Doctoral Dissertation Research: Holocene Climatic and Ecologic History of the Northern Great Basin

这个博士论文研究项目的目标是重建气候，植被和火灾的历史，在北方大盆地的化石花粉和木炭记录在湖泊沉积物芯的检查。 大盆地是一个地形、植被和气候多样的地区，因此，它为研究生态系统对过去各种环境变化的反应提供了一个极好的机会。 本研究以三个不同海拔的湖泊为研究对象，目的是：（1）阐明植被和火状况对有效湿度、温度和其他生物气候变量变化的响应;（2）重建不同海拔重要针叶树种的地理历史;（3）应用北美西部的现代花粉-气候关系来确定过去气候和植被变化的幅度。 过去植被的变化将由地层记录中花粉类型的相对和绝对丰度的变化来确定。 在花粉不能确定物种的情况下，岩芯中植物大化石的存在将有助于确认物种的鉴定。 过去的火灾活动的变化将被推断出在相邻的样品中的宏观木炭积累率的变化。 根据过去的气候和植被对化石花粉数据的解释将基于现代花粉数据和当今气候信息之间的定量关系。 环境变化的年代学将根据一系列放射性碳测年和铅-210测年以及已知火山灰层的年龄来制定。 本研究的成果将有助于更好地了解北方大盆地不同海拔高度全新世森林的发展，以及火和气候在生态历史中的作用，有助于更好地了解（1）过去和现在全球气候变化对大盆地区域植被格局和火状况的影响;（2）现代花粉与气候的关系及其在重建古气候中的应用;（3）全新世北方大盆地人类活动的环境控制。 自1988年以来，美国西部经历了一些大型的，取代看台的火灾。 在2000年，美国有超过800万英亩的土地被烧毁，在2002年的前六个月，有大约250万英亩的土地被野火烧毁。 这些火灾中有许多可能是由于整个西部的极端干燥条件造成的。 在未来气候变化的模型中预测了火灾活动的加剧，这些条件的最佳模拟可能是过去气候比现在更温暖和更干燥的时期。 通过了解过去气候、植被和火灾之间的联系，可以将最近的火灾事件置于十年至千年时间尺度上发生的自然变化的背景下。 关于自然变异范围的资料将有助于美国的土地使用管理人员制定考虑到森林对气候变化和干扰制度的敏感性的战略。 现代花粉和气候模拟物的使用将提高我们根据化石花粉记录重建过去气候条件的能力。 花粉数据是用于重建过去气候的主要陆地数据库，因此这种改进是对古气候学和地理学的重要贡献。 最后，这项研究将有助于考古学提供一个环境背景的文化变化在大盆地。 例如，干旱时期似乎与该区域生计模式的变化有关。 这项研究将有助于澄清这些关系。 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的研究生涯。

The objectives of this doctoral dissertation research project are to reconstruct the climate, vegetation, and fire history in the northern Great Basin from an examination of fossil pollen and charcoal records contained in lake-sediment cores. The Great Basin is a region of diverse topography, vegetation, and climate, and as such it provides an excellent opportunity to study the response of ecosystems to a wide array of environmental changes in the past. By focusing on three lake sites at different elevations, this study will (1) elucidate the response of vegetation and fire regimes to changes in effective moisture, temperature, and other bioclimatic variables; (2) reconstruct the biogeographic history of important conifer species growing at different elevations; and (3) apply modern pollen-climate relations in western North America to identify the magnitude of past climate and vegetation changes. Past changes in vegetation will be determined by changes in the relative and absolute abundances of pollen types in stratigraphic records. The presence of plant macrofossils in the cores will help confirm species identifications in cases where the pollen cannot. Variations in past fire activity will be inferred from changes in the rates of macroscopic charcoal accumulation in contiguous samples. Interpretation of the fossil pollen data in terms of past climate and vegetation will be based on the quantitative relationship between modern pollen data and present-day climate information. The chronology of environmental changes will be developed from a series of radiocarbon dates and lead-210 dates, as well as the age of known tephra layers. The products of this study will be a better understanding of Holocene forest development at different elevations in the northern Great Basin, and information on the role of fire and climate in the ecological history.The results of this research will contribute to a better understanding of (1) the effects of global climate change, past and present, on regional vegetation patterns and fire regimes in the Great Basin; (2) modern pollen-climate relations and their use in the reconstruction of past climates; and (3) the environmental controls on human activities in the northern Great Basin during the Holocene. Since 1988, the western U.S. has experienced a number of large, stand-replacing fires. In the year 2000 over 8 million acres burned in the U.S., and in the first six months of 2002 there have been ~2.5 million acres consumed by wildland fires. Many of these fires may be attributable to anomalously dry conditions throughout the west. Heightened fire activity is predicted in models of future climate change, and the best analogue for these conditions may be past periods when the climate was warmer- and drier-than-present. By understanding the linkages between climate, vegetation, and fire in the past, recent fire events can be placed within a context of natural variations occurring on decadal-to-millennial time scales. Information on the natural range of variability will help land-use managers in the United States develop strategies that consider forest sensitivity to climate change and disturbance regimes. The use of modern pollen and climate analogues will improve our ability to reconstruct past climate conditions from fossil pollen records. Pollen data are the primary terrestrial database used to reconstruct past climate, so this refinement is an important contribution to paleoclimatology and geography. Finally, this study will contribute to archeology by providing an environmental backdrop for cultural changes in the Great Basin. Periods of drought, for example, seem to be associated with changes in subsistence patterns in this region. This research will help to clarify these relationships. 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.