Two decades of low-severity prescribed fire increases soil nutrient availability in a Midwestern, USA oak (Quercus) forest

Abstract

For the last 23years, low-severity prescribed fire has been used to decrease shade and fire tolerant tree species, increase oak (Quercus spp.), and increase herbaceous plant diversity in the East Woods of The Morton Arboretum, Lisle, Illinois, USA. The impacts of these fires on the belowground ecosystem have yet to be measured. Soil (0 to 10cm) and litter samples were collected 12, 19, and 24months following the most recent fire on 40 plots in burned and un-burned control areas. Soil physical, chemical, and biological properties were measured and compared with vegetation composition and structure from these same plots. Compared to un-burned controls, burn plots had greater canopy openness, greater herbaceous richness, and a lower spring/summer herbaceous ratio. Burned plots had higher soil moisture content, pH, electrical conductivity, Ca2+, Mg2+, K+, Na+, NO3−, total N, particulate organic matter (POM), total organic C, and potential N mineralization. Soil microbial biomass and respiration, texture, color, aggregate stability, and hydrophobicity were not different in burned compared to un-burned plots. Indices of litter and soil invertebrate diversity were also not affected by prescribed fire. Three stepwise least squares models predicted woody richness, herbaceous richness, and spring/summer herbs with aspect, litter invertebrate richness, and soil factors (pH, potential N mineralization, C/N ratio, Mg2+, Bray P, and soil invertebrate Simpson index). These results confirm others showing prescribed fire to increase soil nutrient availability. Forest structural changes with fire appear correlated with soil nutrient availability. Decreased soil C, nutrient retention, invertebrate diversity, or increased hydrophobicity and the presence of exotic plants is often observed with high-severity fire; but, these negative impacts do not appear to be present with these long-term, low-severity fires.