Soil erosion in mountain shrub areas: effect of prescribed fire

Abstract

Currently, one of the biggest environmental problems at the global level is the soil loss by water erosion. The erosive agent can cause significant losses of nutrients and organic matter, especially when the soil surface supports a reduced vegetation cover. In Portugal, prescribed fire is a commonly used practice to control the fuel availability and consequently reduce the wildfires risk. However, this practice removes the vegetation cover, leaving the soil more exposed to erosive processes. In this sense, the present work aims to evaluate the effect of prescribed fire on water erosion in shrub areas of the Montesinho Natural Park, NE Portugal. After the fire, 6 erosion plots of 4 m² each (4 × 1 m) were installed to assess soil loss and runoff in the burned area. The results encompass 8 months (March to December 2021), and samples were collected for each rainfall event, making a total of 6 evaluations. The runoff and soil loss (sediment mass) were obtained through calculations that encompassed the runoff, the sediments transported into the runoff collection reservoirs and the sediments deposited on the front of the erosion plots (placement of a device that allows the collection of transported sediments). The average of soil loss was 15.4 g m^-2, the average of runoff was 1.4 mm, corresponding to a runoff coefficient of 4.2%. To evaluate C and N losses, the sediments were separated into 4 size classes (<0.2mm, 0.2-0.5mm, 0.5-2mm, >2mm) and analyzed in laboratory the C and N concentrations. The low total precipitation, during the test period, caused low runoff values and, therefore, low losses of soil, C and N.