Doctoral Dissertation Research: Spatial and Temporal Variability of Post-Fire Conifer Regeneration in Lower Treeline Forests of the U.S. Rocky Mountains

本论文的研究课题是关于野火后环境变化对树木再生的影响。自20世纪80年代初以来，世界许多地区森林生态系统中野火活动的急剧增加与变暖趋势有关。人们提出的问题是，火灾后的恢复是恢复同一类型的森林，还是恢复不同的、可能没有森林的植被类型。在过去大约25年中燃烧的科罗拉多前山脉较低的树线森林的初步观察导致了这样一种假设，即在温暖的气候下，与19世纪末至20世纪中期发生的火灾事件相比，火灾后树木再生较少。尽管许多回顾性研究记录了19世纪末至20世纪中期火灾后树木再生的普遍成功，但这些研究对树木再生的实际时间和丰富程度以及与年度气候变化的潜在关系都是模糊的。很少有研究探讨气候变化如何改变森林对未来气候相关干扰（如火灾）的弹性，这项研究解决了一个悬而未决的问题，即在温暖干燥的条件下，较低的树线落基山脉森林对野火的弹性可能较低。研究目标是：1）通过检查自20世纪80年代中期以来燃烧的一系列较低树线位置的针叶树幼生密度，量化火灾后针叶树的建立和生存，2）检查与火灾严重程度等位置因素相关的针叶树幼生密度的空间变异性（如树木死亡率百分比所示），与草本和木本物种的竞争，与种子源的距离，以及地形变量，包括海拔和坡度，3）分析火灾后针叶树再生与年度气候变化之间的关系，以确定某些气候条件是否限制或有利于建立和生存，和4）通过增加空气温度和检查直接和间接影响，这项研究将有助于了解植被的适应性和可能的缓解活动，以应对持续变暖对落基山脉中部森林的预期影响。 虽然这些森林在历史上表现出很高的弹性野火，火灾的严重程度的变化可能会限制针叶树的能力，重建后，这样的火灾。 更好地了解造成森林火灾后恢复模式的空间和时间变异的因素，可以改进土地管理人员的决策。 这项研究将通过本科生参与实地和实验室工作以及在K-12，学院和社区层面的广泛教育推广来促进科学教育。 本科生参与研究和其他教育推广工作的目标是将代表性不足的群体包括在内。 调查结果将通过同行评审的出版物、会议介绍、在线数据共享和公共教育工作（包括博物馆展览和视频纪录片）传播给其他研究人员、土地管理人员和更广泛的公众。 作为博士论文研究改进奖，该项目将为有能力的学生开展独立的研究生涯提供宝贵的支持。

This dissertation project is about the impacts of increasing environmental variability on tree regeneration following wildfires. Sharp increases in wildfire activity since the early 1980s in forest ecosystems in many parts of the world have been linked to warming trends. Questions have arisen about whether post-fire recovery will be to the same type of forest or to a different, possibly non-forested vegetation type. Preliminary observations of lower treeline forests in the Colorado Front Range that burned during the past approximately 25 years have led to the hypothesis that under a warmer climate there is less post-fire tree regeneration in comparison with fire events that occurred in the late-19th to mid-20th centuries. Although numerous retrospective studies document the general success of tree regeneration following fires in the late-19th to mid-20th centuries, such studies are ambiguous about the actual timing and abundance of tree regeneration and potential relationships to annual-scale climate variability. Few studies have examined how climate change may alter forest resiliency to future climate-related disturbances such as fire, and this research addresses the unanswered question of how lower treeline Rocky Mountain forests may be less resilient to wildfire given warmer, drier conditions. The research objectives are to: 1) quantify post-fire conifer establishment and survival by examining the density of conifer juveniles across a range of lower treeline sites that have burned since the mid-1980s, 2) examine the spatial variability of juvenile conifer densities in relation to site factors such as fire severity (as indicated by percent tree mortality), competition with herbaceous and woody species, distance to seed source, and topographic variables including elevation and slope aspect, 3) analyze relationships between post-fire conifer regeneration and annual climate variability to determine if certain climate conditions limit or favor establishment and survival, and 4) experimentally manipulate microclimate to determine effects on conifer seedling survival and growth by increasing air temperature and examining both the direct effects of warmer temperatures and the secondary effects of changes in relative humidity and soil moisture.This research will contribute to the understanding of vegetation adaptation and possible mitigation activities in response to expected impacts of continued warming on forests in the central Rocky Mountains. Although these forests historically exhibited high resiliency to wildfires, changes in fire severity may be limiting the capacity of conifer trees to reestablish following such fires. Decision-making by land managers may be improved by a better understanding of the factors that drive spatial and temporal variability in patterns of post-fire forest recovery. This research will foster science education through involvement of undergraduates in field and laboratory work as well as extensive educational outreach at the K-12, college, and community level. Undergraduate involvement in research and other educational outreach efforts will target inclusion of underrepresented groups. Findings will be disseminated to other researchers, land managers, and the broader public through peer-reviewed publication, presentation at conferences, online data sharing, and public education efforts including a museum exhibit and video documentary. As a Doctoral Dissertation Research Improvement award, this project will provide invaluable support for a capable student to launch an independent research career.