POSTFIRE DYNAMICS OF EROSIONAL PROCESSES UNDER MEDITERRANEAN CLIMATICCONDITIONS

This paper evaluates the changes in the erosional and hydrological pro cesses after a forest fire under Mediterranean climatic conditions by means of simulated rainfall experiments. The measurements taken in dif ferent seasons demonstrate that immediately after the fire (in summer) the surface runoff and the erosion rates were negligible due to the h igh infiltration rates of the dry and ash covered soils. The winter fo llowing the fire (4 months later) surface runoff and erosion rates wer e very high (57.3%, 148 g m(2)h(-1)) due to the high moisture content, crusting and the low vegetation cover. The following measurements sho w a rapid decrease in the surface runoff, sediment concentration and e rosion rates. The runoff coefficients were always higher in the wet se ason (winter) than in the dry season (summer) as a consequence of the contrasting seasonal soil water regime in mediterranean conditions and were similar to the rates found in scrubland areas not recently affec ted by fire. Three, four and five years later the measurements show ve ry low runoff and erosion rates. Pre-fire runoff rates were reached ea rlier for summer conditions (2 years) than for winter conditions (> 4 years). The natural erosion rates were reached one year after the fire for summer conditions and 18 month later for the winter conditions. S patial variability of runoff and erosion was very low immediately afte r the fire and very high four months later under winter conditions, de creasing gradually with the recovery of the pre-fire conditions: growt h of vegetation, low runoff and negligible erosion rates.