COS 166-5 - The effects of long-term grazing cessation and grazing legacies on vegetation composition, productivity and soil properties in dry Mediterranean grassland

Abstract: East Mediterranean ecosystems are characterized by a long history of anthropogenic activity. In these regions soil properties, vegetation composition and plant traits have been molded by thousands of years of grazing by domesticated livestock. Traditionally, rangeland research refers to soil resources, grazing pressure and grazing history as the main factors affecting rangeland vegetation. A variation in each of these factors may shape vegetation composition and productivity. The aims of this study were to examine how grassland community composition, soil properties, and herbage productivity and quality are affected by periods of grazing cessation, under different grazing intensities and post-fire conditions. We used long-term experimental setup with adjacent grassland plots of different legacies (different grazing intensities, with or without fire history) and grazing cessation for different periods (two years, 18 years, or continuous grazing) at the Karei Deshe experimental range station in Eastern Galilee, Israel. The vegetation was sampled at flowering time, when productivity was at its peak (April). The harvested plants were sorted, defined and divided into functional groups. Following that, samples were dried, weighed and grounded for further nutrients and for nutritional values analysis. Soil samples were collected at the end of the growing season and tested for macro- and micronutrients in the laboratory.

Our results demonstrate that soil inorganic nitrogen increased in plots with high grazing intensity. In the plots exposed to fire, the contents of phosphorus and potassium increased. Plant community composition changed between the different grazing cessation treatments and the different legacies; short-term grazing cessation (two years) led to an increase in abundance of tall perennial grasses, while abundance of short annual grasses and appearance frequency of annual legumes decreased. We found an increase in the cover of perennial species in plots where grazing was excluded for eighteen years. Species richness decreased after two years of grazing exclusion but increased again after eighteen years of grazing exclusion, compared to adjacent control plots under ongoing grazing. Herbage quality was higher in plots with high grazing intensity, even after a long period of exclusion, due to changes in species composition. In addition, fire decreased the overall herbage quality and increased productivity due to the increased amount of high annual grasses.

In summary, grazing and burning history and grazing cessation distinctly affect soil properties, herbage quality, and plant community composition. Different grazing pressures, grazing cessation, and low-frequency fires create a mosaic of areas with different species composition, thus preserving diversity.