Ecological - First Order
Fire Intensity / Burn Severity
Post-fire planning / management
Mixed severity wildfires burn large areas in western North America forest ecosystems in most years and this is expected to continue or increase with climate change. Little is understood about vegetation recovery and changing fuel conditions more than a decade post-fire because it exceeds the duration of most studies of fire effects. We measured plant species composition, conifer seedling regeneration, fuel loads, and ground cover at 15 wildfires that burned 9-15 years previous in five western U.S. vegetation types distributed across eight states including Alaska. The 15 fires were selected for having been previously sampled immediately post-fire and re-sampled one year later, thus providing a re-measurement opportunity for a more powerful analysis of long-term vegetation recovery. These existing field sites were used to partially populate a new stratification of the post-fire landscapes based on one-year burn severity classifications by the Monitoring Trends in Burn Severity (MTBS) Project, elevation, and transformed aspect; additional new sites were then added to fill the stratification, such that our stratified random sampling design was balanced.
In the northern Rockies, plant species diversity a decade post-fire is highest on moderate burn severity conditions, and total fuel load appears to peak in the decade that follows. In dry ponderosa pine forests, burn severity was not as influential on understory plant species composition and cover as climate, particularly precipitation. Seedling regeneration is more affected by distance from seed sources than by burn severity. Across all 5 vegetation types and 14 of the wildfires sampled, we found that vegetation cover, composition, and seedling regeneration 9-15 years post-fire is remarkably resistant to high severity fire effects. The 2002 Hayman Fire in Colorado, where burn severity was extreme, appears to be an exception.
From our suite of field measurements, percent vegetation cover most strongly determines Landsat pixel reflectance. We related overstory and understory cover estimates to remotely sensed trajectories of vegetation recovery, as indicated by annual time series of Normalized Burn Ratio (NBR) extracted from Landsat satellite image time series using the Landsat Trends in Disturbance and Recovery (LandTrendr) algorithm. NBR trajectories provided consistent information on initial burn severity, recovery rate, and percent recovered to pre-fire conditions, which varied by burn severity class from 75% (low) to 60% (moderate) to 48% (high).
We hosted a workshop at the University of Idaho’s McCall Outdoor Science School (MOSS) to share results regarding long-term post-fire vegetation recovery with managers. At the workshop, we also partnered with another FY14 JFSP project (14-1-02-03) that modeled reburn potential. Researchers and managers discussed the implications of long-term vegetation recovery, fuel accumulation, and reburn potential for both fuels and fire management, both in the classroom and on the associated field tour.
We fully funded two graduate students (PhD and MS) and partially funded four other Masters students, all of whom focused their degrees on fire ecology. All of their thesis work has been presented at national professional conferences, and publications of their work are either in review or in preparation. We intend to archive all data collected in the Forest Service Research & Development permanent data archive to promote their broader use.