Effects of plant roots on soil shear strength and shallow landslide proneness in an area of northern Italian Apennines

In areas with similar soil properties and geomorphological conditions, different land uses could promote or reduce the failure probability towards shallow landslides, especially due to differences in the reinforcement acted in the soil by plant roots. In this paper, root density, mechanical properties, and reinforcement provided by different land use types (sowed grasses used to produce animal feed, vineyards cultivated with different agronomical management practices, shrublands, woodlands of broadleaved species) of a representative area of northern Italian Apennines (Oltrepò Pavese hilly sector) were quantified and inserted into a slope stability model to estimate the effects of different land uses on shallow landslide failure probability. Root reinforcement is correlated proportionally to root density in soil and root mechanical properties. Furthermore, a greater root reinforcement in the soil guarantees a lower failure probability of a slope. Sowed grasses and shrublands in abandoned areas are the most land uses which are more prone to shallow landsliding, followed by vineyards with tilled inter-rows. Vineyards with permanent grass cover or alternation in the inter-rows and woodlands promote the stability of slopes in a wide range of steepness (> 21–25° for vineyards with permanent grass cover in the inter-rows, 28–33° for vineyards with alternation in the inter-rows and woodlands). According to these results, possible land use managements acting as mitigation measures for shallow landslides could be implemented.