Numerical Investigation of Crown Fuels Arrangements on Wildfire Behavior Following Fuels Treatments

Abstract

Conventional fuels treatments often simplify forest structure in an attempt to optimize fire hazard reduction. Conversely, forest restoration treatments, aimed at achieving ecological multiple objectives in addition to fire hazard reduction, purposefully retain complex forest structures. The comparative advantage of conventional fuels versus restoration treatments may depend on the severity of the burning environment, residual tree stocking and surface fuel loads. Here, we performed a suite of simulations with the Wildland-urban interface Fire Dynamics Simulator to compare stand-level fire behavior between silvicultural cuttings that either emphasized or reduced forest structural complexity under a range of residual basal areas, surface fuel loads, and burning conditions. These cuttings included distance-based retention, variable retention, and random cuttings, optionally with thinning from below. Rate of spread did increase under more severe burning conditions, and slightly increased after thinning from below or after variable retention cuttings due to the creation of openings. Canopy consumption was lowest when thinning from below and highest after variable retention. While all treatments reduced fire behavior, the differences we observed support the advantage of using conventional fuels treatments where fire hazard reduction is of primary importance. Additionally, the effects of residual basal area, surface fuel load, and burning conditions highlight the multivariate considerations required when planning fuels treatments and assessing performance at stand or landscape scales.