Buffelgrass, a highly competitive and flammable African bunchgrass, is spreading rapidly across both urban and natural areas in the Sonoran Desert of southern and central Arizona. Damages include increased fire risk, losses in biodiversity, and diminished revenues and quality of life. Feasibility of sustained and successful mitigation will depend heavily on rates of spread, treatment capacity, and cost–benefit analysis. We created a decision support model for the wildland–urban interface north of Tucson, AZ, using a spatial state-and-transition simulation modeling framework, the Tool for Exploratory Landscape Scenario Analyses. We addressed the issues of undetected invasions, identifying potentially suitable habitat and calibrating spread rates, while answering questions about how to allocate resources among inventory, treatment, and maintenance. Inputs to the model include a state-and-transition simulation model to describe the succession and control of buffelgrass, a habitat suitability model, management planning zones, spread vectors, estimated dispersal kernels for buffelgrass, and maps of current distribution. Our spatial simulations showed that without treatment, buffelgrass infestations that started with as little as 80 ha (198 ac) could grow to more than 6,000 ha by the year 2060. In contrast, applying unlimited management resources could limit 2060 infestation levels to approximately 50 ha. The application of sufficient resources toward inventory is important because undetected patches of buffelgrass will tend to grow exponentially. In our simulations, areas affected by buffelgrass may increase substantially over the next 50 yr, but a large, upfront investment in buffelgrass control could reduce the infested area and overall management costs.

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We found that the most effective and economical method for establishing native shrubs on extensive areas of retired cropland in southern Arizona makes use of drip irrigation and 3.8-l (1-gal) transplants (outplants). In March 2001, we established a small (8 ha [20 ac]) field trial to test the effectiveness of different combinations of transplanting, seeding, drip irrigation, and furrow irrigation. Treatments utilizing transplants and drip irrigation had higher survival and lower densities of weed species than other treatments tested. Based on these results, we planted again in November 2001 using drip-irrigated transplants to examine the effectiveness of this method over a larger scale (85 ha [210 ac]). As a further refinement of this method, we tested various sizes of container stock and determined that transplants of 3.8-l (1gal) size had superior growth and survival when compared to smaller-sized transplants. The total cost of this method is approximately US$ 4430/ha ($1790/ac), but it is more likely to succeed as compared with direct seedings, which is a commonly used approach to revegetation in southwestern ecosystems. Although a drastic effort, our technique holds promise for revegetating environments in the hottest and driest parts of the Sonoran Desert in southern Arizona.

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