The effect of grazing pressure on species richness, composition and productivity in North Adriatic Karst pastures

We studied the effects of sheep grazing intensity and abandonment on plant species richness and composition, plant life forms and the productivity of North Adriatic Karst pastures. The experimental sites were under controlled grazing regimes (heavy, moderate, light and abandonment) for 10 years. Data were collected during one seasonplant species composition, the number of species and above-ground and below-ground biomass were evaluated. Species richness was significantly reduced with increasing grazing intensity and abandonment. The greatest differences in species composition were recorded for the heavily grazed site owing to the appearance of a group of grasslands species typical of nutrient-rich soil. Heavy grazing increased therophytes and decreased the proportion of chamaephytes and geophytes. Above-ground productivity at the season\u27s peak was typical of subhumid grasslands (up to 500 g ▫$m^-2$▫) and was significantly the highest in the abandoned pasture. Below-ground biomass was significantly the lowest in the heavily grazed sites and the highest in those that were moderately or lightly grazed. We could conclude that grazing intensification and abandonment have significant effects on the structure of these pastures. Low- or moderate-intensity (4-7 sheep ▫$ha^-1$▫) grazing seems to be the most appropriate treatment since it can maintain the species richness and typical floristic composition of those pastures