Drivers of seasonal variation in fire effects on tree crowns

The plume of hot gases rising above a wildfire can heat and kill the buds in a tree crown, which can reduce growth and reproduction, or cause mortality. These effects have often been observed to vary throughout the fire season, but the mechanisms governing this variation are not well understood . Buoyant plume theory for vertical fire temperature distributions combined with energy budget theory for bud heating suggests that seasonal variation in necrosis heights is governed by variation in ambient air temperatures and the phenology of five bud traits: surface area, volume, density, specific heat capacity, and the heat transfer coefficient. We parameterized these theories using historical climate data and published bud trait data to predict seasonal variation in bud necrosis heights for three tree species: Picea glauca , Pinus contorta , and Populus tremuloides . Results showed that seasonal variation in air temperature and bud traits led to seasonal variation in predicted scorch height. An independent effects analysis showed that air temperature and bud traits were important drivers of variation in bud necrosis height, but the relative importance of these variables differed by species. These results highlight the mechanisms by which fire season influences the impacts of wildfires on trees.