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An evaluation of constraints to treeline advance across multiple scales in the Canadian Rocky Mountains

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Title: An evaluation of constraints to treeline advance across multiple scales in the Canadian Rocky Mountains
Author: Davis, Emma L.
Department: Department of Geography, Environment and Geomatics
Program: Geography
Advisor: Gedalof, Ze'ev
Abstract: Plant distributions are changing on a global scale as a result of climate change, with many species shifting to higher latitudes and elevations in response to warming temperatures. Variability exists, however, in how individual species are impacted by climate change, and unexpected responses are commonly observed due to the influence of other biotic and abiotic drivers on species distributions. Understanding factors that influence plant distributions is important given their role in regulating biogeochemical cycles and ecosystem functions, as well as their cultural and aesthetic value. Accurate predictions of species ranges are contingent on knowledge of the full suite of environmental processes that determine the spatial and temporal dynamics of plant distributions. Mountain environments, where plants can be growing at their environmental limits, are expected to be particularly sensitive to climate change. I applied a mixed-methods approach to study various factors influencing the distributions of alpine treeline systems in the Canadian Rocky Mountains (CRMs), where treeline advance has been observed over the past century. Tree-ring analysis was first used to gain insight into the climatic determinants of treeline establishment and advance by analyzing samples collected from nine treeline ecotones in the CRMs. A greenhouse and growth chamber study was then conducted to determine if differences in the properties of soils collected across four treeline ecotones impacted the viability of subalpine tree seedlings. Finally, a seed addition study was implemented at the same study locations to assess how seed availability, herbivory, microsite limitations, and microclimate influence seedling establishment within and beyond the current treeline. Both climatic and non-climatic factors are expected to constrain future treeline advance in the Rocky Mountain region. Tree-ring analyses revealed that substantial advance occurred at all sites throughout the 20th-century, but that the rate of climate warming exceeded the pace of treeline movement. The field and greenhouse experiments suggest that a combination of unsuitable soil and microclimate conditions for seedling establishment are currently the main limitations to treeline advance. Finally, variability in treeline dynamics was observed between study locations, indicating that the responses of individual treelines to future climate change are likely to vary at the site level.
Date: 2018-06
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