EAGER: Demographic models of interior western U. S. tree distributions - climate in the context of competition, disturbance, and natural enemies

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While a century of ecological research has greatly refined our understanding of the factors influencing the distributions of species on the landscape, we have yet to understand their relative roles. This problem has become increasingly urgent in an era of global change, particularly climate change. This project will evaluate the importance of some of the fundamental factors thought to govern tree species distributions and how their importance varies across geographic and environmental gradients. Four dominant and widespread tree species of interior western US forests will be studied. Population modeling will be used to integrate the many factors influencing individual tree growth, survival, and regeneration to capture the forces determining the full life cycle. This project will contribute to developing the scientific workforce and to better management of public lands through the training of a postdoctoral scholar, outreach to K-12 students and teachers, and collaboration with US Forest Service land managers. This project will advance the field of population and community ecology by applying a well-established set of tools and ideas from population ecology (demography, perturbation analysis) at a new scale, to better understand the forces shaping geographic ranges within a niche framework. The objectives are to evaluate 1) the importance of fundamental factors thought to govern species distributions: climate, competition, disturbance, and their interactions; and 2) how their importance varies across geographic and environmental distributions. The analysis will be focused on Pinus edulis, P. contorta, P. ponderosa, and Pseudotsuga menziesii, which span a range of competition-stress-ruderal strategies. Regressions of three key vital rates will be combined to form integral projection models using range-wide data on marked individuals in ~70,000 Forest Inventory and Analysis (FIA) plots across the eight states of the contiguous western US.