DISSERTATION RESEARCH: Testing the limits: effects of climate and competition on conifer distributions at Mount Rainier

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How will climate change affect our forests? Rising temperatures could result in changes in the distribution of species. Indeed, scientists have already observed that many species ranges have moved upward in latitude and altitude as global temperatures have increased during the past century. However, competition with neighboring trees can also affect the distribution of species, with the result that range changes may be more difficult to predict than would be expected based only on the direct effects of temperature. This project will address these issues by examining how climate (including temperature, rain, and snow) interacts with competition to determine the performance of three common tree species at Mount Rainier National Park. Examination of yearly tree growth and climate data that span the last 100 years indicates that climate determines upper range limits for many tree species, but that other factors are important at lower range limits. These patterns will be tested by transplanting seeds and seedlings of species beyond their current range limits and by removing competitors from some areas. In combination with observational data, these experiments will be used to test the hypothesis that biotic factors, such as competition, are more important at the lower range limit, while abiotic factors, such as temperature, control the upper range limit.Predicting the impacts of climate change on trees is a great challenge for natural resource planners and land managers, whose management plans rely on knowing where species occur now and where they will occur in future decades. This research is directly applicable to the National Park Service, especially at Mount Rainier National Park. Old growth forests in the Park currently offer significant ecosystem services, including carbon sequestration and habitat for rare species, and these studies will provide information about how these important ecosystems may change in the future.