Doctoral Dissertation Research: Fire Regimes in the U.S.-Mexico Borderlands: Disentangling the Relative Importance of Top-Down vs. Bottom-Up Controls

20世纪是气候、土地利用（例如放牧和灭火）、森林结构和北美西部大部分地区火灾发生重大变化的时期，最终在20世纪后期发生了越来越大和严重的森林火灾。火灾的频率和生态影响是由气候、燃料和点火的复杂相互作用决定的。不幸的是，灭火的复合效应阻碍了研究进展；自然火灾制度已经改变，使得气候火灾和土地使用的关系几乎不可能破译。然而，为了在潜在的新气候条件下管理森林，土地管理者需要更好地了解气候、土地利用、植被和地形之间的联系，以及这些联系如何影响火灾制度。了解这些联系的协同作用需要记录1900年之前的火灾，以及在没有人为火灾排除的情况下可能发生的火灾。在科罗拉多州立大学William Romme教授的指导下，博士生Jed Meunier将整合生态学和树木年代学方法，收集墨西哥北部几个独特地点过去300多年的火灾历史和气候数据，以探索这些联系。本项目调查了以下问题：1)自上而下（如气候）和自下而上（如土地利用、地形位置、燃料）对地方、地点和区域的火灾控制的相对重要性是什么？2)年内降水模式（冬季西风与夏季风）如何影响林分动态和火灾状况，这些模式是否保持一致或随时间变化？3)林火与低烈度火灾的作用是什么？在过去的一个世纪里，这种作用发生了变化吗？这项工作将阐明1900年前和20世纪（一个极端气候变化和缺乏气候火灾信息的时代）林分动态的干扰和气候控制，为边界以北的森林提供生态模拟。本研究结果将有助于我们了解气候和人为控制对林分动态和火灾的影响。美国和墨西哥面临着类似的生态退化威胁，包括依赖火的生态系统缺乏火，人口压力增加，对自然资源的过度需求以及气候变化。对边境地区降水变率和历史植被变化的长期趋势的基本了解，包括最近20世纪的变化，将有助于为未来的气候变率做好准备。缺乏关于长期趋势和气候变率的现有数据妨碍了资源的规划和适当利用。了解20世纪气候、土地利用、林分结构和火灾的变化及其相互作用，可以为未来的气候变率提供类似的模拟。作为博士论文研究改进奖，该奖项将提供额外的支持，使有前途的学生建立一个强大的独立研究生涯。

The twentieth century was a period of significant change in climate, land use (e.g., grazing and fire suppression), forest structure, and fires throughout most of western North America, culminating in increasingly large and severe forest fires in the late twentieth century. The frequency and ecological effects of fires are determined by a complex interplay of climate, fuels, and ignitions. Unfortunately, the compounding effects of fire suppression have hindered research progress; natural fire regimes have been altered, making climate-fire and land use relationships nearly impossible to decipher. Yet, to manage forests for potentially novel climate conditions, land managers need improved understanding of the linkages among climate, land use, vegetation, and topography and how these linkages influence fire regimes. Understanding the synergy of these linkages requires documenting fires prior to 1900, as well as fires that would have occurred in the absence of anthropogenic fire exclusion. Doctoral student Jed Meunier, under the supervision of Professor William Romme at Colorado State University, will integrate ecological and dendrochronological methods to collect data on fire history and climate for the past 300+ years for several unique sites in northern Mexico to explore these linkages. This project investigates the following questions: 1) What is the relative importance of top-down (e.g., climate) and bottom-up (e.g., land use, topographical position, fuels) controls on fire regimes locally, among sites, and regionally? 2) How do intra-annual patterns of precipitation (winter westerly vs. summer monsoon) impact stand dynamics and fire regimes, and have these patterns remained consistent or changed over time? 3) What has been the role of stand-replacing fire vs. low-severity fire, and has that role changed in the past century? This work will elucidate disturbance and climate controls of forest stand dynamics in both pre-1900 and in the twentieth century, an era of extreme climate variability and paucity of climate-fire information, providing an ecological analogue to forests north of the border. The results of this study will contribute to our understanding of the influences of climate and anthropogenic controls on fire and forest stand dynamics. The U.S. and Mexico face similar threats of ecological degradation, including lack of fire in fire-dependant ecosystems, increasing population pressures, excessive demands on natural resources, and climate change. A fundamental understanding of long-term trends in precipitation variability and historical vegetation shifts in the borderlands region, including recent twentieth century changes, will help prepare for future climate variability. Lack of available data on long-term trends and climate variability hinders the planning and appropriate use of resources. Understanding twentieth century changes in climate, land-use, stand structure, and fire and their interactions may provide an analogue for future climate variability. As a Doctoral Dissertation Research Improvement award, this award will provide additional support to enable a promising student to establish a strong independent research career.