Many ecological models of the structure and dynamics of species distributions are based on the assumption that species are most abundant at the center of their geographic range and least abundant at range margins. Moreover, it is often assumed that species are more stressed and vulnerable to environmental change at range margins. These assumptions are widely accepted but are based on very little empirical evidence. Current models that seek to project shifts in species ranges in response to climate change assume that species at their range margins are limited primarily by climate. This Doctoral Dissertation Research Improvement project will test the validity of this assumption for trees growing in the southern Appalachian Mountains by assessing the relationship between tree growth, climate, disturbance, and species interactions near the center and margins for several dominant tree species. Annually resolved dendroecological data will be used to conduct comprehensive analyses of spatial and temporal variability in tree-growth response and forest-stand dynamics over decades to centuries. The overall goals of this research are to evaluate the impact of climate and disturbance processes on the composition, structure, and dynamics of Appalachian oak-pine forests and to determine if these impacts vary relative to the position within geographic ranges. Forest inventory and tree-ring data collected from sites located in national forests, national parks, and private forest reserves throughout the central and southern Appalachian Mountains will used to compare patterns of tree establishment, growth, and mortality near the center and margins of several species ranges. These comparisons will provide information regarding the factors that limit the geographic distribution of these tree species and how the ranges of the tree species are likely to change in response to climate and disturbance.
Analyzing the relative importance of climate and disturbance on vegetation dynamics of these sites will increase basic understanding of the limits to species distributions and inform conservation efforts aimed at predicting and mitigating the response of tree species to climate change. Dramatic changes in species distributions caused by climate change have been documented and are projected to continue in response to rapid global warming. Climate change poses numerous threats to ecosystem health, including loss of biodiversity, spread of exotic species, and extinction of species. Mitigation of these threats requires an understanding of the mechanisms that influence the structure and dynamics of species ranges. This project will provide information concerning factors that limit the geographical distribution of Appalachian tree species near their southern range boundary and enable more accurate projections of species range dynamics to be modeled. As a Doctoral Dissertation Research Improvement award, this award also will provide support to enable a promising student to establish a strong independent research career.
