Preventing the “Sonoran-geti” with Simulated Herbivory

By Tony Figueroa, Director of Invasive Plant Management

Large patch of buffelgrass in the Sonoran Desert before treatment.

Non-native invasive grasses are creating wildfire risks that our Sonoran Desert ecosystem has not evolved with. When fires move through the desert, very few natives survive, and the time for natural regeneration could span several generations, if ever. These invasive grasses—buffelgrass, fountain grass, and yellow bluestem—evolved with heavy grazing pressure and fire cycles that allow them to outcompete native plants after being burned. Our desert animals don’t eat these non-natives because they are unpalatable, leading to large areas of waist-high grasses that intensify fire risks for our region. In our effort to prevent the conversion of our desert into the “Sonoran-geti” where African grasses have replaced our saguaro forest, we are implementing a “Simulated Herbivory” approach to managing large populations of buffelgrass and fountain grass where wildland and urban areas interface.

Vibrant growth of fountain grass in the Catalina foothills.

Simulated herbivory is a fun name, but it’s just our way of saying we are weed-whacking the grasses down to a height of two inches, similar to what would happen if wildebeests and zebras were grazing on them. Buffel and fountain grass have well-developed roots loaded with energy for vigorous regrowth 2–4 weeks after cutting or grazing. You may have seen this cutting and regrowth occur on a roadside near you; it’s part of what motivated us to implement this idea into our integrated pest management approach for managing large populations of non-native grasses. Once the grasses start growing, we follow up with herbicide applications to the crown of the plant. 

Weed whacking to simulate wildebeest and zebra herbivory.

Fresh growth stimulated without rain.

We always strive to find a better solution for managing plants, and the simulated herbivory strategy has many benefits that motivated us to use it. Spraying grasses with herbicide is only effective when the plant is green and growing—the timing of which is now difficult to rely on due to unpredictable rainfall. Typically, winter and summer rains allow for sufficient green up, when the bulk of our spraying work occurs in the backcountry. Our current drought conditions motivated us to use the simulated herbivory strategy during this past winter and spring. We started cutting down four foot tall grasses along the roadsides near Sunrise and Craycroft in February, and without rain, we had new growth occurring in March. Our crews went out and sprayed those plants using 10% of the herbicide that would have been needed to treat large plants, and we had a much higher treatment success! 

This grass is now much easier to treat!

Simulated herbivory increases the opportunity to manage these invasive plants throughout the year, instantly lessens the fire risk that tall dry grasses present, dramatically reduces the amount of herbicide needed to treat each plant, and increases the likelihood of a successful treatment. It’s an effective strategy that we are introducing throughout the region as a best practice for managing non-native grasses in our community and the Sonoran Desert. 

Tony Figueroa is Director of Invasive Plant Management for Tucson Bird Alliance.