THE IMPACT OF FIRE ON REDISTRIBUTION OF SOIL ORGANIC MATTER ON A MEDITERRANEAN HILLSLOPE UNDER MAQUIA VEGETATION TYPE

Soil organic matter (SOM) changes affect the CO2 atmospheric levels and is a key factor on soil fertility and soil erodibility. Fire affects ecosystems and the soil properties due to heating and post-fire soil erosion and degradation processes. In order to understand fire effects on soil organic carbon (SOC) balance, research was undertaken on a fire-prone ecosystem: the Mediterranean maquia. The spatial distribution of SOC was measured in a Burnt site 6 months after a wildfire and in a Control site. Samples were collected at two different depths (0-3 and 3-10 cm) and SOC was determined. The results show that 41.8 per cent of the SOC stock was lost. This is due to the removal of the burnt material by surface wash. No significant differences in SOC content were found for the subsurface samples between burnt and control plots. Those results show that ashes and charcoal are transported by runoff downslope, and are subsequently deposited in the valley bottom, and this is the key process that contributes the burial of SOC after a forest fire. SOC redistribution by water erosion is accelerated after forest fires, and contribute to the degradation of soils located at the upper part of the hillslopes, but causes the enrichment with SOM of the soils located at the valley bottom. Buried SOC in the bottoms valley terraces will contribute to the sequestration of carbon for longer. Conservation of abandoned terraces is a key policy to avoid land degradation and climate change. Copyright (C) 2010 John Wiley & Sons, Ltd.