Biogeographic patterns of post-fire resilience and vulnerability to conifer loss in forests of California, Oregon, and Washington (U.S.A.)

Highlights

• We map post-fire conifer regeneration up to 15-years post-fire from 1986 to 2021.
• Resilience to high-severity fire at 10-years post-fire declined over time.
• Resilience was lowest in dry forests with species poorly adapted to high-severity fire.
• Resilience was greatest in moist and cold forests despite large declines over time.
• Regeneration failure increased from 48,000 ha in the 2000s to 1.47 million ha by 2021.

Abstract

Although fire is a natural disturbance to which many tree species are adapted, large patches of high-severity fire and increasingly warm, dry conditions pose a risk to conifer regeneration, potentially catalyzing transitions to hardwood or non-forest vegetation. We use 3268 post-fire observations from a spatially balanced sample of 2223 forest inventory plots across 698 fires in Oregon, Washington, and California (U.S.A) to characterize drivers, quantify, and map the presence of natural post-fire conifer regeneration up to 15-years post-fire (1986–2021). Resilience (regeneration probability 10-years post high-severity fire) declined over time, except in the warmest, driest forest types where species are poorly adapted to high-severity fire and resilience was already very low prior to 2000. Resilience was highest in cold and moist forest types but declined over time with decreased seed source availability and increased post-fire climatic water deficit. The predicted area vulnerable to conifer regeneration failure 15-years following high-severity fire increased from 48,000 to 171,000 ha between the 2000s and 2010s, with an increase to 1.47 million ha predicted in fires through 2021. Most of this area occurs in dry forests where regeneration is primarily climate and seed source limited. Vulnerability to regeneration failure is relatively low in moist and cold forest types, but appears to be increasing due to recent large, high-severity fires, drought, and reburns. Results indicate a rapid decline in resilience and acceleration of widespread conifer regeneration failure in the last decade, as recovery rates fail to keep pace with recent changes in climate and fire.

Citation

Reilly, M. J., Zuspan, A., Busby, S. U., Tortorelli, C., & Fried, J. (2026). Biogeographic patterns of post-fire resilience and vulnerability to conifer loss in forests of California, Oregon, and Washington (USA). Forest Ecology and Management, 620, 124106.