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

20世纪是北美西部大部分地区在气候、土地利用(如放牧和灭火)、森林结构和火灾方面发生重大变化的时期，在20世纪后期达到高潮，森林火灾越来越大和严重。火灾的频率和生态影响由气候、燃料和点火的复杂相互作用决定。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-火灾和土地利用的关系几乎不可能被破译。然而，为了针对潜在的新奇气候条件管理森林，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。要了解这些联系的协同作用，需要记录1900年前的火灾，以及在没有人为火灾排除的情况下可能发生的火灾。博士生Jed Meunier在科罗拉多州立大学William Romme教授的指导下，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年的火灾历史和气候数据，以探索这些联系。本项目研究以下问题：1)自上而下(例如，气候)和自下而上(例如，土地利用、地形位置、燃料)控制对当地、站点之间和区域的火灾制度的相对重要性是什么？2)年内降水模式(冬季西风和夏季风)如何影响林分动态和火灾制度，这些模式是否保持一致或随着时间的推移而变化？3)替代林分火灾和低强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世纪森林林分动态的干扰和气候控制，这是一个气候极端多变和缺乏气候-火灾信息的时代，为边界以北的森林提供了一个生态类比。这项研究的结果将有助于我们理解气候和人为控制对火灾和林分动态的影响。美国和墨西哥面临着类似的生态退化威胁，包括依赖于火的生态系统缺乏火、不断增加的人口压力、对自然资源的过度需求以及气候变化。从根本上了解边界地区降水变化的长期趋势和植被的历史变化，包括20世纪最近的变化，将有助于为未来的气候变化做好准备。缺乏关于长期趋势和气候变异性的现有数据阻碍了资源的规划和适当使用。了解20世纪气候、土地利用、林分结构和火的变化及其相互作用，可能会为未来的气候变化提供一个类比。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.