Fuels change quickly after California drought and bark beetle outbreaks with implications for potential fire behavior and emissions

Abstract Background An extreme drought from 2012–2016 and concurrent bark beetle outbreaks in California, USA resulted widespread tree mortality. We followed changes mortality, stand structure, surface canopy fuels over four years after the peak of mortality Sierra mixed conifer pinyon pine ( Pinus monophylla ) forests to examine patterns needle retention death, snag fall across species. then investigated how event affected fuel loading potential impacts on fire hazard emissions. Results Drought beetle-related shifted be more evenly distributed size classes concentrated pines. Substantial loading, density, loads, wildfire emissions occurred within following levels with largest related increases coarse woody debris. Nearly complete for all species except red fir Abies magnifica ). Pine incense cedar Calocedrus decurrens snags fell quickly than Potential behavior modelling suggested that crowning torching decreased as trees dropped dead needles fell, but were transferred fuels, smoldering combustion increased, causing greater Conclusions Our study understanding events caused by disturbances alter have affect two compositionally different seasonally dry forest types. After a major event, high flammability may only last few years, can increase considerably same time period these The accumulation resulting multi-year combined increasing frequency western U.S. lead heavy loads under certain weather conditions result severe effects, particularly types where decades successful suppression has densification.