The effect of fire on microbial biomass: a meta-analysis of field studies

Soil microbes regulate the transfer of carbon (C) from ecosystems to the atmosphere and in doing so influence feedbacks between terrestrial ecosystems and global climate change. Fire is one element of global change that may influence soil microbial communities and, in turn, their contribution to the C dynamics of ecosystems. In order to improve our understanding of how fire influences belowground communities, we conducted a meta-analysis of 42 published microbial responses to fire. We hypothesized that microbial biomass as a whole, and fungal biomass specifically, would be altered following fires. Across all studies, fire reduced microbial abundance by an average of 33.2% and fungal abundance by an average of 47.6%. However, microbial responses to fire differed significantly among biomes and fire types. For example, microbial biomass declined following fires in boreal and temperate forests but not following grasslands fires. In addition, wildfires lead to a greater reduction in microbial biomass than prescribed burns. These differences are likely attributable to differences in fire severity among biomes and fire types. Changes in microbial abundance were significantly correlated with changes in soil CO₂ emissions. Altogether, these results suggest that fires may significantly decrease microbial abundance, with corresponding consequences for soil CO₂ emissions.