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Dissertation/Thesis Abstract

Tree rings, climate variability, and coastal summer stratus clouds in the western United States
by Williams, Alton Park, Ph.D., University of California, Santa Barbara, 2009, 231; 3379534
Abstract (Summary)

Trees are spectacular things. One reason for their splendor is that they record annual growth data in the form of tree rings. In many trees, these rings act as natural climate data recorders: wide rings generally grow during years of optimal climate conditions while thinner rings form in response to poor conditions. I used tree-ring width data from 1,000 sites in the continental United States to evaluate how interannual climate variability impacts tree growth at each of these sites. I then used this information to predict how various scenarios of 21st century climate change might impact growth at these sites. The most substantial, although not surprising, result was that the vast majority of sites in the southwestern United States are sensitive to drought. Southwestern drought is predicted to intensify in the coming century, which should result in reduced growth and increased mortality at many of these sites. I then focused on a single population of Torrey pine trees on Santa Rosa Island, CA. I found that annual tree-ring widths within this population are correlated with rainfall during winter, frequency of ground-level fog during summer mornings, and frequency of higher-altitude stratus clouds during summer afternoons. This suggests that the well known and often detested “June gloom” on California’s coast is essential in reducing summer drought for this and many other species endemic to the region. Finally, I explored the interannual variability in summer fog and stratus-cloud frequency along the California and Oregon coastline. I identified statistical links between increased summer “gloominess” and cold coastal sea surface temperatures, offshore sea surface temperature gradients, coastal northwesterly winds, and strong temperature inversions that cap the cool marine layer. Global climate models disagree upon how these variables are likely to be impacted by rising global temperatures, leaving much uncertainty regarding the future of summertime coastal fog and stratus behavior in California and Oregon. As our understanding of the current global climate change improves, the unique and underexploited environmental datasets used in this study will be helpful in determining how forest growth and cloud behavior may respond to this change.

Indexing (document details)
Advisor: Still, Christopher J.
Commitee: Gautier, Catherine, Leavitt, Steven W., Michaelsen, Joel
School: University of California, Santa Barbara
Department: Geography
School Location: United States -- California
Source: DAI-A 70/11, Dissertation Abstracts International
Subjects: Ecology, Geography
Keywords: Channel islands, Climate change, Fog, Forests, Stratus, Tree rings
Publication Number: 3379534
ISBN: 978-1-109-48382-6
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