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Abstract: The present work aims to assess the effects of wildfires on soil aggregate stability and the role therein of contrasting lithologies as well as of fire-induced changes in organic matter content and soil water repellency. To this end, a pair-wise comparison of neighbouring burned and unburned soils was carried out and complemented by laboratory heating experiments to clarify the role of fire intensity. In total, 18 pairs of adjacent burned and unburned pine forest soils were sampled within one month after wildfire. At each site, five samples were collected of the top 5cm of the A horizon at randomly selected sample points and were mixed in the field to obtain one composite sample per site. Three additional samples were collected at each site but stored separately, and those of three sites were selected for the laboratory heating experiments. Laboratory heating involved five different temperatures ranging from 25 to 460°C. Aggregate stability of the field and laboratory samples was determined using the water drop impact test, organic carbon content using a modified Sauerlandt method and soil water repellency using the ‘Molarity of an Ethanol Droplet’ test. The wildfire effects on field aggregate stability were highly variable and results indicated that these changes depend primarily on organic matter combustion and, thus, fire intensity. Controlled heating up to 220°C either did not alter aggregate stability or increased it with increasing temperature, possibly due to the development of a protective coating of organic compounds inducing water repellency. Heating at 380 and 460°C, by contrast, produced considerable to massive combustion of organic matter and, thereby, very pronounced reduction of aggregate stability as well as water repellency. [Copyright &y& Elsevier]

The article discusses findings of a study which examined the effect of wildfire on soil erodibility for common woodlands in Galicia, Spain. Several definitions of soil erodibility are presented. The criteria for the selection of locations burned by a wildfire included parent material, vegetation and presence of reference sites. Based on the results of the study, there were no significant changes in the particle size distribution of soil found on the burned sites. Another observation from the study was less effect of fire on aggregate stability.

Focuses on three adjacent sites in steeply sloping woodland in Galicia (Northwest Spain), at which surface runoff and associated erosion under simulated rainfall were measured on five occasions between June 1998 and July 1999. How two of the three sites had recently been deforested and topsoil added, and one of these two had been sown with grass, which was germinating at the onset of the study; Impact of deforestation on runoff and erosion rates; Why all three soils were very hydrophobic, which led to higher runoff rates than expected, especially during dry periods; Suggestion that great structural stability prevented there being a significant correlation between runoff rate and soil erosion.