Plant-soil reinforcement response under different soil hydrological regimes

The use of plants against shallow landslides and erosion has received considerable attention over time as it is believed that vegetation provides mechanical and hydrological reinforcement to the soil. However, neither the soil root mechanical reinforcement under different hydrological regimes, nor the hydrological effects of vegetation on soil reinforcement have been properly studied. This paper explores how plants are able to provide mechanical and hydrological reinforcement to soil under different soil hydrological regimes. To do this, we first defined a novel, simple and reproducible laboratory protocol to investigate how changes in soil moisture affect the mechanical effects of vegetation on soil reinforcement. We then explored how plants modify the relevant soil properties and what implications this may have on soil reinforcement. We finally attempted to evaluate the suction stress functions for both fallow and vegetated soil, as a proxy to quantify the hydrological plant-derived soil reinforcement. The results showed that plants significantly increased the soil organic matter and the angle of internal friction, both with relevant hydro-mechanical implications. Vegetation presented a significant mechanical soil reinforcement that was higher at the soil's hydrological transition regime, suggesting the existence of optimum soil moisture content for an effective soil-root reinforcement response. The hydrological regimes also imposed differences in terms of the hydrological reinforcement, which differed between fallow and vegetated soil. However, the derived suction stress function for the fallow soil in the experiments showed differences when compared to the theoretical predictions. Our findings provide a good basis for future research to enhance our understanding of the nature of plant-soil composites and shed light on the sustainable use of vegetation against shallow landslides. (C) 2016 Elsevier B.V. All rights reserved.