Quantification of the mechanical reinforcement of roots of olive trees and their contribution to shallow slope stability

Vegetation can play a positive role in enhancing shallow slope stability, primarily through the mechanical reinforcement provided by plant roots to the soil. The mechanical effects of olive tree roots have not yet been thoroughly investigated. This study aims to quantify mechanical root reinforcement made by olive trees and to assess its impact on shallow slope stability. Field measurements were carried out within a region of the northern Apennines (Italy), to measure root density and length and to collect samples for testing tensile and elastic properties of the roots. Root density and mechanical properties were combined on a Root Bundle Model framework for assessing root mechanical reinforcement. Olive trees root mechanical contribution was then inserted in a probabilistic slope stability model, for estimating the proneness of olive trees to shallow landslides in different sloping soils. The results indicate that tree age significantly influences root characteristics. Olive trees older than 20 years exhibit a more developed root system, up to more than 49-61% roots than younger individuals. Given that root mechanical properties remain largely consistent regardless of age, this translates into greater overall mechanical reinforcement, which reaches average values between 3.49 and 5.29 kPa in older trees. As a result, slopes covered by mature olive trees are potentially less prone to failure, even in areas with steepness up to 19-24 degrees. These mature trees may offer stabilizing effect that may reduce susceptibility to shallow landslides compared to sowed fields, tilled vineyards, or shrublands. While younger olive trees provide a more limited contribution, their root systems still offer enough reinforcement to reduce landslide susceptibility when compared to completely tilled vineyards or sowed areas and shrublands. The findings of this study suggest an important role of olive trees in promoting shallow slope stability and offer insights for land management and landslide risk mitigation.