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Quantifying forest fire variability using tree rings Nelson, British Columbia 1700–present Nesbitt, John Harnisch 2010

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Quantifying Forest Fire Variability Using Tree Rings Nelson, British Columbia 1700–Present by John Harnisch Nesbitt  B.A., Middlebury College, 2001 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in The Faculty of Graduate Studies (Geography) THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver) September 2010 © John Harnisch Nesbitt  Abstract This study uses dendroecology to provide direct evidence of historic forest fires and their effects on stand structure and dynamics at a local scale in the montane forests in southeastern British Columbia (BC). Using tree ages and fire-scarred trees, I determined the historic variability of fires by quantifying stand dynamics in relation to past fires in the mixed-conifer forests surrounding Nelson, a wildland-urban interface community in southeastern BC. I built fire records that extended from 1642–2009 across 18 sites in the ~160,000 hectare study area. Although a watershed-level fire signal is evident, site-to-site differences in fire-scar records and stand dynamics suggest that topography and land use caused variability in the fire histories of the individual sites. Numbers of fire-scarred trees and importance values of fire-tolerant trees decreased significantly with elevation. Fire-intolerant trees were most abundant in the subcanopy across all elevations. Most strikingly, no fires were recorded since 1932 across all sites, suggesting that fire exclusion has been effective and that future stands will likely continue to diverge from historic stands by becoming more dense, more homogenous in species composition, and, as a result, more susceptible to high-severity fires.  ii  Table of Contents Abstract ................................................................................................................................ ii Table of Contents ................................................................................................................ iii List of Tables ......................................................................................................................... v List of Figures ...................................................................................................................... vi Acknowledgements ........................................................................................................... viii CHAPTER 1 INTRODUCTION ..............................................................................................1 Fire as an Ecological Process in Western North America ................................................... 1 Controls on Fire .................................................................................................................... 2 Bottom-Up Controls ....................................................................................................3 Top-Down Controls .....................................................................................................6 Recent Research Trends: Climatic Oscillations ........................................................7 The Impact of Climate Change on Fire Activity .......................................................7 Anthropogenic Impacts ................................................................................................9 Questions and Hypotheses .................................................................................................. 10 CHAPTER 2 RESEARCH DESIGN AND METHODS ........................................................ 13 Study Area Description ...................................................................................................... 13 Experimental and Sampling Design ................................................................................... 15 Field Sampling .................................................................................................................... 17 Forest Composition and Structure ............................................................................. 18 Dendrochronological Analyses ........................................................................................... 18 Crossdating Fire-Scarred Discs ................................................................................ 19 Tree Ages and Age Structures .................................................................................... 20 Tree Growth .............................................................................................................. 23 Site-Level Fire History Analyses ........................................................................................ 24 Fire Regime Analyses ......................................................................................................... 26 Anthropogenic Impacts .............................................................................................. 27 CHAPTER 3 RESULTS ......................................................................................................... 29 Data Summary .................................................................................................................... 29 Site Attributes ............................................................................................................ 29 Forest Composition and Structure ............................................................................. 29 Fire Scar Overview ................................................................................................... 35 Tree Ages and Growth ............................................................................................... 35 Interpretation of Fire History for Individual Sites ............................................................ 36 HNFR1 Stratum ......................................................................................................... 36 HNFR2 Stratum ......................................................................................................... 43 iii  HNFR3 Stratum ......................................................................................................... 47 Fire Regime of the West Kootenays ................................................................................... 50 Fire History: All Sites Combined ............................................................................... 50 Fire Frequency: Comparison of HNFR Strata ........................................................... 56 Fire Severity: Comparison of HNFR Strata ............................................................... 59 Fire Frequency: Comparison of Shores of West Arm Lake ......................................... 61 Fire Severity: Comparison of Shores of West Arm Lake ............................................. 63 Anthropogenic Impacts .............................................................................................. 64 CHAPTER 4 DISCUSSION ................................................................................................... 65 Fire History and Fire Regimes ........................................................................................... 65 Fire and Stand Dynamics ................................................................................................... 69 Human Impacts on Fire Regimes ....................................................................................... 72 Fire Regime Classification in British Columbia ................................................................ 75 Natural Disturbance Type (NDT) .............................................................................. 75 Historic Natural Fire Regime (HNFR) ....................................................................... 78 Cumulative Human Impacts on Fire Regimes and Forest Dynamics ............................... 81 CHAPTER 5 CONCLUSIONS ............................................................................................... 84 Future Analysis ................................................................................................................... 85 REFERENCES CITED .......................................................................................................... 87 APPENDIX A – EVENT PANELS FOR HNFR1 .................................................................. 98 APPENDIX B – EVENT PANELS FOR HNFR2 ................................................................ 104 APPENDIX C – EVENT PANELS FOR HNFR3 ................................................................ 110  iv  List of Tables Table 3.1 Physical characteristics of sample sites in the West Kootenay study area. Sites are grouped by Historic Natural Fire Regime (HNFR) and ranked from low (1) to high (6) elevation within each stratum. Aspect was transformed to linear values from 0 (warm) to 2 (cool) for comparison among strata. Topographic relative moisture index ranges from 0 (xeric) to 60 (mesic) (Parker 1982; Taylor and Skinner 2003). ...................................................................... 31 Table 3.2 Tree density by canopy stratum and composition of live canopy trees by species and fire tolerance for each site, including averages and standard deviations calculated for each stratum. ..................................................................................................................................... 32 Table 3.3 Density of subcanopy trees by species and fire tolerance for each site. ...................... 33 Table 3.4 Density of regeneration by species and fire tolerance for each site............................. 34 Table 3.5 Density of live canopy trees by species and fire tolerance for each site. ..................... 38 Table 3.6 Fire regime classification for individual sites stratified by Historic Natural Fire Regime (HNFR) and listed by elevation within each stratum. Severity of the fire regime was classified using fire-scar and cohort dates as evidence of low-to-moderate and high-severity fires, respectively (Figure 2.3). Time since last fire was calculated relative to 2009, when sampling was completed........................................................................................................................... 39 Table 3.7 Fire regime classification for individual sites stratified by Historic Natural Fire Regime (HNFR) and listed by elevation within each stratum. Severity of the fire regime was classified using fire-scar and cohort dates as evidence of low-to-moderate and high-severity fires, respectively (Figure 2.3). Time since last fire was calculated relative to 2009, when sampling was completed........................................................................................................................... 55  v  List of Figures Figure 2.1 The study area, shaded in yellow, is 159,246 hectares in area and includes portions of West Arm Provincial and Kokanee Glacier Parks in the West Kootenays, southeastern British Columbia. ................................................................................................................................. 13 Figure 2.2 Criteria to differentiate even- from uneven-aged stands based on trees that established continuously versus discontinuously in contiguous versus non-contiguous 15-year age classes (after Taylor & Skinner 1998, Brown et al. 2008). ..................................................................... 22 Figure 2.3 Classification of historic fire severity at the site scale (after Agee 1993; Baker and Ehle 2003)................................................................................................................................. 25 Figure 3.1 The study area surrounding Nelson, British Columbia, Canada was stratified based on the Historic Natural Fire Regime (HNFR) classification (Blackwell et al. 2003) into three classes: high fire frequency (HNFR1 with fire return intervals of 0–35 years in dark red), midfrequency (HNFR2 with fire return intervals of 35–100 years in red), and low frequency (HNFR3 with fire return intervals of 100 years in red). Sites were ranked by elevation from lowest (1) to highest (6) within each HNFR stratum (e.g., 1-1, 1-2 etc.). ................................... 30 Figure 3.2 Frequency of fire grouped by site and sorted by elevation within each stratum of HNFR that recorded fire scars. A composite record documents all fire-scar dates samples from all sites combined through the entire period of record from 1642 to 2009. ................................. 52 Figure 3.3 Fire history and forest age structure for all sites combined. (a) Fire frequency shows number of fire scars recorded per year (bars) and estimated fire dates based on the years in which cohorts of trees established (triangles). (b) Percent trees scarred per year (bars) is the number of fire trees with a fire scar expressed as a percentage of the number of recorder trees in that year (line). Age structure (15-year classes) canopy (c) and subcanopy (d) trees classified as fire tolerant (white bars) and fire intolerant (grey bars). The hashed bar marks the period of European Settlement and Fire Exclusion from1860 to 1944. ...................................................... 53 Figure 3.4 Fire history of the six sites in the HNFR1 stratum. (a) Fire frequency shows number of fire scars recorded per year (bars) and estimated fire dates based on the years in which cohorts of trees established (triangles). (b) Percent trees scarred per year (bars) is the number of trees with a fire scar expressed as a percentage of the number of recorder trees in that year (line). ..... 57 Figure 3.5 Fire history of the six sites in the HNFR2 stratum. (a) Fire frequency shows number of fire scars recorded per year (bars) and estimated fire dates based on the years in which cohorts of trees established (triangles). (b) Percent trees scarred per year (bars) is the number of trees with a fire scar expressed as a percentage of the number of recorder trees in that year (line). ..... 57 Figure 3.6 Fire history of the 10 sites on the north shore of West Arm Lake. (a) Fire frequency shows number of fire scars recorded per year (bars) and estimated fire dates based on the years in which cohorts of trees established (triangles). (b) Percent trees scarred per year (bars) is the number of trees with a fire scar expressed as a percentage of the number of recorder trees in that year (line). ................................................................................................................................. 62 Figure 3.7 Fire history of the eight sites on the south shore of West Arm Lake. (a) Fire frequency shows number of fire scars recorded per year (bars) and estimated fire dates based on the years in which cohorts of trees established (triangles). (b) Percent trees scarred per year vi  (bars) is the number of trees with a fire scar expressed as a percentage of the number of recorder trees in that year (line). .............................................................................................................. 62  vii  Acknowledgements This thesis is the culmination of a longstanding desire to understand forest history in order to advocate for responsible management, and I am indebted to many who helped me along the path to its completion. My interests in the outdoors were first encouraged by my parents who inspired me to climb mountains and ask questions. My sister shares these passions, supporting me both in the field last summer, helping me to core the last of my trees, and now from afar through clutch sessions of proofreading. I would like to offer my deepest thanks to my advisor, Lori Daniels, who shaped this project from its inception with her cohesive vision and passion for strong science readably rendered. I am thankful as well for her research group in the Tree Ring Lab at UBC, where I was fortunate to study for a year and a half in the company of a friendly crew of engaged graduate students, post docs, research assistants, and friends. In particular, I was privileged to overlap with Hélène Marcoux, my twin in research. She brings exuberance to all those near her through her enthusiasm for her learning and zeal for life. I am grateful that we will remain friends even as I leave Vancouver to pursue other studies in science. Friends and supporters are the infrastructure that enabled me to complete this project. In the field last summer I benefited tremendously from the wisdom and commitment of Eugenie Paul-Limoges and Olivia Freeman, my tireless field assistants. They learned the drainages of the West Arm with me from the cab of a pickup as we bounced over countless logging road water bars. At the end of these long drives they accompanied me up steep slopes through Nelson’s rugged forests to collect the samples used in this project. In our research house last summer I benefited from conversations with graduate students and professors from Carelton and Guelph Universities, and particularly would like to thank Ze’ev Gedalof, who recruited me to research fire history in the Kootenays. I am also thankful to Eric Da Silva from Guelph, who hiked me viii  into his sites and graciously responded to questions around his tightly written thesis on fire history. Back in Vancouver, Taylor Martin eased my lab work with his steady diligence mounting, drying, and sanding all 700 plus tree core samples. Similarly, friends in the Geography Department at UBC tempered my stress with breaks for costume building, bike riding, and lessons about Canadian customs and curiosities. In the Kootenays I'd like to acknowledge research collaborators who sustained me throughout the project. First, Deb MacKillop and Randy Harris, from the British Columbia Ministry of Forests and Range, supported this project from the start by providing in-kind support which also came from other supporters: Randy Brieter, City of Nelson Fire Department, Kari Stuart-Smith, TEMBEC Industries, Brue Blackwell, BA Blackwell and Associates. Mike Gall from British Columbia Parks granted permission to conduct research in West Arm and Kokanee Glacier Parks. Rick Kubian extended me a spot at his table following a few rainy days spent sampling in Kootenay National Park during summer 2008, when I also met veteran fire ecologist Bob Gray who made fire-scar disks available for my independent study. Funding for this project came from an NSERC Strategic Grant. Lastly to the people of Nelson and the West Arm too numerous to mention, thank you for facilitating such a smooth summer with assistance securing housing, repairing windows, and sharing hospitality with me across the valley. To friends new and old, I appreciate the unwavering support, encouragement, and enthusiasm for this chapter of my life. Despite my transition away from ecology, I hold an appreciation for the information and beauty I found in these trees and I hope that this work will continue conversations around stewardship for forested landscapes. Any comments and suggestions to improved this paper are welcome, while oversights that remain are wholly my own.  ix  Chapter 1 Introduction Fire as an Ecological Process in Western North America Many disturbances shape the structure and composition of forests, impacting resources such as timber and drinking water, in addition to human communities (Veblen 2003). Across western North America, fire is a contagious disturbance that recurs across multiple scales of space and time in response to controls from climate to topography. Forest management strategies, which aim to both recreate natural patterns of fire through sustainable timber management and ecological restoration and to protect resources through hazard-mitigation treatments, benefit from information about the historic variability of fire. The history of fire frequency and severity can be reconstructed using records from tree rings. At coarse spatial and temporal scales, fire regimes generalize long-term patterns of fire frequency and severity (Pickett and White 1985; Heinselman 1973; Taylor and Skinner 1998; Agee 1993). In southeastern British Columbia (BC) and the United States Pacific Northwest, forest fires tend to decrease in frequency and increase in severity along an elevational gradient from valley bottoms to mountaintops (Agee 1993). At low elevations and in submontane forests, low-to-moderate-severity fires burn more frequently, consuming fine surficial fuels and scarring fire-resistant trees, such as ponderosa pine (Pinus ponderosa) and Douglas-fir (Pseudotsuga menziesii). These frequent fires prevent the buildup of fuels necessary for high-severity fires. Low-to-moderate-severity fires result in heterogeneous, low-density forests that often contain dominant, veteran survivor trees which record multiple fire scars. In contrast, high-severity fire regimes are characterized by stand-replacing fires which result in near total mortality, exposing mineral soil and initiating even-aged cohorts of thin-barked, fire-intolerant trees in subalpine spruce-fir forests. Long fire return intervals and stand-replacing fires typify high-severity fire 1  regimes while shorter return intervals and stand-maintaining fires characterize low-to moderateseverity fire regimes. In southeastern BC, the delineations between fire regimes are neither rigid nor well understood. Mountainous topography introduces variability to fire activity, resulting in mixedseverity regimes which contain variable proportions of low-to-moderate and high-severity fires across all scales (Daniels et al. 2007; Agee 1998). In mountainous regions, steep elevational gradients interfere with the spread of fire and result in mosaics of tree species across the landscape (Schoennagel et al. 2004). As a result, the characteristic patterns of both regimes intermingle, leaving highly complex patches of post-burn effects (Agee et al. 1990).  The  cumulative impact of fires which burn at multiple severities leads to jigsaw-like patches of uneven-aged stands interspersed with even-aged stands at fine scales (Agee 1998). The spatial complexity associated with mixed-severity fire regimes presents classification challenges for ecosystem management strategies which use historic patterns to plan treatments that manage fuels, ecosystem resilience, and forest health, among others (Taylor and Skinner 1998). As a result, local reconstructions of fire history enable managers to prioritize different segments of the landscape for ecological restoration and others for hazard mitigation, based on historic precedents of fire.  Controls on Fire Assessing the natural variability of fires within forested ecosystems requires understanding their controls. Climatic conditions and periodic droughts control fire frequency and severity over broad areas over periods of months to years, while weather and microclimatic conditions influence fire over periods of hours to weeks. Similarly, topography affects fuel accumulation over long periods of years to decades, and through its interactions with microclimate determines 2  fuel moisture and influences the localized spread of fires over periods from hours to days (Schoennagel et al. 2004).  Modern fire exclusion also impacts fuels and subsequent fire  frequency and severity. These controls vary and interact across space and through time to influence fire frequency and severity (Taylor and Skinner 2003; Heyerdahl et al. 2001; Heyerdahl et al. 2002; Johnson and Wowchuk 1993; Gillett et al. 2004). The sections that follow review topographic and climatic controls on fire, and consider the impacts of climatic change on fire regimes. Bottom-Up Controls Local variability in elevation, slope, aspect, and landscape physiography control fire activity and introduce key sources of heterogeneity to fire regimes (Agee 1993). Site-specific factors are classified as bottom-up controls and interact with overarching landscape-scale dynamics to govern fire ignition, behaviour, and effects at fine spatial scales (Heyerdahl et al. 2001). This section reviews the topographic mechanisms that control fire activity and the interactions between topographic controls in mixed-severity fire regimes. Elevation, through its impact on regional temperature and precipitation, controls the distributions of species, and shapes the composition of fuels, fuel moisture, fire season length, and likelihood of ignition (Agee 1993). In general, conditions at higher elevations are damper and cooler than at lower elevations due to the inter-relations between elevation, temperature, and the type and amount of precipitation (Agee 1993). At regional scales, elevation influences climate and can be construed as a top-down control due to its ability to synchronize regional fires irrespective of local conditions (Lertzman and Fall 1998). At the watershed-scale, elevational gradients can isolate forest patches from fire and result in spatial subdivisions of the disturbance regime, therefore acting as a bottom-up control (Lertzman and Fall 1998). 3  The effects of local and regional topography on fire activity have been investigated in southwestern Oregon through a comparative study of fire histories between two sites situated 20 km apart and varying in elevation from 1,300 meters above sea level (m.a.s.l.) to 1,800 m.a.s.l. (Agee 1991). Findings revealed inconsistencies in fire frequency between stratified sites with fires occurring more frequently at lower elevation sites (Agee 1991). Agee (1991) attributed inter- and intra-site fire variability to elevation and associated differences in precipitation. In addition, he noted a conflation of fire regimes at the lower site where proximity to warmer and drier ponderosa pine ecosystems may have resulted in fire contagion – a commonality likely overlooked by many studies but noted by Heyderdahl et al. (2007) and modelled by Jordan et al. (2008). These findings highlight the variability associated with elevational gradients in complex montane terrain and have been widely corroborated (Taylor and Skinner 1998; Veblen et al. 2000; Heyerdahl et al. 2001; Buechling and Baker 2004). Still, these patterns are not definitive as elevational gradients may not always be substantial enough to alter temperature, precipitation, and associated fire activity in the presence of overarching climatic controls (Heyerdahl et al. 2007). In southeastern British Columbia, where snow is the predominant form of precipitation, temperature gradients affect snowfall accumulation and snowpack persistence, and control fire season length (Service 2004; Heyerdahl et al. 2001). At finer scales, fire history records can differ with topography when fires burn continuously in some areas but not in others. Fire refugia are areas in which topographic attributes (Agee 1993; Heyerdahl et al. 2001) and/or site moisture (Everett et al. 2003; Taylor and Skinner 2003) diminished the likelihood of fire consistent with findings from the region (Camp et al. 2007). The individual influences of slope and aspect act in unison to control soil moisture, indirectly affecting fires at the site level. Steep slopes cause fires to spread more rapidly as tree-  4  to-tree transmissions are facilitated when fuel connectivity allows preheating of up-slope fuels (Agee 1993). Topographic breaks, associated with ridges and drainage channels, generally interrupt fuel continuity and inhibit fire spread (Jordan et. al 2005), though these effects vary (e.g. Segura and Snook 1992). In western North America, south-facing slopes receive the most insolation due to more direct exposure to midday sunlight. These slopes are also generally free of snow earlier in the year and thus more arid than comparably mesic north-facing slopes. In conjunction, slope and aspect create microclimates that influence fuel composition and determine evapotranspiration rates which govern fuel moisture but can vary considerably in complex mountainous terrain (Agee and Kertis 1987; Kunkel 2001; Taylor and Skinner 1998). The influence of topographic controls on fire activity have been well quantified in the Klamath Mountains in northern California (Taylor and Skinner 2003) and in the southern interior of BC (Heyerdahl et al. 2007) – regions where mixed-conifer landscapes are characterized by steep, deeply dissected, and highly complex terrain. Other researchers did not detect spatial coherence in fire activity between topographically similar sites in some (Everett et al. 2000; Heyerdahl et al. 2001) or all study sites (Buechling and Baker 2004) – the likely result of overriding climatic conditions or insufficient ranges in elevation necessary for microclimates. While slope and aspect can create signature patterns of fire, the variability of their influences may be overridden by climatic factors that operate at broader spatial scales.  Lightning is the dominant natural source of ignition in forested ecosystems, although sparks from falling rocks, spontaneous combustion from thermal decomposition, and lava from volcanoes may also ignite forest fuels (Agee 1993). Cyclonic and anticyclonic thunderstorms spawn lightning in the Pacific Northwest and are common stochastic phenomena on the coast  5  and interior respectively (Alexander 1927). Storm systems generate lightning strikes which spark ignitions of combustible fuels (Agee 1993). Under anticyclonic conditions, mountain ranges orographically lift air masses causing updrafts and releasing latent heat through condensation. As cumulus clouds form, atmospheric instability induces a charge differential between negatively charged lower clouds and the positively charged ground.  Lightning  discharges that occur between cloud and ground can trigger forest fires in the presence of dry surficial fuels. Annually, thunderstorms generate thousands of lightning strikes that occur primarily during the summer months in the Pacific Northwest and coincide with seasonal droughts that preconditioned forest fuels to burn (Agee 1993). Ignitions are associated with duration of lightning return stroke (Fuquay et al. 1972), antecedent drought (Pickford et al. 1980), and vary by elevation, aspect, and fuel type (van Wagtendonk 1986). Paradoxically mid-elevation areas experience the most lightning starts – the likely results of elevational increases in fuel moisture and lightning strikes (Fowler and Asleson 1984). In general, fuel moisture is a better predictor of fire frequency as number of lightning strikes and fire starts were uncorrelated in the interior Pacific Northwest (Rorig and Ferguson 1999). In summary, local topography can vary widely and may be spatially explicit to control fire activity over short distances with influences that vary in importance but are relatively stable through ecological time (Lertzman et al. 1998). Top-Down Controls Climate controls vegetation, fire, and their interactions within forested ecosystems. Mean annual temperature and precipitation follow long-term climatic variations and determine fuel availability.  Inter-annual to decadal variability in regional climate predetermines fuel  production, fuel moisture, and frequency of ignitions (Heyerdahl et al. 2002). At inter-annual to 6  decadal scales, droughts increase aridity which reduces moisture contents of forest vegetation below ignition thresholds and creates conditions conducive to fires (Gedalof et al. 2005; Heyerdahl et al. 2002). Climatic mechanisms vary at low temporal frequencies in relation to tree age and are differentiated from microclimate, a bottom-up control linked to local topography. While I do not test climate as a driver of fire activity in this thesis, an understanding of relations between climate and fire is important background in understanding sources that shape the variability of fire as climate has been found to synchronize regional fire activity over broad areas (Swetnam 1993) but interact with local, topographic controls to cause heterogeneous patterns of fire variability at small spatial scales mixed-severity regimes (Sibold and Veblen 2006). Recent Research Trends: Climatic Oscillations To differentiate between climate, fuels, and fire, recent research has focused on local analyses which target the dominant historical drivers of fire variability.  Increasingly sophisticated  climatic reconstructions and improved resolution in paleoecological techniques aim to link variability in fire frequency to climatic fluctuations across multiple spatial and temporal scales (e.g. Higuera et al. 2007). Findings reveal non-linear responses of fire to climatic forcings such as El Niño Southern Oscillation (ENSO), Pacific Decadal (PDO), ENSO/PDO interactions, and Atlantic Multidecadal Oscillation (AMO) (Heyderdahl et al. 2002; Westerling et al. 2006). For example, relative humidity governs fire severity at scales of minutes to days while precipitation shapes fire frequency over centuries to millennia (Heyderdahl et al. 2002). The Impact of Climate Change on Fire Activity Amidst mounting concerns that climatic change will result in regional droughts, increasing aridity and altering fire regimes across western North America (Westerling et al. 2006), researchers reconstruct historic interactions between climate, fire, and vegetation to quantify 7  current changes and anticipate likely scenarios.  Mid-tropospheric blocking events divert  precipitation from western North America and increase the length and severity of summer droughts. In an analysis of historic fires in the Northern Rockies, more frequent and prolonged blocking events were attributed to increased area burned since the 1980s (Knapp and Soulé 2007). Similar increases in area burned have been detected since the 1970s across western Canada (Gillett et al. 2004). In the western U.S., Westerling et al. (2006) cited regional increases in fire frequency, duration, and season since the mid-1980s and especially in the Northern Rockies. Drought-fire linkages were corroborated in eastern Washington between 1700 and 1900 but 20th century changes in land-use have interfered with historic drought-fire relations (Hessl et al. 2004). Ecological conditions may also modulate the response of fire to atmospheric forcings with arid stands burning during blocking events and in the absence of antecedent drought (Gedalof et al. 2005). The likely contributions of anthropogenic greenhouse gases to increased temperatures in many regions of North America have generated interest in fire forecasting (IPCC 2001; Karoly et al. 2003).  Relative to ecological timescales, the brevity of the instrumental record makes  statistical projections of fire activity based on forecasted temperatures speculative at best. Nonetheless, modellers infer future fire activity from synoptic weather predictions based upon the extent and duration of summer blocking events. Statistical experiments seek to quantify likely anthropogenic effects on fire activity and predict increases on average of 74-118% in area burned by the end of the century in Canada (Flannigan et al. 2005).  Increasing summer  temperatures projected through global circulation models will continue to increase area burned by extending fire season and decreasing fuel moisture (McKenzie et al. 2004; Gillett et al. 2004). Droughts associated with increasing summer temperatures will serve to precondition mesic  8  ecosystems for fire (Gedalof et al. 2005).  These speculations as to future atmospheric  configurations are based on coarse-scale global circulation models which incorporate stochastic variability that remains incongruent with local reconstructions of fire activity. The variability that unites retrospective and prospective studies highlights the widespread uncertainty surrounding the impacts of climatic change on fire activity. Understanding how future climatic changes will influence fire activity requires information on past fire conditions and climatic variability. Dendrochronologists have extended research throughout western North America and introduced analytical techniques (Arno 1980) and statistical tools (Grissino-Mayer 1999; Reed and Johnson 2004) that refine spatial and temporal extent, spacing, and resolution. In southeastern British Columbia, dendrochronological analyses will continue to address fireclimate interactions with annual resolution and in concert with paleoecological techniques (Mustaphi, in preparation). The functional relevance of climate on fire activity and vegetation dynamics will vary in accordance with anthropogenic influences that interact with climatic and topographic controls to affect fire activity. Anthropogenic Impacts Humans impact forests through modifications that interfere with natural fire activity. Historical influences on fire activity began by natives who set fires to initiate berry production and clear brush from stands to facilitate hunting (Barrett and Arno 1982; Turner 1999). During the 19th century, Europeans spread west across North America and cleared forests to build settlements. Once established, these settlers introduced changes in land use by grazing animals, mining minerals, and harvesting timber. Human impacts were most intense in valley bottoms, where settlers clustered along navigable waterways and converted land from forest to fields, towns, and pasture. 9  Since World War II, aerial fire suppression has altered fire regimes across the Pacific Northwest (Agee 1993). Fire regimes respond differently to fire exclusion with forest type (Agee 1998). In low-severity fire regimes, fire exclusion results in fuel accumulation which has been linked with increased fire severity (Sibold et al. 2006, Sherriff and Veblen 2007). In highseverity fire regimes on the other hand, fuel accumulation matters less as climate is the predominant control on fires that burn at consistently high severities (Johnson et al. 2001, Westerling et al. 2006). Fire suppression efforts are most successful at extinguishing small fires that burn at low-to-moderate severities. As a result, the effects of fire suppression differ with fire regime, with low-to-moderate-severity regimes experiencing more significant changes than highseverity regimes. Responses of fire regimes to suppression have been shown to increase fuels and the risk of high-severity fires in some mixed-severity regimes (Arno et al. 2000). In other areas, fire suppression has had minimal impacts on stand structure and fire regimes (Taylor and Skinner 1998, Veblen 2003). As a result of this disparity, research must assess the historic variability of fire activity in mixed-severity systems to provide targets for managers attempting to emulate natural disturbances through ecological restoration and reduce fire hazard through mitigation.  Questions and Hypotheses My research will reconstruct fire histories and their impacts on vegetation to quantify fire frequency and severity and determine the relative influence of and interactions among topography and human land-use as controls on fire in forests classified by mixed-severity fire regimes along an elevational gradient in the montane forests surrounding Nelson, British Columbia.  10  My research aims to answer the following questions that test the associated hypotheses (stated as predictions with associated measurements): Spatial Variation in Historic Fires 1. Have higher elevation sites experienced less frequent fires than lower elevation sites? Historically, fire frequency varied inversely with elevation according to the following attributes: (1) number of fires, (2) number of fire intervals and percentage of fire-scarred trees, and (3) time since last fire (TSLF). 2. Have higher elevation sites experienced more severe fires than lower elevation sites? Historically, fire severity increased with elevation according to the following attributes: (1) importance values of fire-tolerant versus fire-intolerant species, and (2) structure and number of age classes which indicate even- versus uneven-aged stands and low- versus high severity fires. 3. Which abiotic factors affect fire occurrence? Historically, fire occurrence – measured by the density of fire-scarred trees, snags, and logs observed per hectare – varied inversely with elevation and topographic relative moisture index (TRMI), and was more likely on the south- than north-facing side of Kootenay Lake.  Temporal Variation in Historic Fires 4. Has fire exclusion and suppression reduced fire frequency since the 1940s? Fire exclusion during the 20th century lengthened mean fire return intervals across high- and lowelevation sites relative to three 85-year periods and one 64 year period that correspond with two pre-settlement eras, a single European-settlement era and the modern fire suppression era:  11  i. ii. iii. iv.  Modern fire suppression European settlement and fire exclusion Pre-European settlement I Pre-European settlement II  12  1945–2009 1860–1944 1775–1859 1690–1774  Chapter 2 Research Design and Methods Study Area Description The study area is comprised of 159,246 hectares (ha) located within the Kootenay Lake Forest District on the windward side of the Selkirk Range in the West Kootenay area of southeastern British Columbia (Figure 2.1). The study area stretches east to west from Kootenay Lake to the city of Nelson, and north to south from Kokanee Provincial Park to West Arm Provincial Park. This area includes the drinking water supplies for Nelson, Harrop, Procter, and the North Shore communities situated along West Arm Lake.  Figure 2.1 The study area, shaded in yellow, is 159,246 hectares in area and includes portions of West Arm Provincial and Kokanee Glacier Parks in the West Kootenays, southeastern British Columbia. West Arm Lake bisects the Selkirk range at the bottom of a glacial valley that splits west from Kootenay Lake. Granitic bedrock along with metamorphosed sedimentary rock underlies the study area (Utzig et al. 2003). Soils transition from Brunisols to Podzols with increasing 13  elevation, canopy density, and soil moisture (Utzig et al. 2003; Valentine et al. 1978). North of West Arm Lake, deposits of gold and copper are interspersed in the bedrock (Reesor 1996). The climate in the study area varies along steep elevational gradients. To the north and south of West Arm Lake (580 metres above sea level, m.a.s.l.), steep-sided valleys rise to ridgelines (approximately 2150 m.a.s.l.) and peaks (approximately 3200 m.a.s.l.) over short distances (<10 km) and through moderately dissected terrain. Mean monthly temperature is 8.4 ± 0.7°C (range -2.7°C in Jan. to 19.7°C in July) and mean annual precipitation is 755 mm/year, 43 % occurring April through September (Environment Canada 2008; Castlegar 49°18’N 115°37’48”W, 495 m.a.s.l.). Precipitation and percentage of precipitation that falls as snow increases with elevation, as coastal air masses collide with the Selkirk Mountains (Utzig et al. 2003). Vegetation in the study is described as the “interior wet belt” forest (Utzig et al. 2003) and according to biogeoclimatic ecosystem classification (BEC), vegetation transitions from Interior Cedar Hemlock (ICH) to Engelmann Spruce – Subalpine-fir (ESSF) vegetation zones with elevation (Meidinger and Pojar 1991).  Between 550 and approximately 800 m.a.s.l.,  montane forests contain heterogeneous mixes of ponderosa pine (Pinus ponderosa), Rocky Mountain Douglas-fir (Pseudotsuga menziesii var. glauca), western larch (Larix occidentalis), western redcedar (Thuja plicata), and western hemlock (Tsuga heterophylla).  At higher  elevations, subalpine forests contain Engelmann spruce (Picea engelmannii), subalpine fir (Abies lasiocarpa), grand fir (Abies grandis), and lodgepole pine (Pinus contorta). In the transition zone between the montane and subalpine forests, diverse assemblages of species co-occur. The transition between montane and subalpine species varies through space, over time, and in response to human land-use.  14  Human land use and impacts on the forest varied over time throughout the study area. First Nations were the first to impact the land. Archaeologists documented Sinixt settlements which date from 4,000 to 10,000 years ago and surround navigable waterways in low-elevation forests (Pearkes 2002). First Nations people set fire to forests to initiate berry production and to maintain open stands for hunting, grazing, and communication (Barrett and Arno 1982). European settlers colonized the study area in the 1850s and established placer mines along numerous creeks to extract copper and gold (Utzig et al. 2003). Miners set fire to forests to expose rock outcrops and locate potential mines. They also harvested timber to build mining infrastructure throughout the study area with significant impacts concentrated north of West Arm Lake. As a result, extensive stands of even-aged conifers established towards the end of the mining era, circa 1890 through 1910 (Utzig et al. 2003). Currently, municipal infrastructure includes drinking water supply lines and intake facilities upslope from Nelson into West Arm Provincial Park along Five Mile Creek. Similarly, communities north and south of West Arm Lake draw water from forests sampled in this study.  Experimental and Sampling Design Site selection in the West Kootenay study area followed a stratified random approach to select stands that established prior to European settlement in the 1850s. I searched a Ministry of Forest and Range database of forest cover using a GIS to locate my sites. In British Columbia, the Ministry of Forests and Range inventories forest resources using aerial imagery to assign attributes, such as stand age, species abundance and composition to distinct stands of trees. Forest cover databases demarcate locations of and boundaries between stands and contain numerous biophysical attributes for each stand.  15  To locate patches of old forests that were accessible by hiking, I searched the forest cover database to identify stands that were >3 ha in size in the study area, with estimated stand ages ≥ 200 years, and within 800 m of a passable road. In total, the study area contained 159,247 ha of forest of which 35,116 ha were classified with stand ages ≥200 years, of which 9,956 ha were located within 800 m of a passable road and met my criteria to comprise a population of old and accessible stands. From the resultant subset, I stratified polygons into low-, mid- and highfrequency Historic Natural Fire Regime (HNFR) strata. The HNFR classification is a coarsescale estimate of fire frequency and severity prior to European settlement and based on forest structure, slope, and aspect (Blackwell et al. 2003). The frequency of fire as predicted within each HNFR stratum varies from 0 to 35 years (high-frequency stratum, hereafter "HNFR1") in valley bottoms to >100 years (low-frequency stratum, hereafter "HNFR3") on upper slopes and includes intermediate elevations where fires were predicted to burn every 35 to 100 years (midfrequency stratum, hereafter "HNFR2"). As aspect controls soil moisture and indirectly affects fire activity at the site-level (Agee 1993), I randomly selected three stands for analysis within each stratum and on both sides of West Arm Lake. Due to difficult access to stands in HNFR1 on the south side of the Lake, I only sampled two stands but sampled four stands on the north side of the lake. The location of plots within selected sample sites was determined prior to visiting sites in the field. For each sample site, I selected the point within the stand that was closest to a road and could accommodate sample plots while providing a 100 m buffer between the plot and the edge of the stand to minimize edge effects. I located sites on a map to determine access and land ownership before ensuring that plots contained representative trees suitable for fire history reconstructions. Upon entering a site, I confirmed that stand structure and composition matched  16  population attributes with the forest cover database by inventorying species and measuring diameters of canopy dominant trees.  Field Sampling Field sampling was conducted June through August 2009. At plot centre at each site, I recorded elevation (m.a.s.l.), slope aspect (degrees), angle (degrees), and configuration (convex, convex/straight, straight, concave/straight, concave, Parker 1982) and topographic position (ridge top, upper slope, mid slope, lower slope, valley bottom, Parker 1982), from which I calculated topographic relative moisture index that ranges from 0 (xeric) to 60 (mesic) (Parker 1982; Skinner and Taylor 2003). I also took digital photographs in the four cardinal directions from plot centre to archive stand attributes. At each site, I searched for evidence of fire within a 56.3 m radius of plot centre (1.0 ha circular plot). Trees with fire scars provide direct evidence of low- to moderate-severity fires that scar but do not kill trees (Gutsell and Johnson 1996). Subsequent fires burn the scar tissue and result in scar lobes that can be dated at an annual resolution (Brown and Swetnam 1994). I recorded the species and number of scars on all fire-scarred trees, snags, and logs (hereafter “fire-scarred trees”).  I sampled up to 10 fire-scarred trees per site, prioritizing large and  presumably old trees with multiple scar lobes to reconstruct the longest fire-history record possible (Van Horne and Fulé 2006). I removed a partial section from living trees (Cochrane and Daniels 2008) and cut complete cross-sections from dead trees (Brown et al. 2000; Heyerdahl et al. 2006). Nested in the 1-ha circular fire plot, I sampled two types of plots to document stand composition and structure. I used a density-adapted, n-tree design (Brown 2006) to estimate density and sample the 30 canopy trees (diameter at breast height (dbh) ≥40 cm, MacKillop 17  2003) closest to and within 40 m of plot centre (Heyerdahl et al. 2006; Kipfmueller and Baker 1998). All living trees, plus snags (standing dead trees) and logs with sound sapwood, were included (Johnson et al. 1994; Ehle and Baker 2003). From each sampled individual, I removed an increment core as close as possible to the ground, generally at a height of approximately 50 cm above the ground, and recorded species, dbh, and coring height (Taylor and Skinner 1998). Living subcanopy trees (5cm  dbh > 40cm), saplings (dbh < 5cm and height 1.3m) and seedlings (height < 1.3 m) were sampled in a 15m x 15m quadrat surrounding plot centre. The species and dbh of all subcanopy trees were recorded and up to 15 trees were randomly selected and cored near the ground to estimate age. The number of seedlings and saplings of each species was recorded. Forest Composition and Structure For each stand, I calculated the density (individuals per ha) of living trees of each species in the canopy, subcanopy and regeneration (seedlings and saplings combined) layers. For individual canopy trees, dbh was converted to basal area (BA = 𝜋 (dbh/2)2). At the stand level, relative density and relative basal area of canopy trees were summed to calculate the importance value (IV) of each species. The trees were classified as fire-tolerant (Douglas-fir, ponderosa pine, western larch) or fire-intolerant (western white pine, lodgepole pine, trembling aspen, grand fir, western redcedar, western hemlock, Engelmann spruce, subalpine fir; Agee 1993). The total densities and IVs of fire-tolerant and fire-intolerant trees were calculated for each stand.  Dendrochronological Analyses Cores and discs were processed using standard techniques (Stokes and Smiley 1968). Cores glued to wooden supports and fire-scarred disks reinforced with glue were sanded with 18  progressively finer paper from 80 to 400 or 600 grit. To crossdate samples, I built local and species-specific master ring-width series for Douglas-fir, ponderosa pine, western hemlock, western larch, western redcedar, and Engelmann spruce.  To do so, I selected a subset of  increment cores from large, live trees with sound heartwood and long ring-width series. Cores were visually crossdated, measured to an accuracy of 0.001 mm using a Velmex measuring bench interfaced with a computer, and crossdating was verified using the program COFECHA (Grissino-Mayer 2001a; Holmes 1983). Properly dated and highly-correlated samples were combined into master series for each species that included five to 19 cores, spanned 91 to 300 years and had inter-series correlations of 0.342 to 0.642. Negative/positive marker rings, rings that were less/more than one standard deviation narrower/wider than the average ring width, were used to visually crossdate other samples from living trees. Samples from 70 dead and 195 live trees, plus 40 fire-scarred discs were measured and statistically crossdated against the local and species-specific master ring-width series using the program COFECHA. Crossdating Fire-Scarred Discs I visually crossdated the discs from 11% of fire-scarred trees. I measured the ring-width series of the majority of fire-scarred trees (89%) and statistically crossdated them against the appropriate species-specific master chronology using the program COFECHA (Grissino-Mayer 2001a; Holmes 1983). I confirmed the statistical crossdating by matching narrow rings on each sample with marker years from the master chronologies, then assigned calendar years to each fire scar and to the innermost and outermost rings of each disc. Historically, lightning strikes that occur in the summer months cause the majority of fire ignitions (Agee 1993). To ensure my fire-scar records were accurate at an annual resolution, I determined the season in which fires burned by assessing the position of the tip of the fire scar 19  within the annual ring in which it formed (Baisan and Swetnam 1990). The majority of scars were dormant-season scars that occurred along the boundary between two annual rings. Dormant-season scars are challenging to date because scars result either from fires that burn in the fall (year x), after the annual ring has formed, or in early spring (year x+1), before the new ring begins to form. Modern fire records from the region indicate that fires occur primarily in late-summer or fall when convective storms generate thunderstorms and lightning strikes which ignite dried fuels (Agee 1993; BCMOFR 2010). For dormant-season scars I attributed fire to lightning and assigned scars to the calendar year prior to the dormant season recording the fire using the following rules: i.  First I compared all fire scars at a given site in a given year. When I could determine the seasonality (fall or spring) of at least one scar, I reported all dormant-season scars to be consistent with that observation.  ii.  When seasonality remained uncertain, I assigned dormant-season scars to the calendar year of the fall in accordance with the modern fire record.  I restricted all subsequent analyses to fire-scars that were accurately dated at an annual level. Tree Ages and Age Structures Increment cores (n=540 from canopy trees and n=199 from subcanopy trees) were used to estimate years of establishment of living and dead trees and years of death from snags and logs. I visually crossdated the cores from 54% of living trees and statistically crossdated the ringwidth series of the cores from 32% of living and 74% of all dead trees, as described for the firescarred discs. While cores from 167 crossdated trees intercepted pith, heartwood decay prevented crossdated cores from reaching pith of 454 trees. For these trees, I measured the length of the core and reported the minimum age only when core length was ≥67% of the tree radius (n=113). For the remaining 508 trees, year of establishment of individual trees was estimated as the 20  crossdated year of the innermost ring, minus a correction for cores that did not intercept the pith (Duncan 1989), minus the number of years estimated for trees to grow to coring height. The number of years for the tree to grow to coring height was estimated using the sapling method (Villalba and Veblen 1997; Wong and Lertzman 2001) in which regression equations of age on height were derived for regeneration of shade-tolerant and shade-intolerant species growing in the Kootenay region and applied to individual trees (L.D. Daniels unpublished data). Combined, the average correction for missed piths and coring height was 139 (mean  standard deviation) years; therefore, I compiled tree ages into 15-year classes to assess age structure. At the site-level, age structures were classified as continuous or discontinuous and as evenaged or uneven-aged (Figure 2.2). Trees established continuously when all age classes were contiguous; if not, trees established discontinuously.  At sites where trees established  continuously and within <60 years, stands were classified as even-aged (after Taylor and Skinner 1998), while other stands that established continuously were classified as broadly even-aged (Brown et al. 2008). At sites where trees established discontinuously, the presence/absence of cohorts differentiated between uneven-aged stands that established with/without even-aged groups of trees.  21  Figure 2.2 Criteria to differentiate even- from uneven-aged stands based on trees that established continuously versus discontinuously in contiguous versus noncontiguous 15-year age classes (after Taylor & Skinner 1998, Brown et al. 2008). To detect cohorts that may have established after fire, I counted the number of trees that established in 20-year moving intervals beginning with the oldest tree at each site. I defined a cohort as a group of 5 trees that established within any 20-year period and included 25% of trees in the stand (after Larson and Kipfmuller 2010; Ehle and Baker 2003). For cohorts that coincided with a fire scar, I assumed the cohort resulted from the fire and the cohort was assigned the calendar date of the fire scar (Heyerdahl et al. 2001). Otherwise, the cohort was assigned a date based on the age of the oldest tree and I assumed that a fire initiating the cohort burned at least one year prior to that date.  22  Tree Growth The growth patterns of individual trees were assessed to interpret the conditions in which trees established (Ehle and Baker 2003) and the impacts of fire on the growth of veteran trees that survived fire (Beaty and Taylor 2008). To gauge the conditions under which trees established, I visually compared the 10 innermost rings to all other rings of the core. Initial growth rates were classified as slow or fast if the innermost rings were narrow or wide relative to the remainder of the core. If the rings were comparable in width, initial growth was classified as moderate. For trees with wide rings indicating fast initial growth rates, I assumed they were growing on a site with low tree density and open canopy conditions, likely following disturbance (Ehle and Baker 2003). At the site level, I calculated the percentage of trees in each 15-year age class that exhibited fast initial growth rates. At each site, I used the dates of the fire scars to identify veteran trees. Veteran trees were defined as canopy trees that established prior to and survived at least one fire as indicated by fire scars and cohorts. Fire can influence the growth of surviving trees resulting in a suppression or decrease in radial growth (Brown and Swetnam 1994; Barrett and Arno 1988; Arno and Sneck 1977) or a release or increase in radial growth (Agee 1993; Brown and Swetnam 1994). To detect growth responses in individual veteran trees following fire, I measured the width of 10 rings before and after each fire and calculated the percentage growth change (Beaty and Taylor 2008). I defined minor and major growth suppressions/releases as decreases/increases in growth of 100–149% and ≥150%, respectively, that were sustained at least 10 years. At the site-level, I calculated the percentage of veteran trees in each 15-year age class that showed minor and major release and suppression patterns in growth following each fire. This analysis included veteran trees for which only minimum ages were determined, so that their growth response to fire was assessed although some were not included in age structure histogram. 23  Site-Level Fire History Analyses Fire scars combined with age cohorts and initial growth rates of trees provided evidence of past fires of a range of severities (Sherriff and Veblen 2006, Figure 2.3). To classify historic fires at each site as low-to-moderate-, high- or mixed-severity, I differentiated sites with fire scars (n=11) from those without (n=7). Fires were classified as low-to-moderate- or mixed-severity at sites with multiple fire scar dates (Figure 2.3, left column) (Agee 1993). Low-to-moderateseverity fires included sites with (a) multiple scars but no cohorts and (b) multiple fire scars dates and 1 cohort coinciding with fire. At sites with cohorts that included 50% of trees with fast initial growth rates but were independent of the fire scars, I attributed the cohorts to high-severity fires and scars as evidence of low-to-moderate-severity fires and classified fires as mixedseverity (Baker and Ehle 2003).  For sites without fire scars (Figure 2.3, right column), I  determined fire severity using the presence of cohorts and initial growth rates of veteran trees. I classified fire as high-severity at sites with neither fire scars nor veterans but with cohorts that included 25% of trees with fast initial growth rates. Sites were classified as having no evidence of fire if (a) neither fire scars nor cohorts were present or (b) cohorts and veterans were present, but <25% of the trees had fast initial growth rates.  24  Figure 2.3 Classification of historic fire severity at the site scale (after Agee 1993; Baker and Ehle 2003).  The intervals between fires and time since last fire (TSLF) are measures of fire frequency that can be compared between sites and eras (Gavin et al. 2003). Crossdated fire scars are annually resolved and at sites with multiple scars, fire intervals can be calculated. Cohorts represent additional fire dates inferred indirectly from age structure and can be included along with fire scar dates to more fully understand the historic variability of fire. Therefore, at sites with multiple fire-scar dates or scar and cohort dates, I defined fire intervals as the number of years between scar-to-scar and scar-to-cohort dates and calculated separate minimum, maximum, range, and mean intervals for scars and scars with cohorts to explore differences in fire history using all evidence of fire. To test for differences in fire frequency, I compared the number of  25  intervals at each site using only scar-to-scar intervals to test for differences in fire frequency among strata. I calculated TSLF as difference between 2009 and the most recent fire-scar or cohort date at each site (n=15) using fires inferred from age structures at sites without fire-scar dates by using time since last cohort as a proxy for TSLF.  Fire Regime Analyses To test for variation in fire frequency and severity at coarse spatial scales within the study area, I grouped sites by (1) HNFR strata and (2) location on the north- versus south-shore West Arm Lake. To compare the frequencies of low-to-moderate severity fires of these strata and locations, I compiled composite fire records using the annually-resolved fire scars and used the program FXH2 (Grissino-Mayer 2001b) to (a) calculate the minimum, maximum and range of fire intervals for each stratum and location and (b) test for differences in the Weibull median probability interval (WMPI) and the mean percentage of scarred trees among strata and between locations. In a second set of tests, I compared fire frequency using both the fire scars and dates of cohorts which estimated the timing of high-severity fires. Since the fire dates from cohorts were not as precise as the crossdated fire scars, I adjusted the year of occurrence for cohorts that established within five years of a fire scar in the same stratum or on the same shore before comparing the cohort and fire-scar dates (adjustments of 1–5 yr, mean 2.4 yr) (Heyderdahl et al. 2001). When two cohorts established within five years of each other in HNFR3, where no fire scars were recorded, I included only the date corresponding to the cohort that established first so as not to over represent fires that more likely co-occurred rather than occurred at short intervals (adjustments of 2–3 yr, mean 2.5 yr). As well, I tested for differences in the mean number of fires (low-to-moderate-severity fires only and low-to-moderate- and high-severity fires) and mean TSLF among strata and between locations using a Kruskall-Wallis H-Test and Mann26  Whitney U-test, respectively (SAS 2010). The latter tests compared differences in mean ranks since the data were not normally distributed. For all statistical tests, α = 0.05. I compared the number of sites classified as low-to-moderate-, mixed-, and high-severity within each stratum and location using severity classifications assigned at the site level. To test for differences in historic fire severity among sites, I evaluated three attributes among strata and locations. High importance values of fire-tolerant canopy trees and relative densities of firetolerant trees in the subcanopy and regeneration layers are indicators of past low-to-moderate severity fires (Taylor and Skinner 1998).  Mean values for each of these attributes were  compared among strata and between locations using Kruskall-Wallis H-Tests and Mann-Whitney U-tests, respectively (SAS 2010). Anthropogenic Impacts Across western North America, fire intervals vary in response to different periods of human disturbance (Veblen et al. 2000; Taylor and Skinner 2003; Beaty and Taylor 2008). To test for changes in fire frequency and the potential effects of fire exclusion and suppression during the 19th and 20th centuries, I combined the fire-scar records from all sites and then the fire-scar plus the record of cohorts from high-severity fire from all sites to compare mean fire return intervals (MFRIs) and percent fire-scarred trees during four periods, as follows: i. ii. iii. iv.  Modern fire suppression European settlement and fire exclusion Pre-European settlement I Pre-European settlement II  1945–2009 1860–1944 1775–1859 1690–1774  I based the start of the modern fire suppression period on the end of World War II when the availability of aircraft increased the efficacy of aerial suppression (Agee 1993) and the start of the European settlement and fire exclusion periods on the documented beginning of the gold rush in the study area and subsequent changes in land use (Pearkes 2002). Since the European 27  settlement and fire exclusion period was 84 years, I compared it with the two consecutive 84year periods preceding it. Paired comparisons of fire intervals and percent fire-scarred trees were made for all combinations of periods using the temporal analysis module of FXH2, which included a test for homogeneity of variances and t-tests to compare the means (Grissino-Mayer 2001b).  28  Chapter 3 Results Data Summary Site Attributes The 18 sites used to reconstruct fire history were distributed north (n=10) and south (n=8) of West Arm Kootenay Lake (Figure 3.1). Elevations of sites ranged from 611 meters above sea level (m.a.s.l) to 1725 m.a.s.l. (Table 3.1). Aspects varied widely among sites. Similarly, slope angles ranged from five to 35 degrees and values of topographic relative moisture index (TRMI) ranged from 16 to 47, given the complex terrain of the study area. Forest Composition and Structure The composition of species and structure of stands at each site provides information on the conditions during which stands developed (Beaty and Taylor 2008).  I documented eleven  different tree species throughout the study area, with the dominance of canopy trees varying from site to site (Table 3.2). Individual sites contained between two and five species of canopy trees with fire-tolerant Douglas-fir, ponderosa pine, and western larch generally dominating at low elevations in stratum HNFR1 and fire-intolerant Engelmann spruce and subalpine fir found almost exclusively at higher elevations in stratum HNFR3. Some low-elevation sites contained co-dominant components of fire-intolerant grand fir and western redcedar which, along with western hemlock, were found almost exclusively at sites in strata HNFR1 and HNFR2. Subcanopy and regeneration layers of the study sites were dominated by fire-intolerant species (Tables 3.3 and 3.4). Overall differences in stand composition and structure marked forests at sites characterized by diverse mixes of species growing in a variety of configurations across the study area.  29  Figure 3.1 The study area surrounding Nelson, British Columbia, Canada was stratified based on the Historic Natural Fire Regime (HNFR) classification (Blackwell et al. 2003) into three classes: high fire frequency (HNFR1 with fire return intervals of 0–35 years in dark red), mid-frequency (HNFR2 with fire return intervals of 35–100 years in red), and low frequency (HNFR3 with fire return intervals of 100 years in red). Sites were ranked by elevation from lowest (1) to highest (6) within each HNFR stratum (e.g., 1-1, 1-2 etc.).  30  Table 3.1 Physical characteristics of sample sites in the West Kootenay study area. Sites are grouped by Historic Natural Fire Regime (HNFR) and ranked from low (1) to high (6) elevation within each stratum. Aspect was transformed to linear values from 0 (warm) to 2 (cool) for comparison among strata. Topographic relative moisture index ranges from 0 (xeric) to 60 (mesic) (Parker 1982; Taylor and Skinner 2003).  31  Table 3.2 Tree density by canopy stratum and composition of live canopy trees by species and fire tolerance for each site, including averages and standard deviations calculated for each stratum.  32  Table 3.3 Density of subcanopy trees by species and fire tolerance for each site.  33  Table 3.4 Density of regeneration by species and fire tolerance for each site.  34  Fire Scar Overview Fire-scarred trees were located at 11 of 18 study sites where densities ranged from one to 33 per ha. I sampled and successfully crossdated 45 fire-scarred disks (3 to 10 per site) from nine of the 11 sites (Figure 3.2). The disks contained 68 embedded fire scars. The fire scars occurred primarily on fire-tolerant species such as western larch (15 disks with 18 scars), ponderosa pine (13 disks with 27 scars), and Douglas-fir (7 disks with 9 scars), but also on thin-barked species such as western redcedar (9 disks with 13 scars), and western hemlock (1 disk with 1 scar) which are typically killed but not scarred by fire (Agee 1993). Individual trees contained one to seven fire scars, with the majority (n=32, 71%) recording one scar and 13 recording two or more scars for a total of 19 different fires between 1642 and 2009 (Figures 3.2 and 3.3). Tree Ages and Growth In total 739 trees were cored; 444 cores were from live, canopy trees; 199 were from live, subcanopy trees; and, 96 were from dead snags and logs. I successfully crossdated 550 of 643 (86%) cores from live trees to yield establishment dates (n=459) and minimum ages (n=91). I successfully crossdated 71 of 96 (74%) cores from dead trees to yield year of death (n=55), establishment dates (n=59) and minimum ages (n=12). Of all samples, 168 intercepted pith while establishment dates were estimated for 350 cores and the 103 minimum ages were used only to corroborate age structure information and identify suppression/release events in veteran trees that had survived fires. Establishment dates for all canopy trees ranged from 1639 to 1957 (Figure 3.3), 50% of which had wide rings close to the pith indicating fast initial growth rates, likely in open conditions when inter-tree competition was relatively low. From zero to 27 (average = 9.3) veteran trees survived fires at individual sites. Of the 110 veterans among seven sites for which I 35  assessed radial growth response to fire, major releases (22%) were more common than major suppressions (3%). Subcanopy trees established between 1706 and 1957 (Figure 3.3), only 13% of which had wide rings and fast initial growth rates. Study sites contained one to 16 dead trees with years of death from 1933 to 2008, 78% (n=46) of which died after 1990.  Interpretation of Fire History for Individual Sites HNFR1 Stratum HNFR1-1 At site HNFR1-1 the canopy consisted of Douglas-fir (34 per ha), ponderosa pine (19 per ha), and western larch (2 per ha), growing at a low density of 55 trees per hectare (Table 3.5). Subcanopy density was 355 trees per hectare and included a mix of Douglas-fir (38%), ponderosa pine (25%), lodgepole pine (25%), and grand fir (12%) (Table 3.3). In the regeneration layer (3,374 per ha), Douglas-fir (68%) dominated in the presence of grand fir (28%) and western hemlock (4%) (Table 3.4). Eight fire-scarred ponderosa pines recorded one low-to-moderate-severity fire in 1738 (Figure A.1 in Appendix A). All established between 1642 and 1720. The dates of their outer rings ranged from 1757 to 1790, but they were charred indicating the trees had burned after they died. These dead ponderosa pines predated the living trees on site by > 115 years, with a mean fire return interval of 167 years. All living canopy trees established continuously between 1906 and 1941, forming an even-aged cohort of Douglas-fir, ponderosa pine, and western white pine. The initial growth rates of 19 (70%) of these trees were fast. Subcanopy trees established at the same time as the canopy trees between 1908 and 1957 and with fast initial growth rates observed in three of seven trees.  Assuming this stand  established following a severe fire in or before 1905, time since last fire was at least 104 years  36  and this site was classified as mixed-severity given evidence of both low-to-moderate and highseverity fires (Table 3.6).  37  Table 3.5 Density of live canopy trees by species and fire tolerance for each site.  38  Table 3.6 Fire regime classification for individual sites stratified by Historic Natural Fire Regime (HNFR) and listed by elevation within each stratum. Severity of the fire regime was classified using fire-scar and cohort dates as evidence of low-to-moderate and highseverity fires, respectively (Figure 2.3). Time since last fire was calculated relative to 2009, when sampling was completed.  1 Scars present but not sampled due to advanced decay or wildlife danger tree status. 2 Oldest tree age indicates minimum time since last high-severity fire in stands with no evidence of fire. 3 Time since last fire not reported at stand with a fire-scarred tree that was not dated.  39  HNFR1-2 Douglas-fir trees dominated (143 trees per ha) the canopy at site HNFR1-2, where canopy tree density was 155 trees per hectare (Table 3.5). Subcanopy trees (977 per hectare) were comprised of Douglas-fir (68%) and grand fir (32%) (Table 3.3). The regeneration layer (3,064 per ha) was dominated by grand fir (57%) and included Douglas-fir (39%) and western redcedar (4%) (Table 3.4). The oldest samples were from dead and living fire-scarred ponderosa pines that established in the 1600s (Figure A.2 in Appendix A). Eight low-to moderate-severity fires scarred trees between 1679 and 1891. Fire intervals ranged from 14 to 47 years, with a mean fire return interval of 25.6 years. Time since last fire was 118 years (Table 3.6). The current canopy trees were uneven-aged and established discontinuously between 1732 and 1903 with a cohort in 1891. In the decade following the 1869 fire, six trees established and the growth of two veteran trees released while five others were suppressed. After the 1891 fire, the growth rates of seven veteran trees released, a cohort of 13 trees established of which nine exhibited slow initial growth rates, and all subcanopy trees established between 1892 and 1934. Fire history of the site was classified as low-to-moderate-severity (Table 3.6). HNFR1-3 Canopy trees at site HNFR1-3 consisted of western redcedar (77 per ha), grand fir (51 per ha), Douglas-fir (32 per ha), and western hemlock (19 per ha) (Table 3.5). Density of live canopy trees was 179 trees per hectare. In the subcanopy layer, density was 666 trees per hectare and consisted of western redcedar (93%) and western hemlock (7%) (Table 3.3). In the regeneration layer (5,018 per ha), western hemlock (66%) dominated with grand fir (19%), western redcedar (6%), and Douglas-fir (9%) (Table 3.4). A majority of the 18 fire-scarred trees at this site were burnt remnants of western redcedar snags (n=9) and logs (n=3); many of which were unsafe to  40  sampled. All scarred trees had a single scar and included two living western redcedar trees and one living western larch tree which yielded one consistent fire-scar date of 1897, which was classified a low-to-moderate-severity fire which given the survival of the thin-barked western redcedar trees (Figure A.3 in Appendix A). Time since last fire was 112 years. The canopy trees established continuously between 1898 and 1935. All canopy and subcanopy trees established in an even-aged cohort following fire in 1897, 14 exhibited fast initial growth between 1898 and 1906.  Subcanopy trees established between 1903 and 1937. Fire history of the site was  classified as low-to-moderate-severity. HNFR1-4 A stand of Douglas-fir (136 per ha) with minor components of western redcedar (27 per ha), western larch (20 per ha), and western hemlock (14 per ha) grew in a density of 197 trees per hectare at site HNFR1-4 (Table 3.5). In the subcanopy, western redcedar trees (80%) dominated Douglas-fir trees (20%) and overall density was 1,554 trees per hectare (Table 3.3).  The  regeneration layer (1,732 per ha) consisted of western redcedar (85%), western hemlock (5%), Douglas-fir (5%), and western white pine (5%) (Table 3.4). I found 30 fire-scarred trees that included 13 Douglas-fir trees which were danger trees unsafe to sample despite multiple fire scars visible in charred cat faces and indicating a rich fire history. I also noted ten burnt remnants of western redcedar snags (n=7) and logs (n=3) that were too decayed to sampled. I removed samples from one western larch tree and one Douglas-fir tree which yielded a fire-scar date of 1903 from a low-to moderate-severity fire (Figure A.4 in Appendix A). Assuming this was the last fire to burn at this site, then time since last fire was 106 years (Table 3.6). Of 17 veteran trees that survived the fire in 1903, 47% showed a release pattern in their growth, while the growth of 53% became suppressed following this fire.  41  Canopy trees established  discontinuously in two broad age groups. The oldest trees established from 1669 to 1720, three of four of these trees had fast initial growth rates. The other canopy trees established after 1843, including a cohort after 1855; however only two of these trees had fast initial growth rates. Subcanopy trees established between 1881 and 1938, none of which exhibited fast initial growth rates. Fire history of the site was classified as low-to-moderate-severity (Table 3.6). HNFR1-5 Site HNFR1-5 was a mixed-species stand that included western larch (40 per ha), grand fir (40 per ha), Douglas-fir (15 per ha), western hemlock (4 per ha), and western redcedar (4 per ha) in the canopy (Table 3.5). There were 103 canopy trees and 1,331 subcanopy trees per hectare and a dense regeneration layer of 21,535 individuals per hectare (Tables 3.3, 3.4, and 3.5). Fireintolerant grand fir comprised 60% of subcanopy trees and 92% of the regeneration layer (Tables 3.3 and 3.4). The six fire-scarred samples were from western larch trees which burned at a lowto-moderate-severity in 1869 (Figure A.5 in Appendix A). Time since last fire was 140 years (Table 3.6). Canopy trees were uneven-aged and established discontinuously from 1712 to 1878 with a cohort initiated in 1869; 13 canopy trees (65%) established before the fire in 1869 and were classified as veteran trees. Following the 1869 fire, six veteran trees released and five canopy trees with fast initial growth rates established between 1870 and 1876. All subcanopy trees (n=14) established between 1870 and 1895, forming a distinct post-fire cohort that included some canopy trees (n=8). Fire history of the site was classified as low-to-moderate-severity (Table 3.6). HNFR1-6 At site HNFR1-6, Douglas-fir strongly dominated the canopy (205 of 212 trees per ha) and subcanopy (70% of 444 per ha) layers (Tables 3.5 and 3.3). In the regeneration layer (621 per  42  ha), species composition shifted to fire-intolerant grand fir (57%) and western redcedar (36%), with some Douglas-fir (7%) (Table 3.4). Eight fire-scarred trees containing multiple fire scars were found at this site providing evidence of past low-to-moderate-severity fires; however, all were too decayed to crossdate. The canopy and subcanopy trees formed an even-aged cohort that established continuously between 1894 and 1947; a majority (54%) of these trees exhibited fast initial growth rates (Figure A.6 in Appendix A). Assuming these trees established after a high-severity fire in or before 1893, then time since last fire was at least 116 years and this site was classified as mixed-severity given evidence of both low-to-moderate and high-severity fire (Table 3.6). HNFR2 Stratum HNFR2-1 Douglas-fir (167 per ha) dominated at site HNFR2-1 where density was 209 live trees per hectare (Table 3.5). Subcanopy trees (221 per ha) were comprised of Douglas-fir (40%), western larch (20%), ponderosa pine (20%), and grand fir (20%) (Table 3.3). The regeneration layer (976 per ha) was dominated by grand fir (73%) and included Douglas-fir (27%) (Table 3.4). Two western larch trees and one Douglas-fir tree recorded scars from fire in 1925, more than 20 years after the canopy and subcanopy trees established (Figure B.1 in Appendix B). Time since last fire was 84 years (Table 3.6). Canopy and subcanopy trees established continuously in an even-aged cohort between 1867 and 1903 with fast initial growth rates in 26 trees (87%) that indicate open growing conditions that likely followed a severe fire.  Following a low-to-  moderate-severity fire in 1925, the growth rates of seven veteran trees released while the remaining 19 trees became suppressed. Given evidence of both low-to-moderate and high-  43  severity fires, with a mean fire return interval of 59 years, this site was classified as mixedseverity (Table 3.6). HNFR2-2 HNFR2-2 was a mixed-species stand that included western redcedar (145 per ha), western hemlock (38 per ha), Douglas-fir (30 per ha), and western larch (8 per ha) (Table 3.5). There were 221 canopy trees and 577 subcanopy trees per hectare and a dense regeneration layer of 3,508 individual per ha (Tables 3.3, 3.4, and 3.5). All subcanopy trees were fire-intolerant western redcedar (62%) and western hemlock (38%) (Table 3.3). The regeneration layer was similarly dominated by fire-intolerant western hemlock (80%), western redcedar (15%), and grand fir (5%) (Table 3.4). The seven fire-scarred samples were from western redcedar trees (n=4) and logs (n=3) which burned at a low- to-moderate-severity in 1834 and 1872, with a mean fire return interval of 38 years (Figure B.2 in Appendix B). Time since last fire was 137 years (Table 3.6).  Canopy trees established continuously in a cohort from 1835 to 1894, with  subcanopy trees establishing concurrently between 1841 and 1900 to form a broadly even-aged stand. Fast initial growth rates were observed in nine trees (38%) and the growth of six veteran trees released following fire in 1872. Fire history of the site was classified as low-to-moderateseverity (Table 3.6). HNFR2-3 Canopy trees at site HNFR2-3 consisted of trembling aspen (84 per ha), western redcedar (45 per ha), western hemlock (22 per ha), and Engelmann spruce (6 per ha), with a density of 157 trees per hectare (Table 3.5). In the subcanopy layer, density was 488 trees per ha and consisted of western hemlock (46%), western redcedar (36%), trembling aspen (9%), and Engelmann spruce (9%) (Table 3.3). In the regeneration layer (666 per ha), western redcedar grew exclusively  44  (Table 3.4). Fire history at site HNFR2-3 was reconstructed using three western larch snags and one western larch tree which recorded scars from low-to-moderate-severity fires in 1862, 1923, 1927, and 1932 (Figure B.3 in Appendix B). Time since last fire was 77 years, (Table 3.6). All canopy and subcanopy trees established continuously in an even-aged cohort between 1890 and 1957 with fast initial growth rates observed in 13 trees (57%) which indicate a high-severity fire. Six veteran survivor trees (42%) released following the fire in 1927. Given evidence of both low-to-moderate and high-severity fires, this site was classified as mixed-severity, with a range of fire return intervals from four to 34 years and a mean fire return interval of 18 years (Table 3.6). HNFR2-4 Site HNFR2-4 was a mixed-species stand that included western hemlock (84 per ha), western redcedar (67 per ha), Douglas-fir (8 per ha), and western larch (8 per ha) (Table 3.5). There were 167 canopy trees and 533 subcanopy trees per hectare and a dense regeneration layer of 8,037 individuals per hectare (Tables 3.3, 3.4, and 3.5). Fire-intolerant western hemlock comprised 75% of subcanopy trees and 74% of the regeneration layer. Only one fire-scarred tree was observed. It was a western larch snag with a single-lobed fire scar which indicates fire of low-tomoderate-severity but was not sampled because it included active nesting cavities valuable for wildlife. Canopy trees established discontinuously from 1639 and 1889 to form an uneven-aged canopy (Figure B.4 in Appendix B).  Subcanopy trees included one old individual that  established in 1716; all others established between 1816 and 1939. The three canopy trees that established in 1639, 1673, and 1728 exhibited fast initial growth rates, while all other canopy and subcanopy trees did not. No cohorts were detected. In the absence of dates from cohorts and fire  45  scars, time since fire could not be calculate and this site was excluded from fire frequency analyses despite evidence of low-to-moderate-severity fire. HNFR2-5 At site HNFR2-5 the canopy consisted of western hemlock (43 per ha), western redcedar (38 per ha), and Douglas-fir (13 per ha), growing at a low density of 94 trees per ha (Table 3.5). Density of subcanopy trees was 1,510 per ha and included a mix of western hemlock (41%), western redcedar (35%), and grand fir (24%) (Table 3.3). The sparse regeneration layer (177 per ha) included western redcedar (75%) and western hemlock (25%) (Table 3.4). Fire history at site HNFR2-5 was reconstructed using one western larch snag and one western hemlock tree which recorded fire in 1892 (Figure B.5 in Appendix B). Time since last fire was 117 years (Table 3.6). Canopy trees established discontinuously between 1687 and 1866, four of which grew at fast initial rates. The growth of a majority of veteran survivor trees (14 of 21 trees) was suppressed following the low-to-moderate-severity fire in 1892. Except one tree that established in 1706, subcanopy trees established in an even-aged cohort after fire between 1903 and 1931. Given evidence of both low-to-moderate- and high-severity fires, this site was classified as mixed-severity (Table 3.6). HNFR2-6 Canopy trees at site HNFR2-6 consisted of Engelmann spruce (115 per ha), western redcedar (77 per ha), and western hemlock (23 per ha), with a density of 215 trees per hectare (Table 3.5). In the subcanopy layer, density was 887 trees per hectare and consisted of western redcedar (60%), western hemlock (30%), Engelmann spruce (5%), and subalpine fir (5%) (Table 3.3). The regeneration layer (1,998 per ha) included western redcedar (78%) and western hemlock (22%) (Table 3.4). The canopy and subcanopy trees established continuously between 1864 and 1916  46  forming an even-aged stand with fast initial growth rates observed in 11 trees (38%) (Figure B.6 in Appendix B). Assuming this stand established following high-severity fire c. 1863, time since last fire was 146 years (Table 3.6). Fire history of the site was classified as high-severity (Table 3.6). HNFR3 Stratum HNFR3-1 At site HNFR3-1 the canopy was dominated by Engelmann spruce (105 per ha) with some subalpine fir (28 per ha), forming a density of 133 trees per hectare (Table 3.5).  In the  subcanopy layer, density was 488 trees per hectare and consisted of subalpine fir (64%), Engelmann spruce (27%), and western hemlock (9%) (Table 3.3). In the regeneration layer (1,243 individuals per ha), subalpine fir (78%) dominated Engelmann spruce (18%) and western hemlock (4%) (Table 3.4). The canopy trees established discontinuously between 1797 and 1897 and included one cohort after 1823 in which four trees (14%) established with fast initial growth rates (Figure C.1 in Appendix C). While one subcanopy tree established in 1845, the majority established between 1890 and 1914. Time since last fire equals or exceeds 210 years as determined from the age of the oldest documented canopy tree on site (Table 3.6). In the absence of a precise time since last fire date, this site was excluded from fire frequency analyses and was not assigned a fire-severity classification. HNFR3-2 Canopy trees at site HNFR3-2 consisted of Engelmann spruce (137 per ha) and subalpine fir (22 per ha) (Table 3.5). Density was 159 live trees per ha. Similarly, subcanopy trees (177 per ha) were sparse and consisted of subalpine fir (75%) and Engelmann spruce (25%) (Table 3.3). In the regeneration layer (799 per ha), subalpine fir (100%) grew sparsely (Table 3.4). Canopy and 47  subcanopy trees established continuously between 1854 and 1905 in a broadly even-aged cohort, (Appendix C), that included eight trees (30%) with fast initial growth rates (Figure C.2 in Appendix C). Time since last fire was at least 156 years assuming trees established after highseverity fire on or before 1853 (Table 3.6). Fire history of the site was classified as high-severity (Table 3.6). HNFR3-3 At site HNFR3-3 the canopy consisted of a mix of Douglas-fir (61 per ha), subalpine fir (22 per ha), lodgepole pine (17 per ha), western larch (11 per ha), and Engelmann spruce (6 per ha) (Table 3.5). Density was 117 live canopy trees per ha. In the subcanopy layer, density was 576 trees per hectare and consisted of subalpine fir (84%), lodgepole pine (8%), and Douglas-fir (8%) (Table 3.3). A dense layer of regeneration (4,173 per ha) consisted of subalpine fir (83%), grand-fir (15%), Douglas-fir (1%), and Engelmann spruce (1%) (Table 3.4).  Canopy trees  established continuously from 1864 to 1914 and subcanopy trees established from 1892 to 1934 (Figure C.3 in Appendix C). They formed a broadly even-aged cohort that included 17 trees (49%) with fast initial growth. Time since last fire was at least 144 years assuming high-severity fire initiated this stand on or before 1863 (Table 3.6). Fire history of the site was classified as high-severity (Table 3.6). HNFR3-4 Site HNFR3-4 contained a mix of Douglas-fir (14 per ha), subalpine fir (11 per ha), Engelmann spruce (6 per ha), and western larch (3 per ha) with a density of 34 trees per ha (Table 3.5). This stand also included numerous dead lodgepole pines (≥ 46 per ha). Subcanopy trees grew in a density of 622 per hectare and consisted of subalpine fir (64%), lodgepole pine (29%), and western hemlock (7%) (Table 3.3). Fire-intolerant species dominated the dense regeneration  48  layer (9,411 per ha): subalpine fir (95%), western white pine (3%), lodgepole pine (1%), Engelmann spruce (0.5%), and Douglas-fir (0.5%) (Table 3.4).  Canopy trees established  continuously from 1866 to 1905 and subcanopy trees established from 1892 to 1927 (Figure C.4 in Appendix C). They formed a broadly even-aged cohort that included 19 trees (51%) with fast initial growth. Time since last fire was at least 142 years assuming a severe fire initiated this stand on or before 1865 (Table 3.6). Fire history of the site was classified as high-severity (Table 3.6). HNFR3-5 At site HNFR3-5, the canopy was low-density (127 per ha) and consisted of fire-intolerant subalpine fir (76 per ha) and Engelmann spruce (51 per ha) (Table 3.5). In the subcanopy and regeneration layers, subalpine fir grew exclusively at densities of 222 and 1,021 trees per ha (Tables 3.3 and 3.4). The canopy was broadly even-aged with trees establishing continuously in a cohort between 1851 and 1912 (Figure C.5 in Appendix C). Subcanopy trees established concurrently between 1888 and 1910. Fast initial growth rates were observed in eight trees (35%). Assuming a high-severity fire initiated this stand on or before 1850, time since last fire was at least 159 years (Table 3.6). Fire history of the site was classified as high-severity (Table 3.6). HNFR3-6 At site HNFR3-6, subalpine fir (63 per ha), Engelmann spruce (28 per ha), and western hemlock (4 per ha) grew at a low density of 95 trees per ha (Table 3.5). Engelmann spruce grew exclusively in the subcanopy at a density of 133 trees per hectare (Table 3.3). Similarly, the regeneration layer was low in density (799 per ha) and consisted of subalpine fir (83%), western hemlock (11%), and western redcedar (6%) (Table 3.4).  49  Canopy trees established  discontinuously between 1675 and 1875, with subcanopy trees establishing during a 25 year period between 1872 and 1896 (Figure C.6 in Appendix C). Most trees exhibited slow initial growth rates and no cohorts were detected. In the absence of dates from fire scars and cohorts, records indicate that fires have not burned at any severity during the period of record. Shadetolerant trees establishing discontinuously with slow initial growth rates are consistent with oldgrowth sites studied elsewhere in interior British Columbia where small-scale disturbances such as windthrow create gaps that allow understorey trees to ascend into the canopy and replace trees individually (Antos and Parish 2002). As a result time since last fire equals or exceeds 339 years as determined from the age of the oldest documented canopy tree on site (Table 3.6). In the absence of a precise time since last fire, this site was excluded from fire frequency analyses and was not assigned a fire-severity classification.  Fire Regime of the West Kootenays Fire History: All Sites Combined Between 1642 and 2009, low-to-moderate-severity fires burned leaving fire scars in 19 years: 1679, 1706, 1720, 1738, 1767, 1806, 1832, 1834, 1862, 1869, 1872, 1891, 1892, 1897, 1903, 1923, 1925, 1927, and 1932 (Figures 3.2 and 3.3a). The number of recorder trees varied through time and had two maximums, one between 1738 and 1757 (n=12) and a second maximum between 1925 and 1933 (n=27) (Figure 3.3b). There was only one recorder tree from 1825 to 1833. The percentage of fire-scarred trees varied inversely with the number of recorder trees and generally decreased towards the present (Figure 3.3b). Regional fire years in which two or more sites recorded fire-scars occurred only in 1869 (Figure 3.2). Two cohorts indicated high-severity fires that burned in 1850 and 1863 independently of fire-scar dates, while the remaining seven  50  cohorts indicating high-severity coincided with fire scars in 1862 (two cohorts), 1891, 1892, 1903 or burned in HNFR3 (n=4) within five years of 1850 (1853) and 1865 (1867) (Figure 3.3a).  51  Figure 3.2 Frequency of fire grouped by site and sorted by elevation within each stratum of HNFR that recorded fire scars. A composite record documents all fire-scar dates samples from all sites combined through the entire period of record from 1642 to 2009. 52  Figure 3.3 Fire history and forest age structure for all sites combined. (a) Fire frequency shows number of fire scars recorded per year (bars) and estimated fire dates based on the years in which cohorts of trees established (triangles). (b) Percent trees scarred per year (bars) is the number of fire trees with a fire scar expressed as a percentage of the number of recorder trees in that year (line). Age structure (15-year classes) canopy (c) and subcanopy (d) trees classified as fire tolerant (white bars) and fire intolerant (grey bars). The hashed bar marks the period of European Settlement and Fire Exclusion from1860 to 1944.  53  The fire regime for the entire study area was classified as mixed-severity, as the fire history at individual sites represented all classes, including low-to-moderate-severity (n=7, 39%), high-severity (n=5, 28%), mixed-severity (n=4, 22%), and two sites contained no evidence of recent fires.  Fire scars, providing evidence of low-to-moderate-severity fires, occurred  exclusively below 1,400 m.a.s.l.. For all sites combined, the fire-scar record showed that low-tomoderate-severity fires burned at intervals of one to 39 years and the Weibull median probability interval (WMPI) was 10.4 years (Table 3.7). The WMPI decreased to 9.4 years but the range did not change when both annually resolved fire-scar dates and cohort dates from high-severity fires that occurred independently of fire-scar dates were considered (Table 3.7). Time since last fire, based on fire-scar dates (n=9) and cohort dates (n=6), ranged from 77 to 159 years with an average of 123 years. At the landscape scale, fire-intolerant species increased in dominance from canopy down through subcanopy and regeneration layers. When all sites were combined, the mean importance value for fire-intolerant species among canopy trees was 122 while importance value for firetolerant species was 78 (Table 3.2). In the subcanopy and regeneration layers fire-intolerant species grew in greater densities than fire-tolerant species (Tables 3.3 and 3.4). The relative densities of fire-intolerant subcanopy trees and regeneration layers were 83% and 92%, respectively. Stand structure showed high variability consistent with mixed-severity fire regimes among sites in the study area as live canopy trees ranged in density from 34 to 221 trees per hectare (ha), subcanopy trees from 133 to 1554 trees per ha, and 177 to 21,535 individual per ha in regeneration layers (Tables 3.3, 3.4, and 3.5).  54  Table 3.7 Fire regime classification for individual sites stratified by Historic Natural Fire Regime (HNFR) and listed by elevation within each stratum. Severity of the fire regime was classified using fire-scar and cohort dates as evidence of low-to-moderate and high-severity fires, respectively (Figure 2.3). Time since last fire was calculated relative to 2009, when sampling was completed.  1 Cohort(s) documented from high-severity fires occurred within five years of fire-scar date, and adjusted to align with more precise fire-scar date. * Insufficient data available to calculate Weibull median fire interval. 55  Across all sites, canopy trees established continuously between the mid-1600s and mid1900s (Figure 3.3). In the subcanopy the majority of trees established continuously between 1816 and 1957. Almost three quarters of all canopy trees (n=257, 72%) and nearly all subcanopy trees (n=149, 94%) established since 1860 during a period in which European settlers began impacting the study area. Similarly, most canopy trees (n=230, 74%) and nearly all subcanopy trees (n=123, 90%) established since the last fire burned at their respective study sites. In summary, a large percentage of this landscape is comprised of canopy and subcanopy trees that established during the current fire-free interval which corresponds with fire exclusion and suppression. Fire Frequency: Comparison of HNFR Strata Low-to-moderate severity fires burned more frequently and resulted in a longer record at low elevations as opposed to high elevations, showing a decrease in number of fire scars and fire intervals and increase in time since last fire (TSLF) from strata HNFR1 to HNFR3 (Table 3.7; Figures 3.4 and 3.5). All sites in stratum HNFR1 contained fire-scarred trees, and five of six sites contained fire-scarred trees in stratum HNFR2, while no fire-scarred trees were documented in the HNFR3 stratum. Similarly, the number of fires decreased significantly from strata HNFR1 to HNFR3 (H = 6.47, p = 0.03).  56  Figure 3.4 Fire history of the six sites in the HNFR1 stratum. (a) Fire frequency shows number of fire scars recorded per year (bars) and estimated fire dates based on the years in which cohorts of trees established (triangles). (b) Percent trees scarred per year (bars) is the number of trees with a fire scar expressed as a percentage of the number of recorder trees in that year (line).  Figure 3.5 Fire history of the six sites in the HNFR2 stratum. (a) Fire frequency shows number of fire scars recorded per year (bars) and estimated fire dates based on the years in which cohorts of trees established (triangles). (b) Percent trees scarred per year (bars) is the number of trees with a fire scar expressed as a percentage of the number of recorder trees in that year (line).  57  Fire-scars occurred exclusively at sites in strata HNFR1 and HNFR2.  I found no  significant differences in mean fire return interval (t = 2.01, p > 0.05) or the percentage of recorder trees that were scarred (t = 1.81, p > 0.05) between the HNFR1 and HNFR2 strata (Figure 3.4 and Figure 3.5). In the HNFR1 stratum, the five sites from which fire-scar disks were sampled contained 11 fire-scar dates and two cohort dates from 1679 to 1905 with multiple fire-scar dates occurring at one site (HNFR 1-2) and two sites recording fires in 1869 (HNFR1-2 and HNFR 1-5) (Figure 3.4). Based on the composite fire record for all sites in the HNFR1 stratum, the minimum intervals between fires were six years (1891 to 1897 and 1897 to 1903) based on fire scars only, but was two years based on dates from fire scars (1903) and cohorts (1905) (Table 3.7). Since the "1905" fire was estimated from a cohort this interval is less certain; however, because the sites recording fire were located on different shores of West Arm Lake and c.25 km apart they represent separate fires. The maximum interval between fires within the HNFR1 stratum was 39 years (Table 3.7) between two fire-scar dates from 1767 to 1806 at site HNFR1-2 (Table 3.7). The Weibull median interval between fire scars was 21.3 years for fire scars and for fire scars plus cohorts which both aligned with fire-scar dates (Table 3.7). The last fire detected in the HNFR1 stratum was in 1903 based on fire scars or c.1905 based cohorts (Table 3.7). In the HNFR2 stratum, where fires were recorded from 1834 to 1932, four sites with firescarred trees contained a total of eight fire-scar dates and three cohort dates. Multiple fire-scar dates occurred at two sites (HNFR2-2, HNFR2-3) but no fires burned at more than one site (Figure 3.5). The minimum interval between fires and between fire-scar and cohort dates was two years from 1923 to 1925 and from 1925 to 1927 based on one fire-scarred sample recording  58  scars in 1923 and 1927 along with a second fire-scarred sample from a site across West Arm Lake that recorded multiple scars from fire in 1925 (Table 3.7). The maximum interval between fire scars and fire scars and cohorts was 31 years from 1892 to 1923 between two fire scars (Table 3.7). For the composite fire record for all sites in the HNFR2 stratum, the Weibull median interval between fire scars was 10.5 years and between fire scars and cohorts was 7.4 years (Table 3.7). The last fire in the HNFR2 stratum was in 1932, based on scars and a cohort (Table 3.7). Time since last fire (TSLF) was significantly lower in the HNFR1 and HNFR2 strata than in the HNFR3 stratum (H = 9.72, p = 0.01) but similar between strata HNFR1 and HNFR2 (U = 13, p = 0.40). TSLF averaged 111 years (range = 104 to 140 years) and was based on four firescar and two cohort dates at sites in the HNFR1 stratum (Table 3.7). In stratum HNFR2, TSLF averaged 107 years (range = 77 to 146 years) and was based on four fire-scar dates and one cohort date (Table 3.7). In stratum HNFR3, TSLF averaged 150 years (range = 142 to 159 years) and was based on cohort dates for all five sites. For strata with fire scars, I found no spatial differences in means (t = 2.02, p > 0.05), variances (F = 1.07, p > 0.05), or percent scarred (1.78, p > 0.05) between sites located in strata HNFR1 and HNFR2. Fire Severity: Comparison of HNFR Strata Interpretations of historic fire severity from individual sites were combined to compare severity among the three HNFR strata. In the HNFR1 and HNFR2 strata, fire regimes were classified as mixed-severity and the fire regime in stratum HNFR3 was classified as high-severity (Table 3.6). Historic fires at four of six sites sampled in stratum HNFR1 were classified as low-to-moderateseverity (HNFR1-2, HNFR1-3, HNFR1-4, and HNFR1-5) while fires at the other two sites were classified as mixed-severity (HNFR1-1 and HNFR1-6). Historic fire severities in the HNFR2 59  stratum were most variable and included three sites classified as low-to-moderate-severity (HNFR2-2, HNFR2-4, and HNFR2-5), two as mixed-severity (HNFR2-1 and HNFR2-3), and one as high-severity (HNFR2-6). In stratum HNFR3, four sites (HNFR3-2, HNFR3-3, HNFR34, and HNFR3-5) were classified as high-severity, while the remaining two sites included no evidence of fires in the past 210 and 340 years (HNFR3-1 and HNFR3-6, respectively). Overall, the number of sites classified as mixed- and low-to-moderate-severity was greater for strata HNFR1 (n = 6 of 6) and HNFR2 (n = 5 of 6) versus stratum HNFR3 (n = 0 of 4), but no difference was detected between historical fire severities of strata HNFR1 and HNFR2. Species composition varied consistently with variation in historic fire severities among HNFR strata, as importance values of fire-tolerant canopy trees increased significantly from stratum HNFR3 to HNFR1 (H = 7.32, p = 0.03). When importance values of canopy trees were averaged for all sites in stratum HNFR1, fire-tolerant Douglas-fir were the most dominant species (117), followed by grand fir (27) and western larch (20). In the canopies at sites in stratum HNFR2, fire-intolerant western redcedar dominated (72). Fire-intolerant Engelmann spruce dominated the canopies at sites in stratum HNFR3 (88).  In the subcanopy and  regeneration layers, fire-intolerant species were more abundant than fire-tolerant species in all HNFR strata. The relative densities of fire-intolerant species in these two layers increased significantly from strata HNFR1 to HNFR3 (H= 6.72, p = 0.03 for the subcanopy tree layer; H= 9.06, p = 0.01 for the regeneration layer). While tree composition varied among the HNFR strata, the absolute densities of canopy and subcanopy trees and regeneration showed no directional trend with HNFR strata (H = 4.07 and p > 0.05 for all three layers).  60  Fire Frequency: Comparison of Shores of West Arm Lake Fire records differed between shores of West Arm Lake with more fire scars and a longer record on the south-facing, north shore as opposed to the north-facing, south shore. Fire-scar dates occurred across both shores where low-to-moderate-severity fires burned every two to 39 years across 12 intervals between 1679 and 1925 on the north shore and every four to 30 years across five intervals on the south shore between 1850 and 1932 where results were strongly influenced by one tree which recorded three fire scars within nine years (Site HNFR2-3 in Appendix B) (Table 3.6). On the north-shore of West Arm Lake, six sites contained a total of 13 fire-scar dates with multiple fire-scar dates occurring at two sites (HNFR1-2 and HNFR2-2) and two sites recording fires in 1869 (HNFR1-2 and HNFR1-5) (Figure 3.6). The minimum interval between fires was two years from 1832 to 1834 (Table 3.6). The maximum interval between fires and between fire scars was 39 years from 1767 to 1806 (Table 3.6). For the composite fire record for all sites on the north shore, the Weibull median interval between fires was 18.1 years and between fires including cohorts was 15.8 years (Table 3.6). The last fire recorded by trees on the north shore was a low-to-moderate-severity fire that burned in 1925 (Table 3.6).  61  Figure 3.7 Fire history of the eight sites on the south shore of West Arm Lake. (a) Fire frequency shows number of fire scars recorded per year (bars) and estimated fire dates based on the years in which cohorts of trees established (triangles). (b) Percent trees scarred per year (bars) is the number of trees with a fire scar expressed as a percentage of the number of recorder trees in that year (line).  Figure 3.6 Fire history of the 10 sites on the north shore of West Arm Lake. (a) Fire frequency shows number of fire scars recorded per year (bars) and estimated fire dates based on the years in which cohorts of trees established (triangles). (b) Percent trees scarred per year (bars) is the number of trees with a fire scar expressed as a percentage of the number of recorder trees in that year (line).  62  On the south-shore of West Arm Lake where stand-replacing fires appeared to be more common, three sites contained a total of six fire-scar dates and three cohort dates between 1850 and 1932 with multiple fire-scar dates occurring at one site (HNFR2-3) and no fires burning at more than one site (Figure 3.7). The minimum interval between fires and between fire-scar and cohort dates was two years from 1923 to 1925 and from 1925 to 1927 based on one fire-scarred tree (Table 3.6). For the composite fire record for all sites on the south shore, the Weibull median interval between fires was 12.1 years and between fires including cohorts was 11.6 years (Table 3.6). The last fire recorded by trees on the south shore of West Arm Lake was a low-tomoderate-severity fire that burned in 1932 (Table 3.6). I found no spatial differences in means (t = 0.94, p > 0.05), variances (F = 6.81, p > 0.05), percent scarred (0.84, p > 0.05), or time since last fire (TSLF) (U = 36, p > 0.05) between sites located on north- and south-facing shores of West Arm Lake. TSLF ranged from 84 to 156 years with an average of 124 years based on fire-scar dates (n=6) and cohort dates (n=2) on the north shore. On the south shore, TSLF ranged from 77 to 159 with an average of 122 using dates from cohorts (n=4) and fire scars (n=3). Fire Severity: Comparison of Shores of West Arm Lake Fire severity did not show any significant variance across shores of West Arm Lake. Fire regimes were classified as mixed-severity on both shores of West Arm Lake where individual sites were categorized as low-to-moderate-, high-, and mixed-severity. Forest composition was consistent with no significant difference in mean importance values among canopy trees (U = 27, p > 0.05) and relative densities of trees in the subcanopy (U = 31, p > 0.05) and regeneration layers (U = 57, p > 0.05). Across both sides of West Arm Lake, stands established continuously 63  (north=6; south=5) and discontinuously (north=4; south=3) and often in cohorts following highseverity fires (north=4, south=5) which highlights a mixed-severity fire regime at the landscape scale. Anthropogenic Impacts Over the period of fire history within the study area between 1642 and 2009, 19 fires burned and one regional fire year in which two or more stands recorded fire-scar dates occurred once: 1869. The mean fire return interval could not be calculated for the modern fire suppression period which contained no fire intervals. Of the other three periods, mean fire return intervals from scars and cohorts were shortest during the European settlement period (6.4 ± 6.7 years) and greatest during the Pre-European settlement II period (20.3 ± 7.8 years) with an intermediate interval during the Pre-European settlement I period (14.7 ± 12.1 years). Of the three periods with mean fire return intervals, only the European settlement and fire exclusion period differed from the Pre-European settlement II period (t = 2.8, p = 0.02). The percentage of fire-scarred trees was significantly lower for the Pre-European settlement II period compared to the European settlement and fire exclusion period (t = 3.0, p = 0.01) and for Pre-European settlement I period compared to the European settlement and fire exclusion period (t = 2.7, p = 0.02). Despite the most potential for evidence of fires during the 20th century, results reveal an absence of fire since 1932 across all sites.  64  Chapter 4 Discussion Fires that burn at a range of frequencies and severities are typical of mixed-severity fire regimes, resulting in heterogeneous forests that contain assemblages of even-aged stands from standreplacing fires and uneven-aged stands recruited in episodes of regeneration after low-tomoderate-severity surface fires (Arno 1980; Brown et al. 2000; Kaufmann et al. 2000). Across the entire West Kootenay study area, evidence of historic fires and stand dynamics were consistent with a mixed-severity fire regime with high variability over short spatial scales. Below, I discuss the differences in fire frequency and severity along with variability in forest structure and composition through time before making interpretations and conclusions that aim to assist forest managers.  Fire History and Fire Regimes Few forests that predate European settlement remain in the study area surrounding Nelson, British Columbia. Much of the landscape, especially at low elevations, has been subject to changes in land use including urbanization, grazing and industrial logging (Utizig et al. 2003). Historically, high elevation forests were burned during mineral exploration in the late 19 th century or logged to generate fuels to power the mines (Utizig et al. 2003). Periodically, highseverity, stand-replacing wildfires would have burned forests across all elevations. As a result, only 22% of the current landscape includes canopy trees that are ≥200 years old according to the provincial Vegetation Resource Inventory (2009).  Since these forests were most likely to  include evidence of historic fires including fire-scarred veteran trees, they were the focus of this study. Therefore, the results of my research apply directly to the subset of remnant old forests in the landscape today. Indirectly, this study also represents the dominant historic processes and  65  disturbance regimes of the study area since the sample sites were selected using a stratifiedrandom approach. The fire history records constructed in this study provide multiple lines of evidence for fires that burned in a combination of severities and at variable frequencies since the 1600s, consistent with a mixed-severity fire regime (Taylor and Skinner 1998; Arno et al. 2000; Taylor 2000; Veblen et al. 2000; Buechling and Baker 2004; Wright and Agee 2004). At the 11 of 18 sites for which I documented low-to-moderate-severity fires, scars were numerous on thickbarked fire-tolerant western larch, ponderosa pine, and Douglas-fir trees and also recorded on thin-barked barked western hemlock and western redcedar trees (Agee 1993). Fires recorded by thin-barked species, typically considered fire-intolerant, indicate the low-to-moderate severity of fires. Similarly, some western larch, ponderosa pine, and western redcedar trees that recorded multiple scars included scars on trees that were as small as 6 cm in diameter at a height of 30 cm above the ground and most likely still had thin bark when they first scarred. The fires causing these scars must have been low-to-moderate severity or the trees would have been killed. At five of the seven sites without fire-scarred trees, stand composition and age structure provided indirect evidence of high-severity fire. At these sites, cohorts of trees that established with fast initial growth rates and in the absence of veteran survivor trees provide evidence of high-severity fires, especially at high elevations. The remaining two sites included no evidence of fire. Neither fire-scarred trees nor cohorts indicating high-severity fires were found in either stand; instead, trees were uneven-aged, established discontinuously and initial growth rates were generally slow. At these sites, stand-scale processes, like gap dynamics, are more consistent with the current stand structure and composition than stand-level fires (MacKillop 2003; Antos and Parish 2002).  66  Different measures of fire frequency are reported in fire history studies, with return intervals and time since last fire (TSLF) most commonly reported for forests in which fire scars result from low-to-moderate severity fires (Baker and Ehle 2001; Kou and Baker 2006; Van Horne and Fulé 2006) and fire cycles derived from stand origin dates and TSLF reported for forests dominated by high-severity fires (Johnson and Gutsell 1996). In the West Kootenay study area, stands with fire-scarred trees recorded scars from low-to-moderate severity fires from every 25.3 to 38.0 years. The composite fire record for all sites combined included 67 fire scars during 19 fire years between 1679 and 1932. In individual stands, low-to-moderate-severity fires burned at intervals ranging from four to 46 years, with a median fire return interval of 29.3 years based on the three stands that recorded intervals between low-to-moderate-severity fires. Superimposed on the low-to-moderate severity fires, stand-replacing fires burned at a range of elevations in the study area. Five of 18 sites established between 1850 and 1867 in even-cohorts of trees with fast initial growth rates, indicating high-severity fires which originated new stands and may have killed veteran recorder trees and burned fire-scarred coarse woody debris (Ehle and Baker 2003). For the two old-growth stands, the last stand-replacing fires and stand initiation likely occurred prior to c. 1675 (HNFR3-6) and c. 1800 (HNFR3-1), based on the age of the oldest trees in the stands (Antos and Parish 2002). For these seven sites, TSLF ranged from 142 to 159 years and up to c. 330 years for stands with no evidence of fire. These results were within range of fire return intervals that averaged 80 to 110 years based on time since fire maps drawn from stands approximately 200 km to the north (Johnson et al. 1990). Over the past c. 320 years, fires in the West Kootenays burned at frequencies and in temporal patterns consistent with other studies from the inland Pacific Northwest as well as western North and South America (Kitzberger et al. 2007; Sibold and Veblen 2006; Hessl et al.  67  2004). For example, fire return intervals were shortest (6.4 ± 6.7 years) during the European settlement and fire exclusion period from 1860 to 1944 and longer (20.3 ± 7.8 years) during the Pre-European settlement II period from 1690 to 1774. Between these two periods, from 1770 to 1830, only one fire was recorded in 1806. This gap in the West Kootenay fire record is consistent with a regionally significant fire-free period from c. 1780 to 1830 when few trees scarred from fire and stand-initiating fires were rare in western North and South America (Kitzberger et al. 2007; Sibold and Veblen 2006; Hessl et al. 2004). Several studies have demonstrated that this period corresponds to cool wet climatic conditions that were not conducive for fire (Kitzberger et al. 2007; Sibold and Veblen 2006; Hessl et al. 2004). Following this fire gap, warm dry climate may have been responsible for synchronizing fires, especially during the regional fire year of 1869 when El Niño conditions triggered widespread drought (Hessl et al. 2004; Heyerdahl et al. 2008; Cochrane 2007; DaSilva 2009). Interestingly, the landmark fire year of 1910, reported in local (DaSilva 2009) and regional (Morgan et al. 2008) studies was not recorded by any sites in the West Kootenay study area, indicating the complex interactions between top-down climate, ignition sources, and bottom-up controls of topography and fuels to influence fires. Topography, in the form of elevation, strongly influenced fire frequency in the study area. The steep elevational gradient of this study (>1100 m) resulted in significantly more frequent fires burning at low versus high elevations, consistent with other studies in mountainous terrain (Caprio and Swetnam 1995; Taylor 2000; Heyderdahl et al. 2001). Sites with fire-scarred trees were confined exclusively to areas located below 1,400 m.a.s.l. In these stands, fires burned more extensively on the south-facing shores of West Arm Lake where fire history records  68  were more extensive including a longer period of record with more fire scar dates consistent with similar studies in the region (Heyderdahl 2007).  Fire and Stand Dynamics The composition of canopy trees in mountain forests reflects steep environmental gradients including elevation, fire regimes, and adaptation of species to fire (Agee 1993).  At low-  elevations, fires burned historically at low-to-moderate severities, allowing veteran trees, such as thick-barked Douglas-fir, ponderosa pine, and western larch trees to grow into heterogeneous and relatively low-density stands comparable to Douglas-fir dominated forests found in northern Montana and the inland Pacific Northwestern (Hessl 2004; Heyderdahl 2007; Heyderdahl et al. 2008b; Agee 1993). Three of the oldest five trees in the entire study area established in the mid1600s and were found at lowest elevations at sites HNFR1-1 (pith date = 1642), HNFR1-2 (inner-ring date = 1670), and HNFR1-4 (inner-ring date = 1677). Stand records include a welldocumented history of low-to-moderate-severity fires which periodically consumed surficial fuel and likely maintained low stand density while allowing canopy height to increase above open understories (Brown et al. 2008). In these stands fire-tolerant western larch and ponderosa pine trees survived multiple fires with protective bark that is relatively thick, insulating the cambium on sapling and mature trees (Scher 2002; Howard 2003). Similarly the thick bark on Douglas-fir trees enables them to survive fires when mature but not as saplings or pole-sized trees when thinner bark increases their susceptible to fire (Steinberg 2002). At the highest elevations, forests were composed primarily of fire-intolerant Engelmann spruce and subalpine fir trees. These forests are comparable to subalpine forests in the Colorado Front Range (Schoennagel et al. 2004; Sibold et al. 2006) and the Canadian Rockies (Johnson 1992) where fires burn infrequently but at stand-replacing severities killing thin-barked 69  Engelmann spruce and subalpine fir trees which are susceptible to fire at all life stages (Howard 1996; Uchytil 1991a; Anderson 2003; Uchytil 1991b).  Across all six sites in the HNFR3  stratum, I found no evidence of low-to-moderate-severity fires on fire-scarred trees in stands composed primarily of even-aged trees. In the absence of subsequent fires, stand development includes tree deaths due to competition and within-stand disturbances such as windthrow (Antos and Parish 2002). Shade-tolerant trees establish and recruit from the subcanopy to canopy in these gaps. In stands where a long time has elapsed since stand origin, evidence of the initial cohort is lost as the trees die, decompose and are replaced by trees that established long after the fire. At these sites, and all sites in the absence of fire, stand development has begun responding to internal stand development processes rather than external forces. At intermediate elevations, for sites in the HNFR2 stratum, species composition and age structure more closely resembled patterns documented at low- compared to high-elevation sites. Species included a mix of fire-tolerant Douglas-fir and western larch trees growing among fireintolerant trees such as western redcedar, western hemlock, and Engelmann spruce. Despite the mix of species, fires burned at severities low enough to scar but not kill thin-barked trees typically considered fire-intolerant, such as western redcedar and western hemlock (Agee 1993; Tesky 1991a; Tesky 1991b). At half (n=3) of the stands in the HNFR2 stratum and two (n=2) stands in the HNFR1 stratum, stand-replacing fires also shaped stand structure as evidenced by even-aged cohorts with fast initial growth rates in trees that established following what were likely high-severity fires in stands at HNFR1-1 and HNFR1-6. In terms of age structure, patterns depict an overall trend of fires burning at stand-maintaining severities within these heterogeneous stands, while stands that established in even-aged cohorts more closely resembled stands at higher elevations where few fires resulted in more severe fire effects that decreased in  70  importance through time. The variety of evidence of fires that burned at multiple severities through time and across all of the sites combined, marks fire regimes across this landscape as historically mixed-severity especially lowest elevation stands where stand-replacing and standmaintaining fires burned in a mixed-severity regime. Irrespective of elevation, shade-tolerant species have established in the subcanopy layer and survived in the absence of fire since at least 1932. Tolerance to shade varies inversely with tolerance to fire for the species in the study area (Agee 1993). Thin-barked species like grand fir, western hemlock, and western redcedar trees are fire-intolerant but shade-tolerant in contrast to shade-intolerant thick-barked species, like Douglas-fir, ponderosa pine, and western larch trees that establish in open growing conditions following fire. The relative density of fireintolerant species dominated regeneration across almost all sites (n=17, 94%), with fireintolerant individuals growing exclusively at the majority of sites (n=10, 55%). From low to high elevation, relative densities of shade-intolerant species were highest among grand fir (HNFR1) and transitioned to western redcedar and western hemlock (HNFR2), with Engelmann spruce and subalpine fir dominated regeneration at stands in the highest elevations (HNFR3). In the past, and extensively at low elevations, repeated historic fires would have killed thin-barked understorey and overstorey trees, altered canopy structure, increased understorey light availability, and facilitated the regeneration of shade-intolerant species. Without fire, subcanopy trees have persisted. Fire-free periods enable subcanopy trees to survive and recruit into the canopy when their rates of survival and growth match or outpace mortality of canopy trees (Brown 2006). Therefore, historic fires may have maintained the fire-tolerant, shade-intolerant component of the canopy which is decreasing in the absence of fire as the shade-tolerant, fire-  71  intolerant subcanopy trees recruit creating stands that deviate from historic conditions, especially at low elevations.  Human Impacts on Fire Regimes At many, but not all, individual sites, the current fire free interval exceeds the historic median and maximum intervals. Therefore, at the site level, fire free intervals can be within natural range of variability. Nevertheless, when all sites are considered together, it becomes clear that low-to-moderate severity fires have been reduced in the landscape due to fire suppression. The dearth of fire since 1932 across all sites combined suggests that fire suppression is having a substantial impact on the fire regime of forests in the study area. Had fires burned and scarred trees as frequently throughout the 20th century as they did over the entire fire record, we would have expected six fires between 1945 and 2009 but no scars were recorded at any sites. The effective suppression of fire marks a departure from historic conditions in which fires burned every four to 46 years and in stands at low- and mid-elevations. Prior to European settlement, fires would have been ignited by lightning strikes and First Nations through their land and resource management and would have been limited to periods of conducive weather and climate (Veblen et al. 2000). While First Nations undoubtedly ignited fires prior to European settlement, it is not possible to differentiate between human and lightning ignitions within the tree-ring record (Veblen et al. 2000). Nevertheless, comparisons can be made between fire-scar records from the pre-settlement eras and those from the European settlement eras to characterize changes in land use brought about during settlement from 1860 to 1944. In the Nelson area, the settlement era marked a period in which fires burned more frequently relative to pre-Settlement, in agreement with similar studies along West Arm Lake  72  (Quesnel and Pinnell 2000) and in western North America (Veblen et al. 2000). Early European impacts on forests included the selective harvesting of large trees for railroad and home construction and intentionally set fires for mining exploration (Utzig et. al 2003). Between 1860 and 1870, for example, two stands recorded fire scars and four stands experienced standinitiating fires across six sites and indicating a high frequency of fires coinciding with the beginning of the mining era. These fire scars and cohorts could have resulted from human ignitions that accompanied settlement or followed ignitions by lighting but would have spread regardless due to warm dry conditions (Hessl et al. 2004). Across western North America, settlement coincided with a period when climatic conditions triggering widespread fires that increased in conjunction with settlement in the Colorado Front Range (Veblen et al. 2000) but remain unchanged in the Klamath Range (Taylor and Skinner 1998) or were reduced by grazing livestock following settlement in the Blue Mountains of Oregon and Washington (Heyerdahl et al. 2001) and in the American Southwest (Swetnam et al. 1999). In the second half of the 19th century, fire history records surrounding Nelson increased, resembling records from the Front Range in Colorado where settlement marked a period of more frequent fires ignited by humans across all elevations and linking to mineral exploration (Veblen et al. 2000). During the 20th century, fire history in Nelson corresponds with records from the remote Klamath range along the border between Oregon and California where fires burning into the mid-20th century until aerial suppression became available following World War II (Taylor and Skinner 1998) and unlike areas where fires suppression became effective c. 1910 (Veblen et al. 2000; Daniels et al 2007). Subsequently the in-growth and survival of shade-tolerant and fireintolerant species across all sites likely reflects the efficacy of fire suppression since World War II which may eliminate the legacy of low-to-moderate-severity fires found in forests prior to  73  European settlement in the 1860s. The effects of fire suppression are most clear and pervasive at lowest elevations where historically low-to-moderate-severity fires played an important role in preventing the buildup of fuels necessary for high-severity fires (Schoennagel et al. 2004). In these stands, fire suppression has been effective at eliminating the low-to-moderate-severity fires that contribute to the diverse structures and variable composition found in these heterogeneous forests (Bekker and Taylor 2010). At high elevations, stand-replacing fires burned exclusively in sampled stands. Time since last fire in these stands is consistent with other studies from highseverity fire regimes (Schoennagel et al. 2004). Stand-replacing fires continue to burn at upper elevations during dry summers (e.g. the 8,000 ha Kutetl fire in 2003 (Holt and Machmer 2005) and the 1,075 ha Sitkum fire in 2007 (Rodman 2008). The patterns documented in this study match the broader context of forests in western North America with fire-intolerant species replacing fire-tolerant trees in the absence of fire. Fire suppression serves to homogenize the landscape by preferentially selecting shade-tolerant and fire-intolerant species that can establish under closed canopies and in the absence of fire. The loss of diversity in forest structure within and among stands resulting from fire suppression resembles similar shifts documented elsewhere in western North America where extended firefree periods enable the ingrowth of fire-intolerant trees (Fulé et al. 2003; Moore et al. 2004; Beaty and Taylor 2008; Biondi 1992). As stands become more homogeneous in composition, fire hazard increases as understorey trees provide connectivity for fires to spread in ways that would not have been possible during periods when stand-maintaining fires consumed surficial fuels (Schoennagel et al. 2004). If the current fire-free period continues, fire-intolerant species in the understorey contribute to ladder fuels which occur naturally in subalpine forests but represent deviations with potential consequences for stands in valley bottoms (Schoennagel et al.  74  2004). As a result fire hazard may have become elevated across the entire study area but in particular at low elevations and most consequential where adjacent property and infrastructure intermingle with forests in the wildland-urban interface where fires threatened valuable cultural and economic resources (Blackwell 2010). While modern fire exclusion may alter forests from historic conditions, management can maintain the diversity in these forests following policies build around accurate inventories of forest age and composition that lead to specific plans to recreate patterns of natural disturbance by accounting for fire, biotic disturbances and their interactions through time across the landscape.  Fire Regime Classification in British Columbia In British Columbia, fire regimes are classified according to two systems: Natural Disturbance Type (NDT, B.C. Ministry of Forests and B.C. Ministry of Environment, Lands and Parks 1995) and Historic Natural Fire Regime (HNFR, Blackwell et al. 2003).  These coarse-scale  classification schemes provide overarching guidelines that enable managers to set timber rotations, plan hazard mitigation treatments, and predict likely timing and severity of disturbances according to influences of disturbances across large areas of forest based on dominant ecological attributes but lack precision derived from annual-resolution information on disturbances from dendroecology (Daniels and Gray 2006). Natural Disturbance Type (NDT) The Forest Practices Code Act of B.C. was established in 1995 and included a classification scheme to divide the forest into natural disturbance types (NDTs, B.C. Ministry of Forests and B.C. Ministry of Environment, Lands and Parks 1995). NDTs combine multiple disturbances types, with emphasis on fire, and report mean return intervals for stand-initiating disturbances.  75  For NDTs 1, 2 and 3, mean return intervals are estimated to be 250–350, 200, and 150 years, respectively (B.C. Ministry of Forests and B.C. Ministry of Environment, Lands and Parks 1995). Stand-maintaining fires are acknowledged in NDT4, in which surface fires burn at intervals between 4 and 50 years and stand-replacing fires burn every 150 to 250 years or more. The distribution of NDTs in the landscape is linked to the distribution of biogeoclimatic ecosystem classification (BEC) units (Krajina 1965; Klinka et al. 1991).  BEC zones and  subzones reflect regional and local climate, respectively, and are strongly influenced by elevation (Meidinger and Pojar 1991). Similarly, the mountain forests surrounding Nelson include several NDTs that range with elevation from NDT3, in valley bottoms, to NDT1 along ridgelines. At low elevations, on both shores of West Arm Lake, forests in the study area are classified as NDT3 where diverse stands of fire-tolerant trees dominate in the Dry Warm Interior CedarHemlock (ICHdw) subzone. At mid- to high-elevations, stands transition from NDT3 to NDT2, in the Moist Warm ICH, and NDT1, in the Wet Cold ESSF. The current NDT classification for the West Kootenay study area near Nelson contains no NDT4 and recognizes only stand-replacing fires that burned once every 150 to 350 years. According to the NDT system, fire regimes are misclassified at low-elevation sites situated in NDT3 where the NDT system overestimates historic return intervals of fire based on standreplacing disturbances predicted every 150 years. While these assumptions may be correct for forests at upper elevations, the 150 year return intervals assumed under NDT3 deviate from results at eight sites situated in NDT3: all sites in HNFR1 and two sites in HNFR2 (HNFR2-1 and HNFR2-2). Site-level fire return intervals were calculated at four plots in NDT3 and were more consistent with NDT4 than NDT3 since fires are lower severity and generally more frequent than 150 years including a range of intervals: 167 years (HNFR1-1), 25.6 years  76  (HNFR1-2), 59 years (HNFR2-1) and 38 years (HNFR2-2). In NDT3, five of eight sites were classified as low-to-moderate-severity fire history and three were classified as mixed-severity fire history based on fire scars, tree ages, cohort structures and presence of veteran trees. The situation is more challenge to interpret in NDT2 where fires are predicted to be severe, standreplacing every 200 years but intervals for stand-replacing fires were difficult to assess given multiple human impacts influencing historic fire regimes across seven sites classified as NDT2: HNFR2-3, HNFR2-4, HNFR2-5, HNFR2-6, HNFR3-1, HNFR3-4, and HNFR3-5. At six sites with evidence of fire in NDT2, fire regimes were classified as low-to-moderate severity (n=2), high-severity (n=3), and mixed severity (n=1) based on fire scars, tree ages, cohort structure and presence of veteran trees. Site-level fire return intervals were calculated at one site in NDT2 with a range from four to 34 years and a mean fire return interval of 18 years at site HNFR2-3. Time since last fire ranged from 77 to 212 years across six of the seven sites with evidence of fire in NDT2. At the highest elevations, three sites were classified as NDT1 where results were consistent with descriptions of NDT1 given time since last fire derived from cohorts at sites HNFR3-2, HNFR3-3, and HNFR3-6. Annually-resolved fire history information can be used to critically assess the NDT framework which generalizes variability in the disturbance regime with inaccurate estimates of return intervals, improperly delineated boundaries, and static assessments of stand conditions. Overall there is extensive evidence of many surface fires mixed with stand-replacing fires that burned in the past 150–250 years consistent with NDT4 not NDT3 below 1,400 m.a.s.l. At low elevations, expanding the NDT3 classification up in elevation and inserting an NDT4 classification into the valley bottoms could address the discrepancy between the NDT and these records of fires that burned at low-to-moderate severities comparable to sites located in the East 77  Kootenays (Cochrane 2007).  Higher up in elevation, stand-replacing fires dominated  consistently with NDT3, NDT2, and NDT1 based on results from time since last fire. Finally, assignments made by the NDT system do not respond to changes between historic conditions and current conditions where the absence of fire may enable survival of fire-intolerant trees which may push disturbance regimes away from stand-maintaining and toward stand-replacing severities through time with fuel accumulation at low elevations. Historic Natural Fire Regime (HNFR) More recently, the Historic Natural Fire Regime classification system was created to incorporate information on fire behaviour into a model that used GIS to reclassify 10.5 million hectares of southern British Columbia from the Coast Mountains in the west to the border with Alberta in the east, including the West Kootenay study area (Blackwell et al. 2003). In contrast to the NDT system, the HNFR model was developed specifically to account for fire behaviour by including topography (slope and aspect) in addition to biogeoclimatic units as controls on fire severity. Of the eight HNFR categories that include fire, five occur in the West Kootenay study area: (1) HNFR II occurs at the lowest elevations and represents mixed-severity fires that burned with an average return interval of 0 to 35 years. (2) HNFR IV occurs at mid-elevations on south-facing, warm-aspect slopes of the north shore of West Arm Lake. This class also represents a mixedseverity fire regime with return intervals of 35 to 100 years. (3) HNFR V occurs at mid-elevation on north-facing, cool-aspect slopes of the south shore of West Arm Lake, representing a standreplacing-severity fire regime with return intervals of 35 to 100 years. (4) HNFR VI occurs at upper-elevations on warm-aspect, south-facing slopes where mixed-severity fires are predicted to burn every 100 to 200 years. (5) Finally, HNFR VII occurs at upper-elevations on cool-aspect, north-facing slopes where stand-replacing fires are predicted to burn every 100 to 200 years. 78  Missing from the study stands are HNFR I, where low-severity fires are predicted to burn at intervals that range from 0 to 35 years, and HNFR VIII, where stand-replacing-severity fires are predicted to burn every 200 plus years. Across the study area the model of Historic Natural Fire Regime successfully captures the variability in fire records documented between north- and south-facing shores of West Arm Lake but differs in frequency from results at low- and mid-elevation sites. Sampled stands in the West Kootenay study area corresponded to HNFR II for low-elevation stands in the HNFR1 stratum, HNFR IV for mid-elevation stands in HNFR2 on the south-facing north shore of West Arm Lake, HNFR V for mid-elevation stands in HNFR2 on the north-facing south shore of West Arm Lake, and HNFR VI and HNFR VII for warm- and cool-aspect stands at upper elevations in HNFR3. The model of HNFR accurately discerned the variability in fire severity between shores of West Arm Lake for stands at mid-elevations, in HNFR2, based on differences in fire severity between HNFR IV and HNFR V for south- versus north-facing shores, respectively. On the other hand, predictions based on the model differed from site level results built using fire scars, tree ages, cohort structure and presence of veteran trees. Fire frequency results from low- elevations stands suggest that fire return intervals estimated at 0 to 35 years by the HNFR model are more variable than indicated with intervals of 167 years at HNFR1-1 and 14 to 47 years at HNFR1-2 and no intervals available at the rest of the sites in HNFR1. Severity results from the HNFR1 stratum included sites classified as low-to-moderate severity (n=4) and mixed-severity (n=2) based on fire history and consistent with predictions from the model for mixed-severity fires. At mid-elevations, three sites were located in HNFR IV and classified as low-to-moderate-severity (n=2) and mixed-severity (n=2), recording site level intervals consistent with HNFR classification: 59 and 38 years at HNFR2-2 and HNFR2-3, with no  79  intervals available for HNFR2-4. The remaining three sites in HNFR2 were modeled as HNFR V but included one site, recording site level fire return intervals ranging from 4 to 34, classified as low-to-moderate-severity (HNFR2-2), another site classified as mixed-severity (HNFR2-3), and a third site classified as high-severity (HNFR2-6). The HNFR model diverges from results based on fire frequency and severity from these three sites where fires burned at a variety of severities with frequencies recorded below predicted frequencies based on the model. At the highest elevations, all sites were modeled as 100–200 year fire frequency in HNFR VI and VII with the former anticipated as mixed-severity(n=2) and the latter as stand-replacing severity (n=4). At the two sites located in HNFR VI, fire history was consistent with the model based on frequency, 144 and 146 years since last fire, but inconsistent in terms of severity with both sites classified as high-severity. Finally at the two sites with evidence of fire in HNFR VII, fire history was classified as high-severity with 156 and 159 years since last fire. The two remaining sites in HNFR VII contained no evidence of fire for at least 212 and 338 years based on stand age and inconsistent with predictions for high-severity fires every 100 to 200 years based on the model. Overall the HNFR model improves upon the NDT model by accurately characterizing topographic controls on fire severity and including more categories that capture the variability present on the landscape despite being based on only one local study in the area (Quesnel and Pinnel 2000) and research from similar ecosystems located in adjacent states and in Alberta. Ultimately, the HNFR model could be refined through an expansion of the HNFR II zone in the study area to include warm-aspect stands currently classified as HNFR IV where fire frequency was consistent with stands documented as HNFR II at lower elevations.  80  Cumulative Human Impacts on Fire Regimes and Forest Dynamics In British Columbia, the mandate to suppress fires has affected forest composition in the study area with consequences that may impact communities surrounded by forests in valley bottoms and high-elevation forests differently.  The low incidence of fire since 1932 suggests fire  suppression is having a substantial impact on the fire regime of montane forests in the Nelson area. While modern policies of fire suppression are extending fire-free intervals across all sites, the greatest impacts of fire suppression are at lowest elevations where fires burned most frequently in the past. Forest structures at low- and some mid-elevations stands would likely have burned by subsequent fires reducing the abundance and continuity of fuels and the potential for fire spread.  From an ecological perspective, fire exclusion has negative consequences.  Paradoxically, fire protection may eliminate the same forest structures and attributes that make them valuable. Historic forest composition and structure existed because of fire.  Veteran  survivor trees such as western larch and ponderosa pine support biodiversity by providing nesting sites for birds and forage for ungulates that brows on regeneration in the understorey following fire. These structures that are valuable for biodiversity are linked to fire and will be lost if the current trajectory of fire exclusion continues. Assuming that regeneration replaces canopy trees and that the current fire-free period continues, species will shift in composition towards fire-intolerant species across all sites with escalating fire hazards and consequences at low elevations in areas surrounding communities at the wildland-urban interface. While, the consequences of fire suppression differ based on fire regime, the implications for management are greatest for communities in the wildland-urban interface at lowest elevations. In stand-maintaining fire regimes, suppression enables subcanopy trees to survive and contribute to ladder fuels increasing fire hazard (Swetnam et al. 1999). In mixed-severity regimes where stand-replacing and stand-maintaining fires burn, it is more difficult to discern the 81  impacts of fire suppression of current stands (Veblen 2002). Fire suppression has been most successful at eliminating low-to-moderate-severity fires which are most important from a biodiversity perspective (Agee 1993) and burn in areas closest to human communities in the wildland-urban interface (Filmon 2003). The legacy of the umbrella policy of fire suppression requires treatments that target a range of variability supported by historic conditions. At upper elevations, the consequences of suppression are not as dramatic but may be complicated by factors that interact with fire such as insect outbreaks and climatic warming. Historic fire return intervals were longest at upper elevations so current fire-free intervals that result from fire suppression may remain consistent with historic fire return intervals. Changes to fire regimes at upper elevations may follow influencing factors such as mountain pine beetle (Dendroctonus ponderosae Hopkins; MPB) and climatic change. High elevation forests contain homogeneous stands of lodgepole pines which have been attacked extensively by MPB (Axelson et al. 2009). Stands killed by beetles become more susceptible to high-severity fires as downed logs facilitate fire spread along corridors through post-mortality forests (Agee 1993). In these same stands, climate rather than fuels limits fire resulting in large areas burning during prolonged droughts (Schoennagel et al. 2004). In the coming century, climatic conditions are forecasted to increase the likelihood of prolonged and widespread droughts which may precondition large areas of high-elevation forests to burn at severities beyond control and especially in stands killed by MPB (Westerling et al. 2006). Evidence of these changes have already been documented adjacent to the study area and since 1987 as anticipated warming and increasing aridity were associated with fires that burned extensively and at stand-replacing severities as a result of climate synchronizing droughts over large areas of northern Montana and Idaho (Heyderdahl 2008). As conditions during the fire season become warmer and dryer and  82  growing seasons increase in length, fires will continue to respond at high elevations by burning at higher severities posing threats to communities in terms of smoke. Baseline information on historic variability in fire activity can inform management strategies that attempt to restore forests using approaches that vary from wilderness areas to the wildland-urban interface where reductions in fuels may be needed to reduce fire hazard. On provincial and crown lands, historic components of fires can be reintroduced through prescribed burns that aim to return forests to conditions from a predetermined period of time. By using reference conditions, strategies follow historic conditions with clear goals for stand structure and composition (Swetnam et al. 1999). At the wildland-urban interface, managers can use historic frequencies of fires to evaluate fire risk and mitigate hazards in communities dependent on and situated within forests in the study area. Across the study area, ecological restoration and hazard mitigation can work in tandem to create structures valuable to wildlife in the forest while protecting communities from fire in the wildland-urban interface.  83  Chapter 5 Conclusions The results of this study reveal an extensive history of fires that burned at a mix of frequencies and severities through time and up to 1932 across the entire study area. In the past and in line with other studies, elevation appears to be the predominant control on fire and resultant forest structures (Taylor and Skinner 1998). Historically, fire played an important role in structuring forests that varied significantly between elevations with fire-tolerant trees found exclusively where fires burned frequently in valley bottoms. In these forests, fire return intervals were shorter than the current fire-free period while fire return intervals sites at upper-elevation stands may be influenced by climatic change and mountain pine beetle outbreaks. In valley bottoms, fires burned historically at low-to-moderate severities and were consistently with mixed-severity regimes including components of both stand-maintaining and stand-replacing severities. At upper elevations, fire return intervals were longer as fires burned less frequently but more severely than fires at low elevations. Humans impacted the fire regime during the settlement period increasing fires from 1860 through 1944 but effectively eliminating fires from forests during the second half of the 20th century and across all stands. Modern fire suppression has eliminated low-to-moderate-severity fires across the landscape, triggering a shift in composition from fire-tolerant species to fire-intolerant species. Currently, regeneration in the understorey is dominated by fire-intolerant species that are surviving and persisting as a result of fire suppression and in a pattern that may elevate fire hazard especially at low elevations in the wildland-urban interface. The legacy of human land use and changes in the historic fire regime suggests that current stand structure may not be representative of past stand structure and especially where relatively frequent fires played an integral part in developing local ecosystems. These findings 84  highlight variability in fire history and stand dynamics across the study area along with anthropogenic impacts which may obscure differences in the future as fire regimes may transition away from mixed-severity as a result of fire suppression and resulting in a landscape where fire suppression eradicates fire-tolerant species without intervention by forest managers.  Future Analysis Given scenarios forecasted under conditions of climatic change that may introduce novel conditions resulting from climate-mediated fires, managers will need improved understandings of mechanisms that led to fires in the past to order to address emerging changes and to discern local from regional signals in results (Falk et al. 2007). An initial next step would be to test for synchrony between climatic indices of oceanic-atmospheric teleconnections and historic fires documented in this record. The coincidence between fire and drought would help identify fire susceptibility by climatic and topographic configurations to develop strategies that address specific scenarios of environmental change across the area. For example, historic coherence between fire and climatic indices determines periods of high versus low risk based on ENSO, PDO, and AMO signals. Regional studies show that susceptibility to high-severity fires is enhanced during particularly dry years associated with warm phases of the PDO (Schoennagel et al. 2005; Daniels et al. 2007; Morgan et al. 2008). In the future, predications anticipate fire risk to increase with widespread droughts becoming more common and severe and underscoring the importance of vantage points available through fire history research (Westerling et al. 2006) This retrospective, along with collaborative efforts throughout the Kootenays, provides a high-resolution understanding of the role of fire through time and space by identifying historic fire activity along with the successional trajectory of forests that followed (see Mather, in preparation; Mustaphi, in preparation; Marcoux, in preparation; Da Silva 2009; Daniels et al. 85  2007).  In the future, continued monitoring and resampling will be required to refine our  understanding of these dynamic forests while assessing, managing, and hopefully minimizing our cumulative impacts. Ultimately disease, wind, and anthropogenic incursions may synergise with fire regimes in ways that are poorly understood and often unpredictable (Agee 1998). What is clear is that current policies ought to reflect historic precedents which reveal a landscape shaped by fire. In the absence of intervention, current management policies may exacerbate fire hazard while eliminating forest structures worth protecting across a landscape with a rich but fading legacy of fire.  86  References Cited Agee, J.K. 1991. Fire history along an elevational gradient in the Siskiyou Mountains, Oregon. Northwest Science, 65:188–199. Agee, J.K. 1993. Fire Ecology of Pacific Northwest Forests. Island Press, Washington, DC, USA. Agee, J.K. 1998. The landscape ecology of western forest fire regimes. Northwest Science, 72:24–34. Agee, J.K. 2004. The complex nature of mixed severity fire regimes. In Taylor, L., J. Zelnik, S. Cadwallader, and B. Hughes, editors, Mixed Severity Fire Regimes: Ecology and Management., Spokane, WA, USA. Agee, J.K. and J. Kertis. 1987. Forest types of the North Cascades National Park Service Complex. Canadian Journal of Botany, 65:152–153. Agee, J. K., M. Finney, and R. deGouvenain. 1990. Forest fire history of Desolation Peak, Washington. Canadian Journal of Forest Research 20:350–356. Alexander, G.W. 1927. Lightning storms and forest fires in the state of Washington. Monthly Weather Review, 55:122–129. Anderson, M.D. 2003. Pinus contorta var. latifolia. In Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ [cited July 2010]. Antos, J.A. and Parish, R. 2002. Dynamics of an old-growth, fire-initiated, subalpine forest in southern interior British Columbia: tree size, age, and spatial structure. Canadian Journal of Forest Research, 32:1935–1947. Arno, S.F., Parsons, D.J., and Keane, R.E. 2000. Mixed-severity fire regimes in the northern Rocky Mountains: consequences of fire exclusion and options for the future. In Cole, D.N., S.F. McCool, W.T. Borrie, and J. O'Loughlin, editors, Wilderness science in a time of change conference - Volume 5 - Wilderness ecosystems, threats, and management. Missoula, MT, USA. Arno, S.F. 1980. Forest fire history of the northern Rockies. Journal of Forestry, 39:726– 728. Arno, S. and K. Sneck. 1977. A method for determining fire history in coniferous forests of the mountain West, Ogden, UT: USDA Forest Service, Intermountain Forest and Range Experiment Station General Technical Report. 87  Axelson, J.N., R.I. Alfaro, and B.C. Hawkes. 2009. Influence of fire and mountain pine beetle on the dynamics of lodgepole pine stands in British Columbia, Canada. Forest Ecology and Management, 257:1874–1882. Baisan, C.H., and T.W. Swetnam. 1990. Fire history on a desert mountain range: Rincon Mountain Wilderness, Arizona, U.S.A. Canadian Journal of Forest Research, 20:1559–1569. Baker, W.L. and D.S. Ehle. 2001. Uncertainty in surface-fire history: the case of ponderosa pine forests in the western United States. Canadian Journal of Forest Research, 31:1205–1226. Baker, W.L., T. T., Veblen, and R. L. Sherriff. 2007. Fire, fuels and restoration of ponderosa pine-Douglas fir forests in the Rocky Mountains, USA. Journal of Biogeography, 34:251–269. Barrett, S.W. and S.F. Arno. 1988. Increment-borer methods for determining fire history in coniferous forests. US Department of Agriculture, Forest Service, General Technical Report INT-GTR-244. Barrett, S.W. and S.F. Arno. 1982. Indian Fires as an Ecological Influence in the Northern Rockies. Journal of Forestry, 80:647–651. BCMOF (British Columbia Ministries of Forests). 1995. Biodiversity Guidebook, Forest Practices Code of British Columbia [Online]. BC Ministry of Forests and Water, Land and Air Protection, Victoria, BC. Available:www.for.gov.bc.ca/tasb/legsregs/fpc/fpcguide/biodiv/biotoc.htm [cited July 2010]. BCMOFR (British Columbia Ministry of Forests and Range). 2010. Causes of fires, Protection Branch, British Columbia Ministry of Forests and Range [Online]. BC Ministry of Forests and Water, Land and Air Protection, Victoria, BC. Available:http://bcwildfire.ca/FAQ/causes.htm [cited April 2010]. Beaty, R.M. and A.H. Taylor. 2008. Fire history and the structure and dynamics of a mixed conifer forest landscape in the northern Sierra Nevada, Lake Tahoe Basin, California, USA. Forest Ecology and Management, 255:707–719. Bekker M.F. and A.H. Taylor. 2010. Fire disturbance, forest structure, and stand dynamics in montane forests of the southern Cascades, Thousand Lakes Wilderness, California, USA. Ecoscience, 17:59–72. Biondi, F., J.O. Klemmedson, and R.O. Kuehl. 1992. Dendrochronological analysis of single-tree interactions in mixed pine-oak stands of central Arizona, U.S.A. Forest Ecology and Management, 48:321–333. Blackwell, B.A. 2010. Personal Communication on fuel treatments planned around Nelson, BC. Edited by J.H. Nesbitt.  88  Blackwell, B.A., R.W. Gray, R.N. Green, F. Feigl, T. Berry, D. Ohlson, and B. Hawkes. 2003. Developing a coarse scale approach to the assessment of forest fuel conditions in southern British Columbia. Report submitted to Forest Innovation Investment. Victoria, B.C. Bowman, D.M. 2007. Progress Report: Fire Ecology. Progress in Physical Geography, 31:523–532. Brown, P.M. 2006. Climate effects on fire regimes and tree recruitment in Black Hills ponderosa pine forests. Ecology, 87:2500–2510. Brown, P.M., C.L. Wienk, and A.J. Symstad. 2008. Fire and forest and forest history at Mount Rushmore. Ecological Applications, 18:1984–1999. Brown, P., M. Ryan, and T. Andrews. 2000. Historical surface fire frequency in ponderosa pine stands in research natural areas, central Rocky Mountains and Black Hills, USA. Natural Areas Journal, 20:133–139. Brown, P. and T. Swetnam. 1994. A cross-dated fire history from coast redwood near Redwood National Park, California. Canadian Journal of Forest Research, 24:21–31. Buechling, A. and W.L Baker. 2004. A fire history from tree rings in a high-elevation forest of rocky mountain national park. Canadian Journal of Forest Research, 34:1259–1273. Camp, A., C. Oliver, P. Hessburg, and R. Everett. 1997. Predicting late-successional fire refugia pre-dating European settlement in the Wenatchee Mountains. Forest Ecology and Management, 95:63–77. Caprio, A.C. and T.W. Swetnam. 1995. Historic fire regimes along an elevational gradient on the west slope of the Sierra Nevada, California. In Brown, J.K., R.W. Mutch, C.W. Spoon, and R.H. Wakimoto, Technical Coordinators, Proceedings: Symposium on Fire in Wilderness and Park Management. USDA Forest Service Intermountain Research Station, Ogden, UT, General Technical Report. INT-GTR-320. Cochrane, J. 2007. Forest fires in southeastern B.C. M.Sc. thesis, University of British Columbia, Vancouver, BC. Cochrane, J. and L.D. Daniels. 2008. Striking a balance: safe sampling of partial stem cross-sections in British Columbia. BC Journal of Ecosystem and Management, 9:38–46. Daniels, L.D. and R.W. Gray. 2006. Disturbance regimes in coastal British Columbia. BC Journal of Ecosystems and Management 7:44–56. Daniels, L.D., J. Cochrane, and R.W. Gray. 2007. Mixed-severity fire regimes: regional analysis of the impacts of climate on fire frequency in the Rocky Mountain Forest District. Report to Tembec Inc., BC Division, Canadian Forest Products Ltd., Radium Hot Springs, and the Forest Investment Account of British Columbia. 89  Da Silva, E. 2009. Wildfire history and its relationship with top-down and bottom-up controls in the Joseph and Gold creek watersheds. M.Sc. thesis, University of Guelph, Guelph, ON. Duncan, R., 1989. An evaluation of errors in tree age estimates based on increment cores in Kahikatea (Dacrycarpus dacrydioides). New Zealand Natural Sciences, 16:31–37. Ehle, D.S. and W.L. Baker. 2003. Disturbance and stand dynamics in ponderosa pine forests in Rocky Mountain National Park, USA. Ecological Monographs, 73:543–566. Environment Canada. 2008. Canadian Climate Normals 1971–2000 [Online]. Available:http://www.climate.weatheroffice.ec.gc.ca/climate_normals/results_e.html?Province= ALLandStationName=castlegar%20andSearchType=BeginsWithandLocateBy=ProvinceandProx imity=25andProximityFrom=CityandStationNumber=andIDType=MSCandCityName=andPark Name=andLatitudeDegrees=andLatitudeMinutes=andLongitudeDegrees=andLongitudeMinutes= andNormalsClass=AandSelNormals=andStnId=1105and [cited May 2009]. Everett, R.L., R. Schellhaas, D. Keenum, and D. Spurbeck, and P. Ohlson. 2000. Fire history in the ponderosa pine/Douglas-fir forests on the east slope of the Washington cascades. Forest Ecology and Management, 129:207–225. Falk, D.A., D.M. McKenzie, C. Miller, and A.E. Black. 2007. Cross-scale analysis of fire regimes. Ecosystems, 10:809–823. Filmon, G. 2004. Firestorm 2003: Provincial www.2003firestorm.gov.bc.ca/ [cited May 2010].  Review  [Online].  Available:  Flannigan, M.D., K.A. Logan, B.D. Amiro, W.R. Skinner, and B.J. Stocks. 2005. Future area burned in Canada. Climate Change, 72:1–16. Fowler, P. M. and D.O. Asleson. 1984. The location of lightning-caused wildland fires, northern Idaho. Physical Geography, 5:240–252. Fuquay, D., A.R. Taylor, R.G. Hawk, and C.W. Schmid Jr. 1972. Lightning discharges that cause forest fires. Journal of Geophysical Research, 77:2156–2158. Fulé, P.Z., J.E. Crouse, T.A. Heinlein, M.M. Moore, W.W. Covington, and G. Verkamp. 2003. Mixed-severity fire regime in a high-elevation forest: Grand Canyon, Arizona. Landscape Ecology, 18:465–486. Gavin, D.G., L.B. Brubaker, and K.P. Lertzman. 2003. Holocene Fire History of a coastal temperate rain forest based on soil charcoal radiocarbon dates. Ecology, 84:186–201.  90  Gedalof, Z., D.L. Peterson, and N. J. Mantua. 2005. Atmospheric, climatic and ecological controls on extreme wildfire years in the northwestern united states. Ecological Applications, 15:154–174. Gillett, N. P., A.J. Weaver, F.W. Zwiers, and M.D. Flannigan. 2004. Detecting the effect of climate change on Canadian forest fires. Geophysical Research Letters, 31, L18211, doi: 10.1029/2004GL020876. Grissino-Mayer, H.1999. Modeling fire interval data from the American Southwest with the Weibull distribution. International Journal of Wildland Fire, 9:37–50. Grissino-Mayer, H. 2001a. Evaluating crossdating accuracy: a manual and tutorial for the computer program COFECHA. Tree-Ring Research, 57:205–221. Grissino-Mayer, H. 2001b. FHX2 – Software for analyzing temporal and spatial patterns in fire regimes from tree rings. Tree-Ring Research, 57:115–124. Gutsell, S. and E.A. Johnson.1996. How fire scars are formed: coupling a disturbance process to its ecological effect. Canadian Journal of Forest Research, 26:166–174. Heinselman, M.L. 1973. Fire in the virgin forests of the Boundary Waters Canoe Area, Minnesota. Quaternary Research, 3:329–382. Hessl, A.E., D. McKenzie, and R. Schellhaas. 2004. Drought and Pacific Decadal Oscillation linked to fire occurrence in the inland Pacific Northwest. Ecological Applications, 14:425–442. Heyerdahl, E.K., L.B. Brubaker, and J.K. Agee. 2001. Spatial controls of historical fire regimes: a multiscale example from the interior west, USA. Ecology, 82:660–678. Heyerdahl, E.K., L.B. Brubaker, and J.K. Agee. 2002. Annual and decadal climate forcing of historical fire regimes in the interior Pacific Northwest, USA. The Holocene, 12:597–604. Heyerdahl, E.K., K. Lertzman, and S. Karpuk. 2007. Local-scale controls of a low-severity fire regime (1750–1950): southern British Columbia, Canada. Ecoscience, 14:40–47. Heyerdahl, E.K., R.F. Miller, and R.A. Parsons. 2006. History of fire and Douglas-fir establishment in a savanna and sagebrush-grassland mosaic, southwestern Montana, USA. Forest Ecology and Management, 230:107–118. Heyerdahl, E.K., D. McKenzie, L.D. Daniels, A.E. Hessl, J.S. Littell, and N.J. Mantua. 2008. Climate drivers of regionally synchronous fires in the inland Northwest (1651–1900). International Journal of Wildland Fire, 17:40–49.  91  Higuera, P.E., M.E. Peters, L.B. Brubaker, and D.G. Gavin. 2007. Understanding the origin and analysis of sediment-charcoal records with a simulation model. Quaternary Science Reviews, 26:1790-1809. Holmes, R. 1983. Computer-assisted quality control in tree-ring dating and measuring. Tree-Ring Bulletin, 43:69–78. Holt, R.F. and M. Machmer. 2005. Development of a Restoration and Monitoring Strategy in Relation to Fire Effects and Natural Disturbances in West Arm Provincial Park. Final Report, submitted to BC Ministry of Parks. Howard, J.L. 2003. Pinus ponderosae. In Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ [cited August 2010]. IPCC. 2001. Climate Change 2001: The scientific basis. J.T. Houghton, Y. Ding, M. Nogua, D. Griggs, P. Vander Linden, and K. Maskell, editors. Cambridge University Press, Cambridge, UK. Johnson, E.A. 1992. Fire and vegetation dynamics: studies from the North American boreal forest. Cambridge University Press, NY, USA. Johnson, E.A., G.I. Fryer, and M.J. Heathcott. 1990. The influence of man and climate on frequency of fire in the interior wet belt forest, British Columbia. Journal of Ecology, 78:403– 412. Johnson, E.A., K. Miyanishi, and S.R.J. Bridge. 2001. Wildfire regime in the boreal forest and the idea of suppression and fuel buildup. Conservation Biology, 15:1554–1557. Johnson, E.A., K. Miyanishi, and H. Kleb. 1994. The hazards of interpretation of static age structures as shown by stand reconstructions in a Pinus contorta -- Picea engelmannii forest. Journal of Ecology, 82:923–931. Johnson, E.A. and D.R. Wowchuk. 1993. Wildfires in the southern Canadian rocky mountains and their relationship to mid-tropospheric anomalies. Canadian Journal of Forest Research, 23:1213–1222. Jordan, G.J., M.J. Fortin, and K. Lertzman. 2008. Spatial pattern and persistence of historical fire boundaries in southern interior British Columbia. Environmental Ecological Statistics, 15:523–535. Karoly, D.J., K. Braganza, P.A., Stott, J.M. Arblaster, G.A. Meehl, A.J. Broccoli, and K.W. Dixon. 2003. Climate detection of a human influence on North American Climate. Science, 302:1200–1203.  92  Kaufmann, M.R., C.M. Regan, and P.M. Brown. 2000. Heterogeneity in ponderosa pine/Douglas-fir forests:age and size structure in unlogged and logged landscapes of central Colorado. Canadian Journal of Forest Research, 30:698–711. Klinka, K., J. Pojar, and D.V. Meidinger. 1991. Revision of biogeoclimatic units of coastal British Columbia. Northwest Science, 65: 32–47. Knapp, P.A. and P.T. Soulé. 2007. Trends in midlatitude cyclone frequency and occurrence during fire season in the Northern Rockies: 1900–2004. Geophysical Research Letters, 34, L20707, doi: 10.1029/2007GL031216. Kitzberger, T., P.M. Brown, E.K. Heyerdahl, T.W. Swetnam, and T.T. Veblen. 2007. Contingent Pacific-Atlantic Ocean influence on multi-century wildfire synchrony over western North America. Proceedings of the National Academy of Sciences of the USA, 104:543–548. Kipfmueller, K. and W. Baker. 1998. A comparison of three techniques to date standreplacing fires in lodgepole pine forests. Forest Ecology and Management, 104:171–177. Kou, X. and W. Baker. 2006. A landscape model quantifies error in reconstructing fire history from scars. Landscape Ecology, 21:735–745. Krajina, V.J. 1965. Biogeoclimatic zones and classification of British Columbia. Ecology of Western North America, 1: 1–17. Kunkel, K.E. 2001. Surface energy budget and fuel moisture. In E.A. Johnson and K. Miyanishi, editors, Forest fires, behavior and ecological effects, Academic Press, CA, USA. Larson, E.R and K.F. Kipmuller. 2010. Patterns in whitebark pine regeneration and their relationships to biophysical site characteristics in southwest Montana, central Idaho, and Oregon, USA. Canadian Journal of Forest Research, 40:476–487. Lertzman, K.P. and J. Fall. 1998. From forest stands to landscapes: Spatial scales and the roles of disturbance. In Peterson DL, Parker VT, editors, Ecological scale: theory and applications, Columbia University Press, NY, USA. Lertzman, K., J. Fall, and B. Dorner. 1998. Three kinds of heterogeneity in fire regimes: at the crossroads of fire history and landscape ecology. Northwest Science, 72:4–23. MacKillop, D.J. 2003. Stand structural characteristics and development patterns in oldgrowth interior cedar hemlock forests in southeastern British Columbia. M.Sc. thesis, University of British Columbia, Vancouver, BC. Marcoux, H. Mixed-severity fire regimes: quantifying disturbance and stand dynamics in montane forests of British Columbia. M.Sc. thesis, University of British Columbia, Vancouver, BC, in preparation.  93  Mather, V. M. Sub-rings parameters of four conifer species in the Kootenay Region of British Columbia, Canada. M.Sc. thesis, University of Guelph, Guelph, ON, in preparation. McKenzie, D., Z. Gedalof, D.L. Peterson, and P. Mote. 2004. Climatic change, wildfire, and conservation. Conservation Biology, 18:890–902. Meidinger, D. and J. Pojar. 1991. Ecosystems of British Columbia, Victoria, British Columbia: British Columbia Ministry of Forests. Moore, M.M., D.W. Huffman, P.Z. Fulé, W.W. Covington, and J.E. Crouse. 2004. Comparison of historical and contemporary forest structure and composition on permanent plots in southwestern ponderosa pine forests. Forest Science, 50:162–176. Morgan, P., E.K. Heyderdahl, and C.E. Gibson. 2008. Multi-season climate synchronized forest fires throughout the 20th century, Northern Rockies, USA. Ecology, 89:717–728. Mustaphi, C.C. Late Holocene climate-fire-vegetation interactions in the West Kootenay District, British Columbia, Canada, inferred from lake sediments. Ph.D. dissertation, Carleton University, Ottowa, ON, in preparation. Parker, A.J. 1982. The topographic relative moisture index: an approach to soil-moisture assessment in mountain terrain. Physical Geography, 3:160–168. Pearkes, E.D. 2002. Geography of Memory: Recovering Stories of a Landscape's First People, Kutenai House Press, Nelson, BC. Pickett, S.T.A. and P.S. White. 1985. The Ecology of Natural Disturbance and Patch Dynamics. Academic Press, Orlando, FL, USA. Pickford, S.G., G.R. Fahnestock, and R. Ottmar. 1980. Weather, fuels, and lightning fires in Olympic National Park. Northwest Science, 54:92–105. Pyne, S.J. 2007. Splendour: A Fire History of Canada. UBC Press, Vancouver, BC. Quesnel, H. and H. Pinnell 1998. Application of natural disturbance processes to a landscape plan: the dry warm Interior Cedar-Hemlock Subzone (ICHdw) near Kootenay Lake, BC. In D’Eon, R.G, J.F. Johnson, and E.A. Ferguson, editors, Ecosystem management of forested landscapes: directions and implementation. Papers from the conference on Ecosystem Management of Forested Landscapes, held in Nelson, BC on Oct. 26–28, 1998, UBC Press, Vancouver, BC. Reed, W.J and E.A. Johnson. 2004. Statistical methods for estimating historical fire frequency from multiple fire–scar data. Canadian Journal of Forest Research, 34:2306–2313. Reesor, J. 1996. Geology of Nelson Map Sheet (east half), Open File Map 2721. Geological Survey of Canada. Ottawa, Ontario. 94  Rodman R.F. 2008. Post Wildfire Hazard Assessments, Springer and Sitkum Creek Fires. Submitted to Emergency Management British Columbia. Rorig, M.L. and S.A. Ferguson. 1999. Characteristics of lightning and wildland fire ignition in the Pacific Northwest. Journal of Applied Meteorology, 38:1565–1575. SAS. 2010. SAS. SAS Institute Inc., Cary, NC. Scher, J.S. 2002. Larix occidentalis. In Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ [cited August 2010]. Schoennagel, T., T.T. Veblen, and W.H. Romme. 2004. The interaction of fire, fuels, and climate across Rocky Mountain forests. BioScience, 54:661–676. Segura, G. and L.C. Snook. 1992. Stand dynamics and regeneration patterns of a pinyon pine forest in east central Mexico. Forest Ecology and Management, 47:175–194. Service, R.F. 2004. As the west goes dry. Science, 303:1124–1127. Sherriff, R.L. and T.T. Veblen. 2006. Ecological effects of changes in fire regimes in Pinus ponderosa ecosystems in the Colorado Front Range. Journal of Vegetation Science, 17:705–718. Sibold, J.S. and T.T. Veblen. 2006. Relationships of subalpine forest fires in the Colorado Front Range with interannual and multidecadal-scale climatic variation. Journal of Biogeography, 33:833–42. Sibold, J.S., T.T. Veblen, and M.E. González. 2006. Spatial and temporal variation in historic fire regimes in subalpine forests across the Colorado Front Range. Journal of Biogeography, 33:631–647. Steinberg, P.D. 2002. Pseudotsuga menziesii. In Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ [cited August 2010]. Stokes, M. and T. Smiley. 1968. An introduction to Tree-ring dating. University of Arizona Press, Tucson, AZ, USA. Swetnam, T.W. 1993. Fire history and climate change in giant sequoia groves. Science, 262:885–889. Swetnam, T.W., C.D. Allen, and J.L. Betancourt. 1999. Applied historical ecology: using the past to manage for the future. Ecological Applications, 9:1189–1206.  95  Taylor, A.H. 2000. Fire regimes and forest changes in mid and upper montane forests in the southern Cascades, Lassen Volcanic National Park, California, USA. Journal of Biogeography 27:87–104. Taylor, A.H. and C.N. Skinner. 1998. Fire history and landscape dynamics in a latesuccessional reserve, Klamath Mountains, California, USA. Forest Ecology and Management, 111:285–301. Taylor, A.H. and C.N. Skinner. 2003. Spatial patterns and controls on historical fire regimes and forest structure in the Klamath Mountains. Ecological Applications, 13:704–719. Tesky, Julie L. 1992a. Tsuga heterophylla. In Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ [cited August 2010]. Tesky, Julie L. 1992b. Thuja plicata. In Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ [cited August 2010]. Turner, N.J. 1999. Time to burn, traditional use of fire to enhance resource production by aboriginal peoples in British Columbia. In R. Boyd, editor, Indians, fire and the land in the Pacific Northwest, Oregon State University Press, Corvallis, OR, USA. Uchytil, Ronald J. 1991a. Abies lasiocarpa. In Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ [cited August 2010]. Uchytil, Ronald J. 1991b. Picea engelmannii. In Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ [cited August 2010]. Utzig, P., C. Scott-May, R. Holt, M. Machmer, B. Lewis, C. Wallace, and M. Carver. 2003. Central and Southern Columbia Mountains Ecosections, a Context for Developing Objectives, Strategies and Monitoring Indicators. Kutenai Nature Investigations, Nelson, BC. Valentine, K.W.G., P.N. Sprout, T.E. Baker, and L.M. Lavkulich, editors. 1978. The Soil Landscapes of British Columbia. B.C. Ministry of Environment, Victoria, B.C. Van Horne, M.L. and P.Z. Fulé. 2006. Comparing methods of reconstructing fire history using fire scars in a southwestern United States ponderosa pine forest. Canadian Journal of Forest Research, 36:855–867.  96  Van Wagtendonk, J.W. 1986. The determination of carrying capacities for the Yosemite Wilderness. In Proceedings National Wilderness Conference: U.S. Department of Agriculture, Forest Service General Technical Report. Veblen, T.T., T. Kitzberger, and J. Donnegan. 2000. Climatic and human influences on fire regimes in ponderosa pine forests in the Colorado Front Range. Ecological Applications, 10:1178–1195. Veblen, T.T. 2003. Historic range of variability of mountain forest ecosystems: concepts and applications. The Forestry Chronicle, 79:223–226. Villalba, R. and T.T. Veblen. 1997. Regional patterns of tree population age structures in northern Patagonia: climatic and disturbance influences. Journal of Ecology, 85:113–124. Westerling, A. L., H.G. Hidalgo, D.R. Cayan, and, T.W. Swetnam. 2006. Warming and earlier spring increase western U.S. forest wildfire activity. Science, 313:940–943. Wong, C.M. and K.P. Lertzman. 2001. Errors in estimating tree age: implications for studies of stand dynamics. Canadian Journal of Forest Research, 31:1262–1271. Wright, C.S. and J.K. Agee. 2004. Fire and vegetation history in the eastern Cascade Mountains, Washington. Ecological Applications, 14:443–459.  97  Appendix A – Event Panels for HNFR1 Fire history information for HNFR1 sites including fire events from scars (black triangles) and cohorts (white triangles), age structure, and initial growing conditions for trees that established on site, including suppression and release responses of veteran survivor trees to fires and cohorts when present.  98  99  100  101  102  103  Appendix B – Event Panels for HNFR2  Fire history information for HNFR1 sites including fire events from scars (black triangles) and cohorts (white triangles), age structure, and initial growing conditions for trees that established on site, including suppression and release responses of veteran survivor trees to fires and cohorts when present.  104  105  106  107  108  109  Appendix C – Event Panels for HNFR3 Fire history information for HNFR1 sites including fire events from scars (black triangles) and cohorts (white triangles), age structure, and initial growing conditions for trees that established on site, including suppression and release responses of veteran survivor trees to fires and cohorts when present.  110  111  112  113  

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