Soil properties in fire-consumed log burnout openings in a Missouri oak savanna

Downed logs are known to increase species diversity in many forest ecosystems by increasing resource and structural complexity and by altering fire behavior in fireprone ecosystems. In a frequently burned oak savanna in central Missouri, combustion of downed logs formed patches that have remained free of herbaceous vegetation for more than 3 years. To assess the influence of “log burnouts” on soil conditions we compared soil chemical, biological and physical properties in log burnout zones and beneath surrounding herbaceous vegetation. Soil pH and extractable soil NO3-, P, K+ and Ca2+ were all higher in the log burnouts compared to adjacent soil. There was no difference in total soil N or extractable NH4+. An index of plant N availability was lower and the soil C:N ratio was higher in the burnout patches, though the magnitudes of these reductions do not explain the persistence of the bare patches. We suspect that following log combustion degraded soil aggregate structure and decreased soil porosity alters soil water availability and restricts plant colonization into the log burnouts areas. The modified soil conditions associated with fire-consumed coarse woody debris may have a long-term influence on herbaceous species diversity and spatial distribution in fire-maintained oak savannas.