Vegetation recovery rates provide insight into reburn severity in southwestern Oregon, USA

Like much of western North America, The Klamath-Siskiyou Ecoregion of southwest Oregon and northern California is experiencing a departure from its historical fire regime, with greater proportions of high severity fire and less low to moderate severity fire compared to historical norms. Reburn events (i.e. when wildfires burn through areas that have recently burned) can exacerbate this departure when high reburn severity contributes to a conversion from mixed-conifer forests to an alternative stable state dominated by pyrogenic shrubs. Spatially explicit understanding of the predictors of reburn severity is necessary to identify areas where the risk of high reburn severity should be mitigated and areas where low to moderate severity fire can be encouraged to promote resilience to future wildfires. Previous research concerning drivers of reburn severity has considered the severity of the initial fire, topography, and fuel and weather conditions immediately preceding the reburning fire, but has not evaluated the potential effects of vegetation dynamics after a fire on reburn severity. We investigated whether remotely sensed rates of vegetation recovery following an initial fire, measured by change in Normalized Burn Ratio (NBR) over 2, 5, and 10 years, are important predictors of reburn severity, once other known drivers of fire severity have been accounted for. Though a Random Forests analysis revealed that other variables (notably pre-reburn vegetation cover, average fire season PDSI, and initial fire severity) were more important predictors of reburn severity, vegetation recovery rates after an initial fire were found to be moderately important predictors of reburn severity, with comparable importance to fire weather variables and higher importance than some topographical variables. Short-term (2-year and 5-year) vegetation responses to wildfire representing either delayed mortality or elevated vegetation recovery were both associated with higher reburn severity, as were higher 10-year rates of annual vegetation accumulation. The results indicate that along with previously identified drivers of reburn severity, remotely sensed metrics of vegetation recovery relatively soon after a fire may provide important insight that can support post-fire management decisions and wildfire response planning for future reburn events.

Automated summary

Research shows that the rate of vegetation recovery after a wildfire can be a moderately important predictor of reburn severity, along with other factors such as pre-reburn vegetation cover, fire season PDSI, and initial fire severity. This insight can support post-fire management decisions and wildfire response planning for future reburn events.