Sediment and solute yield in forest ecosystems affected by fire and rip-ploughing techniques, central portugal: A plot and catchment analysis approach

Abstract

In the last two decades, Portuguese forests have undergone important changes in land use and management practices, some of which are posing significant problems as regards long-term sustainability of forestry. This paper examines the degradation processes associated with two events: deep ploughing prior to planting (termed ‘ripploughing’) and forest fire. The research design comprised plot and catchment approaches in which fluxes of water, sediment and solutes for rip-ploughed and burnt pine forest were monitored for the first year after ploughing and fire respectively. Although rip-ploughed areas experienced very high erosion rates at the plot scale (up to 51 t ha −1 yr −1) and enhanced catchment runoff due to increased overland flow (up to 50% of rainfall), catchment sediment yield was small because of sediment storage at the bases of slopes and in channel heads. For burned pine, the destruction of the vegetation and litter layer led to sharp increases in catchment runoff and nutrient losses both as dissolved and suspended sediments. Despite sediment loss at the plot scale being below 3 t ha −1 in the first year after the fire, the catchment suspended sediment loss in storm events was several orders of magnitude higher than for the partly rip-ploughed catchment.