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.

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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

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Figure 2: Images of study sites where samples were collected. (a) Abbott Ridge (b) Avalanche Crest

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Figure 3: Common distribution of tree species at Abbott Ridge study site.

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Figure 4: Common distribution of tree species at Avalanche Crest Field Site

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Figure 5: Tree core sample taken at Abbot Ridge. Note the diameter of tree.

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Table 1: Series intercorrelation values from tree cores collected at both sites

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Table 2: Autocorrelation and mean sensitivity values from tree cores collected at both sites

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Figure 6: Comparison of series intercorrelation, autocorrelation and mean sensitivity values

calculated for Abbot Ridge and Avalanche Crest

15

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.

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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

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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 damage (Resler et al., 2005; Malanson et

al., 2007; Holtmeier & Broll, 2010; Harsch & Bader, 2011; Stueve et al., 2011). Topography and

environmental conditions also influence the distribution of soil nutrients across a stand, resulting

in variable amounts of nutrients available to trees within a stand (Malanson et al., 2007; Stueve

et al., 2011; Elliott, 2012). Depending on the degree of variability within a site, the impact of

8

microsites on individual tree growth within forest stands can be quite high.

Mechanical controls on tree growth often result in a negative feedback response as they

lead to biomass loss through damage and dieback (Harsch & Bader, 2011). Avalanches are

powerful disturbance agents, reducing tree growth and tree density by opening up the forest in

subalpine areas (Christian et al., 2007). In these open environments, wind is a particularly

powerful limiting agent as it creates microclimates by altering local temperatures, altering

moisture levels through increased transpiration and evaporation, and causing mechanical damage

such as flagging, sand or ice blasting (Holtmeier & Broll, 2010). Neighbouring interactions can

also provide mechanical protection for individual trees, as a windward tree is capable of

protecting sheltered trees from wind damage or other hazards (Alftine & Malanson, 2004).

Depending on the amount of exposure, wind can significantly reduce growth rates in individual

trees within a stand.

Varying moisture levels can influence the rate of growth of individual trees within a stand.

Snowpack levels can vary within an area based on their location across the landscape, either

promoting or discouraging snow accumulation (Peterson et al., 2002). The addition of moisture

from snow aids in soil formation and produces favourable conditions for the growth of conifers

(Whiteside & Butler, 2010). On the contrary, high snowpack can also result in a shorter growing

season, limiting the growth rate of trees (Harsch & Bader, 2011). Moisture content is controlled

by climate, local topography and geomorphological conditions, with various features resulting in

different rates of water accumulation or dispersal in an area (Malanson et al., 2007; Elliot, 2012).

One study conducted in Alaska noted that there is a positive correlation between tree growth and

proximity to water because thermoregulatory effects from water bodies created a favourable

microclimate (Stueve et al., 2011). This is further confirmed by the fact that extremely dry areas

9

result in reduced growth rates in trees (Lloyd & Fastie, 2002; Peterson et al., 2002; Malanson et

al., 2007; Elliott, 2012). Overall, varying moisture levels within a stand can influence the growth

rates of trees in an area, which is largely controlled by local climate and topography.

Biotic interactions also influence tree growth rates, with competition and genetic variability

resulting in different growth patterns throughout a stand (Tessier et al., 1997; Alftine &

Malanson, 2004; Malanson et al., 2007; Stueve et al., 2011). Competition between individual

trees for energy, nutrients, moisture and space results in different growth rates, especially when

individuals have an advantage over other trees (Stueve et al., 2011). Also, genetic variation

causes individuals to behave differently compared to neighbouring trees. This is particularly

evident in a trees tolerance level to limiting factors such as nutrient or moisture availability

(Tessier et al., 1997; Malanson et al., 2007). Trees that are able to adapt to local conditions and

compete with other species will have higher growth rates compared to other individuals.

3.0 Methods

3.1 Study Site

Tree ring cores were collected from Abies lasiocarpa trees in Glacier National Park.

Glacier National Park is located within the Selkirk and Purcell Ranges of the Columbia

Mountains in southwestern British Columbia. Sample sites were located below tree line, within

an Engelmann Spruce Subalpine Fir Ecoregion, in the high subalpine zone at Abbott Ridge and

Avalanche Crest (Figure 1)

Abbott Ridge samples were collected at N51o 15.572’ W117

o 30.565’, on the western

aspect of Mount Abbott (Figure 2 & Figure 3). The tree cores were all collected within a draw

with a stream running through the base. The draw was likely part of an ancient rock fall deposit,

over which soils and forest have developed. Outside the draw, mountain hemlock (Tsuga

10

mertensiana) was more abundant. Within the draw, Abies lasiocarpa was dominant, with

decreasing numbers of Abies lasiocarpa present with increasing elevation. Three distinct cohorts

of Abies lasiocarpa were found, with diameters of 40-50cm, 20-30cm and less than 15cm. A

young cohort of Tsuga mertensiana appeared to be developing within the stand. There was a

high occurrence of downed trees at this site.

Samples from Avalanche Crest were collected at N51o 66.228’ W117

o 29.014’ (Figure 2 &

Figure 4) representing an eastern aspect of Avalanche Mountain. Tree cores were taken from a

relatively high graded slope surface. Abies lasiocarpa and Engelmann spruce (Picea

engelmannii) were the dominant species, with sparse Tsuga mertensiana throughout the site. On

all trees, branches were mostly found on the downslope side where sunlight was most available.

As with Abbott Ridge, this site was also located on an old fall deposit. Downed trees and a

cohort of predominantly Picea engelmannii snags were also found on this site.

Figure 1: Map depicting the locations of both study sites within Glacier National Park.

11

Figure 2: Images of study sites where samples were collected. (a) Abbott Ridge (b) Avalanche Crest

Figure 3: Common distribution of tree species at Abbott Ridge study site.

3.2 Sample Collection

Thirteen tree ring samples were collected using a standard 5 mm increment borer at both study

sites (Figure 3). Abies lasiocarpa trees were selected if they had a minimum diameter at breast

height (DBH) of 40 cm, were alive and healthy. Two samples were taken from each tree (180

degrees to each other) perpendicular to the slope in order to ensure that slope creep would not

affect ring width (Figure 5).

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Figure 4: Common distribution of tree species at Avalanche Crest Field Site

Figure 5: Tree core sample taken at Abbot Ridge. Note the diameter of tree.

13

3.3 Sample Preparation and Analysis

Once relatively dry, tree core samples were glued to wooden boards. Cores were sanded

using a belt sander beginning with 80 grit sandpaper, continuing with progressively finer

sandpaper, to expose tree rings as per standard dendrochronology procedures (Speer, 2010). The

samples were then scanned and measured using WinDendro software, a digital tree ring

measurement program.

Ring measurements were analyzed using COFECHA, a computer program designed to

analyze tree ring measurements for cross dating and statistical analysis (Grissino-Mayer, 2001).

Due to technical problems, only 11 cores were analyzed from each site. Initial cross dating and

measurement corrections were contracted to a specialist in the University of Victoria Tree Ring

Laboratory. Based on statistical outputs, it was determined that there were no common growth

patterns within the tree rings and that cross dating of our samples was not possible.

4.0 Results

Series intercorrelation (SI) values were low in most tree cores at both study sites (Table

1). The mean SI value was 0.179 at Abbott Ridge and 0.303 at Avalanche Crest. As a result of

these low numbers, it was not possible to cross date samples taken from the same trees. Of the 22

trees examined, only four of these had significant SI values (AR05, AR13, AC04 & AC10).

Since the computed SI values were low and the cores do not correlate with other trees, it was not

possible to cross date the trees across the stand. Only AC04 and AC10 were able to cross date,

with an overall series intercorrelation of 0.491.

Within individual trees, autocorrelation values were high while mean sensitivity values

were low (Table 2). The mean autocorrelation value was 0.730 at Abbot Ridge and 0.707 at

Avalanche Crest. On the other hand, the average mean sensitivity value was 0.233 at Abbot

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Ridge and 0.218 at Avalanche Crest. By examining these two stands, it is evident there are no

significant differences in autocorrelation and mean sensitivity values at both stands. See Figure 6

for a comparison of the mean SI, autocorrelation and mean sensitivity values for both sites.

Table 1: Series intercorrelation values from tree cores collected at both sites

Abbot Ridge Avalanche Crest

Tree ID SI Value Tree ID SI Value

AR01 0.168 AC01 0.287

AR02 0.053 AC02 0.095

AR03 -0.016 AC03 0.282

AR04 0.438 AC04 0.514

AR05 0.163 AC05 0.350

AR06 0.182 AC06 0.231

AR07 0.101 AC07 0.150

AR08 0.143 AC08 0.321

AR09 0.021 AC09 0.233

AR10 0.264 AC10 0.498

AR11 0.455 AC11 0.377

Table 2: Autocorrelation and mean sensitivity values from tree cores collected at both sites

Abbot Ridge Avalanche Crest

Tree ID Autocorrelation Mean

Sensitivity Tree ID

Autocorrelation Mean

Sensitivity

AR01 0.447 0.237 AC01 0.635 0.283

AR02 0.927 0.205 AC02 0.78 0.285

AR03 0.794 0.276 AC03 0.582 0.175

AR04 0.848 0.230 AC04 0.577 0.206

AR05 0.688 0.306 AC05 0.914 0.212

AR06 0.663 0.244 AC06 0.799 0.262

AR07 0.861 0.185 AC07 0.557 0.248

AR08 0.752 0.232 AC08 0.860 0.191

AR09 0.771 0.188 AC09 0.380 0.196

AR10 0.677 0.240 AC10 0.900 0.174

AR11 0.855 0.221 AC11 0.788 0.162

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Figure 6: Comparison of series intercorrelation, autocorrelation and mean sensitivity values

calculated for Abbot Ridge and Avalanche Crest

5.0 Discussion

5.1 Cross Dating

Stand growth is thought to be controlled by a limiting factor which affects all individual trees in a

similar manner (Speer, 2010). If climate is the limiting factor affecting tree growth in an area, it would be

possible to correlate tree ring growth with local climate data. However, tree ring growth is determined by

both climate and ecological factors (Tessier et al., 1997). When it is not possible to match tree growth to

climate data it is assumed that ecological or environmental effects are limiting tree growth. Cross dating

between samples collected from Abbott Ridge and Avalanche Crest was not possible, signifying that no

stand-wide limiting factor exists, or at least micro-limiting factors are more limiting compared to climate

conditions. It was hypothesized that Abies lasiocarpa growth in both sites would be limited by climatic

fluctuations; however, it was not possible to cross date our samples. The low series intercorrelation

16

values calculated in COFECHA from tree cores at both sites indicate that tree growth in both

stands is a function of individual factors, rather than stand wide climate influences. This does not

mean that climate influences are irrelevant; rather it signifies that other factors are more

influential in controlling the rate of growth of Abies lasiocarpa at both sites.

The presence of different microsites and genetic variability within Abies lasiocarpa at both study

sites are likely contributing to different growth patterns in individual trees. The concept of thresholds is

very pertinent to this investigation, as it is possible that individual trees are responding to the same

environmental factors differently due genetic variations (Tessier et al., 1997; Malanson et al., 2007). As

well, patch scaled tree stands react differently to large scale factors such as climate or temperature due to

certain site specific variables. These physical micro-factors alter individual responses to factors in a

similar way that genetic thresholds alter growth behaviour. Micro-scale growth limiting factors could be

due to abiotic or biotic elements, resulting in to the development of microsite conditions within a stand

(Tessier et al., 1997; Lloyd & Fastie, 2002; Peterson et al., 2002; Malanson et al., 2007; Stueve et al.,

2011; Elliott, 2012).

5.2 Exposure as a Limiting Factor

Exposure levels at Abbott Ridge and Avalanche Crest contributed to different growth rates in

individual trees as a result of mechanical and physiological influences. Mechanical factors disrupt tree

growth and can lead to broken branches, topping, blowdown and sand and ice blasting (Holtmeier &

Broll, 2010). Downed trees were present throughout both study sites, likely as a result of wind and

avalanche disturbance. Physiological disruptions through wind action can lead to altered local climate and

moisture. Variations in temperature across a site, created by differential wind action, can lead to enhanced

or reduced growth depending on local topography. Certain geomorphic features, such as the draw at

Abbott Ridge, would protect tree specimens from wind exposure depending on their location within the

draw. High wind flow leads to increased transpiration and evaporation (Holtmeier & Broll, 2010) and the

removal of moisture from the system inhibits tree growth in areas limited by moisture (Lloyd and Fastie,

17

2002). The variations in climate as a result of exposure levels on both sites likely contribute to differential

growth rates amongst trees in the stand.

5.2 Topography as a Limiting Factor

Topographic relief from draws, boulders and trees were present at both Abbott Ridge and

Avalanche Crest, contributing to variations in growth rates among individual trees. Variations in

topography encourage conditions where individuals will have different exposure levels from potential

growth altering factors (Resler et al., 2005). Exposure to growth factors affects tree growth differently

depending on the factor. Sunlight for example is beneficial up to a threshold level, with both low and high

sun exposure limiting growth (Malanson et al., 2007). The draw within the Abbott Ridge study site was

of particular importance when considering the effects of exposed versus protected trees. Trees on the

slope down into the draw experience more exposure than trees found within the basin. Highly exposed

trees witness more sunlight and less protection from wind. The microclimate within the draw basin is also

different compared to what would be found throughout the rest of the subalpine stand. The presence of a

draw within the Abbott Ridge site contributed to variations in growth rates throughout the stand. The tree

stand at both sites also creates topographical relief from wind for protected trees behind windward trees

(Resler et al., 2005). At both Abbott Ridge and Avalanche Crest, a high amount of downed trees was

documented. When a tree is removed from the stand a gap is left in the canopy, exposing once protected

individuals to elements such as wind or sunlight. The differences in topography across the stand likely

contributed to variations in growth across the stand.

5.4 Pedogenesis as Limiting Factors

Soil development is not homogeneous, and thus, nutrient availability and moisture content are not

evenly distributed throughout the forest canopy (Elliott, 2012). Soils within Abbott Ridge and Avalanche

Crest would have different nutrient concentrations and moisture levels depending on their location within

the stand. Precipitation levels in Glacier National Park are high (1700-2100mm annually), with

approximately 68% of precipitation falling as snow (Environment Canada, 1984). The high

18

amount of snowfall in this region influences moisture levels within soils. The addition of

moisture from snow aids in soil formation and produces favourable conditions for the growth of

conifers (Whiteside & Butler, 2010). Topography and canopy openings throughout both sites

influence the snowpack depth throughout the forest stand. Within the Abbot Ridge site, there was

an intermittent stream present, which likely directs a considerable amount of snowmelt during

the warmer months. This stream impacts moisture levels throughout the site and would create

more optimal conditions for conifer growth in areas with optimal moisture levels. As well,

depressions and steep slopes throughout the site can result in high water levels in some areas and

the rapid movement of water in other areas. Canopy openings within the site increase sunlight

exposure, resulting in drier soils in these regions (Carter & Smith, 1987). Abies lasiocarpa grow

best in low light conditions where moisture levels are higher (Carter & Smith, 1987). Differences

in light exposure throughout a stand can influence growth rates between individual trees within a

stand. Exposure to frost followed by intense sunlight can result in depressions in photosynthesis

for trees growing in exposed sites (Maher & Germino, 2006). Furthermore, when nutrient or

water supply is reduced, sudden or abrupt decreases in yearly growth-ring increments occur

(Bollschweiler & Stoffel, 2010). Although moisture levels, canopy openings and soil profiles

were not examined at either site, differences in these characteristics throughout the site may have

a more direct influence on tree growth when compared to larger scale climate influences.

5.5 Competition and Genetic Variation as Limiting Factors

Competition and genetic variations in individual trees at both sites can lead to differential

growth rates amongst tree species. Competition amongst trees for light, nutrients and moisture is

an important factor in high elevation environments (Holtmeier & Broll, 2010). In these

environments, resources are limited, and having a competitive advantage over other trees is

beneficial for growth. Competition with other vegetation for water and nutrients can result in

19

decreased growth levels in areas where competition is high (Lloyd & Fastie, 2002; Harsch &

Bader, 2011). Genetic variations amongst individual trees can also influence growth rates in both

stands. Trees that are more equipped to deal with local stressors, including decreases in nutrient

and moisture availability, will likely have high growth rates compared to individuals unable to

cope with these stressors (Tessier et al., 1997; Malanson et al., 2007). Interspecific differences in

photosynthetic tolerances to light can impact tree growth and stress tolerance in alpine

environments (Maher & Germino, 2006). Within both stands, understory vegetation and the

presence of other trees likely resulted in competition between individuals, contributing to

varying growth rates amongst trees. Unfortunately, detailed notes for individual trees were not

taken and the genetic variation throughout the stand was not examined, making it impossible to

confirm these responses. However, variations in growth rates amongst individual Abies

lasiocarpa were likely influenced by both of these factors.

5.6. Implications for Dendrochronology and BEC System

The low series intercorrelation values calculated in COFECHA from tree cores at both

sites indicate that tree growth in both stands is a function of individual factors, rather than stand

wide climate influences. Much of the research conducted in subalpine and alpine environments

demonstrate that growth rates at tree line are most influenced by growing season temperatures,

with factors such as moisture and nutrient availability being secondary (Harsch & Bader, 2011).

However, this was not evident in tree cores taken from Abbott Ridge and Avalanche Crest. High

autocorrelation values in the majority of trees on the site indicate that growth in trees is highly

correlated with events in prior years. On the other hand, low mean sensitivity values indicate that

the variability within the rings is low. There were no considerable differences in calculated

statistics for both sites, indicating that trees at both sites are likely influenced by similar factors

and that individual tree growth is largely controlled by factors other than climate. Based solely

20

on the examination of tree cores on both sites, it is not possible to determine the limiting factors

for individual trees within the site. The variations in growth rates within the stand are likely a

result of a combination of exposure, topography, soil, competition and genetic variation

throughout the stand. This contradicts other research that indicates that climate is the dominant

limiting factor in subalpine and alpine environments. Although, some studies have found that the

sensitivity of high-latitude tree growth to temperatures has declined in recent decades, with non-

climatic factors or factors other than temperature becoming increasingly important limits to tree

growth (Lloyd, Fastie, 2002). This sensitivity change can influence the growth of trees in the

subalpine and alpine zones of high latitude areas, including areas in Glacier National Park. As

mentioned earlier, the BEC system promotes a linear approach to understand stand complex

ecosystems (Haeussler, 2011). Based on our study, it is evident that ESSF stand dynamics can be

influenced by a variety of factors, affecting individual trees within a stand differently. Climate

change models will have to take these types of stands into consideration in order to more

accurately predict the responses of tree line environments to global warming.

6.0 Conclusion

In conclusion, this study highlights the influence of microsites on the growth of individual

Abies lasiocarpa trees in the subalpine of Glacier National Park. Although growing season

temperatures are generally the dominant mechanism influencing tree growth at high elevation;

other factors can result in variable growth rates throughout a stand. Factors such as topography,

exposure, soils, competition and genetic variation can have a greater influence on tree growth in

individual stands compared to larger scale climate patterns. As was evident at Abbott Ridge and

Avalanche Crest, small scale variations were the dominant factors influencing growth patterns in

Abies lasiocarpa. This study highlights the need to take both stand level and individual tree level

21

scales into consideration when modelling the response of alpine environments to global

warming. The overall accuracy of this study could have been increased in a number of ways. Our

results are based on the analysis of 11 tree cores from each site; however, the inclusion of more

tree cores would have increased the statistical significance of our results and would have made it

possible to make more definite conclusions. Furthermore, knowing the locations of individual

trees and having detailed notes on potential factors influencing growth rates for each tree would

have allowed for a more detailed analysis of growth factors in these areas. Unfortunately, this

information was not recorded as it was hypothesized that growing season temperatures were the

limiting factor in both stands. Lastly, sampling additional locations within the valley and

collecting cores from trees of other species would have made it possible to better understand tree

growth patterns in this area. Overall, this study highlighted the presence of microsites within

Abies lasiocarpa stands in Glacier National Park, and can be used by resource managers to

further understand tree line dynamics within this area.

22

References

Alftine, K.J. & Malanson, G.P. (2004). Directional positive feedback and pattern at an

alpine tree line. Journal of Vegetation Science. 15(1), 3-12.

Bollschweiler, M. & Stoffel, M. (2010). Tree rings and debris flow: Recent 7

developments, future directions. Progress in Physical Geography. 34(5), 625-645.

Carter, G.A. & Smith, W.K. (1987). Microhabitat comparisons of transpiration and

photosynthesis in three subalpine conifers. Canadian Journal of Botany. 66(5),

963-969.

Christian, R., Susanne, H., Dominik, K. & Peter, B. (2007). Natural avalanche disturbance

shapes plant diversity and species composition in subalpine forest belt. Journal of

Vegetation Science. 18(5), 735-742.

Elliott, G.P. (2012). The role of thresholds and fine-scale processes in driving upper

treeline dynamics in the Bighorn Mountains, Wyoming. Physical Geography. 33(2)

129-145.

Environment Canada. (1984). Ecological Land Classification of Mount Revelstoke and

Glacier National Parks, British Columbia. Vol. I: Integrated Resource Description.

Edmonton: Environment Canada.

Grissino-Mayer, H.D. (2001). Evaluating Crossdating Accuracy: A Manial and Tutorial

for the Computer Program COFECHA. Tree-Ring Research. 57(2), 205-221.

Gruber, A., Baumgartner, D., Zimmermann, J. & Oberhuber, W. (2009). Temporal

dynamic of wood formation in Pinus cembra along the alpine treeline ecotone and

the effect of climate variables. Trees. 23(3), 623-635.

Hamann, A. & Tongli, W. (2006). Potential Effects of Climate Change on Ecosystems

and Tree Species Distribution in British Columbia. Ecology. 87(11), 2773-2786.

Harsch, M.A. & Bader, M.Y. (2011). Treeline form - a potential key to understanding

treeline dynamics. Global Ecology and Biogeography. 20, 582-596.

Haeussler, S. (2011) Rethinking biogeoclimatic ecosystem classification for a changing

world. Environmental Reviews. 19, 254-277.

Holtmeier, F. & Broll, G. (2010). Wind as an ecological agent at treelines in North

America, the Alps and the European Subarctic. Physical Geography. 31(3), 203-

233.

Lloyd, A.H. & Fastie, C.L. (2002). Spatial and temporal variability in the growth and

climate response of treeline trees in Alaska. Climate Change. 52, 481-509.

23

Maher, E.L. & Germino, M.J. (2006). Microsite differentiation among conifer species

during seedling establishment at alpine treeline. Ecoscience. 13(3), 334-341.

Malanson, G.P., Butler, D.R., Fagre, D.B., Walsh, S.J., Tomback, D.F., Daniels, L.D.,

Resler, L.M., Smith, W.K., Weiss, D.J., Peterson, D.L., Bunn, A.G., Hiemstra, C.A.,

Liptzin, D., Bourgeron, P.S., Shen, Z. & Millar, C.I. (2007). Alpine treeline of Western

North America: Linking organism-to-landscape dynamics. Physical Geography. 28(5),

378-396.

Martinelli, N. (2004). Climate from dendrochronology: latest development and results.

Global and Planetary Change. 40(1-2), 129-139.

Peterson, D.W., Peterson, D.L. & Ettl, G.J. (2002). Growth response of subalpine fir to

climatic variability in the Pacific Northwest. Canadian Journal of Forest Research.

32(9), 1503-1517.

Pojar, J., Klinka, K. & Meidinger, D.V. (1987). Biogeoclimatic Ecosystem Classification

in British Columbia. Forest Ecology and Management. 22(1), 119-154.

Resler, L.M., Butler, D.R. & Malanson, G.P. (2005). Topographic shelter and conifer

establishment and mortality in an alpine environment, Glacier national Park, Montana.

Physical Geography. 26(2), 112-125.

Speer, J.H. (2010). Fundamentals of Tree Ring Research. Tuscon: University of Arizona

Press.

Splechtna, B.E., Dobry, J. & Klinka, K. (2000). Tree-ring characteristics of subalpine fir

(Abies lasiocarpa (Hook.) Nutt.) in relation to elevation and climatic fluctuations.

Annals of Forest Science. 57(2), 89-100.

Stueve, K.M., Isaacs, R.E., Tyrrell, L.E. & Densmore, R.V. (2011). Spatial variability of

biotic and abiotic tree establishment constraints across a treeline ecotone in the

Alaska Range. Ecology. 92(2), 496-506.

Tessier, L., Guibal, F. & Schweingruber, F.H. (1997). Research strategies in

dendrochronology and dendroclimatology in mountain environments. Climate Change.

36, 499-517.

Whiteside, C.J. & Butler, D.R. (2010). Adequacies and deficiencies of alpine and

treeline studies in the national parks of the western USA. Progress in Physical

Geography. 35(1), 19-42.