Long-term impacts of an invasive tree disease, bark beetles, and fire
Preprint available here. We characterized long-term patterns of mountain pine beetle (Dendroctonus ponderosae; MPB) attacks and white pine blister rust, an infectious tree disease caused by the pathogen, Cronartium ribicola in Sequoia and Kings Canyon National Parks (SEKI). Our results highlighted that sugar pine has been declining much faster in SEKI than previously documented. If blister rust and MPB trends persist, western white pine may follow similar patterns of decline in the future. Given current spread patterns, blister rust will likely continue to increase in higher elevations, threatening subalpine white pines in the southern Sierra Nevada.
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 review.
Extreme drought effects in the subalpine
To assess the impacts of the recent CA drought on subalpine forests, we collected over 800 tree cores, 1200 stable carbon isotope samples, and extracted DNA from all whitebark pine trees measured. Plots were randomly selected across the majority of the whitebark pine range in the Sierra Nevada (see map on left).
The remote locations and extreme terrain presented a fun challenge for the crew, but thanks to their extreme sense of adventure, we recently finished collecting data and are now analyzing our results. The tree growth patterns and responses to drought were counterintuitive and we’re excited to share our results soon! Here’s a poster my mentee recently presented at ESA, 2020.
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.
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.