Impacts on soil organic matter quantity and composition of a prescribed fire in a eucalypt forest (Sydney, Australia)

In this presentation, we will assess the direct impacts of a prescribed fire on the quantity and composition of organic matter in oligotrophic soils of a dry eucalypt forest (Warragamba, Sydney, Australia). Samples of the litter layer and surface soils horizons (Oa and Ah) were collected immediately before and after the fire. The prescribed fire was carried out September 2014 and was classified of moderate to high severity. In addition to litter and soil, samples of ash (burnt litter) were also collected after the fire.  In order to monitor the temperatures reached by the different soil organic matter pools during the fire, we installed thermologgers at the litter layer (n=30), the surface of the Oa soil horizon (n = 9), and at 1 cm depth within the Ah soil horizon (n =4). All samples were characterized by elemental analysis (total carbon, nitrogen, oxygen and hydrogen), thermogravimetry-differential scanning calorimetry and, a selected subset by solid-state ¹³C nuclear magnetic resonance. The observed changes in quantity and characteristics of the different organic matter pools will be discussed and the relationships between these changes and the temperatures recorded during the burn explored.