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 to assess the effects of forest disturbance on hydrologic response, and to identify 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 basin draining a Calabrian pine forest (Pinus laricio Poiret). Moreover, the analysis also involved studies of forest carbon uptake. Since 1986 the Bonis watershed has been instrumented and precipitation, runoff, throughfall, stemflow and some climatic parameters have been measured. Recently, 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 the interaction between forest cover and throughfall, stemflow and runoff after a thinning treatment. Investigation on CO2 and evapotranspiration with the Eddy covariance methodology has also been performed. Results have shown an increase (more than 50%) of the runoff in the basin after the 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 the forest thinning. In particular, after the thinning, the 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 of this study evidenced the effect of a silvicultural practice on the runoff response thus showing that an appropriate forest management can have a key role in water management at basin scale.