Abstract
Recently, the Alps have undergone abrupt environmental transformations, characterized by widespread forest expansion and increasingly frequent forest disturbance regimes, which are expected to modify the soil and water conservation functions of mountain ecosystems. Nevertheless, the hydrological consequences of accelerating forest cover dynamics in the Alps are poorly understood due to the scarcity of empirical and numerical studies, explicitly dedicated to runoff and sediment dynamics within forested Alpine catchments. Thus, the present study aims to shed vivid light on the downstream impacts of forest changes by elucidating cover-specific runoff and erosion dynamics in four 27-m2 plots (Chapter 2); simulating influences of deadwood cover and its extraction using the WEPP model (Chapter 3); and evaluating transfer mechanisms of runoff and sediment across the scales (Chapter 4) within nested catchments of the Eastern Italian Alps. First, plot-scale observations highlighted the persistently elevated upland runoff and erosion rates resulting from cumulative disturbances. Second, the subsequent modeling analysis, supported by field data, quantitatively demonstrated the marked protective role of deadwood as a biological legacy in disturbed hillslopes. Third, a nested monitoring across a 166 km2-sized new experimental watershed indicated that runoff and sediment yields at finer scales (plots to headwaters) are more susceptible to the characteristics of summer storm events. Given the projected intensification of summer rainstorms interspersed with longer dry periods, runoff and sediment transfer within increasingly forested Alpine catchments would be subject to greater spatial heterogeneity and projection uncertainty. Forests and rivers would be more tightly linked from water and sediment perspectives, calling for the strengthening of integrated watershed management. Whereas continued field monitoring efforts are needed to fully account for the generality of these findings over the entire Alps, the present study would set a milestone toward a better understanding of the alternative functioning of the ‘greening water tower of Europe.’