Results of a long-term study on an experimental watershed in southern Italy

Forested watersheds offer a wide array of benefits. In fact, forest cover affects the hydrological response of a basin, regulating the volumes of water content in the soil through processes of interception, infiltration and evapotranspiration. Altering forest cover can significantly influence water balances at both site and watershed scale. Understanding the relationship between vegetation and streamflow is vital in evaluating the effects of forest disturbance on hydrologic response, and in identifying best management practices in a watershed. The aim of the present research was to evaluate the role of forests in the hydrological processes which occur in a headwater basins draining by a Calabrian pine forest (Pinus laricio Poiret). Moreover, the analysis also involved studies of forest carbon uptake. Since 1986 the Bonis watershed, a mountain basin located in Sila Greca (Calabria), has been instrumented and rain, runoff, throughfall, stemflow and some climatic parameters have been measured. Subsequently, in order to study carbon and water cycle dynamics (for climate change mitigation assessment) and to give information about the amount of water used by plants, a tower with Eddy covariance technique was installed. The study concerned the analysis of precipitation and of the interaction between forest cover and throughfall, stemflow and runoff after a thinning treatment. Investigation on CO2 and evapotranspiration with Eddy covariance methodology has also been performed. Results have shown an increase (more than 50%) of the runoff in the basin after forest thinning (50% of the stems corresponding to 30% of the basal area) while no significant differences in rainfall have been detected before and after forest thinning. In particular, after thinning, runoff coefficient increased from 0.21 to 0.29 during the autumn-winter period, while in the summer season it shifted from 0.16 to 0.41. The results obtained evidenced that forests regulate soil water content availability and are important for water regimentation, especially in Mediterranean environments.