DISSERTATION RESEARCH: The Role of Permafrost and Soil Development in Boreal-Forest Responses to Holocene Climatic Change

人类引起的气候变化预计将导致生物群边界的重大变化。植被对气候变化的反应预测通常假定植被与气候是平衡的；即植被类型的分布是气候条件的直接结果。这项博士论文研究项目将使用古生态方法来测试阿拉斯加的主要森林类型(黑云杉麝香)是否处于气候平衡状态。该项目的研究人员收集了初步数据，这些数据挑战了关于北方森林生态系统如何应对过去气候变化的长期观点。具体地说，大约5000年前黑云杉(一种需要水分的树)的建立并不对应于水分有效性的增加，随后的黑云杉群落表现出很大的稳定性，尽管水分有明显的波动。该项目的目标是研究气候变冷是否导致永久冻土堆积，进而增加土壤水分并导致黑云杉的形成。研究人员将使用来自两个永久冻土-下伏沼泽的泥炭岩芯重建全新世土壤水分、永久冻土和植被的变化。这项拟议的研究有望加强我们对多年冻土在北方森林动态中的作用的理解。支持假定的气候-多年冻土-植被联系的证据将意味着，随着气候变暖，当地永久冻土的丧失将导致生态系统状态的迅速和不可逆转的变化。这个项目是完成博士论文的关键，也将包括对本科生的研究培训。

Human-induced climate change is anticipated to cause major shifts in biome boundaries. Projections of vegetation responses to climate change typically assume that vegetation is in equilibrium with climate; i.e., that the distribution of vegetation types is a direct result of climate conditions. This doctoral dissertation research project will use a paleoecological approach to test whether the dominant forest type in Alaska (black spruce muskeg) is in climatic equilibrium. The investigators of this project have collected preliminary data that challenge long-standing ideas about how boreal-forest ecosystems responded to past climatic change. Specifically, the establishment of black spruce (a moisture-demanding tree) ~5000 years ago did not correspond to an increase in moisture availability, and the subsequent black spruce communities exhibited great stability despite pronounced moisture fluctuations. The goal of this project is to examine whether a climatic cooling resulted in permafrost accretion, which in turn increased soil moisture and led to the establishment of black spruce. The investigators will reconstruct Holocene changes in soil moisture, permafrost, and vegetation using peat cores from two permafrost-underlain bogs. The proposed study promises to enhance our understanding of the role of permafrost in boreal-forest dynamics. Evidence supporting the putative climate-permafrost-vegetation linkages would imply rapid and irreversible change in ecosystem state upon local loss of permafrost in response to warming. This project, which is a key to the completion of a doctoral dissertation, will also involve research training for an undergraduate student.