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Buffelgrass (Pennisetum ciliare) is a highly invasive, nonnative, perennial bunchgrass in the desert Southwest that spreads rapidly and reduces wildlife habitat and biodiversity of native ecosystems by outcompeting native plants.

Desert landscapes naturally have gaps between vegetation. Buffelgrass fills in those spaces, providing a fuel source and carrying fire across a landscape, which increases the frequency and intensity of wildfires. Buffelgrass invasion and subsequent fire can alter ecosystem structure and function and kill iconic species like the saguaro (Carnegiea gigantea), which is not adapted to fire.

To counter this threat, NPS' Saguaro National Park has carried out chemical and mechanical removal treatments over two decades.

Using this data, a team of researchers from the USGS Southwest Biological Science Center, Arizona-Sonora Desert Museum, and Saguaro National Park examined the effectiveness of a decade (2011 - 2020) of chemical and mechanical (manual removal) treatments to reduce buffelgrass with the goal of improving treatment success and invasive management. They assessed how the stage of buffelgrass invasion, treatment type and intensity, and environmental variables influenced reductions in cover.

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Their results showed that treatments have largely been effective at reducing all but the smallest areas occupied by buffelgrass, and chemical treatments had greater or equal effectiveness compared with mechanical treatments.

The greatest reduction in buffelgrass was associated with shorter gaps between treatments (less than 3 years), and to a lesser degree, total years of treatment. Treatments that were conducted on shallow slopes, north- and east-facing aspects, and on higher elevations within one district of the park were more effective.

These findings highlight that resource-intensive treatments in all but the smallest buffelgrass patches have largely been successful.

Opportunities for management improvements include more frequent surveillance, limiting treatment gaps to 3 years or less in areas that have low buffelgrass cover, and a comparison of treated with untreated areas.

Early detection and treatments in new areas of invasion will increase treatment effectiveness because buffelgrass has the potential to increase by orders of magnitude in areas that initially have low invasive grass cover.

Key Takeaways:

• Chemical treatments with glyphosate have produced a level of control that is greater than or equal to that of mechanical removal methods.
• Early detection and treatment of new areas of buffelgrass invasion can increase treatment effectiveness, especially since low levels of the weed can quickly expand by multiple orders of magnitude.
• Treatments are likely to be more effective if spaced at an interval of less than three years.
• Steep slopes with south-facing aspects that favor buffelgrass growth may need more frequent treatment.
• If longer treatment gaps are necessary due to a lack of resources, treatments in areas with less favorable environmental conditions for buffelgrass (e.g., north-facing aspect, low topographic slope) can be cautiously discontinued on a temporary basis.

Read the paper: Li, Y.M., Munson, S.M., Lin, Y.-C., and Grissom, P., 2023, Effectiveness of a decade of treatments to reduce invasive buffelgrass (Pennisetum ciliare): Invasive Plant Science and Management, v. 16, no. 1, p. 27-37, https://doi.org/10.1017/inp.2023.2.