We examined relationships between land disturbance and the extent and abundance of exotic buffelgrass (Pennisetum ciliare) at the interface of cultivated pastures and native desert lands in Sonora, Mexico. Plot and transect surveys of lands inside and outside pasture fences and general linear mixed models revealed complex relationships among buffelgrass, native vegetation, distance from pasture fences, and three categories of land disturbance (undisturbed, moderate, and severe). Results illustrate that buffelgrass invasion is extensive in lands surrounding pastures, and that buffelgrass abundance declines steeply with distance from pasture fences. The role of disturbance is weak but significant in its interaction with distance from the fence. Buffelgrass is more successful at colonizing severely disturbed lands than native vegetation, and its decline in abundance on severely disturbed lands is relatively more gradual than on other disturbance regimes, so landscapes where severely disturbed lands are interspersed with buffelgrass pastures could become centers of extensive buffelgrass invasion. In light of its potential to transform the Sonoran Desert, buffelgrass outside pastures warrants attention in a region-wide control scheme, as well as in future research, which ideally would involve remote sensing.
Nomenclature: Buffelgrass, Pennisetum ciliare (L.) Link.
Management Implications: Buffelgrass (Pennisetum ciliare) is widely understood to be a threat to the Sonoran Desert because of its ability to outcompete native vegetation and introduce a new wildfire regime. Conservationists and land managers tend to focus on buffelgrass as it impinges on protected and urbanized areas, neglecting unprotected rural lands such as ranches. In Sonora, Mexico, ranchers aggressively cultivate buffelgrass, and the resulting pastures serve as large seed sources. Furthermore, buffelgrass pastures in Sonora tend to be surrounded by mixed-use landscapes, with soils disturbed in different ways and to different degrees. This research demonstrates that buffelgrass extends far beyond pasture boundaries, and its invasion of the Sonoran landscape is associated with disturbed (particularly severely disturbed) lands. These findings suggest that an integrated region-wide buffelgrass control scheme must take seriously the existing widespread invasion from Sonoran pastures, as well as the great potential for further invasion facilitated by disturbance in Sonora's heterogeneous and dynamic landscapes. Land managers should not continue to neglect the important role of pastures and their interactions with their surrounding lands in promoting buffelgrass invasion in Sonora, Mexico.