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

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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.