Doctoral Dissertation Research: Century-Scale Forest Dynamics From 20,000-10,000 Yr B.P. in the Western Klamath Mountains, California

University Of California-Berkeley, Berkeley CA

Investigators

Abstract

Long pollen records of terrestrial vegetation change are used to quantify past climatic conditions, to identify mechanisms of past climatic variability, to verify model simulations of past climate, and to reconstruct past biogeographic patterns. A gap currently exists in such records regarding glacial to recent conditions near the coast from central Oregon to central California. The goal of this doctoral dissertation research project is to develop a high-resolution pollen record to reconstruct changes in vegetation in northwestern California over the past 45,000 years, with particular emphasis on the period between 20,000 and 10,000 years ago. A pollen record from Twin Lake, California, near the Oregon border, will partially fill this gap and provide an analysis of forest history and climate dynamics in the Klamath Mountains. Lake sediments collected from Twin Lake indicate that the site contains a continuous record of local vegetation since at least 45,000 radiocarbon years ago. This study will focus on high-resolution pollen analysis of sediments deposited between 20,000 and 10,000 radiocarbon years ago, a period of rapid global and regional climate changes. Sedimentary characteristics such as magnetic susceptibility, organic content, and pollen influx rates will also be measured to identify changes in productivity and erosion rates in the Twin Lake watershed. Accurate chronological control will be ensured through 20 accelerator mass spectrometer radiocarbon dates on sedimentary charcoal and identifiable plant remains. This century-resolution study will complement a 500-year resolution analysis already completed for the entire length of the record, from 45,000 years ago to the present. Pollen data will be will be compared with modern pollen composition from 83 lake sites in the Klamath Region to attempt to quantify past climatic conditions at Twin Lake. The results of this study will serve to fill spatial and temporal gaps in our understanding of the regional variation of past climate change as well as provide insight into mechanisms of climate variability. In addition, the results will provide insight into the effects of rapid climate change on the forest systems of the west coast of North America. The Klamath Mountains region is known for having an unusually high diversity of coniferous tree species (including several endemic species of limited range), and has been recognized as an ecosystem of global significance. Rapid climate change at the end of the last glacial period may provide a reasonable analogue for projected carbon dioxide-induced climate change during the next century. Understanding past forest dynamics may help to predict potential future threats to regional biodiversity due to climate change, and perhaps aid in mitigating their effects. As a Doctoral Dissertation Research Improvement award, this award also will provide support to enable a promising student to establish a strong independent research career.