The Consequences of Buffelgrass Pasture Development for Biodiversity in the Southern Sonoran Desert

Abstract

Decades of overgrazing have left many rangelands in northwestern Mexico in poor condition. This has led to the practice of converting native rangeland plant communities to buffelgrass pastures. Buffelgrass (Pennisetum ciliare) is a perennial bunchgrass native to Africa. Both the extent of buffelgrass pastures within Mexico and the impacts of land conversion on biodiversity and ecosystem functioning. In the present study I address the effects of land conversion on the productivity and diversity of rangelands in the southern Sonoran Desert in the state of Sonora, Mexico. First, using satellite imagery from the Landsat mission, I found that rates of land conversion in the most heavily affected region of Sonora have continued to accelerate over the past three decades and that productivity of buffelgrass pastures is lower than that of native rangeland. Next, I examined the impacts of land conversion on the diversity and structure of plant communities and ant assemblages across a rainfall driven gradient of productivity in central Sonora. The regional extent of this land use change allowed me to explore the interaction between site productivity and land conversion. Within native rangeland I detected strong positive relationships between productivity and the species richness of perennial plant communities, but only weak positive relationships between productivity and species richness of ant assemblages. These results were discussed in the context of species diversity theory. Land conversion reduced the species richness of perennial plant communities by approximately 50% at both local and regional scales, whereas the species richness of ant assemblages was reduced by 17% at the local scale and only 8% at the regional scale. I found no evidence for an interaction between site productivity and land conversion in either plant communities or ant assemblages. The implications of these findings for long-term trajectories of biodiversity in the southern Sonoran Desert are discussed.