Regional patterns of fire recurrence effects on calcareous soils of Mediterranean Pinus halepensis communities

The effects of fire recurrence on soils were studied on calcareous sites of Mediterranean Pinus halepensis-dominated communities in Catalonia (NE Iberian Peninsula). Soil organic horizons and mineral soils of 15 sites consisting in two adjacent areas, one burnt only once (in 1994) and the other burnt twice (in the same 1994 fire but also once before, from 1975 to 1993) were surveyed 9 years after the last fire. Fire recurrence decreased the occurrence and dry mass of soil organic horizons. Total nitrogen concentration in L organic horizon was higher in less recurrently burnt areas. No other significant difference between once- and twice-burnt areas was found for any studied chemical parameter either in organic L and FH horizons or in mineral soils. The present study underlines the fact that fire effects on soil organic horizons are accumulated through consecutive fires.