Soil reinforcement provided by the root system of grapevines : quantification and spatial variability

Rainfall-induced shallow landslides represent a major threat for cultivated steep terrain, including vineyards that are typically established on hillslopes. Vineyards represent high-value cultivation in many countries; there is a tendency to adopt new and more intensive cultivation practices and/or to extend plantations to inappropriate sites, which influences the natural environment. Considerable damage thus increasingly affects vineyards in terms of partial or total destruction of cultivation, structures and infrastructures, as well as the surrounding landscape. However, little research has been conducted to date to investigate the role of grapevine plants on slope stability and to reduce the related impacts on the environment.Aiming to help fill the gap, we carried out a study to quantify the role of vineyards on slope stability by modelling the additional reinforcement to the soil provided by grapevine roots and their spatial distribution (i.e. considering the distance from the trunk) using the Root Bundle Model. A back analysis on a number of shallow landslides that occurred in vineyards was also conducted to validate the results. The area of our investigation was in the northeastern part of Oltrep\uc3\ub2 Pavese, Northern Italy, which is a hilly terrain cultivated for many decades with vineyards and prone to landslide phenomena that in recent years have caused great economic losses to the agricultural sector and damage to buildings and roads. Moreover, abandoned vineyards represent an issue in terms of their "return" to a natural state. Values simulated by modelling and back-calculated from the landslide inventory completely agree and are in the range of reinforcements commonly obtained for many other species. However, in contrast to native species, the spatial variability of the reinforcement in the case of vineyards is lower because of the regularity of planting and the lack of differences in plant age. Additionally, the variability of the rooting depth is negligible because it is controlled by the rootstock.Finally, the results obtained in this work show that the models developed for native species can also be adopted for grapevines and, if coupled with a slope stability model, represent a basis for providing guidelines to design vineyard plantations in those areas susceptible to instability, to support decisions concerning land management and land use change and more generally to reduce environmental impacts