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Evaluation of past-fire mosaics on subsequent wildfire behavior, severity and management strategies - JFSP Final Report

Author(s): Susan J. Prichard, Paul F. Hessburg, Robert W. Gray, Nicholas A. Povak, R. Brion Salter, Camille Stevens-Rumann, Penelope Morgan
Year Published: 2018

The Reburn Project was motivated by a need to better understand wildfires as fuel reduction treatments and to assess the impacts of decades of wildland fire suppression activities on forested landscapes. Our study examined three areas, located in the inland Pacific Northwest, central Idaho and interior British Columbia. Each area had experienced a recent large wildfire event in montane forests. Our first objective was to evaluate what is known about fire-fire interactions and their influence on subsequent large fire events. A second objective was to evaluate how past wildfires might function as transient barriers to subsequent wildfire spread and the effect that landscape position, fire weather, and fireline position (heading or flanking) had on past fires as fuel breaks. We found that regardless of past burn severity, future wildfire severity was mitigated by recent past fires. Our third objective was to create a landscape fire simulation tool that allowed us to explore the impact of wildfires and fire management on the patterns of forest vegetation and fuels across recurrently reburned landscapes. To do this, we created an iterative GIS and fire growth modeling process that used annual historical ignition and weather data to evaluate likely burn mosaics resulting from combined ignitions, surface and canopy fuel patterns, and actual fire weather and topography. With our model, we were able to visualize the actual effects of prior-year fires on ignitions, fire flow on the landscape, and fire containment by fire-fire interactions. We were also able to reveal how lagged effects of time-since-fire patterns and fire weather conditions influenced the efficacy of fire-fire interactions to constrain fire growth or severity patterns. These new utilities provided us with a platform to compare different wildfire management strategies and their efficacy in constraining fire growth and severity patterns. Our results offer a unique perspective on the long-term consequences of wildfire management decisions – in particular, the implications of fire suppression decision for future wildfire event sizes and their severity patterns. Of the four scenarios we modeled, the No Fire and Modern Suppression scenarios represented “boom and bust” landscapes, where well connected mature forests with their complex surface fuel beds were capable of supporting large fire growth and high burn severity impacts. The Partial and No Suppression scenarios revealed fine to meso-scale patch mosaics that provided markedly different options for fire managers due to the remaining effectiveness and durability of prior fire-fire interactions for constraining fire growth and burn severity. The Partial and No Suppression scenarios likewise supported more diverse habitat patchworks. We presented research findings to managers in a series of manager workshops in north-central Washington (Wenatchee, WA), the northern Rockies (Missoula, MT and McCall ID) and interior British Columbia (Quesnel, BC). The goal of each workshop was to provide an exchange of research findings and to obtain fire manager feedback on how alternative landscape management scenarios might be used in wildfire management. Findings are also available on a project website and are being packaged for webinars and wildland fire management courses.

Citation: Prichard S, Hessburg P, Gray R, Povak N, Salter RB, Stevens-Rumann C, and Morgan P. 2018. Evaluation of past-fire mosaics on subsequent wildfire behavior, severity and management strategies - JFSP Project 14-1-02-30 Final Report, 51 p.
Topic(s): Fire & Fuels Modeling
Ecosystem(s): None
Document Type: Technical Report or White Paper
NRFSN number: 18250
FRAMES RCS number: 56749
Record updated: Nov 5, 2018