Doctoral Dissertation Research: Multi-Scale Influences of Climate on Upper Treeline Dynamics Along a Latitudinal Gradient in the Rocky Mountains, USA

预计未来整个落基山脉的气温将继续大范围上升。古生态学和当代研究表明，海拔高度上树线是敏感的温度波动，但降水与温暖的温度一起作用的相应影响仍然不太清楚。这种不确定性在加拿大和瑞典的研究中得到了强调，在这些研究中，上树线的推进仅限于朝南的斜坡，这表明与气候的非线性关系。我们目前对上树线动态的了解主要是基于当地的小规模研究，缺乏对区域大规模模式和过程的了解。本博士论文研究的目标是确定气候的时空动态的关系，多个空间尺度沿着纬度梯度在落基山脉上的树线的影响。这项研究将利用降水偶极子，存在于北纬40度，在美国西部，以证明温度和降水的相对影响上树线动态对比南北向的斜坡。树木年代学技术将使重建树的建立和殖民日期在上树线。将使用PRISM和SNOTEL气候数据沿着统计技术，包括相关性、多元回归和叠加年代分析，对树木建立的气候控制进行调查。如果树木的建立是广泛的同步网站之间，这可能表明温度在调节上树线生态交错动态的压倒一切的重要性。相反，如果脉冲的再生山脉之间的不同，那么温度和降水制度的空间和时间的对齐似乎是最重要的，这项研究的结果填补了我们的理解的影响，气候变化的理论空白上的树线和物理差距在网络上的数据在落基山脉上的树线网站在当地和区域尺度。确定和了解依赖气候的生态过程中区域变异性的原因，如树线的海拔上升，是应纳入未来气候变化情景的重要问题。山区对相对较快的人为气候变化特别敏感，可能对生态、水文和社会系统造成严重影响。揭示气候变化对落基山脉上树线森林的影响将有助于为全球变暖引起的植被变化知识的进步提供必要的框架。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。

Broad-scale increases in temperature are expected to continue throughout the Rocky Mountains in the future. Paleoecological and contemporary research suggest that the elevational extent of upper treeline is sensitive to temperature fluctuations, yet the corresponding influence of precipitation acting in conjunction with warmer temperatures remains less clear. This uncertainty is highlighted in studies from Canada and Sweden where upper treeline advance has been confined to south-facing slopes, suggesting a non-linear relationship with climate. Our current knowledge of upper treeline dynamics is largely based on local, small-scale studies that lack an understanding of regional, large-scale patterns and processes. The goal of this doctoral dissertation research is to determine the influence of climate on the spatiotemporal dynamics of upper treeline in relationship to multiple spatial scales along a latitudinal gradient in the Rocky Mountains. This study will utilize a precipitation dipole that exists at 40 degrees north latitude in the western United States to demonstrate the relative influences of temperature and precipitation on upper treeline dynamics on contrasting north- and south-facing slopes. Dendrochronological techniques will enable the reconstruction of tree establishment and colonization dates at upper treeline. Climatic controls on tree establishment will be investigated using PRISM and SNOTEL climate data along with statistical techniques, including correlation, multiple regression, and Superposed Epoch Analysis. If tree establishment is broadly synchronous among sites, that may suggest the overriding importance of temperature in regulating upper treeline ecotonal dynamics. Conversely, if pulses of regeneration differ between mountain ranges, then the spatial and temporal alignment of temperature and precipitation regimes would appear to be most important.The results of this research fill both a theoretical gap in our understanding of the influence of climate change on upper treeline and a physical gap in the network of data on upper treeline sites in the Rocky Mountains at local and regional scales. Identifying and understanding the causes of regional variability in climate-dependent ecological processes, such as the elevational advance of treeline, constitute vital questions that should be incorporated into future climate change scenarios. Mountain regions are particularly sensitive to the relatively rapid rates of anthropogenic climate change, with potentially severe impacts on ecological, hydrological, and social systems. Revealing the impacts of climate change on upper treeline forests in the Rocky Mountains will help provide the necessary framework for advancements in knowledge concerning vegetation change due to global warming. 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.