Current Research

Massive Drought Mortality in the Sierra Nevada: Consequences for Forest Health

Golden light and red trees in the mixed conifer zone of the Sierra Nevada that experienced a massive wave of tree die back event triggered by the 2012-16 drought that triggered major bark beetles outbreaks

The epic California drought from 2012 to 2015 included historic dryness and warmth. The extended aridity led to significant drought stress in the Sierra Nevada and  induced a massive wave of tree mortality. Understanding the ecosystem dynamics and management challenges created by extensive tree mortality during this period is major priority of resource scientists and managers from across the state. In this project, with co-leads John Battles and Susie Kocher and many collaborators, we seek to quantify the risks posed by a warmer, more drought-prone climate to the vast Sierran conifer forests, and to provide essential information needed to mitigate the impact of over 128 million dead trees. Our field-based approach fills an important knowledge gap, namely a landscape-level perspective on the drought-induced mortality. In 2017 we established eight drought mortality sites with 283 plots across a north-south gradient in the Sierra Nevada. We collect detailed measurements of overstory, understory and fuels components thereby tracking tree condition, cause of death, tree fall rates, fuel accumulation, and the response of regeneration, existing saplings and/or shrubs.

Through this project we have developed a Tree Mortality Data Network made up of scientists across disciplines and agencies, and working across spatial scales. We engage in annual outreach and extension with project partners, land managers and stakeholders from state and federal agencies, and local governments to make our science open, translating results and impacts to land managers and owners in a timely and accessible way.

California Agriculture published “The California Tree Mortality Data Collection Network — Enhanced communication and collaboration among scientists and stakeholders” in June 2019, highlighting key issues and scientific findings of the collaborative.

Rapid Detection of Forest Health Problems with Unmanned Aerial Vehicles – Tools for Forest Managers

UAV image of mixed conifer site near Lake Tahoe with ground points and tree health categories

The 2012-2105 drought in California highlights the interactions between warming temperatures, drought, and insect outbreaks. Compared to pure drought mortality where dead trees no longer compete for resources, insect outbreaks are especially challenging as infested trees are serious vectors of additional mortality to surrounding trees. Forest managers are increasingly faced with the daunting challenge of adaptively managing large landscapes subject to multiple stressors with limited resources. Therefore, it has never been more critical to obtain reliable, rapid and cost-efficient assessments of forest health conditions in space and time. In this project myself and Peter Sprague are working to develop tools for managers to rapidly detect and precisely locate bark beetle attack using nimble and cost-effective Unmanned Aerial Vehicles (UAVs) in mixed conifer forests in the Sierra Nevada. The early detection of beetle infested trees can profoundly influence the role of resource management on mitigating insect spread and outbreak severity. Long-term we are working to extend detection to include stressed trees so that land managers have as much information on stands to aid in their decision making.

Western Spruce Budworm Outbreak Reconstructions at the Sub-Continental Scale

Heavily defoliated canopy intermediates in a pure Douglas-fir forest in the Shoshone National Forest in Wyoming. The forest has been undergoing a western spruce budworm outbreak for over a decade

The Agnese Haury Fellowship at the University of Arizona enabled this project to begin at the Laboratory of Tree-Ring Research in collaboration with Drs. Ann Lynch and Tom Swetnam. Focused on the western spruce budworm (WSBW), the most destructive native conifer defoliator in western North America, I have worked with a large group of collaborators to compile over 200 not publicly archived tree-ring chronologies. Collected over nearly the entire range of this insect, from central British Columbia to southern New Mexico, tree-ring chronologies will be analyzed to look at the spatial and temporal dynamics of WSBW outbreaks at the subcontinental scale.