Maximizing soil ecosystem services for ecological restoration: plant roots influence runoff and erosion processes

The ecological restoration of degraded and constructed environments has usually aimed at reducing onsite (e.g. decline of soil quality) and off-site effects (e.g. contamination of water downstream) and to avoid irreversible situations were ecological succession is arrested. However, with the recent rise of ecosystem service theory and the attempts to quantify these services, there has been a change in the paradigm of restoration ecology in recent years. Restoration ecology can now benefit from the ecosystem services framework and aim to incorporate the maximization of these ecosystem services into projects. Here, we aimed to study the ecosystem services related to soil processes provided by 12 different species regularly used for restoration in the south of France. We studied the soil characteristics and root traits of these 12 species. Each species was grown from seed in a monoculture in 72 inclined steel boxes (0.7 x 0.7 x 0.3 m) and every monoculture was replicated six times with additional six control (bare soil) boxes. Three replicate boxes were used for soil and root sampling and three were equipped with rhizotrons (PVC windows to observe root growth). Every 4 months, root physical properties were assessed and aggregate stability tests were performed. Additionally, rainfall simulations were performed at two vegetation stages (seedling and mature) and before and after cutting the aerial biomass (to disentangle the effects of above- and belowground biomass and to relate results to root traits). Runoff and sediments were also collected after each natural rainfall event. Results showed that species from the Fabaceae family were more efficient at controlling erosion and increasing infiltration rates compared to members of the Poaceae family. However, no significant effect of species or family was found regarding soil aggregate stability during the study period. Our results suggest that erosion and infiltration processes are influenced by plant biomass and traits in the short term, whilst the development of soil aggregate stability is a longer-term process. Therefore, we suggest that herbaceous species of the Fabaceae family have a major potential for rapidlyimproving soil structure on road embankments compared to Poaceae family. A longer-term experiment is now being performed to study the effects of vegetation on soil aggregate stability