The influence of current year fire on leaf litter decomposition rates and microbial enzyme activity in forests undergoing ecological restoration

As a result of fire suppression, open oak woodlands, once characteristic of the interior of the southern USA, are being lost to mesophication. This process leads to changes in the plant community and has the potential to change rates of decomposition and nutrient cycling through changes in environmental conditions or leaf litter composition. Restoration projects to reduce the effects of mesophication include thinning the canopy to remove mesophytic species and prescribed burn regimens to return the plant community to a fire tolerant and dependent one. However it is unclear what effects restoration (or mesophication) has on the decomposition of leaf litter, nutrient cycling, and microbial activity. This study compared leaf litter decomposition rates of six tree species (Quercus stellata, Quercus falcata, Quercus alba, Carya tomentosa, Liquidambar styraciflua, and Ulmus alata) ranging from those characteristic of historical open oak woodland to those that are mesophytic, and determined how these decomposition rates differed between restored and unrestored and burned and unburned portions of an upland oak forest. Decomposition rates were related to microbial extracellular enzyme activity in decomposing litter to examine potential mechanisms for different decay rates. Enzymatic efficiency of decomposition was generally higher in restored sites, but prescribed fire in a given year was important and significantly reduced decomposition rates and enzymatic efficiency. Reductions in decomposition rates due to fire were more evident in mesophytic species than in upland oak species. This combination of results suggests that while restoration increases enzymatic efficiency in years between burns, a fire in a given year can override any effect of past restoration treatment on the enzymatic efficiency of decomposition in these woodlands. Furthermore, decreases in litter abundance following fire, coupled with increased decomposition in years between fires and decreased litter inputs from the thinned canopy should increase solar penetration to the understory and soil layers and promote regeneration of shade-intolerant species that once dominated these ecosystems