Climate effects on post-wildfire forest regeneration trajectories–Large, high-severity wildfires are becoming increasingly common in California, and they often result in complete mortality of established trees and very poor recruitment of tree seedlings. I am collecting and analyzing data on post-wildfire tree regeneration between five and ten years following fire on over a dozen wildfires throughout the state to understand how climatic conditions affect (a) natural tree regeneration and (b) the performance of planted tree seedlings. I am evaluating the influence of spatial climatic variation within each fire perimeter as well as interannual variation in climate following wildfires that occurred in different years. A major objective of this work is to understand under what conditions natural regeneration processes will be sufficient for forest recovery and under what conditions tree planting may have the greatest benefit.
Evaluating the performance and adaptive capacity of Sierra Nevada conifers in the face of climate change–Continued climate change, particularly increasing drought stress, is expected to result in widespread shifts in forest communities, but we know little about the timing of these shifts and the resulting winners and losers. With funding from the National Park Service, I am collecting and analyzing radial growth data (using tree cores and stem cross-sections) from conifers throughout the productive mid-elevation forests of the western Sierra Nevada to understand their limits of climatic tolerance. I am particularly interested in evaluating how climatic tolerance varies among species and among individual populations throughout the range of each species. This information will help in evaluating the potential for populations to adapt to changes in climate and will allow us to make predictions about the particular species and locations likely to experience the greatest shifts under ongoing climate change.
Assisted migration as a management response to climate change–The U.S. Forest Service puts significant resources into replanting many severely burned sites, but it is unclear whether the sites in which the species and ecotypes are planted will remain suitable for those trees as climate changes. The Forest Service has installed a series of experimental plots in which seedlings were planted between 1,000 and 3,000 feet higher in elevation than current protocol specifies. I am monitoring these plantings to understand whether this approach of assisted migration may be a viable management response to climate change.
Environmental drivers of drought-induced tree mortality patterns –Using aerial forest survey data, we evaluated the factors explaining the spatial variation in tree mortality patterns resulting from the recent extreme drought in California. Although drought severity was similar throughout the state, we found that tree mortality was greater in sites that are on average more arid. For a given level of aridity, denser forests had higher mortality, suggesting that water competition is an important factor driving mortality patterns.
Interaction of spatial priority and fire in restoration of Central Valley grasslands–I collaborated with other Young Lab members to test how seeding strategies (planting species in clumps or interspersing seeds) and prescribed fire can be used to restore native plant communities in California Central Valley grasslands.