Impacts of prescribed burnings on litter production, nitrogen concentration, δ13C and δ15N in a suburban eucalypt natural forest of subtropical Australia

Abstract

Prescribed burning is projected to be adopted more frequently with intensifying climate change; thus, a long-term study is necessary to understand the burning impacts on forest productivity and carbon (C) and nitrogen (N) cycling. Litter fall production rate can be used to indicate burning impacts on forest productivity, whereas N concentration, and C and N isotope composition (δ13C and δ15N) can be used to infer burning impacts on C and N cycling in plant-soil system. In this study, the impacts of low-intensity prescribed burning on litter production, N concentration, and C and N isotope compositions were continuously investigated for 6 years at five study sites in a natural eucalypt forest of subtropical Australia. Higher leaf litter production rate, N concentration and δ15N, and lower δ13C could be seen shortly after prescribed burning. The higher leaf litter N concentration and lower δ13C were likely due to the ease of competition for soil N and moisture from understory vegetation in the short term by prescribed burning. Leaf δ15N and N concentration were closely correlated, and seasonal changes in leaf litter production rate, δ13C and δ15N were observed. Burning season and related severity might determine the suppression degree of understory vegetation. Time since fire (TSF) was a significant impact factor influencing the litter fall production rate, N concentration, δ13C and δ15N of leaf litter fall for a decade following prescribed burning. However, monthly rainfall and temperature were less consistent in their impacts. Nitrogen limitation was enhanced by prescribed burning through the removal of litter and understory vegetation in the N poor forest and might be responsible for the long-term burning impacts. Low-intensity prescribed burning might have a long-lasting impact on forest litter productivity in nutrient poor forests in subtropical Australia.