MODELLING THE INFLUENCE OF VEGETATION CLEARANCE IN THE OCCURRENCE OF SHALLOW LANDSLIDES  

R. Massari (rmassari@omniway.sm) and P.M.Atkinson (pma@soton.ac.uk)
University of Southampton, UK  

Several previous studies have found that the removal of a dense vegetation cover often leads to slope instability. In the short term it increases the receipt of precipitation at the ground surface, which can result in accelerated erosion as well as shallow landslides. In the long term, with a gradual decrease in root strength, it may also cause deep landslides. The landslide susceptibility of an area around Monte Nerone, in the Umbro-Marchean Apennines (Italy) was estimated using generalised linear modelling. Geological and geomorphological slope features were stored in a GIS database (Atkinson and Massari, 1998; Massari and Atkinson, submitted). Modelling results confirmed that, particularly for landslides on earth, going from bare soil to ploughed ground, uncultivated, pasture, open forest and forest, there is a clear decrease in landslide susceptibility. Since 50% of the area studied is at present covered by forest, a change in land use of these areas would increase their landslide susceptibility. The statistical model obtained from past earth-slumps and earth-flows was applied to present and possible future conditions. This allowed the forecasting of the effect of vegetation clearance on landslide susceptibility, and the mapping of the most sensitive areas. Overall, around 30% of the area now covered by forest would become unstable. Particularly sensitive are those areas where predominantly marly formations outcrop.