From genes to landscapes: the distribution of western conifers
Date
2013
Authors
Bisbing, Sarah M., author
Cooper, David, advisor
Angert, Amy, committee member
Binkley, Dan, committee member
Sibold, Jason, committee member
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Abstract
Managing and conserving forest ecosystems under a rapidly changing climate will require an understanding of the drivers of species distributions across a gradient of temporal and spatial scales. My dissertation research evaluated the relationship between distributional patterns of tree species and the processes driving these patterns from local to continental scales. I addressed three questions: 1) Which local abiotic and biotic processes are most important in determining the distribution of tree species along a hydrologic gradient in southeast Alaska? 2) How is genetic variation partitioned across the range of Pinus contorta, and is this variation explained by geographic or landscape variables? 3) How will Pinus contorta respond to predicted climate change? At the local scale, I assessed the role of abiotic and biotic constraints in limiting three tree species (Pinus contorta, Picea sitchensis, and Tsuga heterophylla) along a hydrologic gradient in southeast Alaska. I used a Bayesian hierarchical model to identify the strongest predictors of species' occurrence and biomass. Model predictions identified abiotic variables, including soil nitrogen, pH, and depth to water, as the primary factors limiting species' success in anaerobic wetland ecosystems. Competition was identified as the limiting factor in aerobic forest ecosystems. At the continental scale, I quantified the impact of historic evolutionary processes in shaping patterns of genetic diversity across the range of Pinus contorta, a widespread and morphologically variable species. I estimated gene flow and assessed the effect of the landscape on population structure. Gene flow is high across the range of the species, and patterns of variation are most strongly influenced by landscape barriers to gene flow and the environmental variation associated with its heterogeneous range. This suggests that, despite widespread gene flow, subspecies are adapted to local conditions. I then used correlative and mechanistic species distribution models to evaluate potential, future habitat suitability at the species and subspecies levels of Pinus contorta. Model results predict that P. contorta will maintain a large portion of its current habitat, but two of the more geographically constrained subspecies will lose a significant portion of suitable habitat. My work provides an understanding of the ecological and evolutionary processes shaping tree species distributions across a gradient of temporal and spatial scales, from historic to current timeframes and local to range-wide extents. Results from my research show that different processes determine patterns of distribution across this gradient of scales. Linking these patterns and processes will be essential for forest management and conservation in light of a rapidly changing climate.
Description
Rights Access
Subject
species distribution model
Pinus contorta
species distributions
forest ecology
landscape genetics