Grazing intensity gradient inherited from traditional herding still explains Mediterranean grassland characteristics despite current land-use changes

Le gradient d'intensité de pâturage hérité de l'élevage traditionnel explique toujours les caractéristiques des prairies méditerranéennes malgré les changements actuels d'utilisation des terres

Christel Vidaller (1) , Chloé Malik (1) , Thierry Dutoit (1)

1 IMBE - Institut méditerranéen de biodiversité et d'écologie marine et continentale

Grazing is well-known to shape plant populations and plant communities and to affect several compartment characteristics of grazed ecosystems. Semi-natural grassland conservation depends on the maintenance of traditional extensive grazing systems which can exist for centuries, even millennia. However, very few studies have concomitantly investigated the effect of grazing management on plant, forage, litter and soil compartments and the implications of their potential interactions for conservation after recent changes in grazing practices. This study thus aimed to identify the concomitant effects of sheep grazing on the latter compartments of Mediterranean grasslands. We further investigated the effects of a recent change from millenia-old traditional herding to contemporary fenced free grazing. We also sought to determine how this change may impact the agronomic and ecological value of these grasslands. Surveys were carried out at 6 different study sites paired by the two different grazing practices in a French Mediterranean sub-steppic vegetation ("Crau" plain in Southeastern France). Using linear models and distance-based redundancy analysis, effects of grazing intensity, grazing practices and their interactions were tested on plant community, forage, litter and soil physicochemical properties. Our results show that, there was a significant effect of grazing intensity on the four studied compartments, with significantly higher species richness and evenness at moderate grazing intensity. Biomass was also significantly higher at moderate grazing intensity. Digestibility of forage, litter quality and soil fertility decreased significantly under less intensive grazing. Significant differences were also found in the relative size of the areas covered by each plant communities. Recent fenced free grazing led to significantly more intensively grazed zones, with more mesophilous/nitrophilous vegetation. Conversely, in zones traditionally less intensively grazed, the contemporary free grazing led to higher plant species-richness but again with more mesophilous species. Implications for conservation management are that the legacy of millennia-old traditional herding still compensates partly for the effects of changing practice to contemporary fenced free grazing on plant community composition but not on their relative sizes. This indicates an increase in grazing intensity in the remotest zone which could lead to grassland plant community homogenization.

Domaines: Sciences de l'environnement

Christel Vidaller, Chloé Malik, Thierry Dutoit. Grazing intensity gradient inherited from traditional herding still explains Mediterranean grassland characteristics despite current land-use changes. Agriculture, Ecosystems & Environment, 2022, 338, pp.108085. ⟨10.1016/j.agee.2022.108085⟩. ⟨hal-03723042⟩