Effects of land use changes on badland erosion in clayey drainage basins, Radicofani, Central Italy

Hillslopes of the Radicofani area, in the upper valley of the Orcia River (southern Tuscany region, Italy), consist mainly of early Pliocene clayey sediments and are widely affected by frequent badland erosion. Reforestation with frugal conifers has been carried out in the area over the last 50 years. The goal of the present study is to evaluate the impact of reforestation and land use change on erosion rates in nine small drainage basins through a multidisciplinary approach. Geological, geomorphological, hydrological and land use characteristics were analyzed by a diachronic confrontation between pre-reforestation (1954) and post-reforestation (2007) situations. Aerial-photo interpretation and processing in GIS allowed us to quantify changes in areas affected by badland erosion, land use and variations in erosion rates. Moreover, dendrometric data were gathered from 18 circular sample plots in forest stands of 40 years old. This allowed us to evaluate both the adaptability of different forest species to the clayey substrate and reforestation fragmentation. The differences between the pre- and post-reforestation situations led to increases in arable land and forest areas and considerable decreases in erosion rates and badland areas. However, no significant correlation between the erosion rates and the forest area emerged, due to the excessive fragmentation of reforestation cores and relatively small reforested surfaces. Land reclamation seems to have played a more important role in reducing erosion in the clayey substrate. The integrated method presented here is an important tool useful to understand the morphological dynamics of badlands in relation to forest vegetation, and for land planning and management.