Effects of post-fire management on dead woody fuel dynamics and stand structure in a severely burned mixed-conifer forest, in northeastern Washington State, USA

The increasing amount of high-severity wildfire in historical low and mixed-severity fire regimes in western US forests has created a need to better understand the ecological effects of different post fire management approaches. For three different salvage prescriptions, we quantified change in stand structural metrics (snag densities and snag basal areas), dead woody fuel loadings, tree regeneration survival, and percentage change in vegetation cover before and after post-fire logging 1 year after the 2015 Stickpin Wildfire on the Colville National Forest in northeastern Washington State, USA. In a generalized randomized block design three salvage logging prescriptions were randomly assigned within each block: no treatment control (C); standard salvage retention (SSR; thin to 3.4 m²/ha basal area); and mimic green tree thinning (GTR; thin to 10.3 m²/ha basal area). SSR reduced average snag basal area 73–83% to 4.1–8.8 m²/ha (68–674 trees ha−¹). GTR reduced average snag (standing dead trees) basal area 41–71% to 6.5–15.9 m²/ha (90–794 trees ha−¹). There were mixed results for the change in dead woody fuel loadings depending on fuel size class. In general, fine (FWD) and coarse woody (CWD) debris tended to increase immediately post-treatment in logged areas relative to the controls but did not exceed management loading threshold for providing acceptable risk of fire hazard. Treated stands had a significant increase in FWD relative to controls, including the individual 1-, 10-, and 100-hr fuel size classes.The treatment effect differed by experimental block. The 1000-hr sound class did not have a significant treatment effect. Changes in surface fuel loading were inconsequential to modeled wildfire behavior metrics (rate-of-spread, flame lengths). The Fire and Fuels Extension to Forest Vegetation Simulator (FFE-FVS) modeling projected CWD accumulation in the controls exceeded total accumulation in both treatments. Future fuel loadings may affect reburn severity as our simulated wildfire 20 years after harvesting caused significant mortality (89%) to regenerating forest. Almost all blocks showed a decrease in seedling counts pre and post-logging, including the control plots. This study provides empirical data on the effects of different post- fire management strategies that can inform environmental analyses for future post-fire management decision and address social concerns associated with this often-controversial practice (Roccaforte et al., 2012).