Impact of Livestock Grazing on Ecosystem Services in a Mediterranean Ecosystem

Abstract

Livestock husbandry is one of the most important human activities in arid regions of the planet and is the predominant driver of environmental degradation in Mediterranean ecosystems. Nonetheless, despite the very long history of animal husbandry in this region, relatively little is known on the relationship between livestock grazing and the provisioning of ecosystem services in a Mediterranean setting. Methods. This study focuses on mediterranean heathlands (‘phrygana’), a species-rich plant community that is widespread over large areas of the Mediterranean Basin, and a habitat subjected to goat and sheep grazing for almost 10,000 years. We evaluate multiple trophic levels of this community (including vegetation condition and structure, floral resources, as well as populations of primary and secondary consumers), across a spectrum of livestock grazing intensities in island ecosystems in the Aegean Sea (Greece). We also evaluated some of the important ecosystem services provided by phryganic habitats to local human communities, including vegetation productivity, erosion protection, pollination services, disease dilution, and maintenance of biodiversity. Results. Results show that all measured aspects of vegetation condition and structure (vegetation biomass, canopy cover, basal cover, plant species richness and plant diversity) decline monotonically with rising levels of livestock grazing. Furthermore, while increasingly higher herbivore stocking rates result in diminished floral resources, the effects on pollinator populations and diversity are more equivocal. Secondary consumers (Podarcis wall lizards) appear to benefit the most from intermediate levels of grazing intensity. However, foraging rates by honey bees (Apis mellifera), an economically important species in the region, decline as livestock herbivory rates rise, suggesting that there are direct tradeoffs between livestock husbandry and apiculture in these landscapes. Conclusions. Impacts of livestock husbandry on local ecosystems depend on stocking rates used. While at low stocking rates, grazing appears to have either equivocal or both positive and negative effects on different ecosystem services, at higher stocking rates these effects become mostly negative. While there is no specific stocking rate that is likely to minimize all impacts, our results suggest that intensive grazing has clear negative ecological consequences in terms of lost ecosystem services.