Impact of land use changes and of agricultural management in vineyards to shallow landslides susceptibility in a representative area of northern Italian Apennines

Land use is one of the most important factor which can promote or reduce the susceptibility of an area towards shallow slope instabilities. Different plant species guarantee different amounts of additional reinforcement to unstable soil covers, thank to the mecahanical effects of their roots as a function of their density and shear strength properties. Furthermore, land use changes and modifications of management practices in cultivated slopes could cause an increase in the proneness towards these phenomena, due to modification on vegetational types and on farming and tillage operations that could reduce the root additional reinforcement in soil. Hilly areas vocated to viticulture are one of the most affected landscapes that suffere of shallow slope instabilities as a consequence of modification in agricultural management and of land use changes for the abandonement of previously cultivated hillslopes. Therefore, this work aims to analyze the effects of the land use changes and of the different agronomical practices occurring in an area vocated to viticulture prone to shallow landslides triggering. From the point-of-view of land use changes, we analyzed especially the linkage between the location of past shallow landslides events and the possible temporal variations of land cover or of agricultural practices in still cultivated areas. For the effect of agricultural practices in vineyards, we quantified the root reinforcement and the probability of occurrence of shallow landslides on vineyards managed with traditional agricultural techniques of tillage and permanent grass cover as well as the alternation of these two practices between adjacent inter-rows. The research was conducted in several test-sites of the Oltrepò Pavese (Lombardy region, north-western Italy), one of the most important Italian zones for wine production in northern Italian Apennines. The results show that the test-site was characterised by pronounced land abandonment and important changes in agricultural practices. In particular, abandoned cultivated lands that gradually recovered through natural grasses, shrubs and woods were identified as the land use change classes that were most prone to shallow landslides. Regarding the features of the grapevine root system, vineyards with alternation management of inter-rows had the highest root density and the strongest root reinforcement, of up to 45% in comparison to permanent grass cover, and up to 67-73% in comparison to tilled vineyards. As a consequence, slopes with medium steepness (10-18°) were unstable if inter-rows of vineyards were tilled, while vineyards with permanent grass cover or alternation in the inter rows promoted the stability of slopes with higher steepness (>21-25° for vineyards with permanent grass cover in the inter rows, 28-33° for vineyards with alternation). The results of this study yielded important information to establish effective land use management practices able to reduce shallow slope instabilities. This work was supported by the project Oltrepò BioDiverso, funded by Fondazione Cariplo in the frame of AttivAree Program.