Soil chemical properties and forest floor nutrients under repeated prescribed burning in eucalypt forests of south-east Queensland, Australia

The long-term impacts of repeated prescribed-burning on surface (0-30 cm) soil chemical properties and forest floor nutrients in two contrasting native eucalypt forests in south-east Queensland, Australia were assessed. Most effects were confined to the topsoil (0-10 cm). At the dry sclerophyll site, more than 40 years of annual burning had not led to any loss in topsoil total nitrogen and organic carbon but had significantly increased topsoil acid-extractable phosphorus. At the wet sclerophyll site, biennial burning (10 burns) resulted in decreases in topsoil total nitrogen and potentially mineralisable nitrogen despite a shorter experimental period (22 years). The increase in acid-extractable phosphorus with burning on this latter site was not significant. The varying impacts of prescribed-burning on soil chemical properties at the two sites may be partly explained by differences in site quality and in the number of times the forests have been subjected to various burning regimes. These changes may have implications for tree growth in the long term. Repeated burning reduced the weight, organic matter, and nutrient contents of the forest floor at both sites, the decreases being directly proportional to the frequency of burning.