Does the presence of large down wood at the time of a forest fire impact soil recovery?

• Soil nutrients were significantly reduced in severely burned red soils.
• Nutrient-limited conditions from severe soil heating persist for years after fire.
• Fungal and bacterial community compositions varied with burn severity.
• Microbial communities seem to have the capacity to quickly adjust to extreme disturbances.
• Conditions contributing to nutrient-limited red soils pose concern about soil productivity.

Fire may remove or create dead wood aboveground, but it is less clear how high severity burning of soils affects belowground microbial communities and soil processes, and for how long. In this study, we investigated soil fungal and bacterial communities and biogeochemical responses of severely burned “red” soil and less severely burned “black” soil from a burned forest on the eastern slope of the Cascade Range in Oregon. Specifically, we examined the effects of burn severity on soil nutrients and microbial communities for 1–4 years after wildfire. Soil nutrients were significantly reduced in red soils. Soil fungi and bacteria, assessed with molecular methods, steadily colonized both burn severities and soil biodiversity increased throughout the study showing that microbial communities seem to have the capacity to quickly adjust to extreme disturbances. Although richness did not vary by soil type, the fungal and bacterial community compositions varied with burn severity. This difference was greatest in the early time points following the fire and decreased with time. However, nutrient-limited conditions of red soils were detected for four years after the wildfire and raise concern about soil productivity at these sites.