Modelling effects of human-caused fires on rill detachment capacity based on surface burning of soils in forest lands

It is well known that forest fires affect physico-chemical characteristics of soils. However, few investigations have explored the effects of human-caused fires on soil erosion processes, particularly for the parameters used in rill erosion on steep slopes. To fill this gap, this study has evaluated the effects of human-caused fires on the rill detachment capacity (Dc) and rill erodibility (Kr) in the burned soils, compared to the unburned soils, as control soils, in a forest of Guilan province (northern Iran). For measuring Dc, the slopes (3.9, 9.1, 15.3, 23.9, and 32.7%) and water discharges (0.28, 0.38, 0.46, 0.54, and 0.63 L/m s-1) were adjusted to the desired values using a laboratory flume. Moreover, three properties of soils including the organic matter, bulk density and aggregate stability were determined. The results showed that Dc and Kr were significantly higher in the burned soils, compared to the unburned soils (both more than twice), as the consequence of the significant changes in organic matter content, bulk density and aggregate stability (p < 0.01). Compared to unburned soils, when soil organic matter and aggregate stability decrease, Dc increases in burned soils and these differences led to rill development. These changes in soil properties were confirmed by principal component analysis, which did show a clear discrimination between the burned and unburned sites. The model developed can predict the rill detachment capacity according to a simple linear relationship of the selected soil properties and may be used for an appropriate hydrological management of forest soils.