Direct and indirect effects of environmental limitations on white spruce xylem anatomy at treeline

Timo Pampuch,Martin Wilmking,Alba Anadon-Rosell,Mario Trouillier,Jelena Lange

doi:10.5194/egusphere-egu21-15323

Abstract

&lt;p&gt;Treeline ecosystems are of great scientific interest to study the direct and indirect influence of limiting environmental conditions on tree growth. However, tree growth is complex and multidimensional, and its responses to the environment depend on a large number of abiotic and biotic factors and their interactions.&lt;/p&gt;&lt;p&gt;In this study, we analyze the growth and xylem anatomy of white spruce trees (&lt;em&gt;Picea glauca&lt;/em&gt; [Moench] Voss) from three treelines in Alaska (one warm and drought-limited, and two cold and temperature-limited treelines). We hypothesized (1) no difference between the treelines regarding the relationship between tree DBH and height, yet in general (2) faster growing trees at the warmer site. Additionally, we expected to find differences in xylem anatomical traits with trees from the drought-limited site having adapted to drought conditions by (3) forming smaller lumen diameter due to water deficit but (4) a higher xylem anatomical density due to higher temperatures and a longer vegetation period.&lt;/p&gt;&lt;p&gt;Regarding growth in height and diameter, trees at the drought-limited treeline grew relatively (1) taller and (2) faster compared to trees at the temperature-limited treelines. Raw xylem anatomical measurements showed (3) smaller lumen diameters and (4) higher density in trees at the drought-limited treeline. However, using linear mixed-effect models, we found that (i) traits related to water transport like lumen diameter were not significantly correlated with the actual amount of precipitation during the vegetation period but with tree height. We also found that (ii) traits related to mechanical support like density were mainly positively influenced by the mean temperature during the vegetation period.&lt;/p&gt;&lt;p&gt;The differences in lumen diameter found in the raw data can be explained by differences in the growth rates of the trees, since lumen diameter at the lower part of the tree stem needs to increase over time with increasing tree height. The greater wood density at the drought-limited treeline is probably caused by the higher temperature that leads to more biomass production, and potentially longer vegetation periods.&lt;/p&gt;&lt;p&gt;Our study shows that xylem anatomical traits in white spruce can be directly and indirectly controlled by environmental conditions. While lumen diameter is not directly influenced by environmental conditions but indirectly through tree height, other traits like anatomical density show a direct correlation with environmental conditions. Our results highlight the importance of approaching tree growth in a multidimensional way and considering direct and indirect effects of environmental forcing.&lt;/p&gt;

Highlights

Boreal forests play a crucial role for the global carbon cycle, are an important source for timber and non-timber products and provide several ecosystem services (Arneth et al, 2010; Gauthier et al, 2015; Tagesson et al, 2020)
Tree height reconstructions showed that trees from Warm—Dry Treeline (W-D) on average grew faster in height and had a different allometry: they tended to grow taller when compared to trees from Cold— Dry Treeline (C-D) or C-M of the same diameter (Figure 2)
As tree height itself is influenced by various environmental conditions, especially competition, temperature, and water availability (Lines et al, 2012; Fransson et al, 2021), it can be assumed that a large part of the height effects that we found correspond to indirect effects of environmental conditions on xylem anatomical traits related to water transport

Summary

Introduction

Boreal forests play a crucial role for the global carbon cycle, are an important source for timber and non-timber products and provide several ecosystem services (Arneth et al, 2010; Gauthier et al, 2015; Tagesson et al, 2020). Treelines are characterized as the edge of the habitat at which trees are able to grow. This edge is caused by environmental limitations

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Discussion

Conclusion