UC San Diego

Rapid climate change has resulted in shifts in the distribution and abundance of organisms along with changes in timing of biological events (phenology). Such shifts could be the result of direct responses to changes in the environment, or indirect responses resulting from altered biotic interactions between species. In this compilation I investigate the effects of recent and future climate change on the high elevation plant community of California's White Mountains. Chapter 1 investigates if there have been shifts in distribution and abundance of alpine and sub-alpine plant species along an elevational gradient in the White Mountains during the last half- century. Chapter 2 tests how sagebrush encroachment affects alpine plant species and how the plant community responds to experimental removal at three sites along an elevation gradient. Sagebrush presence was expected to lower the abundance of co-occurring alpine plant species and, conversely, sagebrush removal was expected to increase cover of co-occurring species, especially at lower elevations with more favorable growing conditions. Chapter 3 tests how plant species respond to warming and if these responses vary by elevation and the presence of sagebrush. It was expected that alpine species at the lower (warm) margins of their range would respond negatively to warming, with potentially positive responses at high elevations, and that the presence of sagebrush might dampen these responses. Finally, Chapter 4 evaluates how experimental warming and sagebrush presence or absence interact to influence the phenology of photosynthetic biomass production, and flowering of the cushion plant, Trifolium andersonii, and the grass, Koeleria macrantha, at two elevations. Observational findings of this work were that several species in the White Mountains have experienced changes in distribution and abundance over the past half-century. Experimental findings show that climate change is having direct (via warming) and indirect (via species interactions) effects on both individual species cover and phenology and community composition as a whole