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

这项博士论文研究项目的目的是通过对湖泊沉积岩心中含有的化石花粉和木炭记录的研究，重建大盆地北部的气候、植被和火史。大盆地是一个地形、植被和气候多种多样的地区，因此它提供了一个极好的机会来研究生态系统对过去各种环境变化的反应。通过聚焦于三个不同海拔的湖泊，这项研究将(1)阐明植被和火焰状况对有效湿度、温度和其他生物气候变量变化的响应；(2)重建生长在不同海拔的重要针叶树种的生物地理历史；(3)应用现代北美西部的花粉-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决定。岩心中植物大型化石的存在将有助于在花粉无法识别的情况下确认物种鉴定。过去火灾活动的变化将从连续样品中宏观木炭积累速度的变化中推断出来。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现代气候信息之间的定量关系。环境变化的年表将根据一系列放射性碳测年和铅-210测年以及已知的盖佛拉层的年龄编制。这项研究的成果将有助于更好地了解大盆地北部不同海拔高度的全新世森林发育情况，以及火和气候在生态史中的作用。本研究的结果将有助于更好地理解(1)过去和现在全球气候变化对大盆地区域植被格局和火情的影响；(2)现代花粉-气候关系及其在重建过去气候中的应用；(3)全新世期间大盆地北部人类活动的环境控制。自1988年以来，美国西部经历了多起取代立柱的大火。2000年，美国有超过800万英亩的土地被烧毁，而在2002年的前6个月，大约有250万英亩的土地被野火烧毁。这些火灾中的许多可能是由于整个西部异常干燥的条件造成的。在未来气候变化的模型中预测了火灾活动的加剧，对这些条件的最佳类比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。有关自然变化范围的信息将帮助美国的土地利用管理者制定战略，考虑森林对气候变化和干扰制度的敏感性。现代花粉和气候类比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。孢粉数据是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，这项研究将为大盆地的文化变迁提供一个环境背景，从而为考古学做出贡献。例如，干旱时期似乎与该区域生存模式的变化有关。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.