Effects of vineyards in the stability of steep slopes

Slope instability is very common in steep terrains cultivated with vineyards, as testified by numerous recent events in many areas traditionally devoted to wine production, such as different regions in Northern and Central Italy (Langhe, Oltrepò Pavese, Cinque Terre, Valtellina, Prosecco area; Cevasco et al., 2014; Bordoni et al., 2016) and in other European countries (Slovenia, Spain, Germany, France; Van den Eeckhaut et al., 2010). Rainfall-induced shallow landslides are the most widespread phenomena. They usually develop in the first 2 m of soil and are often triggered as a consequence of very intense and concentrated rainfalls. They cause additional effects such as damages to adjacent structures and infrastructures (buildings, roads, railways, etc.), or even injuries and loss of human life, which are commonly observed. Such events, furthermore, generally destroy the cultivations with a great impact on the local economy (loss of plants and soil, need to reshape the fields and new plantation or abandonment). In spite of the diffusion, the persistence, and consequences of shallow landslides on vineyards slopes, no comprehensive studies have been carried out so far to investigate the effects played by vineyards on preventing or promoting shallow landslides triggering. Two types of effects can be recognized. First, land use changes, affecting traditional viticulture areas, can cause modifications on the mechanical and hydrological settings of a slope, decreasing its stability. The main actions, which could affect slope behavior, are due to the changes on the agricultural practices in a cultivated vineyards (Cevasco et al., 2014; Persichillo et al., 2017) or to the complete abandonment of the tillages, with a further re-colonization of natural vegetation composed by shrubs and/or woods (Glade, 2003). Secondly, the mechanical effects of grapevines plants, in terms of providing additional mechanical root reinforcement to soil, can influence the strength of a cultivated slope (Bischetti et al., 2009). It is important a quantification of this reinforcement, taking into account of the effects of soil features and of agricultural practices on a potential decrease or increase in the root reinforcement capacity of grapevine plants. For these reasons, this paper estimates the effects of vineyards on shallow landslides occurrence in cultivated steep slopes considering both these aspects. The North-Eastern area of the Oltrepò Pavese was selected as tested site. This zone is characterized by a traditional viticulture vocation, where several shallow landslides events have occurred since 2009. This research aims to: i) analyse multi-temporal land use changes for assessing the degree of transformation in agricultural practices and(?) their influence on the susceptibility of slopes to shallow landslides; ii) quantify the root einforcement provided by cultivated grapevines plants in slopes characterized by different soil features and by different vineyard managements.