Buffelgrass is a non-indigenous, invasive, C₄ grass that was introduced throughout much of southern Texas, the Southwestern United States, and northern and central Mexico to improve degraded rangelands. The successful introduction and spread of buffelgrass follows a trajectory similar to that of other invasive C₄ grasses in arid and semiarid ecosystems. In the Plains of Sonora of the Sonoran Desert (Mexico) buffelgrass is favored by widespread removal of native vegetation and seeding, but, why, following initial introduction, the species persists remains unclear. In this study, we addressed two concerns associated with buffelgrass invasion in the Plains of Sonora. We hypothesized that under arid rangeland conditions, buffelgrass outcompetes native herbaceous species (1) through rapid acquisition of limiting nutrients (here assumed to be nitrogen) and (2) under conditions with high nitrogen input. In summer 2002, a 2 by 2 factorial experiment was established with buffelgrass removal and nitrogen addition in both intact desert and converted buffelgrass grassland habitats. In winter 2003, we found that, regardless of habitat type, buffelgrass removal had a positive effect on abundance, biomass, and richness of native herbaceous species while addition of nitrogen, as urea (at 50 kg N ha⁻¹yr⁻¹ or 9.18 lbs N ac⁻¹yr⁻¹), and disturbance resulted in reduction in abundance and biomass. Nitrogen addition did not negatively alter buffelgrass cover. Nitrogen addition had the expected result of increasing initial, peak and total NO₃ and NH₄ mineralization with the exception of NO₃ measures in intact desert. Removal of buffelgrass did not result in significant increases in soil NO₃ or NH₄ with the exception of peak NH₄ in intact desert. Results of this study support observations that native herbaceous species are displaced by buffelgrass invasion and that nitrogen pollution will likely favor buffelgrass over the native herbaceous species in this ecosystem.

Nomenclature: Buffelgrass, Pennisetum ciliare (L.) Link (Poaceae), formerly Cenchrus ciliaris L.

Management Implications: Buffelgrass is extensively planted in arid and semi-arid grassland ecosystems across the planet and has been useful in stabilizing soils and increasing productivity in rangelands where there has been widespread drought combined with overgrazing. Nonetheless, grassland conversion to accommodate buffelgrass plantings and invasion of the species itself has caused widespread and extreme collateral damage. In this study, we confirm that buffelgrass displaces native species. The study also demonstrates that high levels of nitrogen addition in low rainfall years results in neutral effects on buffelgrass and significantly negative effects on native herbaceous species. Given buffelgrass' significant negative impacts on biodiversity, its ability to alter fire regimes and establish a positive feedback loop, and its threat to the existence of ecosystems that have aesthetic and economic value in business sectors other than ranching (e.g., tourism in Arizona, United States), management of these rangelands for buffelgrass control is recommended as a high priority. Managers introducing buffelgrass to improve rangelands should take into consideration the species negative impacts on native forb and grass diversity, habitat for mammals and ground-dwelling birds, and the probable irreversible alteration of the ecosystem. In areas of conservation concern where biodiversity is a management goal we advocate (1) rigorous vigilance and immediate removal of nascent foci, (2) where established, an aggressive removal campaign (without the use of fire), (3) outreach to increase public awareness about the negative effects of the species, and (4) where possible, reduced