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

陆地植被变化的长期花粉记录被用来量化过去的气候条件，确定过去气候变化的机制，验证过去气候的模型模拟，并重建过去的生物地理模式。目前，在从俄勒冈州中部到加利福尼亚州中部海岸附近的冰川条件方面，这类记录中存在一个缺口。这项博士论文研究项目的目标是开发高分辨率的花粉记录，以重建过去45,000年来加州西北部植被的变化，特别是2万到10,000年前的时期。来自俄勒冈州边界附近的加利福尼亚州双子湖的花粉记录将部分填补这一空白，并提供克拉马斯山脉森林历史和气候动态的分析。从双子湖采集的湖泊沉积物表明，该遗址包含了至少45,000年前以来当地植被的连续记录。这项研究的重点是对20,000至10,000年前放射性碳沉积的沉积物进行高分辨率的花粉分析，这一时期是全球和区域气候快速变化的时期。还将测量沉积特征，如磁化率、有机质含量和花粉流入速率，以确定双湖流域生产力和侵蚀率的变化。通过20台加速器质谱仪对沉积木炭和可识别的植物遗骸进行放射性碳测年，将确保准确的年代学控制。这项百年分辨率研究将补充已经完成的从45000年前到现在的整个记录长度的500年分辨率分析。花粉数据将与克拉马斯地区83个湖点的现代花粉成分进行比较，试图量化双子湖过去的气候条件。这项研究的结果将有助于填补我们对过去气候变化区域差异的理解的时空空白，并为气候变化的机制提供洞察。此外，研究结果还将深入了解快速气候变化对北美西海岸森林系统的影响。克拉马斯山脉地区以针叶树种的多样性异常高而闻名(包括范围有限的几种特有物种)，并已被公认为具有全球意义的生态系统。上一次冰期末期的快速气候变化可能会为下个世纪二氧化碳引起的气候变化提供一个合理的类比。了解过去的森林动态可能有助于预测未来气候变化对区域生物多样性的潜在威胁，或许有助于减轻其影响。作为博士论文研究改进奖，该奖项还将提供支持，使有前途的学生建立一个强大的独立研究生涯。

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.