Soil reinforcement by the roots of six dominant species on eroded mountainous marly slopes (Southern Alps, France)

In marly catchments of the French Southern Alps, the development of plant root systems is essential to increase slope stability and mitigate soil erosion, prevalent in this area. In a context of land restoration, it is important to be able to evaluate plant efficiency for soil reinforcement. This paper presents the results of investigations carried out on six dominant species from marly gullies. It aims to compare the additional soil cohesion they provide at the early stages of their development. The six following species were collected: two tree species, Pinus nigra and Quercus pubescens, two shrubby species, Genista cinerea and Thymus serpyllum, and two herbaceous species, Achnatherum calamagrostis and Aphyllantes monspeliensis. For each of them, we measured root tensile strength and root area ratio in order to calculate the potential root reinforcement and to compare species suitability to prevent shallow mass movements. Results showed significant differences between species. The herbaceous species A. monspeliensis and the shrubby species G. cinerea provided the highest increase in soil shear strength while the tree species, P. nigra and Q. pubescens were the least efficient. These results, along with the knowledge on vegetation dynamics and species response to erosive constraint, allow us to better evaluate land vulnerability to erosion and the efficiency of restoration actions in eroded marly lands.

Research Highlights
► Juvenile plant species increase soil cohesion by root reinforcement.
► Root reinforcement depends on species and root system type.
► Grasses and shrubs provide higher increase in soil shear strength than young trees.