A Dendrochronology Study of East and West Facing Slopes in Glacier
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A Dendrochronology Study of East and West Facing Slopes in Glacier National Park: A Case Study Examine the Effects of Microclimates in High Elevation Subalpine Fir (Abies lasiocarpa) Stands University of Victoria, Geography Department Geography 477 Michael Guindon & Mike Kit November 8, 2012 1 Abstract Subalpine fir (Abies lasiocarpa) tree cores were collected from two Englemann Spruce Subalpine Fir sites in Glacier National Park, British Columbia. Dendrochronology techniques were used to examine growth limiting factors at each site. Low series intercorrelation values were calculated for most trees, indicating that there were no common growth patterns found between tree cores. Therefore, individual trees within the stand behave differently and are influenced by microsite conditions. Differences in exposure, topography, soils, nutrient availability, moisture level, competition and genetics are likely mechanisms causing different growth rates between trees in both study sites. The behaviour of trees within these sites contradicts most subalpine and alpine tree growth studies and has implications for the Biogeoclimatic Ecosystem Classification system and climate change modelling in subalpine environments. 2 Table of Contents Abstract…………………………………………………………………………... 1 Table of Content…………………………………………………………………. 2 List of Figures & Tables…………………………………………………………. 3 Acknowledgements……………………………………………………………… 4 1.0 Introduction……………………………………………....................................... 5 2.0 Literature Review……………………………………......................................... 5 2.1 Dendrochronology…………………………………….................................... 5 2.2 Biogeoclimatic Ecosystem Classification……………………………………. 6 2.3 Influence of Microsites on Tree Growth…………………………………….. 7 3.0 Methods……………………………………......................................................... 9 3.1 Study Site……………………………………................................................. 9 3.2 Sample Collection…………………………………….................................... 11 3.3 Sample Preparation & Analysis……………………………………................ 13 4.0 Results……………………………………………................................................ 13 5.0 Discussion…………………………………………….......................................... 15 5.1 Cross Dating…………………………………………..................................... 15 5.2 Exposure as a Limiting Factor…………………………................................ 16 5.3 Topography as a Limiting Factor…………………………............................. 17 5.4 Pedogenesis as a Limiting Factor…………………………............................. 17 5.5 Competition and Genetic Variation as Limiting Factors…….......................... 18 5.6 Implications for Dendrochronology and the BEC System……....................... 19 6.0 Conclusion……………………………………………......................................... 20 7.0 References……………………………………………......................................... 22 3 List of Figures and Tables Figure 1: Map depicting the locations of both study sites within Glacier National Park 10 Figure 2: Images of study sites where samples were collected. (a) Abbott Ridge (b) Avalanche Crest 11 Figure 3: Common distribution of tree species at Abbott Ridge study site. 11 Figure 4: Common distribution of tree species at Avalanche Crest Field Site 12 Figure 5: Tree core sample taken at Abbot Ridge. Note the diameter of tree. 12 Table 1: Series intercorrelation values from tree cores collected at both sites 14 Table 2: Autocorrelation and mean sensitivity values from tree cores collected at both sites 14 Figure 6: Comparison of series intercorrelation, autocorrelation and mean sensitivity values 15 calculated for Abbot Ridge and Avalanche Crest 4 Acknowledgements We would like to extend our thanks to Dr. Dan Smith, Dr. James Gardner and Dr. David Atkinson for organizing the field course in Glacier National Park and for the invaluable learning experience they provided us. We would also like to thank Bethany Coulthard for her guidance and assistance with our field work, data analysis and interpretation of our results. The success of our research study would not have been possible without her assistance. Lastly, we would like to thank the remaining teaching assistants and Parks Canada staff for making this learning experience possible. 5 Introduction 1.0 Introduction The growth of subalpine fir trees (Abies lasiocarpa) in the Canadian Rockies is limited by a number of factors at both the stand and individual tree level. Most dendrochronology research describes temperatures during the growing season as the dominant factor affecting tree growth at high elevations (Harsch & Bader, 2011; Martinelli, 2004). As is evident on the landscape, individual trees can behave differently within a stand due to the presence of different microclimates. Factors such as exposure, snow accumulation, sunlight, temperatures, topography and nutrient availability vary across a stand and can result in different growth rates in trees within close proximity to one another (Hotmeier & Broll, 2010; Peterson, Peterson & Ettl, 2002; Resler, Butler & Malanson, 2005; Malanson et al., 2007). Unfortunately, the classification of ecosystems based on similar characteristics promotes a more generalized approach when describing how these systems function. This approach results in the creation of generalized models to characterize the effects of global warming on the movement of tree line in alpine environments (Hamann & Wang, 2006). These models are not entirely accurate as individual stands can behave differently. Through the use of dendrochronology techniques, it is possible to analyze tree growth responses across a stand and to predict the future growth responses of trees based on predicted climate models. The purpose of this study is (1) to use dendrochronology to determine the influence of climate on the growth of Abies lasiocarpa on east and west facing slopes in Glacier National Park and (2) to determine the likely factors affecting the growth of Abies lasiocarpa on an individual tree level. 2.0 Literature Review 2.1 Dendrochronology 6 Dendrochronology techniques can be used to understand the influence of climatic conditions on tree growth within a particular area (Gruber, Baumgartner, Zimmermann & Oberhuber, 2008). By measuring variability in tree ring growth, it is possible to correlate variations in tree ring width with climate data (Splechtna et al., 2000). This analysis allows researchers to understand how climate influences tree growth in these environments. Multiple dendrochronology studies have been conducted in subalpine and alpine environments (Peterson, et al., 2002; Martinelli, 2004) with the assumption that climate is generally the limiting factor affecting tree growth at high elevation. Based on the analysis of 28 tree ring chronologies, it was determined that the growth of trees in the subalpine of the Cascade and Olympic Mountains is limited primarily by short growing seasons (Peterson et al., 2002). This trend is apparent in multiple dendrochronology studies; however, other factors can influence tree growth dynamics within stands in the alpine environment. 2.2 Biogeoclimatic Ecosystem Classification The Biogeoclimatic Ecosystem Classification (BEC) system is a scheme developed to classify ecosystem types in British Columbia (Pojar, Klinka & Meidinger, 1987). The BEC system groups similar areas based primarily on climate, vegetation and soil (Pojar, Klinka & Meidinger, 1987). The areas examined in this study fall within the Engelmann Spruce Subalpine Fir (ESSF) BEC zone. The use of the BEC system is challenged for a number of reasons, including its tendency to invoke a linear thinking to complex ecosystems (Haeussler, 2011). This linear approach is of particular concern when predicting the effects of climate change on tree line systems, including the ESSF zone. By subdividing ecosystems into homogenous spatial units, it is expected that these zones will respond to climate change in the same manner (Hamann & Wang, 2006). Based on climate change models, the ESSF Zone is predicted to shift 86m in 7 elevation by 2025 and 225m by 2085 (Hamann & Wang, 2006). As will be discussed in the following section, stand dynamics at tree line are impacted by a number of variables, highlighting the potential for individual Abies lasiocarpa stands to behave differently to changes in climate conditions. 2.3 Influence of Microsites on Tree Growth Tree growth is controlled by climate and local environment factors, with individual trees responding differently to environmental stressors based on local site conditions (Tessier, Guibal & Schweingruber, 1997; Lloyd & Fastie, 2002; Peterson et al., 2002; Malanson et al., 2007; Stueve et al., 2011; Elliott, 2012). These environmental influences can limit individual tree growth within a stand, concealing large scale climate conditions. Based on this influence, it is possible to have small scale tree growth variation in an area, with limiting factors varying between individual trees. Local topography and the distribution of trees throughout a site results in the formation of microsites by either protecting or exposing individuals to stressors including sunlight, wind, snowpack and moisture (Resler et al., 2005; Malanson et al., 2007; Stueve et al., 2011). Microsites can be created by cliffs, avalanches, other trees, draws and streams. In these locations, tree growth in individuals varies depending on varying degrees of exposure to various environmental conditions such as light and wind. Exposed trees are prone to desiccation and cold induced photo-inhibition as well as other mechanical