A diachronic simulation model of the relationships between grazing and forage production in the rangelands of Lagadas county, Greece

This paper presents the development of a dynamic simulation model of grazing and forage biomass. The aim of the model is to find an ecological balance between livestock numbers and forage production in the Mediterranean rangelands. The model investigates whether management practices are leading to rangeland degradation due to overgrazing or under-grazing. The simulation relates the grazing pressure in with the availability of forage biomass by taking into account through differential equations, the precipitation, the plant decomposition rates, the animal consumption and the number of grazing animals caused by food availability. The model was applied in Lagadas County of northern Greece for a period of 140 years (1961 to 2100). The results of the model show that 140 to 150 sheep equivalent units per Km2 constitute a stocking rate that ensure a balanced utilization of forage biomass. Τhe evaluation of the current management of livestock, shows that the increasing use of supplementary feed, the soil erosion caused by overgrazing and the under-grazing of a large proportion of natural rangelands, prevents the maintenance of ecological balance over time.