Soil organic matter and aggregates affected by wildfire in a Pinus halepensis forest in a Mediterranean environment

Three Mediterranean soils located in the north of the Province of Alicante (Spain) were studied for a year after a forest fire. The percentage of water-stable aggregates (between 0.2 and 4 mm) and organic matter content were measured. Microaggregates (< 0.2 mm) were observed using electron microscopy. The results showed the importance of type of forest fire on soil organic matter and aggregates. Soil structure was more affected by surface fire (which affects mainly brushwood and soil surface) than crown fire (which burns the tops of trees and some brushwood). Accumulation of organic matter from burnt trees and brushwood in areas affected by crown fire and alterations in organic matter content through the soil profile were observed. Surface forest fire affected soil structure more negatively than crown fire as observed using electron microscopy. Soils affected by surface fire may be more easily eroded and recovery of vegetation may be delayed because of effects on soil structure. Organic matter content through the soil profile comparing burnt and adjacent unburnt soil could be used to determine the type of fire.