Climate change shifts infectious tree disease
Combining a long-term study of the epidemic tree disease caused by Cronartium ribicola, with a six-year, field-based assessment of drought-disease interactions, we found evidence that climate change shifted disease prevalence. The shift was asymmetric due to complex host-pathogen interactions and drought occurrences that ultimately contributed to an unexpected decline in mean disease prevalence. Our study underscores that host-pathogen-drought interactions will strongly mediate climate change impacts on infectious disease. Paper in revision (Nature Communications).
Extreme drought effects in the subalpine
Between 2017-18, I designed a study that assessed the impacts of the recent CA drought on subalpine forests in the Sierra Nevada (see map below). Together with collaborators from NPS, USGS, and USFS, we extracted 800 tree cores, 1200 stable carbon isotope samples, and DNA from all whitebark pine trees measured. The remote locations and extreme terrain presented a fun challenge for the crew, but thanks to their insatiable sense of adventure, we recently finished collecting data and are now analyzing our results.
The tree growth patterns and responses were counterintuitive. We found that on average, growth increased during extreme drought, and our stable isotope analysis suggested that photosynthesis also increased throughout most of the Sierra. The genetic data provided evidence that genotypic variation of whitebark pine is relatively low in the Sierra Nevada; the populations are fairly similar across the range. We’re working on two papers that will hopefully be published by 2021!
Forest management impacts on understory species
Fire size and severity are increasing in the western United States. To increase forest resilience to fire, managers are implementing various fuel-reduction treatments. Though treatments can help moderate fire behavior and risk of crown torching, the long-term treatment impacts on introduced, as well as native herbaceous and shrub species, are less well understood. To assess long-term effects of fuel treatments on understory vegetation, we combined a longitudinal experiment (12- to 13-year) comparing mechanical thinning, prescribed fire (that burned twice), mechanical thinning plus fire to untreated control. Paper in review (Forest Ecology and Management).
Mechanisms of bark beetle outbreaks in the Sierra Nevada
I am currently investigating the mechanisms driving mountain pine beetle (MPB, Dendroctonus ponderosae) outbreaks from low to high elevations in the Sierra Nevada. Specifically, we are asking whether post-drought, lagged bark beetle outbreaks are driven primarily by changes in tree density or vulnerability, or rather by beetle population spillover from lower elevation outbreaks. Using a combination of physiological and remote sensing data, we aim to disentangle the complex drivers of MPB outbreaks in the highly vulnerable subalpine forests.