Ecohydrological effects of management on subalpine grasslands: From local to catchment scale

Grassland and pastures are important land uses in subalpine and alpine environments. They are typically subjected to management practices that can change the biophysical structure of the canopy through defoliation and can alter soil hydraulic properties. These modifications have the potential to impact hydrological and energy fluxes as well as the primary productivity of grasslands. We investigate how a series of management practices, such as grass cut, grazing, and the consequent soil compaction due to treading by animals are affecting water resources, flood generation, and grassland productivity in a subalpine region. Results are obtained using a mechanistic ecohydrological model, Tethys-Chloris. The model is first confirmed using energy, water, and carbon fluxes measured at three eddy covariance stations over grasslands in Switzerland and discharge measured in a small experimental catchment. A series of virtual experiments are then designed to elucidate the importance of various management scenarios at the plot and catchment scales. Results show that only severe management actions such as low grass cuts or heavy grazing are able to influence considerably the long-term hydrological behavior. Moderate management practices are typically unable to modify the system response in terms of energy and water fluxes. An important short-term effect is represented by animal-induced soil compaction that can reduce infiltration capacity leading to peak flow considerably higher than in undisturbed conditions. The productivity of vegetation in absence of nutrient limitation is considerably affected by the different management scenarios with tolerable disturbances that lead to higher aboveground net primary production.