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Soil degradation by concentrated runoff and soil erosion induces major environmental and economic damages, notably in agricultural areas under temperate climates. The use of herbaceous vegetation aims to increase the hydraulic resistance and thus reduce runoff and soil erosion while retaining sediments on site. However, the identification of the most suitable species to mitigate runoff is often specific to a phytogeographical territory and hampered by the intraspecific variability, which reduces the transposition of a solution to other territories and the ability to quantify the effects of the vegetation. Using a plant trait‐based approach allows understanding and characterising the direct effects of the vegetation on runoff and soil erosion mitigation as well as on the sediment retention increase. Here, we review the influence of plant aboveground functional types and traits of herbaceous vegetation on the hydraulic resistance and sediment retention and the contentious effects of the functional diversity on the hydraulic resistance and sediment retention, within agricultural catchments. Using this knowledge, we propose applications of the trait‐based approach to design and manage herbaceous hedges for sediment retention and soil erosion control. This review synthesises recent advances regarding the effects of the functional traits on runoff and sediment retention and defines a trait‐based selection method of the plant species for runoff and soil erosion control. [ABSTRACT FROM AUTHOR]

Aims: Plant species diversity impacts ecosystem processes, but its effects on runoff and soil erosion are not fully understood. Herbaceous vegetation control concentrated runoff and soil erosion through the increase of hydraulic roughness which leads to sediment retention. This study aims to investigate the effect of aboveground traits and their divergence (i.e., stem diameter and density, and leaf area and density) on hydraulic roughness and sediment retention in plant communities. Methods: Runoff experimentations were performed, using a sediment input, on three mono-specific and one multi-specific conditions composed of plant species with contrasting traits furthering hydraulic roughness and sediment retention. Results: No effect of trait diversity was found on the hydraulic roughness and sediment retention; which would be explained by the absence of an optimal space use by the traits involved in the increase of the hydraulic roughness. The dominant effect of the community-weighted traits in the plant community drives the effects of the vegetation on the hydraulic roughness and sediment retention. Conclusion: This absence of positive effects of the trait diversity on hydraulic roughness and sediment retention constitutes an important knowledge to model runoff and soil erosion processes and to design herbaceous infrastructures for soil erosion control. [ABSTRACT FROM AUTHOR]

Vegetation controls concentrated runoff and erosion in the European loess belt by increasing hydraulic roughness and sediment retention. Studies of plant effects on runoff velocity are usually based on a taxonomical characterisation and do not consider the effects of aboveground plant functional traits in attempts to understand soil erosion by water. This trait-based plant study investigates aboveground plant functional trait effects of herbaceous hedges on the hydraulic roughness to understand soil erosion. Eight aboveground morphological traits were measured on fourteen indigenous and perennial plant species (caespitose or comprising dry biomass in winter) from north-west Europe with a high morphological variability. For each trait, density-weighted traits were calculated. The effects of traits and density-weighted traits were examined using a runoff simulator with four discharges. The leaf density and area, as well as density-weighted stem and leaf areas, stem diameter and specific leaf area were positively correlated with the hydraulic roughness. Generalised linear models defined the best combinations of traits and density-weighted traits: (1) leaf density and leaf area, (2) density-weighted leaf area and density-weighted projected stem area, and (3) density-weighted leaf area and density-weighted stem diameter. Moreover, the effects of leaf density, leaf area and density-weighted specific leaf area, varied depending on the discharge. This study is one of the first characterisation of aboveground trait effects on hydraulic roughness and highlights that vegetation with large stem density, diameter and leaf area plays a significant role in minimising soil erosion. The selection of plant species can derive from these plant trait effects to design reconstructed herbaceous hedges to minimise soil erosion. [ABSTRACT FROM AUTHOR]

Background: Functional diversity effects on ecosystem processes, like on soil erosion, are not fully understood. Runoff and soil erosion in agricultural landscapes are reduced by the hydraulic roughness (HR) of vegetation patches, which furthers sediment retention. Vegetation with important stem density, diameters, leaf areas, and density impact the HR. A functional structure composed of these negatively correlated traits involved in the increase of the HR would constitute a positive effect of the functional diversity. Methods: Runoff simulations were undertaken on four mono-specific and two multi-specific communities, using herbaceous plant species from North-West Europe, presenting six contrasting aboveground functional traits involved in the HR increase. Results: An effect of dominant traits in the community was found on the HR, identified as the community-weighted leaf density. The non-additive effect of functional diversity on the HR could be explained by the presence of species presenting large stems in the communities with high functional diversity. Conclusion: We argued that functional diversity effect on the HR could change due to idiosyncratic effects of the plant traits, which would be influenced by soil properties, phylogeny diversity, and plant species interactions. These findings constitute an advancement in the understanding of plant trait assemblage on runoff and soil erosion processes. [ABSTRACT FROM AUTHOR]