Abiotic and biotic factors influencing the early stages of vegetation colonization in restored marly gullies (Southern Alps, France)

In the French Southern Alps, erosion-control experiments have been conducted since spring 2002 in marly catchments subjected to a mountainous and Mediterranean climate. Bioengineering works, installed in the gully beds and constituted as vegetation barriers, have been efficient in trapping sediment, thus creating sediment deposits upstream of each barrier. Natural colonization of these deposits by vegetation, which could enhance soil protection against erosion, have therefore been observed. From 2003 to 2005, we investigated the abiotic and biotic factors influencing plant establishment after restoration on 29 bioengineering works constructed in two experimental marly gullies. On the sediment deposits upstream of each structure, we identified the standing vegetation, measured species richness and abundance, and also evaluated vegetation cover on the gully sides. The results indicate that colonization by plants may be influenced by abiotic factors such as the presence of vegetation on the gully sides and climatic conditions. In addition, the ability of the bioengineering works to retain water seems to have an impact on the success of vegetation establishment. Finally, we highlighted changes in growth form proportions over time that may result from biotic factors such as plant–plant interactions. These results allow us to hypothesize on how vegetation evolves over the medium term after ecological restoration of eroded marly gullies in a mountainous and Mediterranean climate.