Climate variability and treeline dynamics in Yellowstone and Grand Teton National Parks
Schrag, Anne Michelle
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Understanding the impacts of climate variability on high-elevation forests is of great importance due to the interest in upper treeline as an indicator of future change in protected mountain systems. While the location of upper treeline is primarily controlled by temperature, investigation of local treeline processes reveals considerable complexity in the spatial and temporal responses of species to various climatic parameters. The focus of the work presented in this thesis is to increase the understanding of the bioclimatic drivers of upper treeline species distribution and abundance in Yellowstone and Grand Teton National Parks. The species of interest in this ecosystem include: subalpine fir (Abies lasiocarpa), Engelmann spruce (Picea engelmannii) and whitebark pine (Pinus albicaulis). The abundance of whitebark pine is of particular interest due to its role as a food source for grizzly bears (Ursus arctos) and its recent decline in many systems due to the combined impacts of an introduced pathogen and native insect outbreaks.Using information on the current distribution of these treeline species, as well as data from soil surveys and spatially interpolated climate data, I was able to model future occurrence of treeline species across the Yellowstone landscape under various climate scenarios. These models provide managers with predictions of possible landscape-scale changes in subalpine forests over the next century. In addition, I used the influence of biophysical setting to examine the spatial and temporal response of species composition and abundance to moisture availability. Moisture availability has been shown to affect local processes, such as growth and recruitment of conifer species, on short temporal scales. Thus, processes that are more closely linked to moisture may serve as important indicators of future change. The results of this research provide information about alpine treeline dynamics that will allow managers to make knowledgeable decisions to protect these forest resources in the face of future change.