Aspect and slope influence plant community composition more than elevation across forest–tundra ecotones in subarctic Canada

• Published in: Journal of Vegetation Science
• Main Authors: Dearborn, Katherine D., Danby, Ryan K.
• Other Authors: Kikvidze, Zaal, Natural Sciences and Engineering Research Council of Canada, W. Garfield Weston Foundation, Queen's University
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2017
• Subjects: Canada; Yukon; Subarctic; Tundra
• Online Access: http://dx.doi.org/10.1111/jvs.12521; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fjvs.12521; https://onlinelibrary.wiley.com/doi/pdf/10.1111/jvs.12521

Abstract Questions How does tree line community composition vary between elevations, aspects and slope angles in the alpine subarctic and what are the specific abiotic factors governing this variability? How do species richness and rates of community turnover vary from low to high elevation across the forest–tundra ecotone? What do the results indicate about future vegetation change? Location Kluane Region, southwest Yukon, Canada. Methods We surveyed plant communities and measured key abiotic variables across forest–tundra ecotones in six alpine valleys, each with a north‐ and a south‐facing slope, in two mountain ranges of southwest Yukon. We used NMS to identify patterns in plant community composition and infer which abiotic variables drive these patterns. We calculated species richness and community dissimilarity at regular elevational intervals to assess trends in richness and rates of community turnover within the ecotone. Results Plant communities varied more with aspect and slope angle than they did with elevation. Aspect‐related differences were driven by warmer soil temperatures and deeper active layers on south‐ compared to north‐facing slopes, while differences related to slope angle occurred only on north‐facing slopes and were driven by soil moisture. Species richness increased with elevation on north‐facing slopes and showed no trend with elevation on south‐facing slopes. Rates of community turnover were higher on south‐facing than north‐facing slopes. Conclusions Plant community composition within the forest–tundra ecotone is driven primarily by soil temperature and, to a lesser extent, soil moisture, both of which vary more in relation to aspect and slope angle than they do between forest and tundra elevations. We recommend that models of vegetation change in subarctic alpine regions address the possibility of change occurring at different rates and in different directions depending on the topographic characteristics of each slope.