Dissertation Research: Dynamics and History of Treeline in the Southern Sierra Nevada

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9411573 Graumlich Concern of the possible ecological consequences of trace-gas induced climatic change has led to examinations of how past variation in climate has influenced community structure and composition. Of particular interest is the paleoecological history of ecotonal boundaries, where species are expected to respond sensitively and predictably to climate change. The elevational position of alpine treeline in the southern Sierra Nevada has shifted over the past several millennia; dead and sub-fossil wood, up to several thousand years old, remains preserved at elevations of up to 80 m higher than present treeline. Previous research has demonstrated that the wood is dateable using dendrochronological methods, providing a temporarily precise record of ecotonal shifts over the last three millennia. This research will use this wealth of paleoecological information to analyze the role of climate in driving past movements of alpine treeline in the southern Sierra Nevada. Long-term records (1000 yr) of seasonal climate fluctuations will be compared with records of treeline movement. Using the technique of stand reconstructions, this study will also investigate how climate variation over the last millennium has affected rates of recruitment and mortality in subalpine forests. %%% Results from this dissertation research will allow quantification of the time-varying relationship between climate and treeline, and exploration of how this relationship is mediated through climatic effects on rates of population processes in subalpine forests.