Temporal changes in soil aggregates and water erosion after a wildfire in a Mediterranean pine forest

The evolution of soil structure after a forest fire was studied on two zones representatives of a typical Mediterranean Pine forest. These zones were in opposite slope orientation but with similar topographical and pedological characteristics. Changes in soil macro-aggregation and water stable micro-aggregation were monitored seasonally during a year after the fire. The water erosion patterns were also studied from August 1993, immediately after the fire, to the end of 1996. The first 5 cm of soil depth were the most affected by fire temperature, showing clear differences on aggregate distribution and temporal variability between zones. In the north-facing soil, a substantial and gradual recovery on soil aggregation was observed mainly in the fraction greater than 5-mm diameter; this reached an increase of 27% in mass of aggregates. In the south slope, the evolution of aggregation was smooth and restricted to the fraction minor than 0.1 mm. These differences between zones are reflected also in their values on soil cohesiveness and compaction, being lesser in the south-oriented soils. Values of erosion parameters show that both zones have the higher soil losses during the immediate period (4 months) after the fire, being more important in the south zone. This zone produced more sediment and runoff (52.42% and 29.95%, respectively) than north-facing soils for the whole period studied. (C) 2001 Elsevier Science B.V. All rights reserved.