Grassland fire effect on soil organic carbon reservoirs in semiarid environment.

The effect of fire on soil organic matter content is highly variable and depends on several factors including fire intensity, soil type and nature of burned material. Grassland in semiarid environment are often managed by shepherds with annual burning in order to enhance pasture recovery. The aim of this work was investigating the effect of fire as grassland management tool on soil organic carbon (SOC) reservoirs and on post-fire plant recovery. The study was conducted on Hyparrenia hirta grassland and Ampelodesma mauritanicus grassland, located in the Province of Palermo, in the north of Sicily. Soil samples were collected at two depth (0-5 and 5-20 cm) before and after experimental fire and soil organic carbon was measured. During grazing fire soil surface temperature was monitored. Biomass of both grassland species was analyzed to determine dry weight and its chemical composition. Our major results showed that SOC varied significantly with land cover, while it is not affected in the short period by grassland fire. Ampelodesma grassland stored more organic carbon (60.5 ± 2 Mg ha-1) compared to Hyparrenia grassland (40.2 ± 1.5 Mg ha -1), thanks lower content in biomass of labile carbon pool. No significant difference in SOC before and after fire may been caused by multiple factors. Firstly, soil temperature measured during fire was low due to poor litter layer, secondly in semiarid environment higher mineralization rate results in lower soil carbon labile pool, thirdly most SOC is stored in the finest soil fractions and thus such physical protected SOC pool is not affected by fire.