The interactive effects of climate and disturbance on tree species distributions
Date
2015
Authors
Renwick, Katherine M., author
Rocca, Monique E., advisor
Hobbs, N. Thompson, committee member
Sibold, Jason, committee member
Stohlgren, Thomas J., committee member
Journal Title
Journal ISSN
Volume Title
Abstract
Climate change is expected to alter species distributions as ranges shift to track favorable temperature and precipitation regimes. Range shifts are already being observed across a wide range of taxa, but many species are not keeping pace with the rate of recent climate warming. This is particularly true for tree species, which often experience significant migration lags due to a variety of non-climatic factors that can hinder range expansion or delay range retreats. Because many other species depend on trees for food or habitat, migration lags in tree species may have cascading impacts on a wide range of taxa that would otherwise face few barriers to migration. The importance of understanding how climate change will affect tree species distributions prompted several related research questions: 1) What factors contribute to the observed lags in tree species distributions? 2) Can biotic disturbances accelerate climate-driven shifts at the range margins of trees species? 3) How important is climate in determining landscape-scale vegetation patterns? My dissertation research addresses these questions using an integrated approach that draws on exiting literature, field sampling, and statistical models to inform our understanding of potential climate change impacts on tree species distributions. Observations of contemporary tree species migrations occurring throughout the world suggest that migration lags are pervasive and can be caused by a wide variety of abiotic factors and biotic processes. Tree migrations are likely to occur episodically when migration constrains are overcome, resulting in temporal variability in the migration rate. Physical disturbances such as fire can reduce competition and initiate periods of rapid change, but the effects of biological disturbances such as insect outbreaks are more nuanced. A case study examining the impacts of climate change and mountain pine beetle (Dendroctonus ponderosae) disturbance at lodgepole pine (Pinus contorta) range margins suggests that while biological disturbances may accelerate a range retreat by killing mature trees, they do not initiate range expansion for the target species. The impact of non-climatic constraints on current tree species distributions was also evident at the landscape scale, and climatic variables alone proved insufficient to explain patterns of co-occurrence among tree species. Together, these findings suggest that Rocky Mountain tree species will not uniformly shift upward in elevation as the climate continues to warm. Range shifts will likely be episodic and idiosyncratic, and forecasts based solely on climate data may over-estimate the rate and under-estimate the landscape-scale heterogeneity of potential distribution changes.
Description
Rights Access
Subject
forest ecology
climate change
range shift