Selective grazing, patch stability and vegetation dynamics in a rotationally-grazed pasture

International audience ; The lack of data on interactions between grazing intensity and livestock species makes it difficult to propose recommendations for the management of biodiversity and production in grassland ecosystems. A productive grassland area was therefore divided into 12 plots that were rotationally grazed by heifers at a high or a low stocking rate or by ewes at the same low stocking rate. Stocking rate appeared more important than grazer species in affecting the initial direction of community changes. Both heifers and ewes preferentially selected for bites containing legumes and forbs, and avoided reproductive grass. In lightly grazed plots, no significant effect of grazer species on sward botanical composition could be detected after four years of treatment application, though legumes were on average three–fold more abundant in plots grazed by heifers than plots grazed by ewes. Selective grazing on legumes and forbs, and avoidance of reproductive grass, can partly explain the stability of fine-scale grazing patterns in plots that were used by heifers. Cattle grazing would thus favour the creation of relatively stable open patches enabling prostrate forbs and legumes to compete with tall grasses. This could result in divergent vegetation dynamics within plots.