COS 175-3 - Improving postfire management decision-making by understanding the consequences of passive and active forest management following large stand-replacing wildfires

Abstract: A warming climate and large, severe wildfires have become the norm in seasonally dry coniferous forests of the interior western USA, causing uncharacteristically large, contiguous, stand-replacing patches (e.g., fire-killed trees). On federal forest lands, implementing postfire management restoration strategies (e.g., salvage logging) is contentious, sparking passionate debates and leading to numerous legal litigations filed to delay or prevent implementation. Forest managers need empirical data to compare the ecological tradeoffs between active (e.g., salvage logging) and passive (e.g., no action) management following large wildfires. Recent large wildfires present unique opportunities to expand the knowledge base for implementing scientifically sound postfire management through the implementation of local management studies as part of a national postfire monitoring network. We collaborated with National Environmental Policy interdisciplinary teams on federal forests and Tribal lands to establish a network of longitudinal experimental studies to quantify treatment effects on forests and vegetation. We use a combination of empirical measurements (e.g., complete randomized block design, paired sample design, stratified random sampling) and computer simulation modeling (Fire and Fuels Extension to Forest Vegetation Simulator (FFE-FVS)) to quantify short (< 1 year)-and long-term ( > 30 year) treatment effects on fuel dynamics and forest succession to addresses key postfire restoration questions: 1) What are the effects of active and passive management on forest structure, dead woody fuel loadings, tree seedling survival and shrub cover?; 2) Do treatments affect overall shrub and seedling regeneration and promote invasion by non-native species?; and 3) Do salvage operations positively or negatively affect rates of natural tree regeneration? In the short term, treated stands had a significant increase in FWD relative to controls, including the individual 1-hr (0.64 cm), 10-hr (0.64-2.54 cm), and 100-hr (2.54-7.6 cm) woody fuel size classes. Post-treatment fine woody fuel loadings (< 0.64 cm) were inconsequential to model-predicted wildfire behavior metrics (rate-of-spread, flame length) important to fire managers. FFE-FVS simulation modeling show a rapid accumulation of dead woody fuels (initial pulse period 0–25 years) in control units exceeding treated units. These changes may contribute to reburn severity of repeat wildfires. Salvage logging is feasible without significantly increasing woody fuel loadings and wildfire hazard, particularly when whole-tree harvesting is used. In conclusion, these projects will help forest managers plan postfire management treatment interventions to effectively steer early seral trajectories toward desirable future conditions and improves the scientific basis for prioritizing postfire restoration treatments, reforestation strategies, and fuel management strategies.