Doctoral Dissertation Research: Cross-Scale Assessment of Spatiotemporal Patterns and Drivers of Fire Effects in Mixed-Severity Fire Regime Forests of the Northern Rockies

本博士论文研究的是从18世纪到现在气候变异性和地形梯度对火灾严重程度景观格局时空变化的影响。火灾频率和每年被烧毁的面积都与区域气候密切相关，近几十年来与全球变暖有关的趋势有所增加。然而，火灾活动增加对生态的影响尚不清楚。作为衡量树木死亡的指标，火灾严重程度直接描述了野火对生态的主要影响之一。但火灾严重程度对气候因素或其他控制因素(即地形因素、植被特征)的敏感度如何，目前还知之甚少。由于许多森林生态系统的火灾严重程度在空间和时间上都不同，因此有必要对火灾严重程度的长时间序列进行量化，以量化异质性的空间模式，这既是为了捕捉全面的火灾影响，也是为了确定这种变化的关键驱动因素。对于以混合严重火灾制度为特征的森林来说尤其如此，在这些森林中，火灾严重程度已知是高度可变的。这项研究将采用空间明确的嵌套研究设计，结合密集的树木年轮采样、对历史高分辨率航空摄影的广泛分析和基于卫星的变化检测方法，以解决三个主要研究目标：1)量化大约1700年至今多个流域内火灾严重程度的时空变化；2)评估气候和地形对火灾严重程度景观格局的控制强度；以及3)比较历史和当代野火的火灾严重程度模式，以评估气候变化对两个时期之间火情变化的作用。这些问题将以道格拉斯冷杉林和西部落叶松混交林为研究对象。落叶松西部落叶松是落基山脉北部两种主要的中低海拔森林，已知它们表现出混合严重的火灾制度。关于火灾严重程度的时空模式如何随时间变化以及哪些因素导致这种变化的信息是科学家、土地管理者和其他对野火过去和未来生态影响感兴趣的人的重要框架。这项研究提供的对气候-火灾严重性关系的详细了解是对未来火灾严重性和土地管理规划的准确建模的新的和必要的基础，以响应当前变化的气候条件。这项研究的结果将发表在各种出版物上，并向学术和管理受众展示。研究结果还将通过与国家公园管理局(NPS)经理、美国农业部(USDA)森林管理局经理和研究人员以及参与相关研究的其他几所大学的调查人员的持续合作而广泛传播。该项目涉及本科生和研究生的培养，作为博士论文，研究改进奖将为处于职业发展关键阶段的有前途的博士生提供必要的支持。

This doctoral dissertation research project is about the influence of climatic variability and topographic gradients on the spatial and temporal variation of landscape patterns of fire severity from the 1700s to the present. Both fire frequency and the annual area burned are strongly related to regional climate and have exhibited increasing trends over recent decades in relation to global warming. However, the ecological effects of increased fire activity are not clearly understood. As a measure of tree mortality, fire severity directly describes one of the major ecological impacts of wildfires. But how sensitive fire severity is to climatic factors or other controls (i.e. topographic factors, vegetation characteristics) is poorly understood. Because fire severity in many forest ecosystems varies over both space and time, long time series of fire severity that quantify spatial patterns of heterogeneity are necessary, both to capture the full range of fire effects and to identify the key drivers of this variation. This is especially true for forests characterized by mixed-severity fire regimes where fire severity is known to be highly variable. This research will adopt a spatially explicit nested research design combining intensive tree-ring sampling, extensive analyses of historical high resolution aerial photography and satellite-based change detection methods to address three primary research goals: 1) to quantify the spatiotemporal variability of fire severity within multiple watersheds from about 1700-present; 2) to evaluate the strength of climatic and topographic controls on landscape patterns of fire severity; and 3) to compare fire severity patterns between historical and contemporary wildfires to assess the role of climate change on fire regime shifts between the two periods. These questions will be examined for Douglas fir (Pseudotsuga menziesii) dominated forests and mixed-conifer western larch (Larix occidentalis) dominated forests, two of the dominant low-middle elevation forests in the northern Rocky Mountains known to exhibit mixed-severity fire regimes.Information about how spatiotemporal patterns of fire severity have varied over time and which factors have driven this variability is an important framework for scientists, land managers and others interested in past and future ecological effects of wildfires. The detailed understanding of climate-fire severity relationships provided by this research is a novel and necessary foundation for accurate modeling of future fire severity and land management planning in response to currently shifting climatic conditions. Results from this research will be published in various publications and presented to academic and management audiences. Findings will also be broadly disseminated through ongoing partnerships with National Park Service (NPS) managers, U.S. Department of Agriculture (USDA) Forest Service managers and researchers, and investigators at other several universities involved in related research. The project involves the training of undergraduate and graduate students, and as a Doctoral Dissertation Research Improvement award will provide needed support to a promising doctoral student at a critical stage of career development.