Interactions between ecological disturbances and biotic interactions that determine ecosystem function and resilience

Students mapping and measuring trees at the H. J. Andrews LTER site in the Cascade Mountains of Oregon.

Forests are experiencing substantial change, including increased frequency/intensity of wildfires and incidences of widespread forest dieback and decline. Despite their sizable impact on forests, the ways in which extreme abiotic events, such as wildfires, heat waves, drought, and strong winds, interact with tree pathogens to accelerate tree mortality remain uncertain. There is an urgent need to advance our understanding of how extreme abiotic events and pathogens interact to determine forest mortality in order to forecast spatiotemporal patterns of tree mortality and mitigate the worst potential outcomes from climate change.            

My research program seeks to address these needs by showing how extreme abiotic events, such as wildfires, alter the role that species interactions play in determining how plant communities recover from wildfire (LaManna et al. 2020 J. Ecology). My lab also addresses these questions through field-based forest inventory plots and detailed assessments of tree pathogens killing large trees. Specifically, my lab has established a network of forest inventory plots that are matched with long-term forest and climate datasets (7 large forest-inventory plots, 30-ha total, each expanded from 1-ha plots surveyed since the 1970s). These plots are slated to join the Smithsonian’s Forest Global Observatory (ForestGEO) Network. In addition, we have collected data to create high-resolution maps of biotic and abiotic factors in these plots including microclimate, microtopography, and fungal microbiome. We are also in the process of mapping the locations of different fungal pathogens within the long-term forest inventory plots and determining what factors drive the spread of pathogens through forest stands over time and how different specific pathogens interact with extreme climate events to drive tree mortality.

With this combination of long-term and in-depth data, we are poised for a robust analysis of spatiotemporal patterns of tree mortality and productivity, their abiotic and biotic causes, and the consequences for tree populations, communities, forest productivity, and C-sequestration. This research will determine why forests are vulnerability to biotic agents and extreme climate events and how these agents might interact to fuel larger future outbreaks. We are actively collaborating with Earth-systems modelers to advance process-based Earth-systems modeling of the influences of pathogen/insect clusters on critical ecosystem functions and forecast future forest die-offs.

Maps showing local, landscape, and regional spatial scales of my research, which also extends to continental and global scales (not shown). Right: PSP long-term forest inventory plot network across the Pacific Northwest region. Center: Long-term forest inventory reference stands (1-ha), circular plots (0.1-ha), and plots expanded by my lab (Forests of Oregon Elevation Gradient, or FOREG plots, which range in size from 3-12 ha) across the Andrews LTER. Nested 1-ha long-term reference stands sit within each expanded FOREG plot. Left: FOREG-02 stem map showing trees from the nested long-term reference stand and circular PSP plots (gray) and new trees and area added in the expand FOREG plot (red; point size reflects tree size).