Climate change impacts on the distribution and performance of plant species at Mount Rainier

Thesis (Ph.D.)--University of Washington, 2014Ongoing anthropogenic climate change has profound implications for species, communities and ecosystems around the world. Yet climate is only one of many important drivers in ecological systems, with topography, soils, disturbance, ontogeny, biotic interactions, land-use and many other factors also playing key roles. To produce useful predictions of climate change impacts that can inform conservation actions, we must first develop an understanding of how climate interacts with other components of the environment to influence ecological dynamics. In this dissertation, I have attempted to identify important interactions of climatic and non-climatic factors that have the potential to surprisingly alter the ways climate change influences the distribution and performance of plant species at Mount Rainier National Park. In Chapter 1, I begin by reviewing some of the important ways climate change is likely to impact Mount Rainier, finding that while the Park's resources will likely be imperiled, Mount Rainier will also become increasingly important for preserving the region's biodiversity because of its relative lack of other pressures (e.g., habitat destruction) and high elevation lands that can serve as refugia for cold-adapted species. Chapter 2 describes observed patterns in climate (temperature and snow disappearance date) at coarse and fine spatial scales, showing that climate can vary as much at fine scales (tens of meters) due to differences in vegetation structure and topography as it does at coarse scales (thousands of meters) due to differences in elevation and exposure to storm tracks. These results imply that some species may only have to migrate small distances to track suitable climate during periods of climate change, which may buffer them from its negative impacts. Chapter 3 presents results from a study in Mount Rainier's subalpine and alpine meadows which found that the interaction of climate and soil constraints on seedling establishment during climate change may cause the range of the meadows to contract at their lower limit faster than they expand at their upper limit, a result that would not be expected from considering climate alone. Chapter 4 includes analyses of tree growth across elevation at Mount Rainier which suggest that the relationship between climate and growth changes with tree size in a species-specific manner, implying that forest responses to climate change will be complex. I end with a synthesis summarizing major findings and suggesting avenues for future research