LB 22-192 - Can prescription burning protect valued resources by reducing wildfire severity? An analysis of empirical evidence.

Prescribed fire is increasingly used by land managers to restore ecological processes, reduce hazardous fuel loads, and to reduce the adverse effects of wildfire to valued resources (e.g., wildlife habitat, ecosystem services, timber, etc.). Empirical estimates of the success of prescribed fire for reducing burn severity to valued resources are somewhat limited, as most evaluations to date have contrasted areas treated with prescribed fire to similar areas without treatment. To expand on this research topic, we used the West Mims wildfire, which spread across 458 km2 of the Okefenokee National Wildlife Refuge (NWR) in 2017, as a case study to quantitatively assess prescribed fire effectiveness in terms of reducing wildfire severity both within and outside of treatment areas. Wildfire severity was measured using Landsat-derived differenced normalized burn ratio (dNBR) index obtained from the Monitoring Trends in Burn Severity (MTBS) program. Prescribed fire history for the Okefenokee NWR was obtained from the US Fish and Wildlife Service (USFWS). Preliminary results indicated that mean wildfire severity (i.e., mean dNBR) was 37% lower in areas that had been treated with prescribed fire prior to the wildfire event. Post-hoc multiple comparisons indicated that fire severity was significantly (P < .05) lower within many of the treatment areas. A moderately strong correlation (R = 0.61) was found between mean dNBR and months since prescribed fire, with the lowest and highest burn severities respectively occurring within 1 to 10 months and more than 30 months after controlled burns were conducted. Analysis of time since treatment was limited to these ranges as the prescribed fire history dataset begins in 2013, ca. 3.5 years prior to the wildfire event. Preliminary results demonstrate that prescribed fire can significantly reduce the adverse effects of wildfire to valued resources, but treatment effects decrease with time. Subsequent analyses will focus on the rasterization of burn-unit boundaries to calculate prescribed fire metrics on a cell-by-cell basis, assessing relationships between burn severity and vegetation, development of predictive models, and scaling the workflow to analyze prescribed fire treatment effects across the US Southeast.