Lake ( A l , A 2 , M l , M 2 , F l , F2), Badger Lake (A3, M 3 , F3) and Pinantan Lake (A4, M 4 , F4) (see Figure 1.2 - Chapter 1). 3.2.2 S M A L L M A M M A L T R A P P I N G Small mammals were sampled within an 8 x 8 trapping grid with 14.3 m spacing (64 traps in total) during June to August 2005 and 2006 (see Appendix 3 for exact dates). Each study site was trapped three times in each year using Longworth-style live-traps, each covered with a 15 x 30 cm board. For each trapping session, traps were prebaited using a mixture of whole oats and sunflower seeds (5.0 grams), and then left open and unattended for two consecutive nights (Edalgo and Anderson 2007). Following this prebaiting session, small mammals were live trapped for three consecutive nights using the same mixture of oats and seeds, plus a slice of apple for water intake. Fresh bedding (moisture wicking synthetic cotton) was provided for each trapping night. Each trapped animal was identified for species and sex, weighed using a Pesola spring balance, assessed for reproductive condition (McCravy and Rose 1992) and classified as either a juvenile or adult (Krebs et al. 1969). Deer mice (Peromyscus maniculatus) were classified as juveniles i f their weight was <15g, and as adults i f £15g (Fairbairn 1977). Southern red-backed voles (Clethrionomys gapperi) were classified as juveniles i f their weight was <18g, and as adults i f £18g. Long-tailed voles (Microtus longicaudus), montane voles {Microtus montanus), and meadow voles (Microtus pennsylvanicus) were classified as juveniles i f their weight was <26g, and as adults i f £26 g (Sullivan and Sullivan 2004 and Klenner and Sullivan 2003). When the number of traps 39 containing animals exceeded 70% of available traps, an additional 50% more traps were added to reduce grid saturation. Finally, each animal was tagged with uniquely-numbered ear tags (Monel #1, National Band and Tag, Newport, K A ) and all live animals were released at the point of capture (Sullivan and Sullivan 2001). Although Sorex spp. (shrews) were not targeted as part of this study, captures of these animals were unavoidable, and this resulted in high mortality of shrews, because of the nocturnal trapping and lack of suitable food. Shrews that died in traps were collected and identified to species following Nagorsen (2002), and live shrews were released at point of capture. 3.2.3 D A T A A N A L Y S I S A randomized-block A N O V A (Zar 1999) was used to analyze the abundance of small mammal species, total number of captures, and total number of captures for each individual species, trapping success, and species diversity indices using the function P R O C G L M in S A S 9.1 (SAS Institute 2006). Where data did not meet the assumptions of normality and/or equal variance, Kruskal-Wall is nonparametric A N O V A using rank transformations were used, with a Tukey-type multiple comparison test to compare pairwise similarities (Zar 1999. Small mammal abundance estimates were calculated from mark-recapture data using the program C A P T U R E (Otis et al. 1978). When the total number of individuals of any species caught was ^ 9, modeled population estimates were not available, so I calculated the minimum number known alive ( M N A ) (Krebs 1966) for each mammal species for each trapping session. The Jolly-Seber stochastic model (Seber 1982) was not used, as data did not conform to the assumptions of equal catchability as checked using Cormack's test of equal catchability (Krebs 1999). Trapping success (animals/trap night) also was calculated for each trapping session, and in each year as an index of abundance. The number of individuals captured during each trapping session was used as a measure of relative density for shrews, northwestern chipmunks {Tamias amoenus), and western meadow jumping mice (Zapus princeps) (Sullivan et al. 1998). Pairwise t-tests were used for all post-hoc tests with an associated significance level of 0.017 (0.05/number of replicate blocks) and all mean data is reported with standard error. Data for M. montanus, M. longicaudus, and M. pennsylvanicus were pooled by year as some sites had very low captures. 40 Spearman's rank correlation analysis (Zar 1999) was used to explore the relationship between the abundance of each small mammal species and the total abundance of species with several stand attributes (see Chapter 2 for details on the methods used for collection of these data). These attributes included snag density (stems/ha), C W D volume (m3/ha), percent aspen, percent Douglas-fir, snag volume (m3/ha), D B H , total plant percent cover, plant richness, number of grass species, shrub cover, herb cover, stand age, percent cover of grass species and C W D decay classes. I used the mean abundance and the total number of individuals captured where applicable for this analysis and correlations were deemed strong when r > 0.50 (Cohen 1988). To summarize similarities in small mammal communities between study sites, a cluster analysis was conducted using average linkage between sites (SAS Institute 2006), with a dendrogram used to display the results (Pearce et al. 2003). The total number of individuals captured for each year for P. maniculatus, C. gapperi, M. montanus, M. pennsylvanicus, M. longicaudus and the total number of captures of T. amoenus, Z. princeps, and Sorex cinereus, Sorex vagrans, and Sorex monticolus were used in this analysis. This analysis was also used to cluster study sites based on similarities in total plant cover, aspen cover, shrub cover, herb cover, snag density (stems/ha), snag volume (m3/ha), total C W D volume (m3/ha), grass species, stand age, and C W D volume (m3/ha). Species diversity was assessed using a number of different indices. These additional indices were used as they provide more information about community composition than species richness, by taking into account the relative abundances of different species. The Simpson's diversity indice (Simpson 1949) is a simple mathematical measure that characterizes species diversity in a community based on the proportion of species relative to the total number of species and provides a measure of species evenness. The Shannon-Wiener index (Pielou 1966) is sensitive to changes in the number of rare species within a community (Peet 1974). This index is based on the degree of difficulty in predicting correctly the species of the next individual sampled, increases with the number of species in the community, and ranges from 0 to approximately 5.0 for biological communities (Washington 1984) and is highest when species proportions are equal (Staudhammer and LeMay 2001). The MacArthur 's diversity index (MacArthur and MacArthur 1961) is sensitive to relative abundances of species and less sensitive to the number of species (Magurran 1988), giving 41 little weight to rare species. These indices convey slightly different information about the diversity and structure of biotic communities. Diversity for small mammals was calculated using the mean estimated abundance of each species trapped at each site during each of three sample periods (from July to August) for a given year (Krebs 1999). A s density has been questioned as an indicator of habitat quality (Van Home 1983), demographic characteristics were calculated to compare habitat quality between stand types. The characteristics used as a means of comparison included the proportion of the population composed of reproductive females, the proportion of the population composed of juveniles (using individual animal weights), and sex ratio. These characteristics allow for an examination of both reproductive success and potential, both of which are important for small mammal population growth and maintenance. 3.3 R E S U L T S Fifteen small mammal species were detected during this study, including a total of 4284 individual small mammals captured during 15761 trap nights. The southern red-backed vole (C. gapperi) and the deer mouse (P. maniculatus) were the most abundant species, representing a total of 2248 individuals captured (52.4% of total individual small mammals captured). Sorex spp. species also were common, as was the northwestern chipmunk, and all three Microtus species. Aspen stands had the highest number of individual captures of southern red-backed voles (C. gapperi), montane voles (M. montanus), meadow voles (M pennsylvanicus), long-tailed voles ( M longicaudus), western jumping mice (Z. princeps), northwestern chipmunks (T. amoenus), common shrews (S. cinereus), vagrant shrews (S. vagrans), and dusky shrews (S. monticolus). The mixedwood stands had more individual deer mice (P. maniculatus) captured than the Douglas-fir and aspen stands. The total number of individuals caught was significantly different between the stand types (^4,7 = 8.71; P = 0.012) (Table 3.1). Aspen stands had significantly more captures than either the mixedwood (fo.on.n = 3.33; P = 0.015) or the Douglas-fir (/0.017,11 = 3.83; P = 0.015), and there was no difference between the mixedwood and the Douglas-fir (^0.017,11 = -0.49; P = 0.640). Aspen stands also had consistently higher number of individuals captured for each trapping session (Figure 3.1). 42 Table 3.1 Total numbers of individuals captured of each small mammal species within aspen (AT) , mixedwood (Mix) , and Douglas-fir (FD) stands during 2005 and 2006. Bold type indicates highest value. Species A T M i x F D Total Deer mice (P. maniculatus) 390 467 307 1164 Southern red-backed vole (C. gapperi) 465 290 329 1084 Montane vole (M. montanus) 370 111 71 552 Meadow vole (M. pennsylvanicus) 233 58 29 320 Long-tailed vole ( M longicaudus) 256 23 4 283 Western jumping mouse ( Z princeps) 36 24 1 61 Common shrew (S. cinereus) 149 15 29 193 Vagrant shrew (S. vagrans) 9 3 0 30 Dusky shrew (S. monticolus) 4 0 0 23 Unidentified live Sorex spp. 151 16 17 184 Northwestern chipmunk (T. amoenus) 250 58 81 389 Short-tailed weasels (Martes ermined) 7 0 1 8 Northern flying squirrel (Glaucomys sabrinus) 13 1 1 15 Red squirrel (Tamiasciurus hudsonicus) 5 0 1 6 Bushy-tailed woodrat (Neotomys cinerea) 1 0 8 9 Total captures 2339 1066 879 4284 3.3.1 D E N S I T Y E S T I M A T E S The mean abundance of southern red-backed voles (C. gapperi) (Figure 3.2) was significantly different between the three stand types in 2005 ( ^ 4 , 7 = 8.81; P = 0.012 ). Aspen stands had a higher mean abundance than the mixedwood (^0.017,11 = 3.22; P = 0.015) and the Douglas-fir stands (?o.oi7,n = 3.94; P = 0.006), but the Douglas-fir and mixedwood stands were not significantly different (^0.017,11 = 0.72; P = 0.497). In 2006, the mean abundance of southern red-backed voles ( ^ 7 = 0.68; P = 0.539) was not different within the stand types. The mean abundance of deer mice (P. maniculatus) was not significantly different within the three stand types in 2005 ( F 4 > 7 =0.43; P = 0.665) or 2006 (F 4 , 7 = 0.14; P = 0.873) (Figure 3.3). 43 June 05 Ju ly 05 A u g 05 June 06 T rapp ing session Ju ly 06 A u g 06 F igure 3.1 Tota l number o f captures o f smal l mammals w i th in each stand type and each trapping session. 44 June July Aug June July Aug 2005 2006 Figure 3.2 Population density and standard error for C. gapperi within all three stand types and all six trapping periods. ca =5 70 60 •S 50 t 40 c -o c o 30 3 a, o c cd <u 20 \ 10 -•— Aspen -o— Mixedwood -•— Douglas-fir P. maniculatus June July Aug June July Aug 2005 2006 Figure 3.3 Population density and standard error for P. maniculatus within all three stand types and all six trapping periods. 45 The mean abundance of montane voles (M. montanus) (Figure 3.4) was significantly different between the three stand types (F4J = 6.83; P = 0.003). Aspen stands had a higher mean abundance than the mixedwood Oo.on.n = 3.21; P = 0.015) and the Douglas-fir stands ffo.oi7,n = 3.20; P = 0.015). The Douglas-fir and mixedwood stands were not significantly different Oo.o 17,11 = 0.013; P = 0.990) in terms of mean abundance of M. montanus. 50 Cj i 40 cd s 5 cd S3 <u C cd 3 O <U 30 20 \ 10 -0 -•— Aspen - o — Mixedwood -•— Douglas-fir M. montanus June July 2005 Aug June July 2006 Aug Figure 3.4 Population density and standard error for M. montanus within all three stand types and all six trapping periods. The mean abundance of long-tailed voles (M longicaudus) (Figure 3.5) was significantly different between the stand types (^4 ,7 = 8.30; P = 0.014). Aspen stands had a higher mean abundance than the Douglas-fir stands (q = 2.64) and the mixedwood stands (q = 3.61). The Douglas-fir and mixedwood stands were not significantly different (q = 0.28) in terms of mean abundance of M. longicaudus. These data only included that from the Monte Lake study block, as no long-tailed voles were captured in the Pinantan Lake or Badger Lake study blocks. 46 40 35 30 25 cd Id a I I 20 C 1 1 5 3 O C cd s 10 5 -0 Aspen Mixedwood Douglas-fir M longicaudus -o June Aug July Aug June July 2005 2006 Figure 3.5 Population density and standard error for M. longicaudus within all three stand types and all six trapping periods. The mean abundance of meadow voles (M. pennsylvanicus) (Figure 3.6) was significantly different between the stand types (F*j = 12.28; P = 0.005). Aspen stands had a higher mean abundance than the Douglas-fir stands (7/o.oi7,n = 3.05) and the mixedwood stands (//o.on.n = 3.61). The Douglas-fir and mixedwood stands were not significantly different (7/0.017,11 = 0.55) in terms of mean abundance of M. pennsylvanicus. The mean abundance of western jumping mice (Z. princeps) was not significantly different between the stand types (F4.7 = 1.32; P = 0.326). 47 25 •3 20 15 10 0 Aspen Mixedwood Douglas-fir M. pennsylvanicus June Aug July Aug June July 2005 2006 Figure 3.6 Population density and standard error for M. pennsylvanicus within all three stand types and all six trapping periods. 3.3.2 T O T A L A B U N D A N C E OF A L L SPECIES One of the most striking differences in the small mammal communities within these stand types was seen in the difference in the total abundance of small mammals. Aspen stands had total mean small mammal abundances that were significantly higher ( F 4 j = 7.29; P = 0.009) than either of the other stand types (Douglas-fir; F4j = 3.40; P = 0.012 and mixedwood; F*j - 3.21; P = 0.015). Again, there was no difference between the Douglas-fir and mixedwood stands {F^j- -0.19; P = 0.857). Interestingly, the mixedwood and Douglas-fir replicates at Pinantan Lake supported a much higher abundance of small mammals than any of the other mixedwood and Douglas-fir replicate stands. The highest total abundance of small mammals, during the final trapping session of 2006, within the Douglas-fir replicate at Pinantan Lake was 252 animals/ha, this corresponds to 259% higher than any of the other Douglas-fir replicate stands during the same period. This same pattern was evident with the mixedwood stand replicate at Pinantan Lake, which also supported the highest total small 48 mammal abundance of 252 animals/ha: this corresponds to 297% higher than the other replicate mixedwood stands. These stands often supported more abundant and nearly as diverse communities of small mammals as the replicate aspen site at Pinantan Lake. 3.3.3 T R A P P I N G S U C C E S S Trapping success (animals/trap night) was significantly different between the study sites for each year (2005: F4J = 9.23; P = 0.011 and 2006: F4J = 8.26; P = 0.014, see Appendix 4 and 5). Aspen stands had significantly higher trapping success than Douglas-fir stands in both 2005 (/0.oi7,n = 3.35; P = 0.012) and 2006 (fo.on.n = 3,87; P = 0.006). The mixedwood and the Douglas-fir stands had similar trapping success in both 2005 (ro.017,11 = 1.00; P = 0.350) and (^0.017,11 = 0.87; P - 0.416). The mixedwood and aspen stands were not significantly different in terms of trapping success in 2005 Oo.o 17,11 = 2.35; P = 0.051) and 2006 Oo.o 17,11 = 3.01; P = 0.019). However, the significance values are still quite low and the biological trend was towards a higher trapping success within aspen stands versus mixedwood stands (Figure 3.7). June July A u g June July A u g 2005 2006 Figure 3.7 Trapping success (animals/trap night), an index of overall abundance, for each stand type and trapping session. 49 3.3.4 I N D I V I D U A L C H I P M U N K A N D S O R E X C A P T U R E S The total number of captures of northwestern chipmunks (T. amoenus) was significantly different between the study sites for both years (2005: F 4 i 7 = 6.79; P = 0.023 and 2006: 7 7 4 , 7 = 7.23; P = 0.019) with aspen stands having significantly more captures than either the mixedwood (2005: /0.oi7,n = 3.20; P = 0.015 and 2006: f0.oi7,ii = 3.51; P = 0.011) or the Douglas-fir stands (2005: /0.oi7,n = 3.18; P = 0.016 and 2006: fo.017.11 = 4.21; P = 0.009). The mixedwood and the Douglas-fir stands had similar numbers of captures of T. amoenus over the two years (fo.017,11 = 0-025; P = 0.981 and r0.oiy,iI = 0.051; P = 0.851) (Figure 3.8). The total number of Sorex spp. captures (Figure 3.9), grouped by live and dead captures and between years, was significantly different between the sites (F^j = 8.25; P = 0.014). Aspen stands had significantly more captures then either the mixedwood (fo.on.ii = 3.45; P = 0.011) and the Douglas-fir stands (f0.oi7,ii = 3.59; P = 0.009) (Figure 3.10). The mixedwood and the Douglas-fir stands had similar numbers of captures of Sorex spp. over the two years (/o.o 17,11 = 0.14; P = 0.893). Aspen stands had a total of 313 Sorex spp. captures of which common shrews (S. cinereus) made up 74.6% of the total identified shrew captures. Shrew captures within Douglas-fir (46) and mixedwood stands (34) were lower and were dominated by S. cinereus - S. monticolus and S. vagrans were rarely. Two other shrew species, S. palustris and S. hoyi, are inhabitants of the interior of British Columbia (Nagorsen 2002) but were not captured here. Shrew species made up a large component of the small mammal community within aspen stands. They also were present to a much smaller degree within mixedwood and Douglas-fir stands. 50 80 ••— Aspen June July Aug June July Aug 2005 2006 Figure 3.8 Total number of captures of northwestern chipmunks for each stand type and each trapping session. June July Aug June July Aug 2005 2006 Figure 3.9 Number of Sorex spp. captures for each stand type and each trapping session. 51 3.3.5 P I N A N T A N L A K E C O M P A R I S O N The Pinantan Lake study block showed a very different pattern of abundance (here compared as animals/trap night) than the other two study blocks (Figure 3.10). The aspen site at Pinantan Lake was relatively similar to all other replicate aspen stands but the Douglas-fir and mixedwood replicates had much higher mammal abundance than in counterpart stand replicates. This pattern was similar for both years of data collection. In fact, these stands had abundance estimates that were typically 50% higher than the other corresponding replicate stands. OH CS H cS g t. <H-I 60 OH OH i-H 1.0 0.9 0.8 H 0.7 0.6 H •3 0.5 H 0.4 Stand averages - 2005 Pinantan Lake sites - 2005 Stand averages - 2006 Pinantan Lake sites - 2006 0.3 I i 1 1 1 1 1 1 A T M I X D F A T M I X D F 2005 2006 Figure 3.10 Comparison of trapping success (animals/trap night) for the aspen (AT) , mixedwood ( M I X ) and Douglas-fir (DF) sites at Pinantan Lake for each year, with the average for each stand type (n = 4). The aspen site at Pinantan Lake had similar values to the overall aspen stand averages but large differences can be seen with the mixedwood and Douglas-fir averages and these overall stand averages. 52 3.3.6 C O R R E L A T I O N A N A L Y S I S OF A B U N D A N C E A N D A T T R I B U T E S The abundance of each species was correlated with each stand attributes except for log classes 1, 2 and 4 (Table 3.2). There were five variables that were most often correlated (£5 occurrences) with the abundance of a particular small mammal species including aspen, total plant cover, number of grass species, shrub cover and herb cover. The eight variables that were most highly correlated with total small mammal abundance were aspen, total plant cover, number of grass species, shrub cover, snag density, C W D volume, plant richness and herb cover. Total small mammal abundance was negatively correlated with the presence of Douglas-fir (r = -0.80; P = 0.002). The amount of Douglas-fir within a stand was the most frequent inversely-correlated attribute with total small mammal abundance (4 occurrences). In terms of the correlations between the abundance of each of the small mammal species (Table 3.3), several species were directly correlated with one another. The abundance of C. gapperi was correlated with the abundance of M. montanus, M. pennsylvanicus, Sorex spp., Z. princeps, and T. amoenus. The abundance of M. montanus and M. pennsylvanicus were directly correlated with the abundance of one another, and C. gapperi, T. amoenus, and Z. princeps. Montane vole abundance also was correlated with Sorex spp. abundance. Northwestern chipmunk (T. amoenus) abundance was correlated with the abundance of M. pennsylvanicus, M. longicaudus, C. gapperi, Z. princeps, and Sorex spp. There were no significant inverse correlations between any two species but the strongest was between deer mice and southern red-backed voles (r = -0.35; P = 0.265). 53 Table 3.2 Spearman's rank correlation matrix of the relationship between stand attributes and mean abundance of each small mammal species. Only correlation values > 0.50 are included and the numbers in bold represent the highest positive or negative correlation values, r > 0.50. P M = (P. maniculatus), C G = (C. gapperi), M M = ( M montanus), M P = ( M pennsylvanicus), M L = ( M longicaudus), Z P = (Z. princeps), and T A = (T. amoenus). Attribute Abundance P M C G M M M P M L T A Z P Sorex spp. Snag density 0.62 - - - - - - - 0.68 0.031 - - - - - - - 0.014 C W D volume 0.58 - - - - - - 0.50 0.56 0.048 - - - - - - - 0.095 0.060 Aspen 0.78 - - 0.56 - - 0.51 0.63 0.71 0.003 - - 0.060 - - 0.087 0.029 0.010 Douglas-fir -0.80 - - - - - -0.56 -0.61 -0.72 0.002 - - - - - 0.059 0.034 0.009 D B H - - - - - -0.64 - - -- - - - - 0.024 - - -Plant % cover 0.69 - - 0.51 - - 0.50 0.62 0.64 0.014 - - 0.063 - - 0.097 0.033 0.025 Grass species 0.73 - 0.83 0.76 0.73 - 0.79 0.64 -0.007 - <0.001 0.004 0.007 - 0.002 0.025 -Shrub cover 0.66 - 0.50 0.54 0.64 - 0.59 - 0.80 0.020 - 0.095 0.073 0.025 - 0.043 - 0.002 Herb cover 0.62 - 0.55 0.57 0.65 - 0.54 - 0.77 0.031 - 0.067 0.055 0.023 - 0.068 - 0.003 Plant richness 0.51 - 0.55 - - - - - -0.087 - 0.064 - - - - - -Stand age - - - - - - 0.59 0.50 0.57 - - - - - - 0.043 0.092 0.053 Class 3 - - 0.65 0.51 - 0.66 - - -- - 0.022 0.093 - 0.020 - - -Class 5 - -0.91 - - -0.53 - - - -- O.001 - - 0.077 - - - -Note: P M ; (P. maniculatus), M P ; ( M pennsylvanicus), C G ; (C. gapperi), M M ; (M. montanus), M L ; ( M longicaudus), T A (T. amoenus), and Z P ; (Z. princeps). Top row values represent the correlation statistic and lower row values the p-value. Table 3.3 Spearman's rank correlation matrix of the relationship between the mean abundance of each small mammal species. Numbers in bold represent significant correlation values where r > 0.50. Spearman's correlation matrix Species P M M P C G M M M L T A Sorex spp. Z P P M 0.24 -0.35 0.03 0.12 -0.15 -0.26 0.11 - 0.436 0.265 0.922 0.718 0.423 0.738 0.738 M P 0.25 0.68 0.83 -0.27 0.59 0.41 0.52 0.436 - 0.016 0.001 0.395 0.042 0.185 0.085 C G -0.04 0.68 0.80 -0.39 0.75 0.58 0.55 0.264 0.016 - 0.002 0.214 0.005 0.047 0.063 M M 0.03 0.83 0.80 - -0.24 0.63 0.52 0.61 0.922 0.001 0.002 - 0.448 0.027 0.082 0.035 M L 0.12 -0.27 -0.39 -0.24 - 0.10 0.28 -0.09 0.718 0.395 0.213 0.448 - 0.768 0.381 0.781 T A -0.15 0.59 0.75 0.63 0.10 - 0.70 0.77 0.423 0.042 0.005 0.027 0.768 - 0.012 0.003 Sorex spp. -0.26 0.41 0.58 0.52 0.28 0.70 - 0.44 0.738 0.185 0.047 0.082 0.381 0.012 - 0.147 Z P 0.11 0.52 0.55 0.61 -0.09 0.77 0.44 -0.738 0.085 0.063 0.034 0.782 0.003 0.147 -Note: P M ; (P. maniculatus), M P ; ( M pennsylvanicus), C G ; (C. gapperi), M M ; ( M montanus), M L ; ( M longicaudus), T A (T. amoenus), and Z P ; (Z. princeps). Top row values represent the correlation statistic and lower row values the p-value. 3.3.7 HABITAT QUALITY Aspen stands consistently had relatively higher mean proportions of reproductive adult females and juveniles within the small mammal communities. The age class ratio was different between the stand types (7*4,7 = 8.67; P = 0.013) (Figure 3.11) with aspen stands having a higher ratio of juveniles than either the Douglas-fir (fo.oi7,n = 4.05; P = 0.005) and the mixedwood stands (fo.017,11 = 3.27; P = 0.016). The mean proportion of reproductive adult females within the three stand types was significantly different (7*4,7 - 8.45; P - 0.013) (Figure 3.12) with aspen stands having a higher proportion than mixedwood (fo.o 17,11 = 3.45; P = 0.011) and Douglas-fir stands (/o.oi7,i 1 = 3.59; P = 0.009). The proportion of reproductive adult females in aspen stands ranged from 37 - 59%, in mixedwood stands from 29-51 % and in Douglas-fir stands from 19 - 47%. The sex ratios within these populations and stand types were similar (7*4,7= 1.96; P = 0.212). u '£ > a o 4—» •*—• "3 -o c3 t*—1 O O 14 12 10 8 2 A - O - Aspen Mixedwood - • — Douglas-fir June July 2005 Aug June July 2006 Aug Figure 3.11 Ratio of adults to juveniles within the small mammal communities of aspen, mixedwood and Douglas-fir stands. 56 C/3 CO _> o 3 -a o a. c o o o 0.7 0.6 -\ 0.5 2 ° - 4 I—< g 0.3 0.2 0.1 O Aspen Mixedwood • — Douglas-fir June July 2005 A u g June July 2006 A u g Figure 3.12 Proportion of reproductive adult females within the small mammal populations of the aspen, mixedwood and Douglas-fir stands. Data points represent proportions along with standard error. 3.3.8 C L U S T E R A N A L Y S I S Cluster analysis of community assemblages of small mammals (Figure 3.13) produced two broad site groupings and five more defined groupings. The first broad grouping showed a similarity between all aspen stands and a mixedwood and Douglas-fir stand (both of which were located at Pinantan Lake). The second broad grouping grouped the remaining Douglas-fir and mixedwood stands based on similarities in their small mammal community assemblages. A t a finer scale, two aspen replicate stands, A l and A 2 , were quite similar. Two other groupings showed similarities in the small mammal communities between an aspen and a mixedwood replicate and an aspen and a Douglas-fir replicate stand. The grouping containing M l , M 2 , F l and F2 is interesting because they were all in one geographic block (Monte Lake). The final grouping with M 3 and F3 also are within the same geographic 57 location (Badger Lake). These results show how similar the small mammal communities are within these stands and within a particular geographic location. Cluster analysis based on similarities in total plant cover, aspen cover, shrub cover, herb cover, snag density (stems/ha), snag volume (m /ha), total C W D volume (m /ha), grass species, stand age, and C W D volume (m3/ha) revealed those stand types that were similar in terms of theses stand characteristics (Figure 3.14). These attributes were identified in correlation analysis as being important correlates for small mammal diversity. A l l aspen, mixedwood and Douglas-fir stands were grouped together based on these characteristics. This reveals that the same stand types had resources structured in a similar way, and may explain why aspen stands generally supported a more abundant small mammal community. 3.3.9 SPECIES D I V E R S I T Y Species richness (number of species caught) for small mammals was significantly higher within aspen stands in both 2005 and 2006 than either the mixedwood or Douglas-fir stands. There was no difference between species richness for either year between the mixedwood and the Douglas-fir stands. The diversity indices, Shannon's, Simpson's and MacArthur 's , all showed a similar pattern for small mammal diversity. Overall, aspen stands had diversity indice values that were higher than the mixedwood stands in five out of eight cases and higher than Douglas-fir stands in seven out of eight cases. In the instances where indices were not different between aspen and the other stand types, these significance values were still quite small and there was a clear biological difference. These diversity indices were not significantly different between the mixedwood and the Douglas-fir stands for any year or indice. The year-to-year stand rank of species diversity within each stand was relatively constant. When these ranks changed, the change was only by one or two positions and was always within the Douglas-fir or mixedwood stands - aspen stands consistently ranked one through four (see Tables 3.4 and 3.5 for overview). 58 s i t e A 1 -A 2 • A 3 A 4 ' F 4 " M l —1 M2 i F 2 F 1 M3 - , F 3 • I . D D . 9 D . — I 1 1 1 1 1 l l D . 7 D . 6 D . 5 D . 4 D . 3 D . 2 D . l 0 . 0 R - 5 q u a r e d Figure 3.13 Dendrogram showing results of a cluster analysis used to group study sites on the basis of similarities in small mammal communities. s i te fll — fie 1 R3 ' FH — ^ Ml 1 M3 -l MH J 1 ME 1 Fl —I FE l . F3 ' FM I I | I I I I 1 1 1 1 0 .3 0 .8 0 .7 0.6 0 .5 0 .M 0.3 O.Z 0.1 0.0 R-Squared Figure 3.14 Dendrogram showing results of a cluster analysis used to group study sites on the basis of similarities in stand attributes (total plant cover, aspen cover, shrub cover, herb cover, snag density (stems/ha), snag volume (m3/ha), total CWD volume (m3/ha), grass species, stand age, and CWD volume (m3/ha). Table 3.4 Small mammal diversity indices for 2005 and each study site. Rank is based on the average rank of all diversity values. 2005 Small Mammal Diversity Indices Site Richness Shannon's Simpson's MacArthur 's Rank A l 10 2.71 0.83 5.83 2 A 2 9 2.71 0.84 6.21 1 A 3 10 2.41 0.79 4.65 3 A 4 9 2.31 0.77 4.27 4 Stand average 9.50 ± 0 . 1 4 2.54 ± 0 . 0 5 0.81 ± 0 . 0 1 5.24 ± 0 . 2 3 M l 5 1.84 0.69 3.07 7 M 2 5 1.37 0.51 2.03 9 M 3 4 0.98 0.42 1.71 11 M 4 7 2.33 0.80 4.98 5 Stand average 5.25 ± 0 . 3 1 1.63 ± 0 . 1 5 0.61 ± 0 . 0 4 2.95 ± 0 . 3 7 FI 5 1.61 0.63 2.64 8 F2 3 1.18 0.54 2.13 10 F3 3 0.44 0.14 1.17 12 F4 6 2.10 0.72 3.77 6 Stand average 4.25 ± 0 . 3 8 1.33 ± 0 . 1 8 0.51 ± 0 . 0 6 2.43 ± 0.27 F4.7; P **27.20; O.001 **9.42; 0.010 5.14; 0.042 **8.67; 0.012 %.017,11/ P *5.62; O.001 *3.14; 0.016 2.12; 0.072 *3.86; 0.006 *^ 0.017,11/ P *6.95; O.001 *4.17; 0.004 3.14; 0.016 *3.15; 0.016 %.017,11/ P -1.32; 0.228 -1.03; 0.337 -1.02; 0.341 -0.71; 0.499 Note: adenotes statistical value for difference between aspen and mixedwood; aspen and Douglas-fir and cmixedwood and Douglas-fir. denotes a statistical difference at a = 0.05 *denotes statistical difference at a = 0.017. 61 Table 3.5 Small mammal diversity indices for 2006 and each study site. Rank is based on the average rank of all diversity values. 2006 Small Mammal Diversity Indices Site Richness Shannon's Simpson's MacArthur 's Rank A l 10 2.83 0.85 6.43 1 A 2 10 2.62 0.82 5.50 2 A3 9 2.60 0.80 4.98 3 A 4 9 2.51 0.80 4.88 4 Stand average 9 . 5 0 ± 0.14 2.64 ± 0 . 0 3 0.82 ± 0 . 0 1 5.45 ± 0 . 1 8 M l 6 1.92 0.69 3.14 9 M 2 7 2.13 0.72 3.46 7 M 3 4 1.26 0.51 2.02 11 M 4 8 2.66 0.82 5.40 5 Stand average 6.25 ± 0.43 1.99 ± 0 . 1 4 0.69 ± 0 . 0 3 3.51 ± 0 . 3 6 F l 5 1.81 0.69 3.18 10 F2 7 1.99 0.69 3.15 8 F3 4 0.57 0.18 1.22 12 F4 7 2.24 0.78 4.46 6 Stand average 5.75 ± 0 . 0 7 1.65 ± 0 . 1 9 0.59 ± 0 . 0 7 3.00 ± 0 . 3 3 Fa.T, P **23.23; <0.001 **8.65; 0.012 3.40; 0.093 **8.63; 0.012 %.017,11/ P *5.53;<0.001 *2.35; 0.051 1.48; 0.183 *3.93; 0.006 *fo.017,l1/ P *6.62; <0.001 *3.59; 0.009 2.60; 0.035 *3.13; 0.016 %.017,11/ P -0.69; 0.512 -1.24; 0.257 -1.12; 0.298 -0.81; 0.446 Note: adenotes statistical value for difference between aspen and mixedwood; aspen and Douglas-fir and cmixedwood and Douglas-fir. denotes a statistical difference at a = 0.05 *denotes statistical difference at a = 0.017. 62 3.4 D I S C U S S I O N The diversity and abundance of small mammals was consistently higher within aspen stands than that of mixedwood and Douglas-fir stands. Also consistent was the similarity of mixedwood and Douglas-fir stands for all variables measured. The presence of a dominant community of aspen, diversity of grass species, and of shrub, herb, and total plant cover were the most frequently correlated variables with both total abundance and the abundance of particular species. The abundance of small mammals within aspen stands reported here are higher than those reported by other authors within temperate North American deciduous forests including riparian forests (Hannon et al. 2002), mixed deciduous forests (Yahner and Smith 1991, Bowman et al. 2000, and McShea et al. 2003) and aspen forests (Iverson et al. 1967, Probst and Rakstad 1987, Stelfox 1995, and Bayne and Hobson 1998) - as compared using trapping success. These results highlight the importance of aspen stands within dry interior British Columbia forests. The mixedwood and Douglas-fir forests also supported relatively abundant communities of small mammals but were dominated by fewer species. The total number of small mammal captures was much higher within aspen stands than either the mixedwood or Douglas-fir stands. What is interesting about this is the fact that these captures were not dominated by a few species, deer mice, red-backed voles, meadow voles, long-tailed voles, montane voles, northwestern chipmunks, and Sorex spp. were all abundant within these stands. Conversely, the total number of captures within mixedwood and Douglas-fir stands was dominated by three species: deer mice, red-backed voles, and montane voles. It also is important to note that this study was part of a larger investigation that used pitfall traps to sample carabid beetles during May and August of 2005. This technique unintentionally resulted in the mortality of small mammals from the study grids, and thus may have influenced population estimates. This mortality factor was significant, averaging 40.25 ± 2.77 animal deaths in aspen stands, 19.75 ± 2.74 in mixedwood stands, and 19.00 ± 2.51 in Douglas-fir stands over the entire pitfall trapping period. This procedure was not replicated in 2006. 63 This study also shows that small mammal diversity within aspen stands rivals that reported elsewhere. Probst and Rakstad (1987) report species richness within mature aspen stands in Michigan of 2 - 7, Bayne and Hobson (1998) reported species richness of 6 species in aspen-mixedwood forests in Saskatchewan, and Stelfox (1995) reported 8 species in aspen-mixedwood forests in Alberta, here the small mammal communities were made up of 9 to 10 species. These studies also show that small mammal communities often are dominated by a few species. Aspen stands here were composed of a diverse community of small mammals that was not numerically-dominated by a single species; rather, six species were numerically abundant, namely deer mice, southern red-backed voles, meadow voles, long-tailed voles, northwestern chipmunks and common shrews. One area, Pinantan Lake, supported a diversity and abundance of small mammals within each of its replicate stand types. In fact, the mixedwood and Douglas-fir sites at this location supported more abundant small mammal communities than the aspen replicate stand. These two sites are characterized as having the highest diversity of grass species identified as well as having shrub cover and herbaceous species diversity approaching those identified within aspen stands (Chapter 2). Therefore, habitat selection by small mammals in this area appears to be strongly dependent on factors that ensure the provision of cover and the availability of food sources (Beaudoin et al. 2004). The southern red-backed vole and the deer mouse were the most numerically abundant small mammal species caught, followed by the three species of voles ( M longicaudus, M. pennsylvanicus, and M. montanus). The southern red-backed vole is a common inhabitant of late successional coniferous and deciduous forest across temperate North America (Burt and Grossenheider 1980). It tends to occur in areas with abundant organic debris composed of stumps, logs, and exposed roots (Yahner 1986) that maintain hypogeous ectomycorrhizal fungi - a major food supply (Maser et al. 1978). Aspen stands appear to possess these stand attributes to a degree that this habitat may be preferentially selected by this vole species. As these voles mostly consume seed and plant material (Burt and Grossenheider 1980, and DeByle and Winokur 1985) their high abundance within these stands also may be a reflection of the diversity and abundance of grass species and herb species, an abundance of shrub cover, and an abundance of downed woody debris - all key components of the needs of southern red-backed voles. The deer mouse is a habitat 64 generalist that occupies a wide variety of habitats (Sullivan et al. 1998) and has a relatively broad diet - consisting of seeds, fruit, and arthropods (Van Home 1983). The ubiquitous deer mouse was the most dominant species found in this study in terms of total individuals captured for all study sites. Numerically, it was only sub-dominant in aspen stands. Deer mice may have been replaced in terms of greatest abundance by southern red-backed voles within aspen stands because of differences in moisture requirements. Southern red-backed voles prefer moist environments (McManus 1974) while deer mice appear more tolerant of xeric habitats (Morris 1996). Aspen stands are generally higher in moisture than coniferous stands (Sheppard 2001) and may be preferentially selected by southern red-backed voles. Other work within aspen stands also has shown that the southern red-backed voles are often the most dominant species in these stands (Probst and Rakstad 1987, and Stelfox 1995). Montane and meadow voles were found in relatively high abundance in 6 of the 12 stands (4 aspen and one each of Douglas-fir and mixedwood). Most microtine rodent species are herbivorous and preferentially select grass and herb food sources (Burt and Grossenheider 1980, Lindroth and Batzi 1984, and DeByle and Winokur 1985). Aspen stands here provided a variety and abundance of this food and the presence of such probably contributed to the relatively high densities of these species. O f interest is that M. pennsylvanicus preferentially selects grassland habitats and typically avoids forested habitats or occurs within forest openings (Burt and Grossenheider 1980) - here it was relatively common within forested sites. The long-tailed vole ( M longicaudus) was restricted to the sites located near Monte Lake and was very abundant within these aspen stands. These animals occurred very sporadically and infrequently within the Douglas-fir and mixedwood stands and appear to preferentially select aspen stands within the study area. Other work has shown that M. longicaudus shows a preference for early successional habitats (Randall and Johnson 1979) which may be related to the abundance of herbs and grasses that provide food and cover (Getz 1985). Aspen stands in this study were characterized as having a diversity and abundance of grasses and herbs which may explain why these sites were preferentially selected. Northwestern chipmunks are habitat generalists and are primarily found in early successional sites (Sullivan and Sullivan 2001). However, they were captured very frequently 65 within aspen sites and less frequently within the mixedwood and Douglas-fir sites. Aspen stands were all mature and the high relative abundance here was probably more related to a variety and abundance of food, they mainly feed on seeds and other plant material (Burt and Grossenheider 1980), and cover. A l l three shrew species were frequently caught within aspen stands; however, S. cinereus was by far the most common species captured. Sorex cinereus is considered a habitat generalist (Yahner 1992) and often is found in association with C. gapperi, M. pennsylvanicus, and P. maniculatus (Wrigley et al. 1979). When it is peaking in abundance it may exceed these species in abundance and is often the most-common shrew species within its geographic range (Wrigley et al. 1979). It has the largest geographic range of all North American shrews and usually prefers mesic habitats (Morris 1996, Innes et al. 1990, and McManus 1974). Again, aspen stands generally are higher in moisture than coniferous stands (Sheppard 2001) and this may be a strong contributor to the differences in abundance between the three stand types. Many small mammal species are subject to cyclic population fluctuations that are characterized by a regular period (the interval between successive density peaks) and highly variable amplitude (the ratio of maximum to minimum population) (Korpimaki and Krebs 1996). The mechanisms driving these long-term fluctuations remain unknown as are the density-dependent or density-independent factors that influence annual fluctuations (Yahner 1992). One thing that is known is that these fluctuations are often synchronous across hundreds of square kilometers (Kalela 1962, and Hansson and Henttonen 1985). The small mammal populations within this study may be at a high point in this cycle or may still be increasing. Evidence for this is seen in the overall high abundance as well as in the second year abundance being higher than the first for all but one species - the meadow vole. A s it is unlikely that these populations wi l l remain at these high levels (Korpimaki and Krebs 1996), it would be interesting to see i f aspen stands serve as 'source populations' when the populations have declined and/or are building again. A long-term monitoring program within these three stand types would be required to build knowledge as to the long-term dynamics of small mammal communities within dry interior B C forests. It would also be useful to incorporate a winter trapping regime in future research, as habitat use in the winter is critical for animals in northern climates (Van Home 1983). 66 Aspen stands supported a dense population of small mammals and this habitat type also may be of superior habitat quality as evident in the demographic characteristics. The relatively higher proportion of reproductive females in aspen stands shows that there is a higher potential for reproduction to occur within these stands. Additionally, there were higher proportions of juveniles in the small mammal populations within these stands; suggesting that reproductive success also may have been higher. The adult sex ratios within these stands were not significantly different; therefore, the difference in the reproductive potential between these stands is likely not a factor of a higher proportion of males or females within these populations. It appears as though small mammals within aspen stands have a higher reproductive potential and success than those within the mixedwood and Douglas-fir stands - density may in fact represent habitat quality in this case. A next step in trying to definitively ascertain whether aspen stands do in fact represent higher habitat quality would incorporate both winter trapping as well as a more rigourous trapping regime that would allow for a closer look at the reproductive capacity of these stands as compared to mixedwood and Douglas-fir stands. The cluster analysis of the specific stand attributes revealed a strong pattern of similar stand attribute characteristics by stand type. As such, it was interesting to see that aspen stands across the landscape supported similar communities of small mammals, as did the mixedwood and Douglas-fir stands. The exception to this can be seen in the sites from Pinantan Lake which cluster together with all of the aspen stands. These stands appear to have similar resources partioned in such a way as to support proportionately similar communities of small mammals. There also appears to be a geographic aspect to the site similarities for the mixedwood and Douglas-fir stands as sites within the same block are more similar than sites within different blocks. This hints at the potential for some other factors affecting these populations beyond the site level characteristics - local abiotic factors such as climate have been shown to affect small mammal communities (Korpimaki and Krebs 1996) and it may be appropriate to measure these attributes for future research. Many rodent species co-occur with one or more similar species (M'Closkey and Fieldwick 1975) and interspecific interactions are common with these species (Douglass 1976). These interspecific interactions can influence the distribution, population levels, and movements of small mammals (Douglass 1976). The co-existence of several species of small 67 mammals often is a consequence of divergent habitat selection (Douglass 1976). Aspen stands, and to a lesser degree mixedwood and Douglas-fir stands, appear to support a diverse and abundant community of small mammals with several numerically dominant species. This appears to be a consequence of habitat complexity and the availability of several habitat niches within these stands. Habitat selection by small mammals is strongly dependent on factors that ensure the provision of cover and the availability of food sources (Beaudoin et al. 2004) - both of which are very well represented within these stands (Chapter 2). There also may be a temporal pattern of abundance and richness within these sites that a two-year study may not have adequately identified. The presence of a dominant community of aspen, diversity of grass species, and shrub, herb, and total plant cover were correlated with both total abundance and the abundance of particular species. The correlations with the plant community attributes are important because they highlight the value of cover and food for small mammals. Other studies have highlighted the importance of downed C W D for small mammal abundance (Bowman et al. 2000). This attribute is of inherent value to many small mammals because it provides microhabitat for many species (Keddy and Drumond 1996). The results of this work do question the prominence of coarse woody debris as the driving force for small mammal species richness and abundance. One study block, Pinantan Lake, where the aspen stand contained the highest volume of downed C W D of all study sites, had a consistently lower abundance of small mammals than the Douglas-fir and mixedwood replicate stand within the same study block - these sites had very low C W D volume. These two sites can be characterized as having the highest diversity of grass species identified as well as having high shrub cover and herbaceous species diversity. Therefore, habitat selection by small mammals in this area appears to be strongly dependent on factors that ensure the provision of cover and the availability of food sources (Beaudoin et al. 2004) other than the amount and distribution of downed coarse woody debris (Craig et al. 2006). Therefore, it becomes important to consider the significance of other habitat elements beyond coarse woody debris for small mammals within managed forests. Correlation analysis based on the abundance of each species revealed a relationship between the abundance of several species. Most surprising was the fact that there were no significant negative correlations; this suggests that habitat specialization is occurring within 68 these sites and this is an effective mechanism for the coexistence among potentially competing species (Morris 1996). Other researchers have found distinct negative correlations between small mammal species. For example, Randall and Johnson (1979) showed that there was a segregation of habitat preference for M. montanus and M. longicaudus and Douglass (1976) demonstrated ecological separation between P. maniculatus and M. pennsylvanicus. For those sites not dominated by a few species, it seems as though; these stands provide adequate resources for ecological separation and niche requirements to the degree that interspecific competition is minimized. A s it has been pointed out that ecological separation occurs with many small mammal species (Anderson et al. 2002), it would also be of interest to examine what effect the seemingly synchronous population increases may have on this ecological separation over the long-term. 3.5 C O N C L U S I O N Small mammal abundance and diversity within aspen stands reported here rivals those reported elsewhere within temperate North American forests. A s these stands are currently being threatened by several anthropogenic influences (Bartos 2001) and current forest management may not be conducive to the maintenance of current stands (Sheppard et al. 2006), it is of vital importance that forest managers recognize the value of these stands and attempt to incorporate their long-term occurrence in to their management plans. 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J . 718 pp. 76 4.0 C H A P T E R F O U R - C A V I T Y - N E S T I N G B I R D C O M M U N I T I E S W I T H I N T H E D R Y I N T E R I O R F O R E S T S OF B R I T I S H C O L U M B I A , C A N A D A : T H E R O L E OF A S P E N 1 4.1 I N T R O D U C T I O N Several authors have identified the potential value of using cavity-nesting birds for ecological studies examining regional biodiversity (Jarvinen and Vaisanen 1979, Croonquist and Brooks 1991, Bradford et al. 1998, Mikusinski et al. 2001, and Nilsson et al. 2001). Cavity-nesting birds strongly tied to forests and are considered to be a very demanding taxonomic group in terms of their ecological requirements (Mikuskinski et al. 2001). The density and diversity of cavity-nesting birds also may have a strong influence on the richness and abundance of other nest cavity breeding and/or roosting species (Martin and Eadie 1999). Cavities created by cavity-nesting birds are used by a host of other secondary cavity-nesting species (Carlson et al. 1998, and Martin et al. 2004). In fact, at least 75 bird and 20 mammal species in North America use tree cavities (Aitken and Martin 2004) and some of these species are partly or entirely dependent on cavity-nesting excavating birds for this critical resource (Martin et al. 2004). The occurrence of a diverse array of cavity-nesting bird species also may indicate several properties of naturally-dynamic forested landscapes such as snag and coarse woody debris abundance and the presence of deciduous trees (Mikuskinski et al. 2001). Overall, cavity-nesting birds are considered an important component of the avifauna of forested ecosystems (Weikel and Hayes 1999) and their presence often is strongly tied to deciduous trees. Deciduous trees are selected preferentially by cavity-nesting birds for nest site location (Angelstam and Mikusinski 1994, Carlson et al. 1998, Aitken and Martin 2004, and Martin et al. 2004) due to a relatively high occurrence of decay fungi such as heart rot (Fomes ignarius) (DeByle et al. 1985). In fact, Martin et al. (2004) found that 95% of cavities used by cavity-nesting species in the interior of British Columbia were located in trembling aspen (Populus tremuloides) trees, although this species only comprised 15% of available trees at their study site. It is generally expected that deciduous stands wi l l support a diverse community of cavity-nesting birds (Sheppard et al. 2006). However, cavity-nesting ] A version of this chapter wi l l be submitted for publication. 77 birds also depend on coniferous trees for foraging (Kreisel and Stein 1999, Weikel and Hayes 1999, Walter and Maguire 2005, Hartwig et al. 2006, and Pechacek 2006). Mixedwood stands, by definition, contain a proportion of deciduous and coniferous trees; as such, mixedwood stands also may support a diverse community of cavity-nesting birds (DeByle et al. 1985) as multiple resources are potentially available - deciduous trees for nesting and coniferous trees for foraging. These sites should support both primary and weak cavity-excavating species. Cavity-nesting bird communities are structured in nest webs that contain primary cavity excavators (PCE), weak cavity excavators (WCE) , and secondary cavity-nesters (Martin and Eadie 1999). This guild classification is based on the mode of cavity acquisition (Aitken et al. 2002). Primary cavity excavators (PCE) birds, such as woodpeckers, sapsuckers and flickers, are those who excavate cavities that are used both by themselves and a host of other species (Daily et al. 1993, and Aitken and Martin 2004). Weak cavity excavators, such as nuthatches and chickadees, excavate their own cavities, use natural cavities or use cavities created by other species (Aitken et al. 2002). Secondary cavity-nesters use cavities created by other species or naturally occurring cavities (Aitken et al. 2002). The relative proportion of each of these different cavity nesting birds may reveal links existing among all cavity-nesting species in the community. For example, a higher proportion of P C E may reveal information about the structural dynamics of the stand. It also may reveal the potential for a larger community of animals to be present (Martin and Eadie 1999). There also is significant intra- and interspecific competition for cavities (Ingold 1994, and Carlson et al. 1998) and the community assemblage of cavity-nesting birds should reflect this competition. Competition and interspecific interactions should influence species distribution patterns of cavity-nesting birds (Stauffer and Best 1982, and Walankiewicz 1991). A s cavity-nesting birds often compete for similar resources, such as access to cavities and snags, ecological separation sometimes occurs between species (Gutzwiller and Anderson 1987). At the relatively fine spatial scale, this separation most often is reflected by the use of different-sized cavities (Martin et al. 2004) as well as by varying cavity height (Stauffer and Best 1982). Although, P C E and W C E species use similar resources, ecological separation of these resources appears to allow for the co-existence of these birds within a given site. It is 78 predicted that the distribution of birds within these guilds may be correlated (Martin and Eadie 1999) with one another at the site scale. The amount, distribution and diversity of habitat elements such as standing Coarse woody debris (SCWD) , downed coarse woody debris ( D C W D ) , as well as stand attributes and understory structure and diversity play vital roles in the life history of cavity-nesting birds (Martin and Eadie 1999, and Hoyt and Hannon 2002). The abundance and diversity of cavity-nesting birds has most often been associated with high snag density (e.g. Raphael and White 1984, Renken and Wiggers 1993, and Bennetts et al. 1996). It also has been associated with large trees (Harestad and Keisker 1989, and Poulsen 2002), trees with heart rot and fungal infections (Daily 1993), aspen volume (Berg 1997), and tall canopies (Gutzwiller and Anderson 1987). Other stand attributes such as D C W D (Lohr et al. 2002) also have been shown to influence cavity-nesting bird communities. A s such, it is important to examine the dynamics of these attributes within study sites to quantify the relationship between these variables and the presence, abundance and diversity of cavity-nesting birds. In this Chapter, I examine the cavity-nesting bird communities within three stand types: aspen, mixedwood and Douglas-fir. Specifically, I explore how diversity and abundance vary within three stand types; aspen, mixedwood, and Douglas-fir. I also explore which stand attributes may be used to best explain both the diversity of and abundance of cavity-nesting birds. 4.2 M E T H O D S 4.2.1 S T U D Y A R E A S This study is part of a larger study examining the biodiversity of aspen stands within the dry, interior forests of British Columbia that also included an examination of small mammal communities and stand attributes. The field work was conducted near Kamloops, British Columbia, Canada (50°43 ' N ; 120°25' W). A l l study sites were located within the Interior Douglas-fir, Thompson dry cool (IDFdki; dry precipitation regime; cool temperature regime) biogeoclimatic zone (Meidinger and Pojar 1991). Four replicate stands of aspen (A), mixedwood (M) and Douglas-fir (F) were selected within three geographically distinct areas 79 (blocks), Monte Lake ( A l , A 2 , M l , M 2 , F l , F2), Badger Lake (A3, M 3 , F3) and Pinantan Lake (A4, M 4 , F4) (see Figure 1.2 - Chapter 1). 4.2.2 C A V I T Y - N E S T I N G B I R D S U R V E Y S Cavity-nesting birds were sampled during 2005 and 2006 using the fixed-radius point count method (Martin and Eadie 1999), with four stations per site, during the approximate breeding season of each species. Because cavity-nesting birds are not easily censused using point-counts (Martin and Eadie 1999), I used playbacks calls for each species. A t each point-count station, the call of each bird species was played twice, followed by thirty seconds of listening time. These calls were played in order from the smallest species to the largest species to reduce competitive exclusion (Griggs 1997). Table 4.1 lists the birds sampled for and the playback order used. A l l cavity-nesting bird species heard and seen within 50 meters in all cardinal directions from the station centre were recorded. Specific detection parameters recorded included horizontal distance from the observer to each bird detected, species, and direction. Activity parameters for each bird also were noted including whether the bird was seen, calling, singing or drumming (Martin and Eadie 1999). To reduce surveyor bias, point count stations were spaced at least 200 meters apart (Martin and Eadie 1999). Each year, three rounds of counts were completed from early M a y to early June. A single observer was used at each site and point count station. We rotated the order and time at which stations were surveyed as well as the sites in which individuals surveyed. Cloud cover, precipitation, and wind speed and direction also were recorded. Point count surveys only occurred under good detection conditions - little wind or noise and no active precipitation -and from 0530 am to 0900 hours. 4.2.3 D A T A A N A L Y S I S Point count surveys typically are used to provide an index of abundance that can be used to make comparisons (Farnsworth et al. 2002, and Petit et al. 1995). For the analysis of point count data, I used the total number of detections per site and the mean number of individuals detected per point count station as indices of relative abundance within a given 80 Table 4.1 Cavity-nesting birds sampled during study as well as playback order and guild association. Playback Order Code Common Name Scientific Name 'Gui ld 1 PvBNU Red-breasted nuthatch Sitta canadensis ' W C E 2 M O C H Mountain chickadee Par us gambeli ' W C E 3 B C C H Black-capped chickadee Parus articapillus ' W C E 4 W B N U White-breasted nuthatch Sitta carolinensis ' W C E 5 D O W O Downy woodpecker Picoides pubescens ' W C E 6 R N S A Red-naped sapsucker Sphyrapicus nuchal is ' P C E 7 H A W O Hairy woodpecker Picoides villosus ' P C E 8 T T W O Three-toed woodpecker Picoides tridactylus ' P C E 9 B B W O Black-backed woodpecker Picoides arcticus ' P C E 10 W I S A Williamson's sapsucker Sphrapicus thyroideus 2 W C E 11 N O F L Northern Flicker Colaptes auratus ' P C E 12 PIWO Pileated woodpecker Dryocopus pileatus ' P C E Note: 'Martin and Eadie (1999) and 2Cooper 1995 site for each species (Martin and Eadie 1999). A randomized block A N O V A (Zar 1999) was used to analyze the total number of detections per site and the mean number of per point count using the function P R O C G L M in SAS 9.1 (SAS Institute 2006). B i rd detection data were analyzed separately for each year and for both years combined where appropriate. Data not conforming to normality and/or equal variance were subject to various transformations. In addition, the mean difference in auditory versus visual detections was tested using a randomized block A N O V A to identify possible differences in detection probability. Pairwise t-tests were used for all post-hoc tests with an associated significance level of 0.017 (0.05/number of replicate blocks) and all mean data is reported with standard error. 81 To summarize similarities in cavity-nesting bird communities between study sites, a cluster analysis was conducted using average linkage between sites (SAS Institute 2006), with a dendrogram used to display the results (Pearce et al. 2003). The mean numbers of detections per plot of each species, for each year, within each study site were used to explore similarities in community assemblages (Oertlie et al. 2005). Also, the number of P C E and W C E species detected for each year was used to compare these communities through cluster analysis. Spearman's rank correlation analysis was used to explore the relationship between the total abundance of cavity-nesting birds, P C E and W C E species with total volume of C W D (m /ha), snag volume (m /ha), snag density (stems/ha), downed C W D volume (m /ha) and percent aspen and Douglas-fir (see Chapter 2). These variables all were autocorrelated (r > 0.65; P ^ 0.0230) with each other, save the amount of Douglas-fir, but as there is potential biological significance associated with each of these variables. I used this analysis to explore correlations between the abundance of each cavity-nesting bird species. I also tested to see i f there was a correlation between the abundance of each of the W C E species and the abundance of P C E species. I used the relative abundance (mean number of detections per point count station) of each species in these analyses. Species diversity was assessed using a number of different indices. These additional indices were used as they provide more information about community composition than species richness, by taking into account the relative abundances of different species. The Simpson's diversity indice (Simpson 1949) is a simple mathematical measure that characterizes species diversity in a community based on the proportion of species relative to the total number of species and is a measure of species evenness. The Shannon-Wiener index (Pielou 1966) is sensitive to changes in the number of rare species within a community (Peet 1974). This index is based on the degree of difficulty in predicting correctly the species of the next individual sampled, increases with the number of species in the community, and ranges from 0 to approximately 5.0 for biological communities (Washington 1984) and is highest when species proportions are equal (Staudhammer and LeMay 2001). MacArthur 's diversity index (MacArthur and MacArthur 1961) is sensitive to relative abundances of species and less sensitive to the number of species (Magurran 1988), giving little weight to rare species. These indices convey slightly different information about the diversity and structure of biotic communities. Diversity for cavity-nesting birds was calculated using the 82 mean estimated abundance of each species trapped at each site during each of three sample periods (from July to August) for a given year (Krebs 1999). Diversity for cavity-nesting birds was calculated using the mean number of detections per plot of each species, for each year, within each study site (Krebs 1999). 4.3 R E S U L T S 4.3.1 T O T A L D E T E C T I O N S A total of 1541 detections of fourteen cavity-nesting bird species were made during 288 point count surveys. Dominant species across all sites included the mountain chickadee, red-breasted nuthatch, black-capped chickadee, red-naped sapsucker, and the downy woodpecker. Incidental detections of boreal chickadees (Parus borealis) and pygmy nuthatches (Sitta pygmaea) were made but not included in the analysis. The total number of bird detections (Figure 4.1) was significantly different between the stand types in 2005 (F4j = 8.90; P = 0.012) and 2006 (F 4 , 7 = 37.69; P = <0.001). Aspen stands had significantly more detections then either the mixedwood Oo.o 17,11 = 3.98; P = 0.005) and the Douglas-fir stands Oo.on.n = 3.19; P = 0.015) in 2005. The Douglas-fir and mixedwood stands had similar total detections in 2005 Oo.o 17,11 = 0.79; P = 0.4547). In 2006, aspen stands had significantly more detections then either the mixedwood (^ 0.017,11 = 8.39; P = <0.001) or the Douglas-fir stands Oo.oi7,n = 6-12; P = O.001) . The Douglas-fir and mixedwood stands had similar total detections in 2006 O0.017.11 = 2.27; P = 0.057). 83 500 400 300 <u I 200 c ioo ^ . ..f. A T M I X F D A T M I X F D 2005 2006 Figure 4.1 Total number of cavity-nesting bird species detections for each year (2005 and 2006). Note: A T refers to aspen, M I X to mixedwood, and F D to Douglas-fir. 4.3.2 T O T A L SPECIES D E T E C T I O N S The total number of detections for each species was higher within aspen stands as compared to the mixedwood and Douglas-fir stands for all cavity-nesting bird species with the exception of Williamson's sapsuckers (S. thyroideus) (Figure 4.2). The mixedwood stands had more total detections of all cavity-nesting bird species versus the Douglas-fir stands with the exception of the black-capped chickadee (64 within Douglas-fir and 51 in mixedwood stands). The test for differences in the mean proportion of detections of auditory versus visual detection revealed no difference by stand type ( F 4 ] 7 = 3 . 1 1 ; / ' = 0.108) in these detections. 84 <^  ^ ° o ° <0° ^ ^ # ^ * < ^ •<> Cavity-nesting bird species Figure 4.2 Total number of cavity-nesting bird detections by species and stand type. See Table 4.1 for species codes. 4.3.3 M E A N N U M B E R OF DETECTIONS There were significant differences in the mean number of detections per point-count station of both WCE and PCE species within aspen, mixedwood and Douglas-fir stands (Table 4.2 and Appendix 6). In terms of WCE, there was no difference in the mean number of detections of mountain chickadees, red-breasted nuthatches, white-breasted nuthatches and Williamson's sapsuckers within the three stand types. There was a difference in the mean number of detections per point-count station for black-capped chickadees and downy woodpeckers with aspen stands having significantly more detections than mixedwood and Douglas-fir stands. There was no difference between mixedwood and Douglas-fir stands. 85 Table 4.2 Mean number of detections per point count station for all cavity-nesting bird species recorded in aspen (AT) , mixedwood ( M I X ) , and Douglas-fir (FD) stands for both sampling years, and results of A N O V A analysis, t-tests conducted at a = 0.017, examining differences in the number of detections of each species. Bold type indicates stand type with highest mean value. See Appendix 6 for exact test statistical values. A T M I X F D Species (w=24) (w=24) (»=24) Pattern 3 f 0.017,11 <0.017,11 Red-breasted nuthatch Sitta canadensis 1.55 1.46 1.15 - ** **** **** Mountain chickadee Parus gambeli 1.35 1.23 0.97 - ** **** Black-capped chickadee Parus articapillus 1.20 0.53 0.67 A T > M I X & F D * *** *** Red-naped sapsucker Sphyrapicus nuchalis 0.99 0.51 0.30 A T > F D * *=t=* Downy woodpecker Picoides pubescens 0.69 0.17 0.08 A T > M I X & F D * *** *** Hairy woodpecker Picoides villosus 0.48 0.14 0.07 A T > M I X & F D * *** *** White-breasted nuthatch Sitta carolensis 0.26 0.24 0.17 - ** **** **** Northern flicker Colaptes auratus 0.35 0.21 0.08 A T > M I X & F D * *** *** Pileated woodpecker Dryocopus pileatus 0.31 0.09 0.10 A T > M I X & F D * *** Three-toed woodpecker Picoides tridactylus 0.11 0.04 0 — ** **** **** Black—backed woodpecker Picoides arcticus 0.10 0.03 0 — ** **** **** Williamson's Sapsucker Sphyrapicus thyroideus 0.05 0.04 0.06 - ** **** **** Mean total detections per point count station 7.44 4.69 3.65 A T > M I X & F D * *** *** * P < 0.05, **P> 0.05, ***P< 0.017, ****P> 0.017, aaspen and mixedwood, "aspen and Douglas-fir CO For P C E birds, pileated woodpeckers, northern flickers, red-naped sapsuckers and hairy woodpeckers each had a greater mean number of detections within aspen stand than mixedwood and Douglas-fir stands. 4.3.4 W E A K - A N D P R I M A R Y C A V I T Y - E X C A V A T I N G C O M P A R I S O N The total number of detections of W C E and P C E species was higher within aspen stands during both years - with the exception of mixedwood sites having more detections of W C E in 2006 over aspen sites in 2005 (Figure 4.3). The total number of detections of P C E species was higher within all four aspen stands than either of the other stand types. O f the total detections within aspen stands, 36% were of P C E species in 2005 and 34% in 2006. O f the total detections within mixedwood stands, 17% were of P C E species in 2005 and 10% in 2006. O f the total detections within Douglas-fir stands, 18% were of P C E bird species in 2005 and 26% in 2006. c o T3 450 400 H 350 H 300 A 250 H 4) | 200 C o AT05 AT06 MIX05 MIX06 FD05 FD06 Stand type Figure 4.3 Comparison o f total number o f detections by stand type and year (2005 and 2006) for primary cavity-excavating (PCE) and weak cavity-excavating ( W C E ) birds Note- A T refers to aspen, M I X to mixedwood, and F D to Douglas-fir and 05 and 06 correspond to 2005 and 2006. 87 The mean number of detections of weak cavity excavating and primary cavity excavating species (Figure 4.4) was different between the stand types ( F ^ = 8.67; P = 0.012). Aspen stands showed a higher mean proportion of P C E versus W C E species than the Douglas-fir stands (to.017,11 = 4.05; P = 0.005) and the mixedwood stand (to.017,11 = 3.27; P = 0.016). There also was a marked change in the proportion of detections of cavity-nesting birds from 2005 to 2006, especially for W C E species. Specifically, five cavity-nesting bird species showed a marked change in abundance over the two years (Figure 4.5). These included four W C E and one P C E species. The mountain and black-capped chickadee showed the largest increases in the mean number of detections at all sites. The mean number of detections increased the most for the mountain chickadee during the study period. The white- and red-breasted nuthatches also showed increases in the mean number of detections. Only the hairy woodpecker showed a decrease in the mean number of detections per point count station. 88 c o s O o o a. u o-1-<u X! s c c 1) o § < n i i r A l A 2 A3 A4 M l M 2 M3 M 4 FI F2 F3 F4 A l A2 A3 A4 M l M 2 M3 M 4 FI F2 F3 F4 ASPEN MIXEDWOOD DOUGLAS-FIR Figure 4.4 The relative abundance of primary cavity-excavating and weak cavity -excavating species within each study site. 89 c 3 O o o C O -a 1> 3 C C 2.25 2.00 1.75 1.50 1.25 1.00 0.75 H 0.50 8 0.25 c C 3 < 0.00 H W B N U H A W O R B N U B C C H M O C H •v—• •v o - • o -• •o Session 1 Session 2 Session 3 Session 1 Session 2 Session 3 2005 2006 Figure 4.5 Number of detections per point count station for the five species that showed a marked change during the two-years of sampling. Four weak cavity-excavating species increased in abundance while one primary cavity-excavating species ( H A W O ) decreased in abundance. A l l other species were slightly more abundant in the second year or showed no change. 4.3.5 C O R R E L A T I O N The total abundance of cavity-nesting bird species was correlated with total volume of C W D (m3/ha), snag volume (m3/ha), snag density (stems/ha), downed C W D volume (m3/ha) and % aspen (Table 4.3). P C E and W C E bird abundance was correlated with total volume of C W D (m3/ha), snag volume (m3/ha), downed C W D volume (m3/ha) and percent aspen. W C E bird abundance also was correlated with snag density. Correlation analysis revealed a strong positive relationship between the total abundance of P C E and W C E species in both 2005 (r 2 = 0.79; P - 0.002) and 2006 (r 2 = 0.82; P <0.001). For individual species, the abundance of mountain chickadees, black-capped chickadees, red-breasted nuthatches, and downy woodpeckers, was correlated with the abundance of several P C E species (Table 4.4) - Williamson's sapsuckers were not correlated with the abundance of any P C E species. 90 The abundance of all six P C E birds showed significant correlations with the abundance of other P C E species. 4.3.6 C L U S T E R A N A L Y S I S Cluster analysis of cavity-nesting bird community assemblages (Figure 4.7) produced two general groupings. The first grouping included all four of the aspen stands. The second general branch of the dendrogram showed a similarity in cavity-nesting bird communities between the majority of Douglas-fir and mixedwood stands. Cluster analysis of assemblages of P C E and W C E (Figure 4.8) birds produced three site groupings. The first branch of the dendrogram contained all four replicate aspen sites, whose cavity-nesting bird communities were quite different than the other study sites. The second branch of the dendrogram showed a similarity in cavity-nesting bird communities between the majority of Douglas-fir and mixedwood stands. The third branch of the dendrogram was exclusively occupied by a single mixedwood stand. 91 Table 4.3 Results of Spearman's rank correlation analysis of the total abundance of cavity-nesting birds and the total abundance of primary cavity-excavating (PCE) and weak cavity-excavating (WCE) species with various stand level attributes. Bo ld values represent correlation coefficients and values in parantheses are significance values. Attribute Total abundance P C E W C E Total volume (m3/ha) *0.66 0.57 *0.78 (0.020) (0.055) (0.002) Snag volume (m3/ha) *0.59 0.52 *0.73 (0.042) (0.080) (0.007) Snag density (stems/ha) *0.63 0.48 *0.76 (0.028) (0.112) (0.004) Downed C W D (m3/ha) *0.71 *0.59 *0.79 (0.010) (0.042) (0.002) Live aspen density (stems/ha) *0.79 *0.64 *0.91 (0.002) (0.025) (<0.001) Live Douglas-fir density(stems/ha) *-0.76 *-0.63 *-0.87 (0.004) (0.027) (<0.001) Snag class 7 . 5 - 10 cm 0.25 0.17 0.27 (0.430) (0.602) (0.391) 1 0 - 2 5 cm *0.76 *0.65 *0.73 (0.004) (0.022) (0.007) 25 - 35 cm *0.82 *0.82 *0.78 (0.001) (0.001) (0.003) > 35 cm *0.56 0.44 *0.61 (0.060) (0.151) (0.037) significant at a = 0.05. 92 Table 4.4 Results of Spearman's rank correlation analysis between the respective abundance (mean number per point count station) of the cavity-nesting bird species. Bold values represent correlation coefficients and values in parantheses are significance values. Note: bird codes are available in Table 4.1. Species RNSA PIWO NOFL HA WO TTWO BBWO M O C H B C C H RBNU W B N U WISA DOWO RNSA - 0.56 0.86 0.78 0.79 0.37 0.45 0.69 0.33 0.33 0.38 0.87 - (0.060) (O.001) (0.003) (0.002) (0.235) (0.141) (0.014) (0.298) (0.292) (0.229) (<0.001) PIWO 0.56 - 0.60 0.45 0.36 0.41 0.58 0.64 0.33 0.30 0.12 0.61 (0.060) - (0.040) (0.139) (0.255) (0.180) (0.050) (0.026) (0.293) (0.339) (0.708) (0.035) NOFL 0.86 0.60 - 0.73 0.68 0.36 0.32 0.73 0.31 0.19 0.02 0.81 (<0.001) (0.404) - (0.007) (0.015) (0.250) (0.305) (0.007) (0.332) (0.545) (0.944) (0.001) HA WO 0.78 0.45 0.73 - 0.74 0.56 0.48 0.67 0.54 0.28 0.14 0.66 (0.003) (0.139) (0.007) - (0.006) (0.060) (0.117) (0.016) (0.071) (0.385) (0.657) (0.012) TTWO 0.79 0.36 0.68 0.74 - 0.31 -0.01 0.44 0.31 0.64 0.32 0.80 (0.002) (0.255) (0.015) (0.006) - (0.319) (0.971) (0.155) (0.331) (0.026) (0.312) (0.002) BBWO 0.37 0.41 0.36 0.56 0.31 - 0.36 0.34 0.16 0.23 0.16 0.60 (0.235) (0.180) (0.250) (0.060) (0.319) - (0.249) (0.277) (0.620) (0.473) (0.617) (0.040) M O C H 0.45 0.58 0.32 0.48 -0.01 0.36 - 0.45 0.36 -0.25 0.15 0.24 (0.141) (0.050) (0.305) (0.117) (0.971) (0.249) - (0.122) (0.247) (0.436) (0.639) (0.459) B C C H 0.69 0.64 0.73 0.67 0.44 0.34 0.47 - 0.21 0.08 -0.17 0.57 (0.014) (0.026) (0.007) (0.016) (0.155) (0.277) (0.122) - (0.516) (0.802) (0.608) (0.052) R B N U 0.33 0.33 0.31 0.54 0.31 0.16 0.36 0.21 - 0.34 -0.06 0.17 (0.298) (0.293) (0.332) (0.071) (0.331) (0.620) (0.247) (0.516) - (0.277) (0.851) (0.605) W B N U 0.33 0.30 0.19 0.28 0.64 0.23 -0.25 0.08 0.34 - 0.27 0.39 (0.292) (0.339) (0.545) (0.385) (0.026) (0.473) (0.436) (0.802) (0.277) - (0.391) (0.204) W1SA 0.38 0.12 0.02 0.14 0.32 0.16 0.15 -0.17 -0.06 0.27 - 0.38 (0.229) (0.708) (0.944) (0.657) (0.312) (0.617) (0.639) (0.608) (0.852) (0.391) - (0.217) DOWO 0.87 0.61 0.81 0.66 0.80 0.60 0.24 0.57 0.17 0.39 0.38 -(O.001) (0.035) (0.001) (0.012) (0.002) (0.040) (0.459) (0.052) (0.605) (0.204) (0.217) -S i t e fil PlH Ml —I FI — 1 F3 FH M2 FE M3 I 1 1 1 1 1 1— 1.0 0.S 0 .8 0 .7 0 .6 0 .5 0 .4 R-Squared —I 1 1 1 0.3 0.£ 0.1 0.0 Figure 4 .6 Dendrogram showing results of a cluster analysis used to group study sites on the basis of similarities in the abundance of each cavity-nesting bird species. Si te flspen 1 -flspen 3 fispen 2 1 flspen H Mix 1 —] Mix 3 —' Mix Z F i r 3 F i r 1 I F i r M ' F i r Z ' Mix M 1 I I I I I 1 1 1 1 1 1 1.0 0.S 0.8 0 .7 0.E 0.5 0.H 0.3 0 .2 0.1 0 .0 R -Squared Figure 4.7 Dendrogram showing results of a cluster analysis used to group study sites on the basis of similarities in the abundance of the communities of primary cavity-excavating and weak cavity-excavating birds. 4.3.7 SPECIES D I V E R S I T Y Species richness (number of species observed) for cavity nesting birds was significantly higher within aspen stands in both 2005 and 2006 than either the mixedwood or Douglas-fir stands (Tables 4.5 and 4.6). There was no difference between species richness for either year between the mixedwood and the Douglas-fir stands. The diversity indices (Shannon's, Simpson's and MacArthur's) show a similar pattern. The Shannon indice was significantly different between stand types in 2005 and 2006. This index value was significantly higher in aspen stands versus Douglas-fir stands. The difference between aspen and mixedwood stands was significant in 2005 and 2006. In terms of the Simpson's index, there was a significant difference between stand types in 2005 but not in 2006. This index value was only significantly higher in aspen stands versus Douglas-fir stands and mixedwood stands in 2005. The MacArthur's index was significantly different between stand types in 2005 but not in 2006. This index was significantly different by stand type when both years are combined ( F 4 7 = 11.04; P = 0.007) with aspen stands having significantly higher index values than the Douglas-fir (F4J = 4.19; P = 0.004) and the mixedwood stands (F 4 , 7 = 3.94; P = 0.006). Overall, aspen stands had diversity index values that were higher than the mixedwood and Douglas-fir stands in seven out of eight cases. These diversity indices were not significantly different between the mixedwood and the Douglas-fir stands. The year-to-year stand rank of species diversity within each stand was relatively constant. When these ranks changed, the change was only by one or two positions and was always within the Douglas-fir or mixedwood stands - aspen stands consistently ranked one through four. 96 Table 4.5 2005 cavity-nesting bird diversity indices and stand rank, overall diversity, together with results of A N O V A s and post-hoc tests analyzing differences in these indices between stand types. 2005 Bi rd Diversity Indices Site Richness Shannon's Simpson's MacArthur's Rank A l 10 2.84 0.86 6.73 3 A 2 12 3.13 0.88 7.57 1 A3 10 2.85 0.84 6.13 4 A 4 11 3.10 0.88 7.85 2 Stand average 10.75 ± 0 . 2 4 2.98 ± 0 . 0 4 0.87 ± 0 . 0 1 7.07 ± 0 . 2 0 M l 8 2.41 0.75 4.08 10 M 2 9 2.73 0.79 4.70 7 M 3 7 2.15 0.72 3.56 11 M 4 9 2.72 0.82 5.57 5 Stand average 8.25 ± 0 . 2 4 2.50 ± 0 . 0 7 0.77 ± 0 . 0 2 4.48 ± 0.22 F l 7 2.16 0.70 3.38 12 F2 9 2.72 0.81 5.33 6 F3 8 2.44 0.79 4.54 8 F4 8 2.63 0.76 4.22 9 Stand average 8.00 ± 0 . 2 0 2.49 ± 0 . 0 6 0.77 ± 0 . 0 2 4.37 ± 0 . 2 0 **8.41 6.90 **8.57 **15.92 P 0.012 0.022 0.012 0.003 % . 0 1 7 , l 1 *3.76 3.27 *3.45 *7.98 P 0.007 0.014 0.011 0.002 '0 .017,1 1 *3.17 3.17 *3.28 *4.78 P 0.016 0.016 0.014 0.002 % . 0 1 7 , l 1 -0.68 -0.09 -0.17 -0.20 P 0.517 0.924 0.868 0.845 Note: adenotes statistical value for difference between aspen and mixedwood; aspen and Douglas-fir and °mixedwood and Douglas-fir. **denotes a significant difference at a =0.05 *denotes a significant difference at a =0.017. 97 Table 4.6 2006 cavity-nesting bird diversity indices and stand rank, overall diversity, together with results of A N O V A s and post-hoc tests analyzing differences in these indices between stand types. 2006 Bird Diversity Indices Site Richness Shannon's Simpson's MacArthur's Rank A l 11 2.98 0.85 6.43 2 A 2 12 3.08 0.88 6.70 1 A 3 11 2.89 0.84 6.33 3 A 4 11 2.95 0.84 6.19 4 Stand average 11.25 ± 0 . 1 3 2.98 ± 0 . 0 3 0.85 ± 0 . 0 1 6.41 ± 0 . 0 5 M l 7 2.10 0.74 4.08 10 M 2 9 2.59 0.83 5.75 5 M 3 8 2.00 0.66 3.18 11 M 4 8 2.67 0.82 5.67 6 Stand average 8.00 ± 0 . 2 4 2.35 ± 0 . 0 9 0.77 ± 0 . 0 2 4.67 ± 0 . 3 1 FI 7 2.09 0.73 3.65 12 F2 8 2.37 0.79 4.71 8 F3 8 2.33 0.81 5.32 7 F4 8 2.47 0.77 4.33 9 Stand average 7.75 ± 0 . 1 3 2.34 ± 0 . 0 5 0.78 ± 0 . 0 1 4.50 ± 0.17 < ^4,7 **30.50 **8.95 3.24 5.20 P O.001 0.011 0.101 0.041 %.017,11 *7.00 *3.23 2.02 3.01 P O.001 0.015 0.083 0.016 '0.017,11 *6.50 *3.23 2.35 2.66 P O.001 0.015 0.051 0.033 %.017,11 -0.50 O . 0 1 0.33 -0.26 P 0.632 1.000 0.754 0.806 Note: adenotes statistical value for difference between aspen and Douglas-fir; aspen and mixedwood and c mixedwood and Douglas-fir. **denotes a significant difference at a =0.05 *denotes a significant difference at a =0.017. 98 4.4 D I S C U S S I O N The diversity and relative abundance of cavity-nesting birds reported here is equal to or greater than that reported in other studies within similar forests (Martin and Eadie (1999) for Douglas-fir and aspen forests; Stelfox (1995) for aspen-mixedwood forests). Part of this may be attributed to the relatively high diversity of cavity-nesters within the study region (Griggs 1997), but it also is a product of aspen and its associated stand attributes and their importance to cavity-nesting birds. Aspen trees preferentially are selected for nest sites even when they are a minor component of a forest (Martin and Eadie 1999, and Harestad and Keister 1989). The relatively high density of cavity-nesting birds reported here also may be a product of high snag densities within aspen stands (Raphael and White 1984). To some degree, it also may be a product of the current outbreak of mountain pine beetle (Dendroctonus ponderosae) in British Columbia - the largest ever recorded for North America (Martin et al. 2006). It is expected that an increase in beetle densities may increase the population density, breeding success and winter survival of forest bird species (Martin et al. 2006). The densities also may be a factor of the sampling used, namely playbacks that are designed to attract species. It was not uncommon for 2 - 6 birds of a particular species to respond to any one playback call - especially red-breasted nuthatches, chickadees and red-naped sapsuckers. Also, in an exploration of the population trends of each of the bird species from data collected during the North American Breeding Bird Survey (Sauer et al. 2005) several cavity-nesting bird species appear to show an eruptive population trend - these patterns also have been studied and confirmed elsewhere (Koenig 2001, and Koenig and Knops 2001). Those species showing this eruptive potential include the mountain chickadee, black-capped chickadee, red-naped sapsucker, and the red-breasted nuthatch, all species found in relatively high densities here, and probably linked to high winter survival (Koenig and Knops 2001). Several extrinsic factors may be playing a role in the relatively high overall abundance of cavity-nesting birds reported here compared to other studies. It also is interesting to see similarity in the communities of these birds within the stand types, as revealed by the cluster analysis. Aspen stands supported similar communities of P C E and W C E species as did the mixedwood and Douglas-fir stands. These stands appear to have similar resources partitioned in such a way as to support proportionately similar 99 communities of cavity-nesting birds. Mixedwood stands contain a relatively large component of aspen trees, which one would have expected to have translated into a more abundant bird community - at least as compared to Douglas-fir stands - yet I found no difference here. There are potentially other factors contributing to this pattern including a lack of suitable nest trees. Martin and Eadie (1999) found a surprisingly weak negative correlation with the abundance of P C E and W C E species during their work in mixed-deciduous forests in north-central British Columbia; explanations for this included competition or different habitat preferences. The diversity and potential community assemblage of cavity-nesters in north-central British Columbia is similar to the community of cavity-nesters in my study area, yet their results contrast sharply with the very strong positive correlation seen in this study. Access to resources likely plays a role in shaping the composition of cavity-nesting bird communities (Lawler and Edwards 2002) and the density of snags may be the resource (Raphael and White 1984) that most strongly shapes the community assemblage of cavity-nesting birds (Brawn and Balda 1988). Competition for nest sites also can have strong effects on community composition (van Balen et al. 1982). The aspen sites here do not appear to be limited by the availability of nest sites, as snag densities were in the order of 173-370 per ha. Both classes of excavating species appear to be able to preferentially select nest sites within these stands and interspecific competition is potentially limited to the degree that these two guilds are able to overlap in abundance and specific habitat use. Overall, communities of cavity-nesting birds and the resources they require within the interior and the north-central part of British Columbia appear to be structured quite differently. Like other investigators, I found significant correlations between snag density and the abundance of cavity-nesting birds (Raphael and White 1984, and Ohmann et al. 1994). Snags and the volume of snags are both critical for both P C E and W C E species (Harestad and Keister 1989) as the life history of these birds are tied to these snags. The positive correlation between the abundance of cavity-nesting birds and aspen may be attributed to the fact that cavities arise more prevalently in deciduous versus coniferous trees (Poulsen 2002) and that aspen trees preferentially are selected for nest sites (Martin et al. 2004). The relationship between cavity-nesting birds and downed C W D may be a factor of foraging patterns exhibited by individual bird species but is more likely a factor of stand characteristics. As 100 expected, the abundance of cavity-nesting birds also was strongly correlated with the abundance of larger diameter snags. Cavity-nesting birds have been shown to preferentially select trees with larger D B H (Harestad and Keister 1989). Regression analysis revealed a relationship between the same variables noted in the correlation analysis. This highlights the importance of these attributes for cavity-nesting birds. A s many cavity-nesting bird species are subject to both inter- and intraspecific competition for cavities (Ingold 1994, and Martin et al. 2002) it was expected that there would be some positive and negative correlations between the abundance of specific cavity-nesting species. Several species exhibited strong positive correlations in their abundance and the abundance of other species, but there were few negative correlations - none of which were strong or significant. The positive correlations may be a reflection of the presence of a particular resource that all species depend on. It also may reflect that these resources are not limited and competition for nest sites may not be occurring. Again, the potential availability of snags did not appear to be limited within aspen stands, but probably was within the Douglas-fir and mixedwood stands. Although there is a strong association with diversity and abundance of cavity-nesting birds with aspen stands, other studies have shown that coniferous-dominated stands also serve as important areas for foraging (Martin and Eadie 1999, and Martin et al. 2006). Mixedwood stands therefore potentially provide two key resources for cavity-nesting birds -nest sites and foraging trees. It is surprising that these stands did not support a more abundant or diverse community of cavity-nesting birds. Cavity-nesting birds within these stands were far less abundant and diverse than aspen stands, and no different than Douglas-fir stands. It becomes important to identify the limiting resource within these stands especially with the consideration that aspen may be threatened. Are suitable nesting sites the limiting resource for cavity-nesting birds within mixedwood and Douglas-fir stands? Is there still the potential for these stands to support a larger community of birds i f nest sites are artificially created using nest boxes and snag creation? Other studies have shown that woodpecker abundance increases when artificial cavity boxes are added to a stand (e.g. Franzreb 1997, and Ingold 1998). There is value in assessing whether an increase in the availability of cavities within mixedwood and Douglas-fir forests would cause changes in the community dynamics of cavity-nesting birds within these forests. It would also be important to assess and compare 101 fledgling success within aspen stands to that within mixedwood and Douglas-fir stands that had cavity densities artificially increased. This would allow for an examination as to whether their affinity for aspen is specifically due to this hardwood resource or to snag volume (m /ha) and density (stems/ha). Several cavity-nesting bird species studied here are known to be migratory while others are year-round residents (Griggs 1997). This work was conducted while all bird species were potentially present in the study area and during the breeding season of these species. Coniferous dominated stands also may be preferentially selected during the non-breeding season, especially during the winter months, as these areas are important for foraging (Martin and Eadie 1999, and Martin et al. 2006). Additionally, habitat use in the winter is critical for the survival and reproductive success many animals in northern climates (Van Home 1983). Therefore, it would be important to conduct this work during the non-breeding season to assess the relative use of aspen, mixedwood and Douglas-fir stands for year-round resident cavity-nesting birds. Playbacks of barred owls (Strix varia) could be used during this season as cavity-nesting birds are known to respond to these calls (Wilkins and Dusak 2006). This work would help to identify the year-round value of each of these stand types within the dry interior forests of British Columbia. There is a strong potential that forest management practices could have a significant impact on the overall diversity of forest bird and mammal communities (Martin and Eadie 1999), especially with the decline of aspen stands. There also is potential for forest management practices such as retention harvesting where all aspen and Douglas-fir are retained together to meet most of the needs of cavity-nesting birds (Martin and Eadie 1999). The retention harvesting of stands within dry interior British Columbia forests also could help to augment the cavity-nesting bird communities i f clumps of large, decadent snags are left after harvesting. Snags are an important component of ecosystems for cavity-nesting birds and there is a relationship between the richness of cavity-nesting birds and snag density and volume. A s cavity-nesting birds require important structural characteristics of natural forests such as dead standing trees and large deciduous trees (Angelstam and Mikuskinski 1994) it is important that these components are retained in managed forests. 102 4.5 C O N C L U S I O N Although no cavity-nesting bird species was restricted solely to aspen stands, the abundance of all species, save the Williamson's sapsucker, typically was much higher within aspen stands. These results highlight the importance of aspen stands in the dry interior forests of British Columbia. These stands support a diverse and abundant community of P C E and W C E birds; as such, they are extremely important for all of the species. Aspen stands clearly are declining within western North America (Bartos 2001), and they support a relatively diverse and abundant community of cavity-nesting birds: the management of these stands therefore becomes a serious issue. A s the presence of a diverse community of cavity-nesting birds may reflect a diversity of secondary cavity-nesting species (Martin and Eadie 1999) the importance of maintaining these stands becomes even more critical. 103 4.6 L I T E R A T U R E C I T E D Aitken, K . E. H . , K . L . Wiebe., and K . Martin. 2002. Nest-site reuse patterns for a cavity-nesting bird community in Interior British Columbia. The Auk. 119(2): 391-402. Aitken, K . E. H . , and K . Martin. 2004. Nest cavity availability and selection in aspen-conifer groves in a grassland landscape. Canadian Journal of Forest Research. 34: 2099-2109. Angelstam, P., and G . Mikuskinski . 1994. Woodpecker assemblages in natural and managed boreal and hemiboreal forests - a review. Annales Zoologica Fennica. 31: 157-172. Bartos, D . L . 2001. Landscape dynamics of aspen and conifer forests. U S D A Forest Service Proceedings. R N M R S - P - 1 8 . Bennetts, R .E . , G . C . White, F . G . Hawksworth., and S.E. Severs. 1996. 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Characteristics of foraging sites and the use of structural elements by the pileated woodpecker LDryocopus pileatus) on southeastern Vancouver Island, British Columbia, Canada. Annales Zoologici Fennici. 43(2): 186-197. Hoyt, J.S., and S.J. Hannon. 2002. Habitat associations of black-backed and three-toed woodpeckers in the boreal forests of Alberta. Canadian Journal of Forest Research. 32: 1881-1888. Ingold, D.J. 1994. Influence of nest-site competition between European starlings and woodpeckers. Wilson Bulletin. 106(2): 227-241. Ingold, D.J. 1998. The influence of starlings on flicker reproduction when both naturally excavated cavities and artificial nest boxes are available. Wilson Bulletin. 110(2): 218-225. Jarvinen, O., and R . A . Vaisanen. 1979. Changes in bird populations as criteria of environmental change. Holarctic Ecology. 2: 75-80. Koenig, W . D . 2001. Synchrony and periodicity of eruptions by boreal birds. The Condor. 103: 725-735. 105 Koenig, W.D. , and J . M . H . Knops. 2001. Seed-crop size and eruptions of North American boreal seed-eating birds. Journal of Animal Ecology. 70(4): 609-620. Krebs, C.J. 1999. Ecological Methodology. Benjamin/Cummings Publishing Company, California. Kreisel, K . J . , and S.J. Stein. 1999. Bi rd use of burned and unburned coniferous forests during winter. Wilson Bulletin. 111(2): 243-250. Lawler, J.J., and T .C . Edwards, Jr., 2002. Composition of cavity-nesting bird communities in montane aspen woodland fragments: the roles of landscape context and forest structure. The Condor. 104: 890-896. L loyd , D. , K . Angove, G . Hope., and C. Thompson. 1990. A guide to site interpretation for the Kamloops forest region. Research Branch, Ministry of Forests, Victoria, British Columbia, Canada. Lohr, S . M . , S.A. Gauthreaux., and J.C. Ki lgo . 2002. Importance of coarse woody debris to avian communities in loblolly pine forests. Conservation Biology. 16(3): 767-777. MacArthur, R . H . , and J.W. MacArthur. 1961. On bird species diversity. Ecology. 42: 594-600. Magurran, A . E . 1988. Ecological diversity and its measurement. Princeton University Press, Princeton, New Jersey. 192 pp. Martin, K . , and J . M . Eadie. 1999. Nest webs: A community-wide approach to the management and conservation of cavity-nesting forest birds. Forest Ecology and Management. 115:243-257. Martin, K . , K . E . H . Aitken., and K . L . Weibe. 2004. Nest sites and nest webs for cavity-nesting communities in interior British Columbia, Canada: nest characteristics and niche partitioning. The Condor. 106: 5-19. Martin, K . , A . Norris., and M . Drever. 2006. Effects of bark beetle outbreaks on avian biodiversity in the British Columbia interior: Implications for critical habitat management. B C Journal of Ecosystems and Management. 7(3): 10-24. Meidinger, D . , and J. Pojar. 1991. Ecosystems of British Columbia. Special Report Series Number 6. Research Branch, Ministry of Forests, Victoria, British Columbia, Canada. Mikusinski , G . , M . Gromadzki., and P. Chylarecki. 2001. Woodpeckers as indicators of forest bird diversity. Conservation Biology. 15(1): 208-217. Nilsson, S.G., J. Hedin., and M . Niklasson. 2001. Biodiversity and its assessment in boreal and nemoral forests. Scandinavian Journal of Forest Research. 16(3): 10-26. 106 Oertli, S., and A . Muller , D . Steiner, A . Breitenstein., and S. Dorn. 2005. Cross-taxon congruence of species diversity and community similarity among three insect taxa in a mosaic landscape. Biological Conservation. 126(2005): 195-205. Ohmann, J .L. , W . C . McComb. , and A . A . Zumrawi. 1994. Snag abundance for primary cavity excavating cavity-nesting birds on nonfederal forest lands in Oregon and Washington. Wildlfie Society Bulletin. 22: 607-620. Pearce, J .L. , L . A . Venier, J. McKee , J. Pedlar., and D. McKenney. 2003. Influence of habitat and microhabitat on carabid (Coleoptera: Carabidae) assemblages in four stand types. Canadian Entomologist. 135(3): 337-356. Pechacek, P. 2006. Foraging behavior of Eurasian three-toed woodpeckers (Picoides tridactylus alpinus) in relation to sex and season in Germany. The Auk. 123(1): 235-246. Peet, R . K . 1974. The measurement of species diversity. Annual Review of Ecology and Systematics. 5: 285-307. Petit, D.R. , L . J . Petit, V . A . Saab., and T . A . Martin. 1995. Fixed-radius point counts in forests: factors influencing effectiveness and efficiency. U S D A Forest Service General Technical Report. PSW-GTR-149 . Pielou, E .C . 1966. The measurement of diversity in different types of biological collections. Journal of Theoretical Biology. 13: 131-144. Poulsen, B .O . 2002. Avian richness and abundance in temperate Danish forests: tree variables important to birds and their conservation. Biodiversity and Conservation. 11: 1551-1566. Raphael, M . G . , and M . White. 1984. Use of snags by cavity-nesting birds in the Sierra Nevada. Ecological Monographs. 1-66. Renken, R . B . , and E.P. Wiggers. 1993. Habitat characteristics related to pileated woodpecker densities in Missouri. Wilson Bulletin. 105(1): 77-83. Sauer, J.R., J.E. Hines., and J. Fallon. 2005. The North American Breeding Bird Survey, Results and Analysis 1966 - 2005. Version 6.2.2006. U S G S Patuxent Wildlife Research Center, Laurel, M D . S A S Institute. 2006. S A S / S T A T Users Guide, Version 9.1. Cary, North Carolina. Sheppard, W.D. , P .C. Rogers, D. Burton., and D . L . Bartos. 2006. Ecology, biodiversity, management, and restoration of aspen in the Sierra Nevada. General Technical Report. R M R S - G T R - 1 7 8 . Fort Collons, C O : U S . Department of Agriculture, Forest Service, Rocky Mountain Research Station. 122 pp. 107 Simpson, E . H . 1949. Measurement of diversity. Nature. 163: 688. Staudhammer, C . L . , and V . M . LeMay. 2001. Introduction and evaluation of possible indices of stand structural diversity. Canadian Journal of Forest Research. 31:1105-1115. Stauffer, D.F. , and L . B . Best. 1982. Nest-site selection by cavity-nesting birds in riparian habitats in Iowa. Wilson Bulletin. 94(3): 329-337. van Balen, J .H. , C .J .H. Booy, J .A. van Franeker., and E.R. Osieck. 1982. Studies on hole-nesting birds in natural nest sites: availability and occupation of nest sites. Ardea. 70: 1-24. Van Home, B . 1983. Density as a misleading indicator of habitat quality. Journal of Wildlife Management. 47(4): 893-901. Walankiewicz, W. 1991. Do secondary cavity-nesting birds suffer more from competition for cavities or from predation in a primeval deciduous forest? Natural Areas Journal. 11(4): 203-212. Walter, S.T., and C C . Maguire. 2005. Snags, cavity-nesting birds, and silvicultural treatments in Western Oregon. Journal of Wildlife Management. 69(4): 1578-1591. Weikel, J. M . , and J.P. Hayes. 1999. The foraging ecology of cavity-nesting birds in young forests of the Northern Coast range of Oregon. The Condor. 101: 58-66. Wilkins, H .D . , and M . S . Dusak. 2006. Effect of time and barred owl playbacks on winter detections of woodpeckers in east-central Mississippi. 5(3): 555-560. Zar, J .H. 1999. Biostatistical analysis. Prentice Hal l , Upper Saddle River, N . J . 718 pp. 108 5.0 C H A P T E R F I V E - M A N A G E M E N T C O N S I D E R A T I O N S A N D C O N C L U S I O N S 5.1 O V E R V I E W OF R E S U L T S In this chapter I review some of the results of this work and comment on possible future work. The pattern and significance of these results for small mammals and cavity-nesting birds can be seen in Table 5.1. The significance of these results is most often associated with factors that are tied to the life-history characteristics for these species and also may be related to a strong pattern of affinity for aspen stands. 5.2 I M P L I C A T I O N S F O R A S P E N M A N A G E M E N T 5.2.1 A S P E N E C O S Y S T E M M A N A G E M E N T Although the current value of aspen as a timber product is fairly low in B C , its value in terms of contributing to ecological integrity on the landscape is high - forest managers should consider this when developing management plans. Whenever possible, aspen stands should be maintained on the landscape by allowing for historical disturbance regimes, including fire, to ensure the continuation and propagation of these ecosystems (Campbell and Bartos 2001). With the abundant evidence that these stands are declining within western North America (Bartos 2001), coupled with the fact that they support a diverse and abundant faunal and floral community, the management of these stands becomes an important issue. Several techniques are available for the management of aspen forests in western North America. Techniques that could help maintain aspen on the landscape include the use of commercial harvest, prescribed fire, mechanical root stimulation, removal of competing vegetation, protection of regeneration from herbivory, and in limited circumstances, regenerating aspen from seed (Sheppard 2001). However, there also is value in using a "hands-off approach in a management program (Campbell and Bartos 2001). Decisions about managing individual aspen stands should be based on their health, vigour, and role in the surrounding ecosystem. If a stand is showing little sign of decline, disease, or distress from competition, and contains multiple age classes, it is unlikely that any immediate 109 Table 5.1 Overview of results showing measurement, pattern and significance for each focal taxa/attribute measured. Note: A = highest in aspen, M = highest in mixedwood, and D F = highest in Douglas-fir. Focal taxa/ attribute Measurement Pattern Significance Stand attribute Plant richness A Food and cover Plant cover A Food and cover Shrub cover A Food and cover Stand age A = D F Stand attributes Snag density A Access to nesting and roosting sites Snag volume A Access to nest sites C W D volume A Cover, food sources, nesting sites Small mammals Total abundance A Higher recruitment, habitat quality, and aspen affinity Deer mice M Habitat generalist Vole spp. A Availabili ty of multiple resources Sorex spp. A Higher moisture availability N W chipmunks A Food and cover availability Mammal richness A Availability of multiple resources Diversity indices A Lack of community dominance Cavity-nesting birds Total abundance A Aspen affinity P C E abundance A Increased nest site availability for secondary cavity-nesters W C E abundance A Availability of nest sites Bi rd richness A Availabili ty of multiple resources Diversity indices A Lack of community dominance 110 management intervention is necessary to preserve its existence in the landscape. Even stands that are declining may not require active intervention i f they are successfully regenerating. The aspen stands studied within the dry interior forests of B C may be in need of management action because they appear to be declining as evident by the high density of snags (47 - 85% dead trees). Healthy aspen stands commonly have between 6 and 20% dead standing trees (DeByle and Winokur 1985). Harvesting operations within western North America typically have treated aspen as a species of little value and silviculture practices often employ considerable effort to ensure that aspen regeneration does not limit coniferous tree growth (DeByle and Winokur 1985). These practices have contributed to the decline of aspen within these forests (White et al. 1998, and Bartos 2001). A s the conservation of biological richness often is recognized as an important ecological criterion of forest sustainability (Canadian Council of Forest Ministers 1995), forest managers need to appreciate that the maintenance of aspen on the landbase is extremely important as they serve as areas of high biological richness. 5.2.2 S T A N D M A N A G E M E N T There is a potential that current forest management could be implemented to the degree that it may be beneficial for cavity-nesting bird communities. For example, during retention harvesting, all aspen and Douglas-fir could be retained together as this may provide for most needs of cavity-nesting birds to be met (Martin and Eadie 1999). The retention harvesting of stands within dry interior B C forests could also help to augment cavity-nesting bird communities i f clumps of large, decadent snags are left after harvesting. Snags are an important component of ecosystems for cavity-nesting birds and there is a relationship between the richness of cavity-nesting birds and snag density and volume. A s cavity-nesting birds require important structural characteristics associated with natural forests such as dead standing trees and large deciduous trees (Angelstam and Mikuskinski 1994) it is important that these components are retained in managed forests. Identifying the value of aspen trees within managed forests also is of critical importance. Also , where the goal is to increase biodiversity within coniferous stands in the interior of B C , snags could be created in established stands with open canopies, where snag recruitment is expected to be low due to 111 suppression by natural mortality, by kil l ing trees or inducing rot. The value of kil led or treated trees for cavity-nesters within managed forests has not been adequately documented. Cavity-nesting birds and small mammals require structural characteristics of natural forests such as dead standing trees and complex vegetative structure (Angelstam and Mikuskinski 1994, and Bowman et al. 2000) whose presence may be severely reduced in managed forests. Management of these forests requires that these structural characteristics remain in place and current forest management has begun to recognize the value of these attributes (Carey 2000). The results of this work illustrate the potential importance of retaining large snags and live trees during thinning and harvesting operations in managed forests. Leaving large, remnant snags may provide nesting habitat for cavity-excavators in early and mid-successional stands. These snags also may serve as future sources of downed woody debris for small mammals and other flora and fauna. These large snags are gradually lost and not replaced in stands managed for rotation lengths that optimize timber production. 5.3 F U T U R E W O R K A N D C O N S I D E R A T I O N S 5.3.1 S M A L L M A M M A L L I M I T A T I O N S A N D F U T U R E W O R K Small mammals are known to be cyclic (Korpimaki and Krebs 1996) and there is potential that this phenomenon may have influenced the results of this study. This temporal variation in small mammal species abundance may confound or obscure comparisons among sites (Wilson and Carey 2000). Therefore, it is important to expand the time frame for future work to account for the cyclic nature of small mammal populations. This also may help to identify i f aspen stands are preferentially selected and i f they also maintain higher abundance of small mammals during the low phase of the cycle. Habitat selection during periods of low population levels may provide an indication of superior habitats, as reduced intraspecific competition should allow animals to predominantly settle in the best habitats (Thompson 2004). This work was also conducted during the summer months only and these results may not hold for other seasons (Wilson and Carey 2000). Thus, it would also be of interest and value to repeat the small mammal trapping during other seasons. Metapopulation theory suggests that animals live in subpopulations of favourable patches that are connected through dispersal (Opdam 1991). Source and sink population 112 theory suggests that these patches may contain both favourable and suboptimal conditions where favourable patches supply surplus animals to fill the suboptimal habitats (Pulliam 1988). Identifying source-sink dynamics is of fundamental importance for conservation but is often limited by an inability to determine how immigration and emigration influence population processes (Peery et al. 2006). As there is potential that aspen stands here may be serving as source populations producing surplus individuals that emigrate to sink populations it is important that this potential source-sink dynamic is explored. It would also be of interest to see i f density-dependent dispersal (Matthysen 2005) may be influencing this dynamic. Small mammals would be of interest for this work as they are relatively easy to sample (Doster and James 1998, and Sutherland et al. 2000). In order to assess these dynamics and relationships it becomes necessary to conduct intensive mark-recapture and radio telemetry studies to describe the patterns of dispersal and to correlate them with density-dependent dispersal patterns. Juvenile animals often are the predominant dispersers (Wolff 1994) and they would be the most suitable candidates for this work. 5.3.2 C A V I T Y - N E S T I N G B I R D L I M I T A T I O N S A N F U T U R E W O R K Several cavity-nesting bird species studied here are known to be migratory while others are year-round residents (Griggs 1997). This work was conducted while all bird species were potentially present in the study area and during the breeding season of these species. There is potential that coniferous dominated stands may be preferentially selected during the non-breeding season, especially during the winter months, as these areas are important for foraging (Martin and Eadie 1999, and Martin et al. 2006). Therefore, it would be important to conduct this work during the non-breeding season to assess the relative use of aspen, mixedwood and Douglas-fir stands for year-round resident cavity-nesting birds. Playbacks of barred owls (Strix varia) could be used during this season as cavity-nesting birds are known to respond to these calls (Wilkins and Dusak 2006). This work would help to identify the year-round value of each of these stand types within the dry interior forests of British Columbia. There is a strong association with both the diversity and abundance of cavity-nesting birds with aspen stands within this study; however, mixedwood stands potentially provided two key resources for cavity-nesting birds - nest sites and foraging trees. As such, it is 113 surprising that these stands did not support a more abundant or diverse community of cavity-nesting birds. Cavity-nesting birds within these stands were far less abundant and diverse than aspen stands, and no different than pure Douglas-fir stands. As such, it becomes important to identify the limiting resource within these stands especially with the consideration that aspen may be threatened. Are suitable nesting sites the limiting resource for cavity-nesting birds within mixedwood and Douglas-fir stands? Is there still the potential for these stands to support a larger community of birds i f nest sites are artificially created using nest boxes and snag creation? Other studies have shown that woodpecker abundance increases when artificial cavity boxes are added to a stand (e.g. Franzreb 1997, and Ingold 1998). There is value in assessing whether an increase in the availability of cavities within mixedwood and Douglas-fir forests would cause changes in the community dynamics of cavity-nesting birds within these forests. It would also be important to assess and compare fledgling success within aspen stands to that within mixedwood and Douglas-fir stands that had cavity densities artificially increased. This would allow for an examination as to whether their affinity for aspen is specifically due to this hardwood resource or to snag volume (m3/ha) and density (stems/ha). 5.3.3 S T A N D A T T R I B U T E L I M I T A T I O N S A N D F U T U R E W O R K Results of this study show that aspen stands had significantly higher snag density and volume, coarse woody debris volume, plant diversity, and total shrub and plant cover than mixedwood and Douglas-fir stands. This is potentially important as these attributes may directly affect biological diversity (Voller and Harrison 1998) and ecosystem function (Spies et al. 1998, and Loreau et al. 2001). However, this study examined relatively few study sites and it would be valuable to increase the number of replicates in which to sample these attributes in order to identify i f this pattern is consistent across and entire landbase. Coarse woody debris (CWD) often is cited as being extremely important for the life history of many small mammal species. However, this study shows that other habitat characteristics are likely as important for small mammal species. Other researchers have also begun to question the prominence of C W D in driving abundance patterns of small mammals (Craig et al. 2006). It would be valuable to further examine this prominence by experimentally manipulating the volume of C W D within a particular stand. For example, the 114 volume of C W D could be increased in Douglas-fir stands and decreased in aspen stands to examine the effect of these actions on small mammal communities. It would also be of value to combine these manipulations with a manipulation of size and decay class distribution to explore the influence of these patterns on small mammals. 5.4 C O N C L U S I O N Within dry interior B C forests, aspen is usually a minor forest type surrounded by, or included within, drier coniferous forests. Evidence suggests that these stands may serve as oases of plant and animal diversity (Sheppard et al. 2006) - the work completed here supports this evidence. These stands support a diverse and abundant community of small mammals and cavity-nesting birds. These stands also support a large volume and density of coarse woody debris and snags as well as a rich and abundant community of plants. These forests are potentially extremely important for ecosystem integrity within these dry interior forests of B C as they may serve as source populations for small mammals and they may be preferentially selected for nest site location for cavity-nesting birds. Forest managers in B C should recognize that these stands are extremely important for biodiversity and there is a need to maintain this forest type on the landscape. 115 5.5 L I T E R A T U R E C I T E D Angelstam, P., and G . Mikuskinski . 1994. Woodpecker assemblages in natural and managed boreal and hemiboreal forests - a review. Annales Zoologica Fennica. 31: 157-172. Bartos, D . L . 2001. Landscape dynamics of aspen and conifer forests. U S D A Forest Service Proceedings. R N M R S - P - 1 8 . Bayne, E . M . , and K . A . Hobson. 1998. The effects of habitat fragmentation by forestry and agriculture on the abundance of small mammals in the southern boreal mixedwood forest. Canadian Journal of Zoology. 76: 62-69. Bowman, J. C , D. Sleep, G.J . Forbes., and M . Edwards. 2000. The association of small mammals with coarse woody debris at log and stand scales. Forest Ecology and Management. 129: 119-124. Campbell, R . B . , and D . L . Bartos. 2001. 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Predation and population cycles of small mammals. Bioscience. 4 6 ( 1 0 ) : 754-764. Loreau, M . , S. Naeem, P. Inchausti, J. Bengtsson, J.P. Grime, A . Hector, D . U . Hooper, M . A . Huston, D . Raffaelli, B . Schmid, D . Tilman., and D . A . Wardle. 2001. Biodiversity and ecosystem functioning: current knowledge and future challenges. Science. 294(5543): 804-808. Opdam, P. 1991. Metapopulation theory and habitat fragmentation: a review of holarctic breeding bird studies. Landscape Ecology. 5(2): 93-106. Martin, K . , and J . M . Eadie. 1999. Nest webs: A community-wide approach to the management and conservation of cavity-nesting forest birds. Forest Ecology and Management. 115:243-257. Martin, K . , K . E . H . Aitken., and K . L . Weibe. 2004. Nest sites and nest webs for cavity-nesting communities in interior British Columbia, Canada: nest characteristics and niche partitioning. The Condor. 106: 5-19. Martin, K . , A . Norris., and M . Drever. 2006. Effects of bark beetle outbreaks on avian biodiversity in the British Columbia interior: Implications for critical habitat management. B C Journal of Ecosystems and Management. 7(3): 10-24. Maser, C , R. Anderson, K . Cromack, J.T. Williams., and R . E . Martin. 1979. Dead and downed woody material. In. Thomas, J.W. (Ed.), Wildlife habitats in managed forests: the Blue mountains of Oregon and Washington. U S D A Agricultural Handbook 553. pp 78-95. 117 Matthysen, E. 2005. Density-dependent dispersal in birds and mammals. Ecography. 23: 403-416. McShea, W.J . , J. Pagels, J. Orrock, E. Harper., and K . Koy . 2003. Mesic deciduous forest as patches of small-mammal richness within an Appalachian mountain forest. Journal of Mammalogy. 84(2): 627-643. Peery, M . Z . , B . H . Becker., and S.R. Beissinger. 2006. Combining demographic and count-based approaches to identify source-sink dynamics of a threatened seabird. Ecological Applications. 16(4): 1516-1528. Probst, J.R., and D.S. Rakstad. 1987. Small mammal communities in three aspen stand-age classes. Canadian Field Naturalist. 101(3): 362-368. Pulliam, H.R. , and B.J . Danielson. 1991. Sources, sinks, and habitat selection: a landscape perspective on population dynamics. American Midland Naturalist. 137: S50-S66. Sheppard, W . D . 2001. Manipulations to regenerate aspen ecosystems. U S D A Forest Service Proceedings R M R S - P - 1 8 . 2001. Spies, T. A . , J.F. Franklin., and T . B . Thomas. 1988. Coarse woody debris in Douglas-fir forests of western Oregon and Washington. Ecology. 69(6): 1689-1702. Stelfox, J .B. (editor). 1995. Relationship between stand age, stand structure, and biodiversity in aspen mixedwood forests in Alberta. Jointly published by Alberta Environmental Centre ( A E C V 9 5 - R 1 ) , Vegreville, Alberta, and Canadian Forest Service (Project No. 0001A), Edmonton, Alberta. 308 pp. Sullivan, T.P., D.S. Sullivan., and P . M . F . Lindgren. 2000. Small mammals and stand structure in young pine, seed-tree, and old-growth forest, southwest Canada. Ecological Applications. 10(5): 1367-1383. Sutherland, G.D. , A . S . Harestad, K . Price., and K . P . Lertzman. 2000. Scaling of natal dispersal distances in terrestrial birds and mammals. Conservation Biology. 4(1): 16. Thompson, I .D. 2004. The importance of superior-quality wildlife habitats. The Forestry Chronicle. 80(1): 75-81. Voller , J., and S. Harrison (editors). 1998. Conservation Biology Principles for Forested Landscapes. U B C Press, Vancouver, British Columbia. 243 pp. Washington, H . G . 1984. Diversity, biotic and similarity indices: a review with special relevance to aquatic ecosystems. Water Research. 18: 653- 694. Weikel, J. M . , and J.P. Hayes. 1999. The foraging ecology of cavity-nesting birds in young forests of the Northern Coast range of Oregon. The Condor. 101: 58-66. 118 White, C . A . , C E . Olmsted., and C E . Kay. 1998. Aspen, elk, and fire in the Rocky Mountain national parks of North America. Wildlife Society Bulletin. 26(3): 449-462. Wilkins, H .D. , and M . S . Dusak. 2006. Effect of time and barred owl playbacks on winter detections of woodpeckers in east-central Mississippi. 5(3): 555-560. Wilson, S . M . , and A . B . Carey. 2000. Legacy retention versus thinning: influence on small mammals. Northwest Science. 74(2): 131-145. Wolff, J.O. 1994. More on juvenile dispersal in mammals. Oikos. 71(2): 349-352. Yahner, R . H . , and H.R. Smith. 1991. Small mammal abundance and habitat relationships on deciduous forested sites with different susceptibility to gypsy moth defoliation. Environmental Management. 15(1): 113-120. 119 APPENDIX 1 - UBC RESEARCH ETHICS BOARD'S CERTIFICATE OF APPROVAL The University of British Columbia Animal Care Certificate Application Number: A05-03 56 Investigator or Course Director: John D. Nelson Department: Forest Resources Mgt Animals Approved: Voles Birds - Other Invertebrates Mice Start Date: May 2, 2005 Approval Date: July 6, 2005 Funding Sources: Funding Agency: NCE: National Centers of Excellence Funding Title: A systems approach to integrating ecological, economic and social values within the SFM framework for tree farm licence 49 Unfunded title: N/A 120 The Animal Care Committee has examined and approved the use of animals for the above experimental project. This certificate is valid for one year from the above start or approval date (whichever is later) provided there is no change in the experimental procedures. Annual review is required by the CCAC and some granting agencies. A copy of this certificate must be displayed in your animal facility Office of Research Services and Administration 102, 6190 Agronomy Road, Vancouver, V6T 1Z3 Phone: 604-827-5111 Fax: 604-822-5093 121 APPENDIX 2 - VEGETATION TABLES Site Species A l A2 A3 A4 M l M2 M3 M4 F l F2 F3 F4 Shrubs/deciduous trees Acer glabrum 0.73 1.84 Alnus crispa 0.29 0.29 Alnus rubra 0.44 4.80 3.20 1.38 Amelanchier alnifolia 11.89 2.11 0.96 0.16 1.29 1.13 0.68 2.71 0.20 1.24 0.51 Arctostaphylos uva-ursi 1.29 0.50 0.13 0.07 4.44 Chimaphila umbellata 1.88 1.71 0.08 1.13 Clematis occidentalis 0.07 0.07 0.07 0.62 0.20 0.31 Cornus stolonifera 0.38 0.13 Gaultheria hispidula 0.53 Goodyera oblongifolia 0.22 0.11 0.24 0.69 0.87 0.40 1.64 0.11 0.84 Hieracium albiflorum 0.04 0.80 0.20 0.04 0.09 0.53 1.68 0.62 Hieracium umbellatum 0.69 0.24 0.16 Juniperus communis 0.09 1.00 Linnaea borealis 4.69 0.42 1.18 0.38 3.61 3.98 6.23 2.62 3.42 0.06 Lonicera utahensis 0.47 0.16 3.49 Mahonia aquifolium 0.20 2.96 1.64 1.38 0.24 0.58 3.33 3.16 0.44 Pachistima myrisinites 5.40 1.78 2.43 0.27 2.42 1.08 1.11 Physocarpus malvaceus 0.07 Species A l A2 A3 A4 M l Shrubs/deciduous trees continued Populus tremuloides 0.22 3.36 0.38 6.05 0.60 Pseudotsuga menziesii Ribes lacustre 0.42 0.20 0.40 Rosa acicularis 11.42 16.71 9.33 16.36 1.38 Rosa gymnocarpa 2.51 0.73 0.56 0.09 Rubus parviflorus 0.22 6.62 3.62 2.56 Rubus pedatus Rubus pubscens Salix spp 0.18 Sheperdia canadensis 8.93 2.18 Spiraea betufolia 14.62 10.31 4.20 4.11 9.76 Symphoricarpus albus 3.49 40.56 4.47 16.69 3.42 Vaccinium membranaceum 0.38 1.31 1.31 0.73 Viburnum edule 0.84 Total 67.84 91.48 26.89 58.18 30.81 Site M2 M3 M4 FI F2 F3 F4 0.51 2.44 0.42 0.36 4.44 0.13 0.69 0.42 0.93 0.93 0.18 2.69 0.16 4.64 0.80 1.56 0.29 1.99 0.22 0.04 0.56 0.31 1.40 6.04 4.44 2.62 3.04 6.99 21.93 1.53 2.02 1.91 2.22 0.60 7.80 0.18 1.16 31.38 22.91 24.89 25.35 24.88 25.42 16.07 36.44 . Site S p e C 1 C S A l A2 A3 A4 M l M2 M3 M4 FI F2 F3 F4 Grasses Agropyron spicatum 0.20 2.58 Agrostis scabra 1.38 0.15 0.18 0.38 Bromus tectorum Calamagrostis rubescens 19.49 4.11 4.51 4.88 8.19 14.62 1.47 3.69 26.98 11.33 7.06 Carexspp. 0.42 0.82 0.18 0.89 0.73 1.26 10.8 Danthonia intermedia 0.09 0.89 Elymus glaucus 3.23 1.40 1.16 0.54 0.07 0.09 1.38 Festuca camestris 0.18 1.00 1.16 Festuca occidentalis 0.25 3.00 0.60 2.18 0.98 0.24 1.34 0.41 Koeleria macrantha 0.50 0.13 1.41 Phleum pratense 0.13 0.62 0.09 Poapratensis 0.07 0.09 2.58 1.59 0.56 Total 24.55 8.95 9.97 7.78 9.66 14.62 3.88 7.70 28.00 13.40 9.32 16.43 Site Species A l A2 A3 A4 M l M2 M3 M4 F l F2 F3 F4 Moss/Lichens Aulacomnium palustre 0.73 Brachythecium albicans 0.51 0.41 0.44 0.98 0.38 0.17 0.04 0.09 3.26 Campylium stellatum 0.13 0.09 Ceratodon purpureus 0.09 0.09 Cladonia cariosa 0.02 Cladonia cornuta 0.16 0.04 Cladonia sulphurina 0.20 0.04 Cratoneuron fdicinum 0.34 0.04 0.07 Dicranoweisia crispula 0.18 0.51 Hylocomium splendens 2.84 Hypnum revolution 0.09 Letharia vulpina 1.09 Mnium spinulosum 0.82 0.13 0.11 0.31 0.13 Nephroma resupinatum 0.20 Orthotrichum speciosum 0.04 0.07 0.16 0.11 Parmelia sulcata 0.07 Peltigera canina 0.49 0.1 0.06 2.56 1.96 2.52 0.80 1.04 0.87 Peltigera neckeri 0.11 Physconia muscigena 0.07 0.02 Site Species A l A2 A3 A4 M l M2 M3 M4 Fl F2 F3 F4 Moss/Lichen continued Pleurozium schreberi 0.22 0.78 0.93 1.42 0.51 7.72 3.84 2.82 9.47 6.33 1.91 Ptilium crista-castrensis 1.33 Pylaisiella polyantha 0.07 0.11 0.25 Rhytidiadelphus loreus 0.93 0.02 Rhytidiadelphus triquetrus 0.40 0.80 1.40 Rhytidiopsis robusta Saniona uncinata 0.29 Schistidium apocarpum 0.20 Tetraphis pellucida 0.02 0.07 Timmia austriaca 0.24 0.22 Total 1.91 3.04 2.16 3.61 4.92 15.60 4.41 0.04 5.90 12.39 10.99 3.11 Site Species ATI AT2 AT3 AT4 M l M2 M3 M4 FD1 FD2 FD3 FD4 Herbs Achillea millefolium 0.04 1.37 0.47 Actaea rubra 0.44 0.67 1.33 0.47 0.04 Allium cernum 0.24 0.16 Amsinckia menziesii 0.04 Antennaria microphylla 1.13 0.12 Antennaria neglecta 0.06 3.79 0.58 Antennaria racemosa 1.56 0.44 Aralia nudicaulis 1.29 0.07 4.80 1.58 1.47 Arnica cordifolia 4.04 2.33 3.53 0.90 2.64 6.31 0.09 0.07 2.31 1.40 0.27 3.02 Arnica latifolia 0.30 0.20 Artemesia dracunculus 1.07 Aster conspicuus 2.78 1.00 6.16 0.27 0.78 4.69 0.41 1.22 0.09 1.73 Balsamorhiza sagittata 2.04 Campanula rotundifolia 0.13 0.44 0.42 Campion spp. 0.11 0.04 0.31 0.07 Castilleja miniata 0.31 0.13 Clintonia uniflora 0.16 Cirsium arvense 0.29 0.19 Cornus canadensis 0.07 4.20 2.76 4.06 0.31 0.04 Crepis atrabarba 0.11 Disporum trachycarpum 1.40 14.56 1.09 1.20 2.28 Epilobium angustifolium 0.67 0.11 4.38 0.13 1.29 1.51 Erigeron speciosus 0.27 0.13 2.22 0.22 Fragaria virginiana 2.22 1.02 2.58 4.08 0.24 2.07 0.04 1.60 1.78 Site Species A l A2 A3 A4 M l M2 M3 M4 FI F2 F3 F4 Herbs continued Galium boreale 0.38 0.92 Galium trijlorum 1.51 5.34 1.16 0.88 0.11 0.44 0.09 0.01 Gentianella amarella 0.04 0.38 Hieracium albiflorum 0.04 0.80 0.20 0.04 0.09 0.53 1.68 0.62 Hieracium umbellatum 0.69 0.24 0.16 Lathyrus nevadensis 1.08 0.27 1.93 0.17 0.40 1.2 Lathyrus ochroleucus 0.09 0.16 1.44 0.07 Leucanthemum vulgare 0.04 Lilium columbianum 0.62 1.02 1.20 0.33 Lupinus arcticus 1.29 Lupinus sericeus 0.07 9.00 Moehringia lateriflora 0.22 Orthelia secunda 0.11 0.73 0.36 0.82 0.16 0.18 0.31 Osmorhiza chilensi 0.93 4.00 2.73 1.32 0.96 0.16 0.76 0.11 0.36 0.20 0.2 Pedicularis bracteosa 0.04 0.42 0.51 Petasites frigidus 0.29 Piperia unalaschensis 0.02 Pteridium aquilinum 0.29 Senecio pseudaureus 0.76 0.07 Smilacina racemosa 1.82 0.91 3.89 0.51 0.93 3.02 0.49 0.40 Smilacina stellata 1.21 3.47 4.11 0.18 0.6 Streptopus roseus 0.18 0.16 1.11 0.12 1.27 1.67 Streptopus streptopoides 0.13 Taraxacum officinale 0.33 2.62 0.31 1.24 0.53 4.80 3.84 OO Species A l A2 A3 A4 Herbs continued Thalictrum occidentale 0.22 3.07 9.38 4.84 Tragopogon dubius Trifolium pratense 0.53 0.13 Urtica diocica 13.09 Verbascum thapsus Vicia americanum 0.13 0.47 0.80 0.54 Viola adunca 0.18 0.20 0.36 0.13 Viola canadensis 4.42 0.42 Viola glabela 0.73 Unknown spp. 0.09 Total 20.35 40.38 83.02 31.12 Site M l M2 M3 M4 FI F2 F3 F4 4.62 1.29 0.40 0.38 0.24 3.49 0.62 0.89 0.09 0.07 0.29 0.51 0.27 0.44 1.00 1.71 0.98 0.36 2.53 0.38 14.40 20.24 6.88 10.99 12.12 9.76 16.05 21.63 APPENDIX 3 - TRAPPING DATES Year Dates Block Sites Year Dates Block Sites 2005 May 30 - June 1 Monte Lake M1,M2, F2 2006 June 1 -3 Badger Lake A3, F3, M3 June 2 - 4 Monte Lake A l , A2,F1 June 6 - 8 Pinantan Lake A4, M4, F4 June 8 - 10 Pinantan Lake A4, M4, F4 June 15 - 17 Monte Lake A l , A2, F l June 11 - 13 Badger Lake A3, F3, M3 June 18 - 21 Monte Lake M1,M2, F2 July 3 - 5 Monte Lake A l , A2,F1 June 26 - 28 Badger Lake A3, F3, M3 July 6 - 8 Monte Lake A3, F3, M3 June 29 - July 1 Pinantan Lake A4, M4, F4 July 13- 15 Pinantan Lake A4, M4, F4 July 3 - 5 Monte Lake A l , A2, F l June 26 - 30 Badger Lake M1,M2, F2 July 6 - 8 Monte Lake M1,M2, F2 July 24 - 26 Monte Lake A l , A2, F l August 1 -3 Badger Lake A3, F3, M3 July 27 - 29 Monte Lake M1,M2, F2 August 4 - 6 Pinantan Lake A4, M4, F4 August 3 - 5 Pinantan Lake A3, F3, M3 August 9 --11 Monte Lake A l , A2, F l August 10 - 12 Badger Lake A4, M4, F4 August 14 - 16 Monte Lake M1,M2, F2 APPENDIX 4 - 2005 small mammal capture overview Session 1 Session 2 Session 3 Site Captures Trap Nights Effort Captures Trap Nights Effort Captures Trap Nights Effort A l 12 192 0.06 121 192 0.63 169 256 0.66 A2 39 192 0.20 138 192 0.72 231 350 0.66 A3 61 192 0.32 150 192 0.78 195 256 0.76 A4 27 192 0.14 101 256 0.39 141 192 0.73 M l 10 192 0.05 63 192 0.33 55 192 0.29 M2 12 192 0.06 40 192 0.21 70 192 0.36 M3 48 192 0.25 95 192 0.49 131 192 0.68 M4 19 192 0.10 154 256 0.60 276 350 0.79 Fl 9 192 0.05 51 192 0.27 66 192 0.34 F2 9 192 0.05 71 192 0.37 45 192 0.23 F3 28 192 0.15 57 192 0.30 87 192 0.45 F4 30 192 0.16 121 256 0.47 183 298 0.61 Total 304 2304 1162 2496 1649 2854 APPENDIX 5 - 2006 small mammal capture overview Session 1 Session 2 Session 3 Site Captures Trap Nights Effort Captures Trap Nights Effort Captures Trap Nights Effort A l 176 256 0.69 204 320 0.64 266 384 0.69 A2 173 256 0.68 177 288 0.61 241 317 0.76 A3 169 256 0.66 175 296 0.59 178 295 0.62 A4 102 192 0.53 114 192 0.59 163 245 0.67 M l 48 192 0.25 117 224 0.52 112 224 0.50 M2 27 192 0.14 72 192 0.38 98 192 0.51 M3 72 192 0.38 81 192 0.42 105 192 0.55 M4 98 192 0.51 122 192 0.64 145 187 0.78 FI 44 192 0.23 57 192 0.30 79 190 0.42 F2 37 192 0.19 74 183 0.40 82 192 0.43 F3 66 192 0.34 58 192 0.30 106 192 0.55 F4 86 192 0.45 153 256 0.60 205 282 0.73 Total 1098 2496 1404 2719 1780 2892 APPENDIX 6 - MEAN NUMBER OF DETECTIONS PER POINT-COUNT STATION Primary cavity-excavating Weak cavity-excavatin Site RNSA PIWO NOFL HA WO TTWO BBWO MOCH BCCH RBNU WBNU WISA DOWO A l 0.79 0.21 0.42 0.31 0.08 0.08 1.17 1.00 1.17 0.33 0 0.63 A2 1.09 0.21 0.25 0.79 0.22 0.26 1.46 0.88 1.17 0.33 0.25 1.33 A3 0.75 0.38 0.38 0.42 0.28 0 1.17 1.05 1.91 0.72 0 0.58 A4 1.50 0.42 0.42 0.5 0.03 0.08 1.63 1.27 1.96 0.36 0.17 0.63 M l 0.29 0.13 0.08 0.13 0 0.12 1.17 0.44 1.54 0.35 0 0.13 M2 0.64 0 0.13 0.17 0.22 0 0.50 0.36 1.41 0.36 0.25 0.29 M3 0.62 0.04 0.13 0.25 0 0 1.91 0.63 1.50 0.08 0 0.04 M4 0.58 0.29 0.24 0.09 0 0 1.34 0.48 1.38 0.11 0.08 0.22 Fl 0.21 0.04 0.09 0.17 0 0 0.92 0.56 1.38 0.19 0 0 F2 0.50 0.04 0.13 0.08 0 0 0.63 0.71 0.91 0.17 0 0.21 F3 0.38 0.12 0.08 0 0 0 1.05 0.38 1.12 0.36 0.08 0.04 F4 0.42 0.17 0.04 0.09 0 0 1.29 0.59 1.17 0.22 0.17 0.08 FA,I 9.44 13.82 19.23 9.53 2.64 2.16 1.26 25.01 2.32 2.44 0.09 11.93 P 0.010 0.004 0.001 0.010 0.140 0.186 0.340 <0.001 0.168 0.157 0.915 0.006 '0.017,11 3.73 4.79 5.89 4.09 - - - 5.43 - - - 4.48 P 0.007 0.002 <0.0'01 0.005 - - - 0.001 - - - 0.003 '0.017,11 2.81 4.28 4.64 3.36 - - - 6.64 - - - 3.93 P 0.026 0.004 0.002 0.012 - - - <0.001 - - - 0.006 '0.017,11 -0.922 -0.51 -1.25 -0.73 - - - 1.21 - - - -0.55 P 0.387 0.628 0.251 0.489 - - - 0.267 - - - 0.598 Note: Bold type indicates highest value 

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