COS 106-4 - Drivers of post-fire tree regeneration across gradients of climate and burn severity in Eastern WA, USA

Tuesday, August 8, 2023

2:15 PM – 2:30 PM PDT

Location: E141

Presenting Author(s)

AG

Angela Darlene Gonzalez

University of Washington, United States

Coauthor(s)

DD

Daniel C. Donato

Natural Resource Scientist
Washington State Department of Natural Resources, United States
JH

Joshua S. Halofsky, PhD

Natural Resource Scientist
Washington State Department of Natural Resources, Washington, United States
BH

Brian J. Harvey

Assistant Professor
University of Washington
Seattle, Washington, United States

Abstract: Climate change is directly and indirectly impacting forest ecosystems through a combination of drought, warming, and changes in wildfire size and severity. Increasing fire activity in the coming decades is expected to be a major catalyst for ecosystem change under climate warming, triggering changes that can unfold slowly in the absence of disturbance. Much attention has been focused on post-fire tree regeneration failure at warmer, drier ecotone settings across the western US, but climate-driven changes in post-fire regeneration may be occurring across elevational gradients. Further, the drivers of post-fire tree regeneration may vary considerably from the warm/dry edge of forests where moisture is limiting to the cold/wet edge of forests where energy is limiting. Post-fire regeneration dynamics have been documented across the Western US, yet they are virtually unstudied across elevation gradients in eastern Washington, USA. A better understanding of the response of eastern Washington forests to large wildfires will be crucial for managing eastside forests. We conducted a survey of post-fire seedling regeneration across 30 fires that burned in eastern Washington, USA between 2012–2017. Over 300 plots were stratified by fire severity, and a moisture/productivity gradient utilizing key variables: elevation, aspect classes, and forest type classes. Our objectives were to 1) characterize post-fire tree regeneration across regional gradients, including identifying contexts where tree regeneration has not occurred by ~ 5 years post-fire, 2) identify important drivers of post fire tree regeneration, 3) test the strength of these drivers and assess how they vary across a gradient of energy to water limits on tree growth. Using generalized linear mixed models, we assessed the impact and strength of drivers on post-fire seedling abundance, growth rates, and community composition. Preliminary results suggest tree seedling abundance varied across forest types, with severely burned dry forest plots having the lowest seedling abundance. Additionally, seedling abundance declined with increasing distance to seed source. Our study provides critical insights into natural post-fire regeneration in the East Cascades and provides knowledge for managing changing landscapes and conditions across important gradients of environmental conditions.