UC Berkeley

During this century, climate warming and altered precipitation patterns will lead to habitat changes that may be detrimental to long-lived tree species. Giant sequoia, Sequoiadendron giganteum, is an iconic Sierra Nevada tree species with populations that tend to be small and highly fragmented, making them especially vulnerable to rapid environmental change. For tree species like giant sequoia, long generation times can limit migration outside of current range boundaries to track climate change. Thus, attention needs to be paid to the risks of adaptative mismatches between a population and its environment. In the face of climate change, genetic diversity is the ultimate source of variation upon which selection can act to allow adaptive responses that mitigate this phenomenon. This dissertation is an investigation of the patterns of extant genetic diversity in giant sequoia at multiple spatial scales, and the processes that shape and move diversity, with a focus on the adaptive potential of populations. Specifically, the chapters of this dissertation will address the following topics in detail: 1) Patterns of range-wide population connectivity and estimation of recent and historic gene-flow; 2) Mating parameters and the dispersal dynamics of pollen and seed within giant sequoia populations; 3) Pattern and climatic drivers of local adaptation and identification of potential genomic regions of adaptive significance. The knowledge gleaned from this research will provide comprehensive background information for giant sequoia regarding the extant genetic diversity, the potential for diversity to spread through gene flow, and the risks of future loss of genetic diversity for a locally restricted species under a changing climate. By highlighting both populations of conservation need, (i.e. isolated or genetically depauperate populations) and those that may contain diversity that can serve as pre-adapted variation for future conditions, this research will be an invaluable asset to forest managers seeking to maintain viable giant sequoia populations into the future.