Positive and negative effects of forest management on water and sediment in a small experimental catchment: the Vernegà River, Catalonia, Spain
Xavier ÚBEDA, University of Barcelona, Spain
Forest management is an important practice to reduce the risk of forest fire in Mediterranean forests and to increase forest productivity. Such management on forest cover has hydrological and geomorphological implications on soils and in the fluvial system (Sala and Farguell, 2002; Úbeda et al, 2020).
In 2005, a shrub removal in a mixed Mediterranean forest composed by pines, evergreen oaks and cork oak trees, affected 15% of the Vernegà study catchment, an intermittent stream of 2.5 Km2 located in the Gavarres Massif, in Catalonia (Spain). The shrub removal enhanced the water circulation through the catchment by reducing the rainfall interception and increasing water infiltration in the ground. As a result, water flow increased in discharge but also in time, by reducing in 30 days on average the time that the catchment run dry throughout the year. Annual runoff increased from 81.9 mm to 92 mm after the shrub removal.
In addition, soil erosion increased and consequently, an increase in suspended sediment concentrations were detected in the stream. The combination of the increase in discharge and in suspended sediment concentrations resulted in increased sediment yields. Sediment yield before shrub removal was estimated in 940 kgkm-2yr-1, while after it sediment yield increased by one order of magnitude and reached 4,350 kgkm-2yr-1 (Farguell et al. 2022).
Despite the beneficial results of the forest management for the forest and for water circulation enhancement, negative impacts on soils and sediments have been detected. The sudden increase of soil particles mobilisation and the sediment accumulation within the catchment should be viewed as a negative impact on fluvial systems, and introduction of less aggressive forest management techniques should be considered.
Keywords: Forest management|Water yield|Sediment transport|sediment budget|Vernegà River
A104278JF