Postfire treatments alter forest canopy structure up to three decades after fire

Abstract

We evaluated the effects of postfire management on forest structure in mixed-conifer forests of northeastern Washington, USA. Postfire treatments were harvest-only, harvest combined with planting, planting-only, and postfire prescribed fire. We used aerial light detection and ranging (LiDAR) to measure vertical and horizontal components of postfire forest structure over a period of 2 to 32 years after fires. We compared treated areas to control areas with similar bioclimatic environments and past fire severity. We used niche overlap statistics to quantify distributions of individual forest structure components and PERMANOVA to assess forest structural response to the presence or absence of treatments, past fire severity, time since treatment, and bioclimatic setting. Harvest alone after fire decreased dominant tree height and reduced vertical canopy complexity and the cover of tall trees. Harvest combined with planting increased dominant tree height, vertical complexity, and cover in lower height strata. Planting and prescribed fires showed little difference in forest structure relative to untreated controls. Overall, the burn severity of the initial fire was the strongest influence on postfire structure, and many aspects of vertical and horizontal forest structure showed little difference with increasing time since fire.