Wildfires leave behind a patchwork of living and dead vegetation relative to burn severity. As warmer and drier conditions in the western US continue to cause larger and more frequent wildfire events, one major concern of having larger patches of high-severity burns is that they are too far from living trees and vegetation for effective seed dispersal after fire – which can slow forest recovery and even lead to the conversion of forests to non-forested ecosystems. However, large fires can also enhance biodiversity and restore ecologically and culturally important plants, making it critical for managers to understand the relationship between wildfire size and patterns of burn severity to anticipate potential ecological effects.  

To address these issues, Northwest CASC researchers published a study examining the relationship between future fire sizes and burn severity patterns across forested regions of Wyoming, Montana, Idaho, Washington, Oregon, and northern California. They analyzed satellite data of 1,615 fire events from 1985-2020 to understand the relationship, then simulated burn severity patterns for future fire sizes keeping the total area burned constant. In other words, the researchers asked how burn severity patterns would differ if one million hectares burned in many small fires versus a few large ones. After confirming that larger fires result in larger areas of high severity burns, they found that in the largest fire-size future scenarios, about 15% of burned area would exist outside the range of seed dispersal distance from living trees. These may be areas where management could consider post-fire replanting after large fires.  

Findings from this Northwest CASC study can help managers plan for future wildfires of various sizes, make real-time decisions, and inform post-fire actions.  

This work was supported by the Northwest CASC Project titled “Changing Fires, Changing Forests: The Effects of Climate Change on Wildfire Patterns and Forests in the Pacific Northwest.”