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Productivity analysis of silvicultural treatments in cedar and hemlock stands on northern Vancouver Island Nery, Victor Ramirez 2012

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PRODUCTIVITY ANALYSIS OF SILVICULTURAL TREATMENTS IN CEDAR AND HEMLOCK STANDS ON NORTHERN VANCOUVER ISLAND  by  Victor Ramirez Nery B.A.Sc, Universidade Federal de Viçosa, 2008  A THESIS SUBMITTED IN PARTIAL FULLFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF  MASTER OF SCIENCE in The Faculty of Graduate Studies (Forestry)  THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver)  August 2012 © Victor Ramirez Nery, 2012  ABSTRACT Due to many favourable characteristics such as a moist and mild climate year round, the absence of fire or a major insect infestation and disease, the coastal coniferous forests of northern Vancouver Island are among the most productive forests in British Columbia. However, the productivity rates in the area vary in a mosaic pattern of two very distinctive forest types: low-productivity “CH” and medium-productivity “HA”. These types have two very different productivity responses to silvicultural treatments. In 1987-88 a factorial trial called Salal Cedar Hemlock Integrated Research Program (SCHIRP) was established to analyse growth effects of fertilization and stand density on western red cedar (Thuja plicata Donn ex D. Don) and western hemlock (Tsuga heterophylla (Raf.) Sarg.) at these two different sites. Previous projects involving these sites measured the height and the DBH after 10 and 15 growing seasons, and have been recently re-measured again after 22 years since establishment. Fertilizer was applied three times after planting (NPK + NP + N); stand density was established at: 500, 1500 and 2500 stems/ha. Fertilizer application significantly increased the height and volume of both species at all treatment combinations and sites. However, there was a significant difference in growth patterns between red cedar and hemlock. Depending on the site fertility and treatment used, the stand volume of fertilized red cedar increased from 123% to 351% and fertilized hemlock volume increased from 106% to 2190% compared to the non-fertilized counterparts. In most cases, higher densities had much greater volume per hectare than lower density stands; however, density caused a significant decrease in the average height of both species at CH sites. Possibly due to the latest application of fertilizer, an increase in periodic annual increments of volume was also observed across all treatments. To further explore the potential of silvicultural treatments, biomass and carbon content were also estimated in this study. Results indicated a positive growth response of total (above + belowground) biomass generated by fertilization, especially at the higher density plots. CH sites have shown the best increment response to fertilization; however, even at its highest levels, averages were still low if compared to HA sites. Overall, the best treatments were found to be high density fertilized hemlock stands on HA sites. This treatment not only had the greatest height, volume and biomass in the whole experiment, but was also the most efficient for C capture. After 22 growing seasons, the results of this research reinforces the idea that fertilization is still a reliable and effective tool to increase nutrient availability and productivity of these forests; it suggests that the focus of silvicultural treatments such as fertilization and increased stand density should be directed mostly towards the more productive HA sites.  ii  TABLE OF CONTENTS  ABSTRACT ........................................................................................................................................................................................... ii TABLE OF CONTENTS .....................................................................................................................................................................iii LIST OF TABLES ................................................................................................................................................................................ v LIST OF FIGURES .............................................................................................................................................................................. vi LIST OF ABBREVIATIONS .............................................................................................................................................................vii ACKNOWLEDGEMENTS .............................................................................................................................................................. viii 1  INTRODUCTION ........................................................................................................................................................................ 1 1.1  THE SCHIRP STORY .................................................................................................................................................... 1  1.2  TREE GROWTH RESPONSE TO SILVICULTURAL PRACTICES ........................................................................... 4  1.3  CARBON SEQUESTRATION ......................................................................................................................................... 8  1.4  ROOT BIOMASS .............................................................................................................................................................. 9  1.5  FERTILIZATION EFFECT ON BIOMASS AND CARBON .................................................................................... 10  1.6  CARBON CONTENT OF BIOMASS ........................................................................................................................... 12  2  OBJECTIVES ........................................................................................................................................................................... 13  3  MATERIALS AND METHODS ............................................................................................................................................ 14 3.1  STUDY AREA ................................................................................................................................................................ 14  3.2  SILVICULTURAL TREATMENTS AND EXPERIMENTAL DESIGN ................................................................... 15  3.3  DATA COLLECTION, VOLUME AND PERIODIC ANNUAL INCREMENT CALCULATION ............................................................................................................................................................. 17  4  3.4  BIOMASS AND CARBON CALCULATION .............................................................................................................. 17  3.5  STATISTICAL ANALYSIS .......................................................................................................................................... 18  RESULTS ................................................................................................................................................................................. 20 4.1  FERTILIZER EFFECT ON AVERAGE HEIGHT AND VOLUME ........................................................................... 20  4.2  SPECIES X FERTILIZATION INTERACTION .......................................................................................................... 20  iii  4.3  STAND DENSITY X FERTILIZATION INTERACTION .......................................................................................... 21  4.4  OPTIMAL SILVICULTURAL COMBINATIONS ...................................................................................................... 22  4.5  PERIODIC ANNUAL INCREMENT DIFFERENCES BETWEEN THE 1997-2002 AND 2002-2009 PERIODS ................................................................................................................................................... 23  4.6  BIOMASS AND CARBON ........................................................................................................................................... 35  5  DISCUSSION ........................................................................................................................................................................... 39  6  CONCLUSIONS AND RECOMMENDATIONS .................................................................................................................. 48  7  CHALLENGES AND FUTURE RESEARCH ....................................................................................................................... 50  REFERENCES.................................................................................................................................................................................... 52 APPENDIX A ................................................................................................................................................................................ 61  iv  LIST OF TABLES Table 4.1 Mixed model analyses of average height and volume for CH and HA sites.....................................32 Table 4.2 Mixed model analyses of periodic annual increment in height and volume for CH sites by measurement period (1997-2002 and 2002-2009). ..........................................................................................................33 Table 4.3 Mixed model analyses of periodic annual increment in height and volume for HA sites by measurement period (1997-2002 and 2002-2009). ..........................................................................................................34 Table A - 1 Average height and volume per treatment (after 10 growing seasons). .......................................... 61 Table A - 2 Average height and volume per treatment (after 15 growing seasons). ..........................................62 Table A - 3 Average height and volume per treatment (after 22 growing seasons). ..........................................63 Table A - 4 Periodic annual increment in height and volume on CH and HA sites during each measurement period (1997-2002 and 2002-2009). ..........................................................................................................64 Table A - 5 Tukey’s honestly significant difference test of periodic annual increments in height and volume between the two measurement periods (1997-2002 and 2002-2009). ......................................................65 Table A - 6 Estimated Biomass of each tree component (Mg ha -1) on CH sites (after 22 growing seasons). ..............................................................................................................................................................................................................66 Table A - 7 Estimated Biomass of each tree component (Mg ha -1) on HA sites (after 22 growing seasons). ............................................................................................................................................................................................66 Table A - 8 Carbon content of above and belowground biomass in each treatment on CH sites after 22 growing seasons. ...........................................................................................................................................................................67 Table A - 9 Carbon content of above and belowground biomass in each treatment on HA sites after 22 growing seasons. ...........................................................................................................................................................................67 Table A - 10 Average basal area per treatment. ...............................................................................................................68  v  LIST OF FIGURES Figure 4.1 Average height development in each treatment at CH sites, 1997 – 2009.......................................24 Figure 4.2 Average height development in each treatment at HA sites, 1997 – 2009. .....................................25 Figure 4.3 Average volume development in each treatment at CH sites, 1997 – 2009. ...................................26 Figure 4.4 Average volume development in each treatment at HA sites, 1997 – 2009....................................27 Figure 4.5 Periodic annual increment in height between the two measurement periods on CH sites. ........28 Figure 4.6 Periodic annual increment in height between the two measurement periods on HA sites.........29 Figure 4.7 Periodic annual increment in volume between the two measurement periods on CH sites. .....30 Figure 4.8 Periodic annual increment in volume between the two measurement periods on HA sites. .....31 Figure 4.9 Biomass of each component on CH sites......................................................................................................36 Figure 4.10 Biomass of each component on HA sites. ..................................................................................................37 Figure 4.11 Total Carbon sequestered per treatment on CH and HA sites. ...........................................................38  vi  LIST OF ABBREVIATIONS  Cw  Western red cedar  Hw  Western hemlock  CH  Cedar & hemlock  HA  Hemlock & amabilis  C  Carbon  N  Nitrogen  DBH  Diameter at breast height  PAI  Periodic annual increment  PAI-H  Periodic annual increment of height  PAI-V  Periodic annual increment of volume  HSD  Honestly significant difference  S.E.  Standard error  SCHIRP  Salal Cedar Hemlock Integrated Research Program  F0  Control (non-fertilized)  F1  Fertilized  Mg ha-1  Megagrams (Tonnes) per hectare  Mg C ha-1  Megagrams (Tonnes) of carbon per hectare  vii  ACKNOWLEDGEMENTS I would like to first and foremost thank Dr. Cindy Prescott for the opportunity, guidance and understanding not only as a supervisor, but also as a great friend throughout the good and bad times of my degree. Some gracious thanks also to my committee members; Dr. Peter Marshall and Dr. Harry Nelson for the helpful guidance throughout this project. This thesis would also not have come together as it has, without the help of Dr. Gordon Weetman and his invaluable knowledge and expertise, and the help and support of Dr. Sue Grayston, Dr. Sue Watts and Dr. Valerie LeMay. I would like to thank Western Forest Products for its support and all Port McNeill employees in which were very helpful in my adventure against bad weather and salal. A special thanks to Annette van Niejenhuis and her insightful knowledge and motivation to make me keep going. Thanks also to NSERC and the Faculty of Forestry Internal Awards program for the much needed financial support. This thesis would not be possible without the help, support and encouragement of Jorma Neuvonen, Dan Naidu and Gayle Kosh; and the tolerance of my eternal talks and stories of all the student members of BEG, especially Carolyn, Ali and Jason. A warm thank you to all my personal friends who were also an important part of this accomplishment. At last my biggest thank you is for my parents, grandmother and sister in which were always supporting and encouraging me to pursue my dreams. To my future wife Courtney: without your unconditional love and help, none of this would be possible! “pax et bonum”  viii  Dedico esta tese aos meus pais, a minha noiva, a minha avó e a minha irmã; sem vocês essa conquista não seria possível.  Start by doing what is necessary; then do what is possible; and suddenly you are doing the impossible.  -  Saint Francis of Assisi  ix  1  INTRODUCTION  1.1  THE SCHIRP STORY The forests of northern Vancouver Island in British Columbia are typically of oceanic  influence and mostly dominated by western hemlock (Tsuga heterophylla (Raf.) Sarg.), amabilis fir (Abies amabilis Dougl.), western red cedar (Thuja plicata Donn) with some Sitka spruce (Picea sitchensis (Bong.) Carr.) on the outer coastline and lodgepole pine (Pinus contorta var. contorta Dougl.) found in the very poorly drained sites. These forests sometimes vary in a unique and abrupt mosaic pattern of two very distinctive forest types. This phenomenon most commonly occurs on well to imperfectly drained sites and is found at middle to upper slope terrain where they are divided in CH and HA types (Prescott et al., 1996). Pre-harvesting observations have described the CH (Cedar & Hemlock) forests as of old growth composition, mostly dominated by western red cedar reaching up to a 1000 years old with some western hemlock and a great quantity of the ericaceous shrub salal (Gaultheria shallon Pursh) intertwined in the understory. Typically they are uneven-aged with an irregular canopy and of a late-seral stage. The second forest type called HA (Hemlock & Amabilis) is a much younger natural second-growth stand that originated following a wind-throw in 1906. Composed primarily of western hemlock and amabilis fir, HA forests are typically even-aged, with a regular canopy and in a mid-seral stage (Lewis, 1982; Prescott et al., 1996). Although characteristically different, based on the dominant species, topographic and mineral soil characteristics, Lewis (1982) classified them under the same ecosystem, hypothesizing that they were different stages of the same successional sequence; HA being a seral stage of the mature CH forest. These ecosystems are now classified under the Biogeoclimatic Ecosystem  1  Classification (BEC) system as the Coastal Western Hemlock (CWH) zone at maritime or hypermaritime subzones (Banner et al., 1993; Green and Klinka, 1994.). The large concentration of high-grade old-growth western red cedar of unsurpassed form and stature in CH forests, along with a booming North American economy, led to this secluded region being transformed into a logging haven by the early 1960s, resulting in large areas of cutovers. It was observed that these areas regenerated very slowly, leading foresters to recommend the following silvicultural treatment: slashburn, replant with Sitka spruce seedlings (these were the only available species at that time) and reduce competition by removing the heavy cover of salal on these sites (Prescott and Weetman, 1994). The initial results were promising, but by the age of 6-8 years these plantations started to show signs of severe nutritional deficiency associated with nitrogen and phosphorus, consequently resulting in very slow growth (Weetman et al., 1989b). The problem of nutrient deficiency was not found on neighbouring HA sites (Weetman et al., 1989a). Messier (1993) suggested that the poor growth in CH sites could be mostly related to low nutrient availability in the soil and competition for nutrients between the salal and conifers. Lewis (1982) hypothesized that simulating a wind-throw type of disturbance could perhaps help to convert slowly regenerating CH sites into a site that responds in a similar way to an HA site. The discussion led to the idea to test different silvicultural treatments such as stand establishment densities, fertilization and scarification, as possible tools to improve performance in CH sites. A large trial called SCHIRP (Salal Cedar Hemlock Integrated Research Program) was assembled in 1988 on the north of the Island by the University of British Columbia, the Canadian Forest Services, the BC Ministry of Forests and Western Forest Products Inc. (Prescott and Weetman, 1994). 2  Early studies by Weetman et al. (1989ab) on these sites confirmed the expected N and P deficiency on salal-dominated CH sites as positive responses to fertilization of red cedar, hemlock and spruce were observed. Poor growth performance of CH sites is mostly related to low nutrient supply capability of the forest floor (Weetman et al., 1989a). Positive effects of fertilization on red cedar and hemlock at SCHIRP have been continuously reported at CH sites (Weetman et al., 1989ab; Prescott and Weetman, 1994; Prescott et al., 1996; Blevins and Prescott, 2002; Bennett et al., 2003) and more recently in HA sites as well (Pratt et al., 1996; Negrave et al., 2007). Negrave et al. (2007) also suggested that the elevated growth rates in the fertilized sites at SCHIRP after 10 growing seasons since the last application indicate a continuous and prolonged effect of fertilizer treatment. The role of salal, only found in abundance on CH sites, on the poor performance of these sites is inadequately understood. A significant increase in N uptake by red cedar and hemlock has been observed following salal removal, indicative of strong competition for available N between conifers and salal (Weetman et al., 1989ab; Messier, 1993). It was also noted that red cedar generally grows much better than hemlock on CH sites (Weetman et al., 1989b). This could be related to the fine roots of hemlock and salal tending to be concentrated at the same depth in the upper forest floor, which would lead to stronger competition for nutrients between these two species. In contrast, red cedar fine roots are normally concentrated in the first 10 cm of mineral horizon thus reducing competition between red cedar and salal (Bennett et al., 2002). deMontigny and Weetman (1990) also hypothesized an allelopathic effect of salal in the growth of seedlings; however, after 10 years of fertilization and salal-removal trials, only fertilization increased N and P content in the soil and there was little improvement on the growth of conifers with salal removal compared to the effects of fertilization alone (Bennett et al., 2003).  3  Hemlock in heavily salal-dominated CH sites exposed to fertilization of N and P tended to do very well for the first 10 years (Bennett et al., 2003), but Negrave et al. (2007) noted that after 10 growing seasons, the hemlock growth response in fertilized CH sites was tapering off whereas red cedar was showing greater growth rates. The amount of research conducted on HA sites pales in comparison to the number of CH studies. Nevertheless, some surprising results were shown through analysis of tree response on CH and HA sites with 15 years of treatment. Negrave et al. (2007) determined that both red cedar and hemlock on HA sites showed a much greater and sustained increase in volume and periodic annual increment (PAI) compared to the fertilized CH areas. Thus, although slow conifer growth is more problematic on CH sites, the greatest responses to silvicultural treatments may occur on HA sites.  1.2  TREE GROWTH RESPONSE TO SILVICULTURAL PRACTICES In nature, tree productivity is mostly dependent on environmental factors such as solar  radiation, temperature, water and nutrient availability. As radiation, temperature and water are mainly regulated by uncontrollable external forces; foresters tend to primarily focus on manipulating nutrient availability to increase forest productivity (Binkley, 1986). Fertilization is currently one of the most common and effective silvicultural practices to increase nutrient availability (McMahon, 1992; Ingerslev et al., 2001; Coyle et al., 2008). Most cases of poor forest productivity associated with nutrient deficiencies originate from shortages of the macronutrients N and P. Nitrogen limitation is the most common cause of poor growth in temperate forests, (Fisher and Binkley, 2000) but is common in many other forest 4  ecosystems as well (Assmann, 1961). Nitrogen fertilization has resulted in positive growth response in several plantations of a variety of species around the world (Chappell et al., 1991; Tanner et al., 1998; Ingerslev et al., 2001). The main problems with N fertilization are related to efficiency and longevity. On average only 20 – 30% of the added N will end up entering the tree. Most applied N will become immobilized in the soil or be lost through volatilization and/or leaching (Nason and Myrold, 1992). In terms of longevity, it has been suggested that applying a single large dose or several small doses of N could overcome the immobilization capacity of the soil, consequently increasing N availability (Miller, 1988; Prescott, 1993). Prescott et al. (1995) reported a positive growth response and increased N availability after 15-23 years of N fertilization in jack pine (Pinus banksiana Lamb.) forests. There have also been reported cases of long-term positive growth response and increased N availability after N fertilization in Douglas-fir (Pseudotsuga menziesii) forests (Binkley and Reid, 1985; Prescott et al., 1993). However, increases in productivity following N fertilization are generally reported to be short-lived, usually lasting just a few years (Miller, 1981; Fisher and Binkley, 2000). Phosphorus deficiencies are most common in the tropics, but also occur in certain temperate regions (Bot et al., 2000; Fisher and Binkley, 2000). Nitrogen fertilization applied in great amounts can also create P limitations (Fisher and Binkley, 2000). In contrast to N, P fertilization is reported to have a much longer-lasting effect, possibly even persisting more than a decade (Fisher and Binkley, 2000). On northern Vancouver Island, P added to N fertilization has been reported to prolong the increase in productivity compared to N-fertilization alone (Bennett et al., 2003; Blevins et al., 2006). Phosphorus limitations in wet, organic soils have been  5  reported to limit growth and N cycling (White and Reddy, 2000), and P fertilization has been reported to increase levels of N mineralization (Cote, 2000; White and Reddy, 2000). In addition to enhancing site productivity and aboveground tree biomass, fertilization may influence soil properties such as pH, microbial biomass, soil enzyme activity, and the amount and characteristics of the light soil fraction (Gregorich et al., 1994). However, in a review, Nohrstedt (2001) could not find any clear evidence of forest health deterioration at several extensive N fertilization trials in Sweden. Even under similar climatic and nutrient conditions, tree productivity can vary greatly depending on the species (Weetman and Mitchell, 2005) and their inherited genetic potential (ElKassaby et al., 2005). Through evolution, tree species have developed different physiological priorities and strategies in response to external conditions. Nutrients therefore have different rates of efficiency depending on the species (Prescott et al., 1989; Dicus and Dean, 2001). One example is red cedar’s stronger capacity to tolerate flooded areas (Krajina et al., 1982), thus potentially giving red cedar greater productivity on such sites. According to Klinka et al. (2000) western hemlock and western red cedar are species of high productivity potential. However, the productivity of the two species can vary greatly even within the biogeoclimatic area. In general, hemlock tends to have a much greater SI (Site Index; height of dominant trees at 50 years of age) than red cedar. On the most productive sites, a red cedar SI of 24 is overshadowed by a SI 32.6 of hemlock. However, on the lowest quality sites, hemlock and red cedar have similar SI values of 8 (B.C. Ministry of Forests, 2011). Continuous studies on northern Vancouver Island have shown hemlock to be much more sensitive to, and less productive on, nutrient-poor salaldominated sites than red cedar (Weetman et al., 1989ab; Prescott and Weetman, 1994; Prescott et al., 1996; Bennett et al., 2003; Negrave et al., 2007). 6  Although red cedar tends to have a lower productivity rate than hemlock, red cedar plantations can be highly profitable because of the current high market for red cedar wood (B.C. Ministry of Forests, 2012). Given its natural tendency to produce large limbs and multiple tops, it is suggested that red cedar be planted densely to produce high-quality lumber (Burns and Honkala, 1990). Dense plantations are not as essential for increased quality in hemlock plantations, but hemlock is especially capable of growing in very dense situations at very high productivity rates (Burns and Honkala, 1990). Hemlock forests are ranked as one of the most productive forests in the world, although the market price for hemlock is not usually as favourable as for red cedar (B.C. Ministry of Forests, 2012). Growth response to fertilization also varies between the species. Hemlock has variable response to fertilization (Burns and Honkala, 1990; Brown, 2003). Bennett et al. (2003) and Blevins et al. (2006) suggested that this variability in growth response may be linked to P deficiency. At the SCHIRP site, hemlock did not respond to second application of N alone, but hemlock fertilized with N + P had steady growth improvements. When fertilized, hemlock tends to have a stronger initial growth compared to red cedar (Weetman et al., 1989ab; Prescott et al., 1996; Bennett et al., 2003). Interestingly, Negrave et al. (2007) observed that red cedar was responding better after 10 years of fertilization. Fine roots of hemlock tend to be concentrated at the upper forest floor, while red cedar fine roots normally concentrate at the first 10 cm of mineral horizon (Bennett et al., 2002). Negrave et al. (2007) suggested that this difference in root location in the soil profile could be responsible for their different growth behaviours. Hemlock would initially take advantage of surface-application fertilizers, but later on would not be able to capture the fertilizer that leached deeper into the soil. Conversely red cedar with its deeper roots would respond later, when nutrient supply deeper in the profile becomes elevated.  7  According to Oliver and Larson (1996), establishment density should not influence height growth and consequently SI. However, other studies have shown that where nutrient availability is limited, increasing planting density could potentially reduce tree size and growth by further reducing the limited amount of soil nutrients available (Nilsson, 1994; Negrave et al., 2007). Negrave et al. (2007) observed that on low-productivity salal-dominated CH sites, increasing stand density decreased mean height growth of both red cedar and hemlock. Density did not affect height on higher-productivity HA sites.  1.3  CARBON SEQUESTRATION Rising atmospheric concentrations of greenhouse gases (GHG) such as CO 2 is a major  environmental issue believed to be intensified by a combination of fossil-fuel combustion along with deforestation (Melillo, 1996). In an attempt to mitigate this problem, British Columbia (BC) implemented the Greenhouse Gas Reduction Targets Act in 2007. With this Act, the province has created its own Cap-and-Trade system, generating a demand for C sequestration projects to maintain its carbon neutral status achieved in 2011 (B.C. Ministry of Environment, 2011). Carbon sequestration under this Act can be achieved either by capture and storage, or through establishing natural C sinks (Pacific Carbon Trust, 2011). Carbon sequestration through forestry is now seen as a possible new business opportunity for the BC economy; offering an alternative income to the conventional forest products through the generation of carbon credits (Greig and Bull, 2009). Carbon accounting is complex and prone to a great number of errors; therefore, choosing the right approach to accurately calculate the amount of C sequestered in each project is crucial (Brown, 2002; Melson, 2011).  8  To estimate the amount of C sequestered in a forest, the first step is to measure the total biomass per unit area. Total biomass includes both aboveground and belowground (root) biomass. Aboveground biomass is usually calculated with the aid of site-specific biomass regression equations; however, the development of such equations can be costly and timeconsuming. With the pressure of the government and industry to find a simpler and less costly way to measure biomass, generalized equations were developed which could be applied across broader geographic regions (Gholz et al., 1979; Standish et al., 1985). Compared to site-specific equations, generalized equations tend to be less accurate especially in more extreme case scenarios. Generalized equations are becoming much more accurate and easier to use in Canada because they are now based on much larger data sets. These equations now use currently available inventory data as an input, and they can now be fine-tuned by incorporating species and site class as variable factors (Lambert et al., 2005; Boudewyn et al., 2007; Ung et al., 2008; Kivari et al., 2011).  1.4  ROOT BIOMASS Roots are known to hold a substantial proportion of the tree’s total biomass (Santantonio  et al., 1977; Cannell, 1982). However; compared to the number of aboveground biomass studies, very few studies have been conducted on root biomass and dynamics. Furthermore, studies of belowground biomass suffer from inconsistent sampling methods and experimental design (Brown, 2002). These studies are also extremely labour intensive and their costs can be prohibitive. Fortunately, a consistent structural relationship between aboveground and root biomass has been observed across several different forest environments (Bray, 1963; Santantonio et al., 1977). These allometric relationships are closest between coarse root and aboveground 9  biomass (Santantonio, 1990; Steele et al., 1997). Since fine roots comprise only a small portion of the total root biomass, approximation of total root biomass as a function of total aboveground biomass is reasonable, with fine root biomass being added as a proportion of the total root biomass (Li et al., 2003). In an attempt to better understand nutrient cycling and to more easily estimate roots share in total tree biomass and C sequestration, several researchers started to develop general equations for aboveground-root biomass relationships (Kurz et al., 1996; Cairns et al., 1997; Li et al., 2003). Root/aboveground ratios usually vary between 0.20 and 0.30 regardless of latitude, species and soil type (Cairns et al., 1997). However, Kurz et al. (1996) and Li et al. (2003) observed a significant difference in ratios between hardwood and softwood species in Canada, and developed separate equations for them. Today, the carbon budget model of the Canadian forest sector (CBM-CFS3) uses ratios of 0.222 for softwood species, and a non-linear model for hardwood species (Li et al. 2003).  1.5  FERTILIZATION EFFECT ON BIOMASS AND CARBON Fertilization increases aboveground biomass in several different species and plantations  around the world (Chappell et al., 1991; Tanner et al., 1998; Canary et al., 2000; Ingerslev et al., 2001); since C is an essential part of biomass, fertilization is expected to increase C sequestration in aboveground biomass (Birdsey et al., 1993; Huntington, 1995; Canary et al., 2000). Less is known about the effects of fertilization on production, growth and decomposition of fine roots (Prescott et al., 1999; Qualls, 2000; Kalbitz et al., 2000; Neff and Asner, 2001; King et al., 2002). Several studies have shown a decrease in root biomass as a proportion of total biomass  10  after fertilization (Vogt et al., 1986; Sands and Mulligan, 1990; Haynes and Gower, 1995; Misra et al., 1998; Giardina et al., 2004) leading to the suggestion that fertilization reduces belowground allocation. However, a decline in root/aboveground biomass ratios also occurs as stands age (Bernardo et al., 1998; Misra et al., 1998; Coleman et al., 2004; Coyle and Coleman 2005; Coyle et al., 2008). This has led prompted some researchers to suggest that fertilization might simply be generating larger and more developed trees instead of generating a shift in allocation. When developmentally equivalent stands were compared (rather than chronologically similar stands), little to no change was found in root/aboveground biomass ratios between fertilized and non-fertilized stands (King et al., 1999; Coleman et al., 2004; Coyle and Coleman 2005; Coyle et al., 2008). This demonstrates that fertilization does not actually change root allocation as previously thought. It just generates larger trees (which have lower root/shoot ratios then smaller trees). It is now being recommended that comparisons should be conducted between developmentally equivalent stands instead of chronologically equivalent stands for future studies of fertilization, root biomass allocation and C sequestration. Fertilization is also known to increase early wood content and decrease late wood in trees (Smith et al., 1977; Brooks and Coulombe, 2009; Ulvcrona and Ulvcrona, 2011). Nevertheless, in a study of C content among 41 North American species, Lamlom and Savidge (2003) found that C content of early wood is higher than late wood in all species. Therefore, it is assumed that fertilization would at least not decrease the C content of trees. However, further research is needed to more accurately determine the impact.  11  1.6  CARBON CONTENT OF BIOMASS A conversion factor of 50% C in total plant biomass is applied in most C models today  (Wenzl, 1970; Brown and Lugo, 1982; Harmon et al., 1990; Thuille et al., 2000). Birdsey (1990) reported average carbon content of 49.1% to 52.1% in softwood and hardwood species. However, Lamlom and Savidge (2003) found a significant difference in C content between softwood species (47.21% - 55.2%) and hardwood species (46.27% – 49.97%). The average C content of western red cedar and western hemlock was 51.54% and 50.60% respectively. Therefore, each tree species may have a unique C content (Savidge, 2000; Lamlom and Savidge, 2003). Choosing the right C content along with the biomass model is critical to accurately estimating the total C sequestered in a stand.  12  2  OBJECTIVES The objectives of this research were to compare the long-term (22-year) growth  responses of western red cedar and western hemlock plantations on CH and HA sites to N+P fertilization, and to estimate the amounts of C sequestered in tree biomass. Specifically, the research addressed the following questions:   Does fertilizer increase height and volume among all treatments in CH and HA sites?    Does fertilizer response differ between western red cedar and western hemlock?    Does fertilizer response differ among different stand densities?    Which combination of silvicultural practices produced the greatest amount of volume?    How did annual height and volume growth change over the measurement period?    Does fertilizer increase biomass predictions among all treatments?    How do different densities affect biomass predictions among all treatments?    Does fertilizer increase C content predictions among all treatments?    Which combination of silvicultural treatments produced the greatest increment in C content?    Which combination of silvicultural treatments produced the greatest total amount of C content?  13  3  MATERIALS AND METHODS  3.1  STUDY AREA The SCHIRP study is situated between the cities of Port McNeill and Port Hardy (50º  60’N, 127º 35’W) on the northern part of the Vancouver Island, British Columbia, Canada. The site is located in the Submontane Very Wet Maritime part of the Coastal Western Hemlock Biogeoclimatic zone (CWHvm1) where elevations do no surpass 600m (Green and Klinka 1994). According to Lewis (1982), the study area has a precipitation average of 1900mm annually, most of which occurring between the months of October and February. These high precipitation levels generate intense summer fog and overcast conditions throughout the year; thus, there are low amounts of direct sunlight in the region (1.5 hours/day in December and 6.4 hours/day in July), and most of the light reaches the trees by diffuse radiation (McKay and Morris, 1985). Average temperatures are 2ºC in January and 14ºC in august, with a mean annual average of 7.9ºC (Prescott et al., 1996). The site is undulating terrain at approximately 50m of elevation. The surface material is mainly composed of deep unconsolidated moraine and fluvial outwash ranging from over 1m deep blankets of overlying sediments to shallow layers with exposed volcanic bedrock. Soils typically are well-drained to imperfectly-drained Duric HumoFerric Podzols with some rocky knolls and wetlands in the depressions (Lewis, 1982). The soil texture ranges from silty clay loams to fine sand with high coarse fragment content. It is also characteristic in this area to find some organic soils of wetland origin as well as Folisols (Negrave et al., 2007). This study analyzed two distinctive forest types in the CWHvm1, CH and HA. CH sites which are mostly dominated by western hemlock and western red cedar with an open  14  uneven-aged structure at the climax stage and irregular canopies. CH sites have a well-developed understory dominated mostly by salal and compact surface organic layers of around 10-45 cm (Negrave et al., 2007). HA sites are at a mid-seral stage with dense, even-aged structure, uniform canopies, very poor understory development and are mostly comprised of amabilis fir and western hemlock. They have a thinner (5 – 10 cm) and more friable surface organic layer than CH sites (Negrave et al., 2007). Based on topographic and mineral soil characteristics, Lewis (1982) could not differentiate between these two distinctive forest types and considered them to be seral stages of the same ecosystem. However, Prescott and Weetman (1994) measured much lower N and P availability in CH forests compared to adjacent HA forests, and concluded that this was responsible for the low productivity of CH sites. It was also observed that CH forest floors tended to have higher levels of moisture in humus than HA floors, leading Prescott et al. (1996) to suggest that excessive moisture may underlie the low nutrient availability in CH sites and cutovers.  3.2  SILVICULTURAL TREATMENTS AND EXPERIMENTAL DESIGN The study sites were CH and HA forests initially logged in 1986, broadcast-burned in  1987 and planted between late 1987 and early 1988. Ninety-six plots were assembled in a 3-km² area; 48 in the CH area and 48 in the HA area. Each plot contained 64 sample trees of the same species, either western hemlock or western red cedar. The treatments applied were fertilization and tree density. The three densities chosen were: 500 stems/ha, 1500 stems/ha and 2500 stems/ha; plot size and tree spacing varied with density. In plots of 500 stems/ha, trees were  15  spaced in a 4.5 x 4.5 m pattern, and the plot size was 36 x 36 m (54 x 54 m including the buffer zone). In the 1500 stems/ha plots, trees were spaced in a 2.6 x 2.6 m pattern, and plots were of 21 x 21 m (32 x 32 m including buffer zone). Lastly, the 2500 stems/ha plots were spaced at 2 x 2 m, and the total size was 16 x 16 m (36 x 36 m including buffer zone). Buffer zones were planted at the same time and density as the original plots. Four rows of buffer trees on each side were implemented for the 500 and 1500 stems/ha plots and ten rows of buffer trees were implemented in the 2500 stems/ha plots. Fertilizer was applied in by multiple applications. At the time of planting, plots received 60g of slow-release Nutricote® per seedling which provided 10 g of N, 2.5 g of P and 5 g of K. Fertilizer was spread in a 15-cm radius around each seedling; the total amount of fertilizer per hectare varied depended on the tree density in the plot. A second application was done five growing seasons later (early 1993). On this occasion 225 kg/ha of N (urea 46:0:0, N:P:K) and 75 kg/ha of P (triple superphosphate 0:45:0, N:P:K) was applied by helicopter broadcast. A last broadcast application was done after eleven growing seasons (early 2004); an extra 225 kg/ha of N (urea 46:0:0, N:P:K) was applied. The experiment was arranged in a fully crossed factorial combination of 2 x 3 x 2: two species (hemlock or red cedar); three levels of density (500, 1500 and 2500 stems/ha); and two types of fertility (control or fertilized). Each forest type (CH or HA) was divided into four blocks, and each of the twelve possible combinations of species-density-fertility was replicated in each block. In total each forest type had 48 plots; four replications of twelve different treatment combinations. All combinations were randomly assigned within each block.  16  3.3  DATA COLLECTION, VOLUME AND PERIODIC ANNUAL INCREMENT CALCULATION  The height and diameter of all trees in the 96 plots were measured in late 1997, 2002 and 2009. Height was measured to the nearest cm using a hypsometer Vertex III® from Haglof©. Diameter was measured at breast height (1.3 m above root collar) using mechanical calipers from Haglof©. Tree volume was calculated using BC Ministry of Forest’s taper equations for immature western red cedar and immature western hemlock (British Columbia Forest Service, 1976). Periodic annual increment (PAI) rates were calculated as:  Where:  Y = Yield (height and volume) at specific measurement year T = Year of measurement  3.4  BIOMASS AND CARBON CALCULATION Total volume calculated previously was first transformed into total aboveground biomass  using updated volume-to-biomass regression coefficients provided by the BC Ministry of Forests and Range (Kivari et al., 2011). These regression coefficients were divided into separate aboveground tree sections (bole, branch, bark and foliage), and were selected based on BEC  17  zone and tree species. Total aboveground biomass was estimated based on the sum of the biomass of all tree sections. Root biomass was estimated using a linear regression equation created by Li et al. (2003) and being used currently in the Carbon Budget Model of the Canadian Forest Sector (CBMCFS3). The equation is shown below:  Where:  RBs = Root Biomass (softwood) ABs = Aboveground Biomass (softwood)  Total biomass was calculated as the sum of total aboveground biomass and root biomass. Total C content was estimated by multiplying total biomass by the conversion factor of 0.5154g C/g biomass for western red cedar and 0.5060g C/g biomass for western hemlock (Lamlom and Savidge, 2003).  3.5  STATISTICAL ANALYSIS In order to analyze the overall growth effect after 22 growing seasons, a general linear  mixed model (PROC Mixed in SAS) was used. The experiment was arranged in a fully crossed factorial combination of 2 x 3 x 2 and a mixed-effects model was applied for each combination  18  within: two species (hemlock or red cedar); three types of density (500, 1500 and 2500 stems/ha); and two types of fertility (control or fertilized): (  Where:  )  (  )  (  )  (  )  = Results of the combination of the ith species, jth density level and kth fertility level. = Overall Mean = Species effect = Density effect = Fertility effect = Residual error  Block was incorporated as a random effect in the model. Significant levels within treatments and their interactions were compared by adjusting the least square means for Tukey’s (HSD) test. This model was applied with respect to the following variables: tree height, stand volume, PAI 1997-2002 and PAI 2003-2009. A natural logarithm (ln(x)) was applied to all variables to homogenize the variances. Tukey’s HSD test was used to analyze the correlation between PAI 1997-2002 and PAI 2003-2009 within single treatments. Significant levels were set as α=0.05 and all analyses were done using SAS version 8.2 (SAS Institute In., Cary, North Carolina, 2001).  19  4  RESULTS Average values for all treatments between 1997 and 2009 are presented in Tables A-1, A-  2 and A-3. Average height development as a function of species and site is shown in Figures 4-1 and 4-2; average volume development as a function of species and site is shown in Figures 4-3 and 4-4. Mixed model analyses of overall averages of height and volume for CH and HA sites are summarized in Table 4-1. Periodic annual increments (PAI) of height and volume of the 1997-2002 period (Table A-4) are compared with their respective 2002-2009 measurements (Table A-4) in Figures 4-5, 46, 4-7 and 4-8; as a function of species and site. Statistical analyses of PAIs are summarized in Tables 4-2 and 4-3.  4.1  FERTILIZER EFFECT ON AVERAGE HEIGHT AND VOLUME After 22 growing seasons, the fertilizer regime applied increased both the average height  and volume for all densities, species and sites compared to the respective control treatments (Table A-3). Differences are statistically significant (Table 4-1) and become increasingly prominent in successive measurements (Figures 4-1, 4-2, 4-3 and 4-4).  4.2  SPECIES X FERTILIZATION INTERACTION On CH sites, total height and volume averages (Table 4-1) show significantly different  growth responses of western red cedar and western hemlock to fertilization. The PAI of height and volume for both periods (1997-2002 and 2002-2009) also significantly differed between red cedar and hemlock on CH sites (Table 4-2). Although western hemlock trees were much smaller 20  than western red cedar trees on the CH control sites, the response of western hemlock to fertilizer was much greater than western red cedar, so that by 2009 western hemlock height was similar to that of western red cedar, and their volume was just slightly lower than western red cedar (Table A-3). On HA sites average total height and volume (Table 4-1), and the PAI of height and volume for both periods (1997-2002 and 2002-2009) (Table 4-3) did not significantly differ among the two species. However, independent of fertilization and stand density, western hemlock averaged much higher total and PAI of height and volume than did western red cedar (Table A-3 and A-4), and the volume of fertilized hemlock on CH was approaching that of unfertilized hemlock on HA (Table A-3).  4.3  STAND DENSITY X FERTILIZATION INTERACTION Average tree height on control (unfertilized) sites decreased at higher stand densities. In  contrast, height growth on fertilized plots was more uniform among the different stand densities (Figures 4-1 and 4-2). Statistical analysis of total height confirmed a significant interaction between fertilization and stand density on CH sites; although p values were low, this interaction was not significant on HA sites (Table 4-1). For PAI of height there was no significant interaction between fertilization and stand density on either CH and HA sites for the early (19972002) period, but during the more recent (2002-2009) period there was a significant interaction at both sites (Tables 4-2 and 4-3). Stand volumes at the higher stand densities (1500 and 2500 stems/ha) were substantially greater than those at the low (500 stems/ha) density after fertilization (Figures 4-3 and 4-4). This is most apparent in 2009 measurements, especially at HA sites. Statistical analysis of total 21  volume indicated significant interaction between stand density and fertilization for HA sites (Table 4-1), however, no significant interactions were found for PAI of volume for both periods (Table 4-3). On CH sites, total volume average and PAI of volume indicated no significant interaction between stand density and fertilization (Tables 4-1 and 4-2).  4.4  OPTIMAL SILVICULTURAL COMBINATIONS The best total volume growth in the entire experiment was fertilized western hemlock  planted at 2500 stems/ha on HA sites (Figure 4-4). After 22 growing seasons, this combination generated the greatest average volume of all treatments (380 m³/ha) (Table A-3), and the best PAI of volume during both time periods (Table A-4). The second greatest volume was fertilized western hemlock planted at 1500 stems/ha on HA sites, which had slightly larger trees than the plots planted at 2500 stems/ha on HA sites (Table A-3) and the best PAI in height during both time periods (Table A-4) (although total average volume fell behind due to the lower number of trees per hectare). Western red cedar provided the best responses on CH sites, whether fertilized or not (Figure 4-3); CH sites did not achieve such great volumes as HA sites (Figure 4-4). The greatest average volume after 22 growing seasons on CH sites was achieved by fertilized western red cedar planted at 2500 stems/ha (140 m³/ha) (Table A-3). The second best treatment was fertilized red cedar at 1500 stems/ha. Western red cedar had a greater volume response to fertilization than western hemlock on CH sites (Figure 4-3).  22  4.5  PERIODIC ANNUAL INCREMENT DIFFERENCES BETWEEN THE 1997-2002 AND 2002-2009 PERIODS  HEIGHT: With respect to height growth, measured as PAI between the two measurement periods (Figures 4-5, 4-6, 4-7 and 4-8) there was a significant (Table A-5) reduction in annual height growth of western red cedar in the control plots, on both CH and HA sites. Height growth rates of fertilized western red cedar at 2500 stems/ha increased during the first measurement period (1997-2002) (Figures 4-5 and 4-6). Changes in growth rates of western hemlock were found only at higher densities (1500-2500 stems/ha), especially in fertilized plots. On CH sites, height growth rate in fertilized 1500 and 2500 stems/ha plots increased, whereas on HA sites, height growth rate decreased in the second period in fertilized 1500 and 2500 stems/ha plots, and in control 2500 stems/ha plots (Figures 4-5 and 4-6).  VOLUME: The latest PAI of volume (2002-2009) significantly increased in fertilized plots compared to earlier (1997-2002) growth rates at CH sites. With the exception of western red cedar at 500 stems/ha, growth rates in control plots were similar during both periods (Figure 4-7). On HA sites, volume growth rates of fertilized western red cedar increased in the second period (20022009). In contrast, growth rates on control sites remained not significantly different during both periods. Western hemlock increased volume growth rates only for fertilized low-to-medium densities (500-1500 stems/ha) plots. At 2500 stems/ha, growth reduced at a rate similar to the first period (1997-2002) and with the exception of western hemlock at 500 stems/ha density, growth rates of trees on control sites were similar during both periods (Figure 4-8). 23  a)  13 12 11  10 9  Cw-F0-500 Cw-F0-1500 Cw-F0-2500 Cw-F1-500 Cw-F1-1500 Cw-F1-2500  Height ( m )  8 7 6 5 4 3 2 1 0 1996  b)  1998  2000  2002  2004  2006  2008  2010  2002  2004  2006  2008  2010  13 12 11 10 9  Hw-F0-500 Hw-F0-1500 Hw-F0-2500 Hw-F1-500 Hw-F1-1500 Hw-F1-2500  Height ( m )  8 7  6 5 4 3 2 1 0 1996  1998  2000  Figure 4.1 Average height development in each treatment at CH sites, 1997 – 2009. a) western red cedar (Cw); b) western hemlock (Hw); control (F0), fertilized (F1); three densities (500, 1500 and 2500 stems/ha); (mean ± S.E.).  24  Height ( m )  a)  Height ( m )  b)  18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 1996  18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 1996  Cw-F0-500 Cw-F0-1500 Cw-F0-2500 Cw-F1-500 Cw-F1-1500 Cw-F1-2500  1998  2000  2002  2004  2006  2008  2010  2002  2004  2006  2008  2010  Hw-F0-500 Hw-F0-1500 Hw-F0-2500 Hw-F1-500 Hw-F1-1500 Hw-F1-2500  1998  2000  Figure 4.2 Average height development in each treatment at HA sites, 1997 – 2009. a) western red cedar (Cw); b) western hemlock (Hw); control (F0), fertilized (F1); three densities (500, 1500 and 2500 stems/ha); (mean ± S.E.).  25  a)  170 160 150 140 130  Volume ( m³ ha-1 )  120 110  Cw-F0-500 Cw-F0-1500 Cw-F0-2500 Cw-F1-500 Cw-F1-1500 Cw-F1-2500  100 90 80 70 60  50 40 30 20 10 0 1996  b)  2000  2002  2004  2006  2008  2010  2002  2004  2006  2008  2010  170 160 150 140 130 120  Volume ( m³ ha-1 )  1998  110  Hw-F0-500 Hw-F0-1500 Hw-F0-2500 Hw-F1-500 Hw-F1-1500 Hw-F1-2500  100 90 80 70 60 50 40  30 20 10 0 1996  1998  2000  Figure 4.3 Average volume development in each treatment at CH sites, 1997 – 2009. a) western red cedar (Cw); b) western hemlock (Hw); control (F0), fertilized (F1); three densities (500, 1500 and 2500 stems/ha); (mean ± S.E.).  26  Volume ( m³ ha-1 )  a)  Volume ( m³ ha-1 )  b)  420 400 380 360 340 320 300 280 260 240 220 200 180 160 140 120 100 80 60 40 20 0 1996  420 400 380 360 340 320 300 280 260 240 220 200 180 160 140 120 100 80 60 40 20 0 1996  Cw-F0-500 Cw-F0-1500 Cw-F0-2500 Cw-F1-500 Cw-F1-1500 Cw-F1-2500  1998  2000  2002  2004  2006  2008  2010  2002  2004  2006  2008  2010  Hw-F0-500 Hw-F0-1500 Hw-F0-2500 Hw-F1-500 Hw-F1-1500 Hw-F1-2500  1998  2000  Figure 4.4 Average volume development in each treatment at HA sites, 1997 – 2009. a) western red cedar (Cw); b) western hemlock (Hw); control (F0), fertilized (F1); three densities (500, 1500 and 2500 stems/ha); (mean ± S.E.).  27  0.80  a)  0.70 0.60  1997-2002 2002-2009  m year-1  0.50  *  * 0.40  * 0.30  *  0.20 0.10 0.00  Cw-F0-500 0.80  b)  0.70 0.60  Cw-F1-500 Cw-F0-1500 Cw-F1-1500 Cw-F0-2500 Cw-F1-2500  1997-2002 2002-2009 *  *  m year-1  0.50 0.40 0.30 0.20 0.10 0.00  Hw-F0-500  Hw-F1-500 Hw-F0-1500 Hw-F1-1500 Hw-F0-2500 Hw-F1-2500  Figure 4.5 Periodic annual increment in height between the two measurement periods on CH sites. a) western red cedar (Cw); b) western hemlock (Hw); control (F0), fertilized (F1); three densities (500, 1500 and 2500 stems/ha); asterisks indicate significant different averages (p < 0.05, mean ± S.E.). 28  1.00  a)  0.90  1997-2002  0.80  2002-2009  0.70  *  m year-1  0.60 0.50  *  *  0.40  *  0.30 0.20 0.10  0.00  Cw-F0-500 1.00  b)  Cw-F1-500 Cw-F0-1500 Cw-F1-1500 Cw-F0-2500 Cw-F1-2500  0.90  1997-2002  0.80  2002-2009  *  *  0.70  m year-1  0.60  *  0.50 0.40 0.30 0.20 0.10 0.00  Hw-F0-500  Hw-F1-500 Hw-F0-1500 Hw-F1-1500 Hw-F0-2500 Hw-F1-2500  Figure 4.6 Periodic annual increment in height between the two measurement periods on HA sites. a) western red cedar (Cw); b) western hemlock (Hw); control (F0), fertilized (F1); three densities (500, 1500 and 2500 stems/ha); asterisks indicate significant different averages (p < 0.05, mean ± S.E.). 29  16  a)  14 12  1997-2002  *  2002-2009  *  m³ ha-1 year-1  10  * 8 6 4  * 2 0  Cw-F0-500 16  b)  14  12  Cw-F1-500  1997-2002  2002-2009  *  10  m³ ha-1 year-1  Cw-F0-1500 Cw-F1-1500 Cw-F0-2500 Cw-F1-2500  * *  8 6 4 2 0  Hw-F0-500  Hw-F1-500  Hw-F0-1500 Hw-F1-1500 Hw-F0-2500 Hw-F1-2500  Figure 4.7 Periodic annual increment in volume between the two measurement periods on CH sites. a) western red cedar (Cw); b) western hemlock (Hw); control (F0), fertilized (F1); three densities (500, 1500 and 2500 stems/ha); asterisks indicate significant different averages (p < 0.05, mean ± S.E.). 30  30  a)  25  1997-2002 2002-2009  *  m³ ha-1 year-1  20  * 15  10  * 5  0  Cw-F0-500 30  b)  25  Cw-F1-500  Cw-F0-1500 Cw-F1-1500 Cw-F0-2500 Cw-F1-2500  1997-2002 *  2002-2009  m³ ha-1 year-1  20  15  10  5  * *  0  Hw-F0-500  Hw-F1-500  Hw-F0-1500 Hw-F1-1500 Hw-F0-2500 Hw-F1-2500  Figure 4.8 Periodic annual increment in volume between the two measurement periods on HA sites. a) western red cedar (Cw); b) western hemlock (Hw); control (F0), fertilized (F1); three densities (500, 1500 and 2500 stems/ha); asterisks indicate significant different averages (p < 0.05, mean ± S.E.). 31  Table 4.1 Mixed model analyses of average height and volume for CH and HA sites. Treatment CH Sites: Height *Spp *Fert *Den Den x Spp *Spp x Fert *Den x Fert Den x Spp x Fert  NDF  DDF  F  p  1 1 2 2 1 2 2  33 33 33 33 33 33 33  28.17 437.23 35.1 1.72 53.71 4.64 2.06  <0.0001* <0.0001* <0.0001* 0.1941 <0.0001* 0.0167* 0.1430  1 1 2 2 1 2 2  33 33 33 33 33 33 33  111.73 544.6 5.63 0.63 48.09 2.65 3.07  <0.0001* <0.0001* 0.0079* 0.5404 <0.0001* 0.0853 0.0598  1 1 2 2 1 2 2  33 33 33 33 33 33 33  50.52 68.46 0.25 0.95 2.68 3.2 0.2  <0.0001* <0.0001* 0.7840 0.3962 0.1110 0.0535 0.8162  1 1 2 2 1 2 2  33 33 33 33 33 33 33  23.67 95.02 31.93 2.42 3.76 12.13 0.59  <0.0001* <0.0001* <0.0001* 0.1042 0.0611 <0.0001* 0.5610  Volume *Spp *Fert *Den Den x Spp *Spp x Fert Den x Fert Den x Spp x Fert HA Sites: Height *Spp *Fert Den Den x Spp Spp x Fert Den x Fert Den x Spp x Fert Volume *Spp *Fert *Den Den x Spp Spp x Fert *Den x Fert Den x Spp x Fert  NDF = Numerator degrees of freedom, DDF = Denominator degrees of freedom; Spp = Species, Fert = Fertilization, Den = Density; asterisks indicate p value < 0.05. 32  Table 4.2 Mixed model analyses of periodic annual increment in height and volume for CH sites by measurement period (1997-2002 and 2002-2009). Treatment CH Sites: PAI-H (1997-2002)  NDF  DDF  F  p  *Spp *Fert *Den Den x Spp *Spp x Fert Den x Fert Den x Spp x Fert  1 1 2 2 1 2 2  33 33 33 33 33 33 33  24.13 52.49 18.16 0.50 8.23 1.58 1.46  <0.0001* <0.0001* <0.0001* 0.6086 0.0071* 0.2205 0.2472  1 1 2 2 1 2 2  33 33 33 33 33 33 33  1.19 319.95 16.68 0.70 23.73 8.91 0.16  0.2825 <0.0001* <0.0001* 0.5049 <0.0001* 0.0008* 0.8518  1 1 2 2 1 2 2  33 33 33 33 33 33 33  107.28 277.31 3.47 1.22 50.13 1.64 2.86  <0.0001* <0.0001* 0.043* 0.3076 <0.0001* 0.2088 0.0712  1 1 2 2 1 2 2  33 33 33 33 33 33 33  85.78 601.53 5.00 0.42 34.70 2.72 2.12  <0.0001* <0.0001* 0.0127* 0.6592 <0.0001* 0.0806 0.1362  PAI-H (2002-2009) Spp *Fert *Den Den x Spp *Spp x Fert *Den x Fert Den x Spp x Fert PAI-V (1997-2002) *Spp *Fert *Den Den x Spp *Spp x Fert Den x Fert Den x Spp x Fert PAI-V (2002-2009) *Spp *Fert *Den Den x Spp *Spp x Fert Den x Fert Den x Spp x Fert  NDF = Numerator degrees of freedom, DDF = Denominator degrees of freedom; Spp = Species, Fert = Fertilization, Den = Density; asterisks indicate p value < 0.05. 33  Table 4.3 Mixed model analyses of periodic annual increment in height and volume for HA sites by measurement period (1997-2002 and 2002-2009). Treatment HA Sites: PAI-H (1997-2002)  NDF  DDF  F  p  *Spp *Fert Den Den x Spp Spp x Fert Den x Fert Den x Spp x Fert  1 1 2 2 1 2 2  33 33 33 33 33 33 33  24.17 43.61 0.25 1.22 2.65 2.51 0.31  <0.0001* <0.0001* 0.7835 0.3084 0.1128 0.0966 0.7332  1 1 2 2 1 2 2  33 33 33 33 33 33 33  20.76 62.58 0.03 1.13 0.06 3.46 0.08  <0.0001* <0.0001* 0.9734 0.3355 0.8035 0.0431* 0.9279  1 1 2 2 1 2 2  33 33 33 33 33 33 33  9.58 50.85 12.88 0.08 0.23 1.85 0.04  0.0040* <0.0001* <0.0001* 0.9204 0.6356 0.1734 0.9620  1 1 2 2 1 2 2  33 33 33 33 33 33 33  7.46 69.53 12.01 0.14 0.05 1.80 0.08  0.0100* <0.0001* 0.0001* 0.8668 0.8225 0.1808 0.9271  PAI-H (2002-2009) *Spp *Fert Den Den x Spp Spp x Fert *Den x Fert Den x Spp x Fert PAI-V (1997-2002) *Spp *Fert *Den Den x Spp Spp x Fert Den x Fert Den x Spp x Fert PAI-V (2002-2009) *Spp *Fert *Den Den x Spp Spp x Fert Den x Fert Den x Spp x Fert  NDF = Numerator degrees of freedom, DDF = Denominator degrees of freedom; Spp = Species, Fert = Fertilization, Den = Density; asterisks indicate p value < 0.05. 34  4.6  BIOMASS AND CARBON Average values for biomass are presented in Table A-6 (CH sites) and A-7 (HA sites),  separated into aboveground tree sections (bole, branch, bark and foliage), aboveground biomass, root biomass and total biomass. Average values for C content are presented in Table A-8 (CH sites) and Table A-9 (HA sites) and are separated into total aboveground carbon, root carbon and total carbon. After 22 growing seasons, biomass (aboveground, root and total) was much greater in fertilized treatments on both CH (Figure 1-1) and HA sites (Figure 1-2). Denser treatments also had greater biomass in all treatments and sites (Figures 1-1 and 1-2) with the exception of nonfertilized hemlock on CH sites, where biomass decreased at 2500 stems/ha (Figure 1-1). Fertilization greatly increased C content in all treatments at all sites (Figure 1-3). The treatments which had the greatest gains in C content relative to controls were western hemlock at 2500 stems/ha on CH sites (2190% increase; Table A-8) and western red cedar at 1500 stems/ha on HA sites (309% increase; Table A-9). Fertilized western hemlock at 2500 stems/ha on HA sites showed the highest amount of C content among all treatments in this study (125.1 Mg C ha1  ; Table A-9). On CH sites, the highest C content was for western red cedar at 2500 stems/ha  (40.569 Mg C ha-1; Table A-8).  35  a)  70 60  Biomass (Mg ha-1)  50  Foliage Branches Root  Bark Wood  40 30 20 10 0 10 20  Cw-F0-500  b)  70 60  Biomass (Mg ha-1)  50  Foliage Branches Root  Cw-F1-500  Cw-F0-1500 Cw-F1-1500 Cw-F0-2500 Cw-F1-2500  Bark Wood  40 30 20 10 0 10 20  Hw-F0-500  Hw-F1-500  Hw-F0-1500 Hw-F1-1500 Hw-F0-2500 Hw-F1-2500  Figure 4.9 Biomass of each component in control (F0) and fertilized (F1) plots at three densities (500, 1500 and 2500 stems/ha) on CH sites. a) western red cedar (Cw); b) western hemlock (Hw).  36  220  a)  200 180  160  Foliage Branches Root  Bark Wood  Biomass (Mg ha-1)  140 120 100  80 60 40 20 0 20 40  Cw-F0-500 220  b)  200 180 160  Foliage Branches Root  Cw-F1-500  Cw-F0-1500 Cw-F1-1500 Cw-F0-2500 Cw-F1-2500  Bark Wood  Biomass (Mg ha-1)  140  120 100 80 60  40 20 0 20  40 60  Hw-F0-500  Hw-F1-500  Hw-F0-1500 Hw-F1-1500 Hw-F0-2500 Hw-F1-2500  Figure 4.10 Biomass of each component in control (F0) and fertilized (F1) plots at three densities (500, 1500 and 2500 stems/ha) on HA sites. a) western red cedar (Cw); b) western hemlock (Hw).  37  100  a)  90 80  Fertilized  Control  70  Mg C ha-1  60  50 62.27 C/N (Kg/Kg)  40 30  65.69 C/N (Kg/Kg)  34.04 C/N (Kg/Kg)  76.70 C/N (Kg/Kg) 45.05 C/N (Kg/Kg)  49.23 C/N (Kg/Kg)  Hw-500  Hw-1500  20 10  0  Cw-500 140  b)  130 120 110  Cw-1500  Cw-2500  Fertilized  Hw-2500 173.50 C/N (Kg/Kg)  Control  163.25 C/N (Kg/Kg)  100  Mg C ha-1  90 111.73 C/N (Kg/Kg)  80 70  84.83 C/N (Kg/Kg)  60 50  37.30 C/N (Kg/Kg)  40 30  23.25 C/N (Kg/Kg)  20 10 0  Cw-500  Cw-1500  Cw-2500  Hw-500  Hw-1500  Hw-2500  Figure 4.11Total Carbon sequestered per treatment at three densities (500, 1500 and 2500 stems/ha). Western red cedar (Cw); western hemlock (Hw); a) CH sites; b) HA sites; data labels = fertilizer efficiency (ratio C/N (Kg/Kg)) 38  5  DISCUSSION The results of this study are consistent with those of earlier studies that reported  positive effects of fertilization on red cedar and hemlock on CH sites (Weetman et al., 1989ab; Prescott and Weetman, 1994; Prescott et al., 1996; Blevins and Prescott, 2002; Bennett et al., 2003). Increases in tree height and volume after fertilization have also been reported earlier on HA sites in the SCHIRP experiment (Pratt et al., 1996; Negrave et al., 2007). This analysis after 22 growing seasons (6 since the last N application and 17 since the last N+P application) supports previous observations of a significant increase in height and volume after fertilization regardless of site type, species and stand density, and reinforces the conclusion that fertilization is a reliable and effective tool to increase nutrient availability and productivity on these sites. The response of hemlock to fertilization has been described as unpredictable by Burns and Honkala (1990) and Brown (2003). However, it has been suggested that this unpredictability in growth response may be linked to P deficiency, and that when properly fertilized with N + P, hemlock has shown steady growth improvements (Bennett et al., 2003; Blevins et al., 2006). Although there is a general positive response among both red cedar and hemlock, previous analysis of CH sites have shown a much greater growth response by hemlock to fertilization compared to red cedar (Weetman et al., 1989ab; Prescott et al., 1996; Bennett et al., 2003). This difference in responses was reinforced by Negrave et al. (2007), who detected a statistically significant interaction between fertilization and species on CH sites. The analysis conducted in this research also found the same significant interaction between fertilization and species in CH sites. The increase in height growth of red cedar was 37.8%, 59.8% and 61.7% (at 500, 1500 and 2500 stems/ha), and in volume of about 219.5%, 351.2% and 333.2% (500, 1500 and 2500 stems/ha). In contrast, fertilization increased hemlock height by 121.4%, 117.6% and 39  198.4% (500, 1500 and 2500 stems/ha), and volume by 1118.9%, 809.7% and 2189.7% (500, 1500 and 2500 stems/ha). On HA sites, there was no significant interaction between fertilization and species. Growth increase due to fertilization were 25.6%, 55.9% and 79.7% (500, 1500 and 2500 stems/ha) for red cedar height, and about 123.5%, 308.6% and 276.5% (500, 1500 and 2500 stems/ha) for red cedar volume. Hemlock on HA sites increased by 29.3%, 65.1% and 68.8% (500, 1500 and 2500 stems/ha) in height, and by 106%, 243% and 193% (500, 1500 and 2500 stems/ha) in volume. Negrave et al. (2007) also reported no interaction between fertilization and species on HA sites. Little is known about density X fertilization interactions in monocultures in the Pacific Northwest. In this study, average tree height at non-fertilized and fertilized sites significantly decreased at higher stand densities on CH sites. Negrave et al. (2007) contended that these conditions generate higher stress and competition in areas where nutrient availability is a growthlimiting factor. Even though negative responses to density are not commonly expected for topheight trees (Oliver and Larson 1996), previous research at CH sites has shown a significantly negative effect of density on both average height, and top-height (Negrave et al., 2007). Also, even after fertilization, average height was still negatively affected by density on CH sites. This could indicate that the increase in nutrient availability did not fully eliminate the effects of stress and competition caused by the high density; although, fertilization is causing a general increase in height. In contrast, average heights on HA sites did not significantly differ among different densities. These differences are most likely due to the much greater nutrient availability on HA sites compared to the low soil nutrient supply capacity of CH sites (Weetman et al., 1989ab;  40  Prescott et al., 1996). The results of density on average height for both CH and HA sites found in this study are consistent with past observations (Negrave, 2004). This study has showed a significant interaction between density and fertilization in average height on CH sites, despite the fact that no evident change in behavioural patterns between fertilization and density was seen. Although this interaction was not observed in the past (Negrave, 2004), it can be justified by the expected faster reaction of hemlock to the new addition of N fertilizer (Weetman et al., 1989ab; Prescott et al., 1996; Bennett et al., 2003), especially at 500 stems/ha. This quick differentiation in the pattern of fertilized hemlock compared to the more predictable and steady decrease of average height at higher densities seen in red cedar and hemlock could have generated enough change to cause this significant interaction between density and fertilization. HA sites, on the other hand, have shown only a small change in behavioural patterns that could justify an interaction between fertilization and density. On non-fertilized HA sites, a small decrease in average height can be noticed for higher densities, and an increase in height at more dense fertilized sites is also evident. However, in this case differences were found to be not significantly different. This result agrees with past observations (Negrave, 2004). Average volumes on CH sites are also clearly impacted by density and fertilization. Commonly, density would impact average volume through the addition of extra trees per hectare. However, non-fertilized red cedar and hemlock volume on CH sites tend to vary little between densities and in some cases an increase in density generated a small reduction in volume. Differently from non-fertilized plots, fertilized plots showed a significant jump in average volume, which translates into higher volumes at higher densities. This is possibly due to the very low nutrient availability on these sites (Prescott et al., 1996) and the extra nutrients provided by 41  the fertilization treatment reducing the amount of nutritional stress of these trees, allowing them to grow with less nutrient competition. On HA sites, average volumes had a much more predictable response among the different densities. Average volumes increased at higher densities regardless of whether fertilization occured. This outcome is most likely due to the much greater nutrient availability on HA sites (Weetman et al., 1989ab; Prescott et al., 1996); however, a fertilization x density interaction was found in this case. Even though volume increased at higher densities in non-fertilized plots, the increase was mild and steady. After fertilization, average volume tended to jump greatly from 500 stems/ha to 1500 and 2500 stems/ha. This interaction was not observed in the last observation (Negrave, 2004), which could indicate that this increase in average volume could possibly be due to the extra application of N fertilization two years after Negrave’s observations. According to this study, the best total volume growth overall was fertilized western hemlock planted at 2500 stems/ha on HA sites, averaging 379.68 m³/ha after 22 growing seasons. This is supported by previous results of Pratt et al. 1996 and Negrave et al. 2007. HA sites have long been reported to have greater nutrient availability (Weetman et al., 1989ab; Prescott et al., 1996) and greater productivity compared to CH sites, regardless of which species chosen (Negrave et al., 2007). Hemlock is generally more productive than red cedar, not only in HA sites but also in most of British Columbia (B.C. Ministry of Forests, 2011), and it is also known to be especially capable of growing in very dense situations with very high productivity rates (Burns and Honkala, 1990). Furthermore, hemlock responds very well to fertilization either in the short (Pratt et al., 1996) or the long term (Negrave et al., 2007). All originally fertilized treatments in the SCHIRP experiment received an extra 225kg/ha of N in early 2004. However, only two years prior to this, the long-term positive effect of the 42  1993 fertilization was still been noticed (Negrave, 2004). Nothing was known about the effects of this new fertilization on growth, and due to age the densest and most productive plots were in the initial stage of crown competition when this occurred. It is important to note that the 2004 fertilization did not include P, unlike the 1993 treatment. The application of P in addition to N fertilizer has been shown to be crucial for reliable positive response of hemlock plantations (Bennett et al., 2002); however, 17 growing seasons has passed since the last P application and little is known about the consequences of this, especially in hemlock. To better understand the after-effects of the additional fertilization, a comparison of annual growth between the two periods (1997-2002 and 2002-2009) was essential. Most significant variables and interactions remained unchanged during the two measurement periods, and only two significant differences were found. First, species no longer significantly impacted on annual height growth in the 2002-2009 period on CH sites. Red cedar generally responds better than hemlock on CH sites (Negrave et al., 2007); however, in the latest measurement period, PAI of height of both species were similar, possibly due to a better initial response of hemlock to the new N application. A faster response of hemlock to fertilization had been suggested previously because of its shallower root profile (Bennett et al., 2002). A density x fertilization interaction was also found in the PAI of height of the 2002-2009 period on both CH and HA sites. During the 1997-2002 period, there was a gradual reduction in annual height growth on CH sites among the higher density stands. Averages were more uniform in the 20022009 period, suggesting that this interaction was possibly caused by the additional fertilization treatment of 2004. However, many plots had already achieved crown closure (Fertilized cedar and hemlock at 2500 stems/ha in HA sites) by the 2002-2009 period on HA sites, and in several cases, competition was also occurring for light. Volume graphs suggested that trees were gaining  43  much greater amounts of volume than in the previous period, and annual height growth values on HA sites were more erratic between the two measured periods. This uncertainty could be the potential cause of this observed new interaction. PAI of height and volume in non-fertilized sites showed a general reduction or nonsignificant change between periods. The only two significant increases noticed were in PAI of volume of red cedar on CH sites and hemlock on HA sites, both at the 500 stems/ha density only. This could indicate that nutrient availability in non-fertilized plots remained similar across the two periods, and only at the lowest stand density and with the most productive species at specific site were the trees able to access a bigger pool of nutrients with time. In the particular case of PAI of height in red cedar, a significant decrease in height growth at all sites was noticed. However, volume growth of red cedar remained steady during the two measurement periods, suggesting that red cedar was exhibiting much greater basal area growth than previously measured. Fertilized stands had much greater variance in response than non-fertilized stands. In PAI of height, fertilized hemlock at higher densities on CH sites had an unusual spike in growth in the latest measurement (2002-2009); this was most likely due to the capacity of hemlock to quickly respond to the fertilizer added during this period. In contrast, PAI of height of fertilized hemlock at higher densities on HA sites significantly decreased. The reason for this could be that these sites had the tallest and biggest trees in the entire experiment. Tree height growth can be relatively independent of stand density, except in extremely crowded conditions (Mitchel, 1975; Hann and Ritchie, 1988; Oliver and Larson, 1996). These trees are now close to, if not already at crown closure, and competition for nutrients and possibly light it is now greater than ever, and fertilization might not be increasing nutrient availability sufficiently to compensate for this. The 44  results of this study in regards of PAI of volume of fertilized red cedar and hemlock at both CH and HA sites, showed a general significant increase in volume growth from the past measurement period (1997-2002). This increase is not as evident in annual height increment, indicating that trees are now increasing more greatly in basal area. This significant spike in annual volume growth was also not seen in the best treatment available (fertilized hemlock at 2500 stems/ha on HA sites), which were already at crown closure. Growing space can be a limiting factor for secondary growth as well (Oliver and Larson, 1996). This could indicate that fertilized hemlock on HA sites is the first example of strong competition for light in this experiment. This experiment suggests an overall significant increase in biomass due to fertilization. Several other studies have also reported increases in tree and stand biomass due to fertilization (Chappell et al., 1991; Tanner et al., 1998; Canary et al., 2000; Ingerslev et al., 2001); Negrave (2004) also measured a significant increase in biomass at these same sites after fertilization. In most cases in this study, denser stands generated greater biomass. However, nonfertilized red cedar and hemlock trees on CH sites had the smallest gain in biomass at higher stand densities, and in one case (non-fertilized hemlock at 2500 stems/ha) a reduction of biomass was noticed. This can be attributed to the low nutrient availability of these sites (Weetman et al., 1989ab; Prescott et al., 1996). The extra trees added by increasing stand density cannot grow fully because of the increased nutritional competition caused by the extra demand (Negrave, 2004). On HA sites, similar impacts occur, but biomass continued to increase because of the higher nutrient availability on these sites. In contrast, when fertilized, biomass on both CH and HA sites increased substantially at higher stand densities. Presumably, nutrient availability has  45  increased to the point where belowground competition between trees is no longer limiting to growth (Negrave, 2004).  CARBON CONTENTS: Carbon content had a direct linear relationship with biomass, and so was greatly increased by fertilization in this study. However, the efficiency of use in sequestering C varied; the additional C sequestered per kg of N was: 34.04, 62.27 and 65.69 C/N (Kg/Kg) for red cedar (500, 1500 and 2500 stems/ha, respectively) and 45.05, 49.23 and 76.7 C/N (Kg/Kg) for hemlock at CH sites. On HA sites, the values were: 23.25, 84.83 and 111.73 C/N (Kg/Kg) for red cedar (500, 1500 and 2500 stems/ha, respectively) and 37.3, 163.25 and 173.5 C/N (Kg/Kg) for hemlock. According to the results of this analysis, the combination of silvicultural treatments which produced the greatest increment in C content due to fertilization was 2500 stems/ha of hemlock on CH sites. This combination produced the greatest relative gain of volume, biomass and C content of all treatments if compared to its non-fertilized counterpart. Carbon content in this treatment increased 2190% due to fertilization. Although this treatment was by far the best case scenario both for increment of C content as well as for efficiency in the use of fertilizer on CH sites, it was not nearly as good as most of all other treatments in HA sites. The numbers above clearly show the much greater efficiency in the use of fertilizer for high density hemlock stands on HA sites. Hemlock at 2500 stems/ha on HA sites only had a relative increment of 193% compared to the non-fertilized counterpart, but by far most efficiently used the fertilizer to capture C. This treatment also produced the greatest total amount of C among all treatments in  46  this experiment (125.1 Mg C ha-1). The values for additional C sequestered per kg of N also highlight the poor efficiency in sequestering C in the low density stands. Although large increments in C were seen in this study due to fertilization, the values for C content and gains are similar to those of high productivity stands in North America (Simpson et al., 1993; Canary et al., 2000; Brown, 2002; Adams et al., 2005; Coyle et al., 2008).  47  6  CONCLUSIONS AND RECOMMENDATIONS Several silvicultural trials have been established and monitored within the SCHIRP  program and silvicultural recommendations have been formed and revisited following each remeasurement. Initially, the main focus was how to improve productivity of CH sites, and control of salal and fertilization was recommended to improve very slow growing hemlock on CH sites (Weetman et al., 1989ab; Prescott and Weetman, 1994; Prescott et al., 1996; Bennett et al., 2002; Blevins and Prescott, 2002; Blevins and Niejenhuis, 2003). However, following the unexpected observations of greater growth response on HA sites, Negrave et al. (2007) concluded that these sites were of much greater interest and that investment should be focused on these sites, whilst on CH sites, red cedar should be planted at moderate densities (<1500 stems/ha) and carry no further investment (Negrave et al., 2007). The results of this analysis support Negrave’s et al. (2007) recommendation - high stand densities on HA sites support the greatest volume production and C sequestration. On HA sites, the recommendation depends on the industry’s choice and future market pricing. Although fertilized red cedar does not grow as fast as hemlock on HA sites, red cedar commands a much higher price in the market (B.C. Ministry of Forests, 2012). Depending on projections, the lower production of red cedar could easily be compensated by the greater aggregated value the timber would bring. In contrast, if the focus is on cheaper production of wood, biomass gain and/or C sequestration, then hemlock would be the better choice. High densities are recommended because this suppresses lateral limbs and understory (Oliver and Larson, 1996), thereby reducing competition and increasing wood quality. Fertilization treatments can be extremely costly and accurate models are necessary to predict growth responses to fertilization treatments. Fertilization during early stages of 48  plantations can be only justified if growth responses are known to be strong and prolonged (Binkley, 1986), and compound interests tends to increase the extra cost of the treatment very quickly. Recommendations should not only be based on mensuration responses, but rather on a combination of productivity and economic. Therefore, in this study, fertilization is only recommended when short rotations or multiple fertilizations are planed (i.e., on HA sites). On CH sites, planting costs should be kept at minimum, possibly even considering natural regeneration instead of planting seedlings.  49  7  CHALLENGES AND FUTURE RESEARCH Much is still unknown in regards to the long-term responses of red cedar and hemlock  to fertilization, and the influence of stand densities and site fertility thereon. For aboveground biomass, some studies suggest that stem shape and taper might be altered by fertilization (Valinger, 1992; Waterworth, 2009); but there is yet to exist taper equations which take into account such conditions. The accuracy of biomass equations is also considered a problem and most equations used to calculate volume-to-biomass are based upon large scales and very little data. Tree productivity is highly dependent on weather (Oliver and Larson, 1996) and the unpredictable changes in weather between different measurement years has the potential to decrease accuracy at the estimation of annual growth average. More research is needed to improve the data pool and thereby reduce error. Despite these shortcomings, estimates of aboveground biomass and C contents are much more reliable than estimates of belowground biomass. More research is needed to test the assumption that biomass of coarse roots is proportional to the aboveground biomass and is largely a function of tree age (King et al., 1999; Coyle and Coleman 2005; Coyle et al., 2008) rather than the result of a shift in allocation following fertilization (Vogt et al., 1986; Sands and Mulligan, 1990; Haynes and Gower, 1995; Misra et al., 1998; Giardina et al., 2004). Even less is known about the changes in fine root production and turnover in response to nutrient amendment. King (2002) has observed in loblolly pine plantations an increased net production of fine roots after fertilization. However, estimates can vary greatly between different methods (Nadelhoffer and Raich, 1992; Makkonen and Helmisaari, 1999; Ostonen et al., 2005) and the lack of a reliable and consistent methodology to estimate fine root turnover throughout most studies creates an almost impossible situation to compare results and to, therefore, better 50  understand these responses. Overall, more research still needed to fully understand forest responses to fertilization and consequently better predict its outcomes not only at aboveground, but mostly important to the belowground level as well.  51  REFERENCES Adams, A., Harrison, R., Sletten, R., Strahm, B., Turnblom, E., and Jensen, C. 2005. Nitrogenfertilization impacts on carbon sequestration and flux in managed coastal Douglas-fir stands of the Pacific Northwest. For. Ecol. Manage. 220: 313-325. Assmann, E. 1961. 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Species  Fertilization  Density (stems/ha)  Height (m)  F0 F1 F0 F1 F0 F1 F0 F1 F0 F1 F0 F1  500 500 1500 1500 2500 2500 500 500 1500 1500 2500 2500  3.32(0.16) 4.74(0.16) 2.97(0.19) 4.76(0.20) 2.81(0.07) 3.84(0.39) 2.44(0.15) 5.41(0.31) 2.05(0.14) 4.25(0.24) 1.52(0.04) 4.37(0.33)  1.68(0.24) 5.74(0.74) 2.96(0.79) 16.03(2.77) 3.73(0.24) 13.00(3.39) 0.38(0.12) 5.61(1.15) 0.42(0.17) 6.28(1.24) 0.12(0.02) 11.87(3.58)  F0 F1 F0 F1 F0 F1 F0 F1 F0 F1 F0 F1  500 500 1500 1500 2500 2500 500 500 1500 1500 2500 2500  3.93(0.56) 4.93(0.34) 3.33(0.28) 5.20(0.36) 2.78(0.64) 4.96(0.33) 5.33(0.72) 6.61(0.26) 4.92(0.81) 7.62(0.16) 4.74(1.11) 7.44(0.55)  3.61(1.22) 7.10(1.62) 5.12(1.28) 23.83(4.92) 7.41(4.43) 31.82(6.02) 5.97(2.22) 12.95(1.16) 13.24(5.23) 47.44(4.41) 19.23(10.15) 63.82(12.92)  Volume (m³/ha)  CH Sites: Cw Cw Cw Cw Cw Cw Hw Hw Hw Hw Hw Hw HA Sites: Cw Cw Cw Cw Cw Cw Hw Hw Hw Hw Hw Hw  Cw = Western Redcedar, Hw = Western Hemlock; F0 = Control, F1 = Fertilized; (standard error in brackets)  61  Table A - 2 Average height and volume per treatment (after 15 growing seasons). Species  Fertilization  Density (stems/ha)  Height (m)  Volume (m³/ha)  F0 F1 F0 F1 F0 F1 F0 F1 F0 F1 F0 F1  500 500 1500 1500 2500 2500 500 500 1500 1500 2500 2500  5.37 (0.30) 7.15 (0.24) 4.53 (0.27) 6.73 (0.30) 4.08 (0.17) 5.72 (0.53) 3.65 (0.13) 8.06 (0.60) 3.17 (0.15) 5.92 (0.50) 2.27 (0.09) 5.95 (0.67)  8.96 (1.53) 22.38 (2.45) 12.69 (2.96) 48.04 (7.71) 14.16 (1.47) 44.37 (10.43) 1.69 (0.30) 21.59 (4.27) 2.38 (0.52) 22.86 (4.79) 1.10 (0.15) 37.55 (12.40)  F0 F1 F0 F1 F0 F1 F0 F1 F0 F1 F0 F1  500 500 1500 1500 2500 2500 500 500 1500 1500 2500 2500  5.85 (0.62) 7.29 (0.50) 5.08 (0.42) 7.66 (0.58) 4.23 (0.88) 7.27 (0.39) 7.65 (0.99) 9.65 (0.31) 7.12 (1.34) 11.68 (0.36) 7.04 (1.72) 11.61 (0.58)  12.21 (3.21) 24.01 (4.84) 18.90 (4.11) 77.16 (15.60) 25.75 (13.61) 100.55 (15.52) 19.84 (7.16) 40.97 (3.31) 42.18 (17.84) 152.72 (15.00) 63.31 (32.49) 194.72 (30.08)  CH Sites: Cw Cw Cw Cw Cw Cw Hw Hw Hw Hw Hw Hw HA Sites: Cw Cw Cw Cw Cw Cw Hw Hw Hw Hw Hw Hw  Cw = Western Redcedar, Hw = Western Hemlock; F0 = Control, F1 = Fertilized; (standard error in brackets)  62  Table A - 3 Average height and volume per treatment (after 22 growing seasons). Species  Fertilization  Density (stems/ha)  Height (m)  Volume (m³/ha)  F0 F1 F0 F1 F0 F1 F0 F1 F0 F1 F0 F1  500 500 1500 1500 2500 2500 500 500 1500 1500 2500 2500  7.51 (0.44) 10.35 (0.28) 6.04 (0.35) 9.65 (0.55) 5.43 (0.34) 8.78 (0.64) 5.43 (0.32) 12.02 (0.97) 4.38 (0.23) 9.53 (0.90) 3.17 (0.15) 9.46 (0.87)  24.33 (4.43) 77.74 (6.06) 28.43 (6.23) 128.27 (18.25) 32.29 (5.02) 139.88 (26.07) 5.56 (0.82) 67.77 (11.27) 8.58 (1.37) 78.05 (16.17) 5.05 (0.81) 115.63 (27.72)  F0 F1 F0 F1 F0 F1 F0 F1 F0 F1 F0 F1  500 500 1500 1500 2500 2500 500 500 1500 1500 2500 2500  8.27 (0.53) 10.39 (0.70) 6.99 (0.54) 10.90 (0.71) 6.21 (1.27) 11.16 (0.62) 10.62 (1.34) 13.73 (0.65) 10.17 (1.97) 16.79 (0.37) 9.72 (2.26) 16.41 (0.70)  29.54 (6.36) 66.02 (11.84) 44.07 (9.38) 180.07 (33.03) 66.18 (36.18) 249.17 (33.95) 48.61 (16.03) 100.11 (11.42) 94.82 (40.13) 325.20 (26.74) 129.58 (62.14) 379.68 (47.11)  CH Sites: Cw Cw Cw Cw Cw Cw Hw Hw Hw Hw Hw Hw HA Sites: Cw Cw Cw Cw Cw Cw Hw Hw Hw Hw Hw Hw  Cw = Western Redcedar, Hw = Western Hemlock; F0 = Control, F1 = Fertilized; (standard error in brackets)  63  Table A - 4 Periodic annual increment in height and volume on CH and HA sites during each measurement period (1997-2002 and 2002-2009). PAI-H (m/year) 1997-2002  PAI-H (m/year) 2002-2009  PAI-V (m³/ha*year) 1997-2002  PAI-V (m³/ha*year) 2002-2009  Fertilization  Density (stems/ha)  Cw Cw Cw Cw Cw Cw Hw Hw Hw Hw Hw Hw  F0 F1 F0 F1 F0 F1 F0 F1 F0 F1 F0 F1  500 500 1500 1500 2500 2500 500 500 1500 1500 2500 2500  0.42 (0.01) 0.48 (0.01) 0.32 (0.01) 0.39 (0.01) 0.26 (0.01) 0.38 (0.01) 0.26 (0.01) 0.53 (0.01) 0.24 (0.01) 0.31 (0.01) 0.18 (0.01) 0.32 (0.01)  0.31 (0.01) 0.46 (0.01) 0.22 (0.01) 0.42 (0.01) 0.20 (0.01) 0.44 (0.01) 0.26 (0.01) 0.56 (0.01) 0.19 (0.01) 0.51 (0.01) 0.14 (0.01) 0.50 (0.01)  1.46 (0.09) 3.32 (0.13) 1.93 (0.12) 6.40 (0.28) 2.08 (0.13) 6.25 (0.35) 0.26 (0.02) 3.18 (0.15) 0.37 (0.03) 3.31 (0.18) 0.19 (0.02) 5.11 (0.31)  2.19 (0.12) 7.92 (0.31) 2.25 (0.14) 11.46 (0.55) 2.57 (0.16) 13.59 (0.79) 0.54 (0.04) 6.63 (0.24) 0.87 (0.06) 7.91 (0.35) 0.51 (0.05) 11.19 (0.52)  HA Sites: Cw Cw Cw Cw Cw Cw Hw Hw Hw Hw Hw Hw  F0 F1 F0 F1 F0 F1 F0 F1 F0 F1 F0 F1  500 500 1500 1500 2500 2500 500 500 1500 1500 2500 2500  0.40 (0.01) 0.47 (0.01) 0.36 (0.01) 0.49(0.01) 0.34 (0.01) 0.45 (0.01) 0.47 (0.01) 0.61 (0.01) 0.44 (0.02) 0.82 (0.01) 0.47 (0.02) 0.82 (0.01)  0.34 (0.01) 0.44 (0.01) 0.27 (0.01) 0.45 (0.01) 0.29 (0.01) 0.54 (0.01) 0.43 (0.01) 0.59 (0.01) 0.43 (0.01) 0.72 (0.01) 0.39 (0.01) 0.66 (0.01)  1.73 (0.11) 3.41 (0.19) 2.76 (0.16) 10.81 (0.55) 3.65 (0.30) 13.78 (0.67) 2.82 (0.17) 5.7 (0.21) 5.83 (0.41) 21.14 (0.69) 8.87 (0.62) 26.32 (0.99)  2.45 (0.16) 6.02 (0.31) 3.59 (0.23) 14.63 (0.84) 5.78 (0.64) 21.27 (1.17) 4.12 (0.24) 8.66 (0.32) 7.52 (0.55) 24.74 (0.96) 9.61 (0.01) 26.77 (1.11)  Species CH Sites:  PAI-H = Periodic annual increment of height, PAI-V = Periodic annual increment of volume; F0 = Control, F1 = Fertilized; Cw = Western Redcedar, Hw = Western Hemlock; (standard error in brackets).  64  Table A - 5 Tukey’s honestly significant difference test of periodic annual increments in height and volume between the two measurement periods (1997-2002 and 2002-2009).  Species  Fertilization  Density (stems/ha)  PAI-H p values between 1997-2002 and 2002-2009  PAI-V p values between 1997-2002 and 2002-2009  F0 F1 F0 F1 F0 F1 F0 F1 F0 F1 F0 F1  500 500 1500 1500 2500 2500 500 500 1500 1500 2500 2500  <0.0001* 0.2650 <0.0001* 0.5120 <0.0001* <0.0001* > 0.9999 0.6790 0.0570 <0.0001* 0.5120 <0.0001*  0.0040* <0.0001* > 0.9999 <0.0001* > 0.9999 <0.0001* 0.6590 <0.0001* 0.9890 <0.0001* > 0.9999 <0.0001*  F0 F1 F0 F1 F0 F1 F0 F1 F0 F1 F0 F1  500 500 1500 1500 2500 2500 500 500 1500 1500 2500 2500  <0.0001* 0.6840 <0.0001* 0.0790 0.0210* <0.0001* 0.5590 0.9960 > 0.9999 <0.0001* 0.0030* <0.0001*  0.3810 <0.0001* > 0.9999 <0.0001* 0.9940 <0.0001* 0.0020* <0.0001* 0.8100 0.0010* > 0.9999 0.9970  CH Sites: Cw Cw Cw Cw Cw Cw Hw Hw Hw Hw Hw Hw HA Sites: Cw Cw Cw Cw Cw Cw Hw Hw Hw Hw Hw Hw  PAI-H = Periodic Annual Increment of Height, PAI-V = Periodic Annual Increment of Volume; F0 = Control, F1 = Fertilized; Cw = Western Redcedar, Hw = Western Hemlock; asterisk indicate p value < 0.05.  65  Table A - 6 Estimated biomass of each tree component (Mg ha-1) on CH sites (after 22 growing seasons). Root Biomass  Total Biomass  7.72 1.62 1.03 0.83 11.20 2.49 Cw-F0-500 24.67 5.19 3.29 2.66 35.80 7.95 Cw-F1-500 9.02 1.90 1.20 0.97 13.09 2.91 Cw-F0-1500 40.70 8.56 5.43 4.39 59.07 13.11 Cw-F1-1500 10.25 2.15 1.37 1.10 14.87 3.30 Cw-F0-2500 44.38 9.33 5.92 4.78 64.41 14.30 Cw-F1-2500 2.25 0.29 0.30 0.12 2.96 0.66 Hw-F0-500 27.46 3.50 3.71 1.44 36.12 8.02 Hw-F1-500 3.48 0.44 0.47 0.18 4.57 1.01 Hw-F0-1500 31.63 4.04 4.28 1.65 41.59 9.23 Hw-F1-1500 2.05 0.26 0.28 0.11 2.69 0.60 Hw-F0-2500 46.85 5.98 6.34 2.45 61.62 13.68 Hw-F1-2500 * Cw = Western Redcedar, Hw = Western Hemlock; F0 = Control, F1 = Fertilized  13.69 43.75 16.00 72.18 18.17 78.71 3.62 44.13 5.59 50.83 3.29 75.30  Treatment*  Wood  Branches  Bark  Foliage  Total Aboveground  Table A - 7 Estimated biomass of each tree component (Mg ha-1) on HA sites (after 22 growing seasons). Treatment*  Wood  Branches  Bark  Foliage  Total Aboveground  Root Biomass  9.37 1.97 1.25 1.01 13.60 Cw-F0-500 Cw-F1-500 20.95 4.40 2.79 2.26 30.40 Cw-F0-1500 13.98 2.94 1.86 1.51 20.29 Cw-F1-1500 57.14 12.01 7.62 6.16 82.92 Cw-F0-2500 21.00 4.41 2.80 2.26 30.48 Cw-F1-2500 79.06 16.62 10.54 8.52 114.74 Hw-F0-500 19.70 2.51 2.66 1.03 25.90 Hw-F1-500 40.57 5.18 5.49 2.12 53.35 Hw-F0-1500 38.42 4.90 5.20 2.01 50.53 Hw-F1-1500 131.77 16.81 17.82 6.89 173.30 Hw-F0-2500 52.50 6.70 7.10 2.75 69.05 Hw-F1-2500 153.85 19.63 20.81 8.05 202.33 * Cw = Western Redcedar, Hw = Western Hemlock; F0 = Control, F1 = Fertilized  3.02 6.75 4.50 18.41 6.77 25.47 5.75 11.84 11.22 38.47 15.33 44.92  Total Biomass 16.62 37.15 24.80 101.33 37.24 140.21 31.65 65.19 61.75 211.77 84.38 247.25  66  Table A - 8 Carbon content of above and belowground biomass in each treatment on CH sites after 22 growing seasons.  Treatment*  Aboveground Carbon (Mg C ha-1)  Root Carbon (Mg C ha-1)  Total Carbon (Mg C ha-1)  5.77 1.28 7.06 Cw-F0-500 18.45 4.10 22.55 Cw-F1-500 6.75 1.50 8.24 Cw-F0-1500 30.44 6.76 37.20 Cw-F1-1500 7.66 1.70 9.37 Cw-F0-2500 33.20 7.37 40.57 Cw-F1-2500 Hw-F0-500 1.50 0.33 1.83 Hw-F1-500 18.28 4.06 22.33 Hw-F0-1500 2.31 0.51 2.83 Hw-F1-1500 21.05 4.67 25.72 Hw-F0-2500 1.36 0.30 1.66 Hw-F1-2500 31.18 6.92 38.10 * Cw = Western Redcedar, Hw = Western Hemlock; F0 = Control, F1 = Fertilized Table A - 9 Carbon content of above and belowground biomass in each treatment on HA sites after 22 growing seasons.  Treatment*  Aboveground Carbon (Mg C ha-1)  Root Carbon (Mg C ha-1)  Total Carbon (Mg C ha-1)  Cw-F0-500 7.01 1.56 8.57 Cw-F1-500 15.67 3.48 19.15 Cw-F0-1500 10.46 2.32 12.78 Cw-F1-1500 42.74 9.49 52.23 Cw-F0-2500 15.71 3.49 19.20 Cw-F1-2500 59.14 13.13 72.27 Hw-F0-500 13.11 2.91 16.02 Hw-F1-500 27.00 5.99 32.99 Hw-F0-1500 25.57 5.68 31.24 Hw-F1-1500 87.69 19.47 107.16 Hw-F0-2500 34.94 7.76 42.70 Hw-F1-2500 102.38 22.73 125.11 * Cw = Western Redcedar, Hw = Western Hemlock; F0 = Control, F1 = Fertilized 67  Table A - 10 Average basal area per treatment.  Species  Fertilization  Density (stems/ha)  F0 F1 F0 F1 F0 F1 F0 F1 F0 F1 F0 F1  500 500 1500 1500 2500 2500 500 500 1500 1500 2500 2500  F0 F1 F0 F1 F0 F1 F0 F1 F0 F1 F0 F1  500 500 1500 1500 2500 2500 500 500 1500 1500 2500 2500  Basal Area (m²/ha) 1997  Basal Area (m²/ha) 2002  Basal Area (m²/ha) 2009  CH Sites:  Cw Cw Cw Cw Cw Cw Hw Hw Hw Hw Hw Hw  0.65 (0.07) 2.63 (0.39) 2.00 (0.24) 6.02 (0.58) 1.20 (0.30) 4.07 (0.81) 5.46 (0.87) 12.91 (1.93) 1.59 (0.10) 4.79 (0.45) 4.75 (1.16) 12.4 (2.67) 0.21 (0.06) 0.73 (0.11) 2.11 (0.36) 5.64 (0.85) 0.30 (0.11) 1.27 (0.24) 2.79 (0.50) 7.60 (1.36) 0.10 (0.01) 0.72 (0.09) 5.14 (1.22) 12.07 (2.62)  5.74 (0.94) 16.64 (1.05) 7.50 (1.38) 26.13 (3.16) 8.86 (1.12) 29.00 (4.20) 1.84 (0.18) 12.55 (1.41) 3.55 (0.45) 16.79 (2.58) 2.55 (0.32) 24.65 (3.65)  HA Sites: Cw Cw Cw Cw Cw Cw Hw Hw Hw Hw Hw Hw  1.21 (0.38) 2.36 (0.50) 1.94 (0.43) 7.76 (1.37) 2.67 (1.47) 10.37 (1.71) 2.02 (0.63) 4.38 (0.33) 4.76 (1.59) 13.94 (1.12) 6.49 (2.99) 18.14 (2.92)  3.28 (0.78) 6.19 (1.12) 5.48 (0.97) 19.03 (3.31) 7.29 (3.30) 25.43 (3.55) 4.93 (1.39) 9.72 (0.61) 10.69 (3.40) 29.54 (2.35) 14.89 (6.08) 36.39 (4.25)  6.44 (1.28) 13.47 (1.98) 10.27 (1.68) 34.02 (5.63) 14.27 (6.28) 44.47 (5.19) 9.01 (2.18) 16.86 (1.28) 17.08 (4.86) 43.41 (2.96) 22.84 (8.13) 50.45 (4.37)  Cw = Western Redcedar, Hw = Western Hemlock; F0 = Control, F1 = Fertilized; (standard error in brackets)  68  

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