Vertebrate community response to livestock in a Mediterranean rangeland system: Rethinking the role of grazing in biodiversity conservation

Background/Question/Methods

With the move away from traditional agricultural practices towards more intensive livestock production, land abandonment and intensification simultaneously threaten ecosystems worldwide. Research has shown negative ecological impacts of both undergrazing (such as increased risk of wildfire due to biomass accumulation), and overgrazing (which can result in soil erosion and decreased productivity). The uneven grazing resulting from this shift in agricultural practices is of particular concern in the Mediterranean, a biodiversity hotspot with a high level of endemic species. Livestock husbandry has been practiced in the Mediterranean since antiquity and plays a vital role in the local economy. Our study, therefore, investigates how current livestock grazing practices in the Mediterranean influence vertebrate diversity. The aim of this study is to determine the optimal level of livestock grazing to provide guidelines for sustainable grazing management in the region. Our research was based in Naxos, the largest island in the Greek Cyclades. We compared vertebrate richness along a continuum of grazing intensities. Using a number of habitat measures including vegetation biomass, canopy gap, vegetation structural heterogeneity, insect richness, and insect biomass, we modeled terrestrial, avian, and total vertebrate richness to better understand the ecological impacts of livestock grazing on this system.

Results/Conclusions

We found that terrestrial and avian species vary in their response to current livestock grazing pressures on the island. Terrestrial species respond in accordance with the intermediate disturbance hypothesis; the highest terrestrial species richness is found at sites with moderate amounts of grazing, peaking at 3.5 animals per hectare. Passerine species richness on the other hand, is best explained by the vegetation structural heterogeneity at a site. We found no clear relationship between current grazing conditions and vegetation structural heterogeneity. Instead, we hypothesize that vegetation structure is shaped by historic grazing and fire disturbance rather than the grazing pressure recorded at the time of the study. Our findings suggest that the trend towards agricultural abandonment and intensification negatively impacted terrestrial vertebrate populations in the Mediterranean. Light to moderate grazing optimizes terrestrial vertebrate richness while allowing for sustainable economic returns from livestock production.