Community Responds to Invasive Grass Threat
by Barb Skye Siegel (Revised 7/2002)

The Sonoran Desert Weedwackers is a community network of volunteers coordinated by the Southern Chapter of the Arizona Native Plant Society. This weed eradication program operates in cooperation with Pima County Parks and Recreation-Tucson Mountain Park (TMP), Pima County Sonoran Desert Conservation Plan (SDCP), Saguaro National Park (SNP), Sonoran Arthropod Studies Institute (SASI) and Tucson Botanical Gardens (TBG) and the Arizona Sonora Desert Museum (ASDM). The purpose of the program is to clear infestations of fountain grass (Pennisetum setaceum) and buffelgrass (Pennisetum ciliare), and other exotic species that threaten native plant populations in the Sonoran Desert region.

Fountain grass was introduced as an ornamental plant and is widely used in residential and commercial landscaping. Buffelgrass is used extensively in Mexico and the Southwest rangelands as a forage crop for cattle. These African grasses crowd out native Sonoran Desert species by creating monocultures that consume scarce water and nutrient resources. Washes and roadsides are most vulnerable to infestations. However they can spread into undisturbed desert as well.

Buffelgrass (tan growth) in theTucson Mountains

Another major concern is the ability of these grasses to spread fire quickly. Our native plants are typically killed in the high-temperature fires fueled by fountain grass and buffelgrass. Both of these African savanna-adapted grass species re-establish soon after a fire when they can spread more quickly without competition. In contrast, Sonoran Desert vegetation can take decades to reestablish following a fire.

For several years, the National Park Service (NPS) has controlled invasive exotics growing within the boundaries of the East and West Units of the Saguaro National Park. Pima County Parks also has a long history of weed eradication programs. Similar to the Sonoran Desert Weedwacker program, volunteer crews work under the direction of professional staff. The difference with the Weedwacker program is that its focus is on developing a community group of dedicated volunteers interested in the long-term eradication of exotic weeds in the Tucson Mountains and Sabino Canyon.

Weedwacker work crew with eradicated buffelgrass

The Sonoran Desert Weedwacker program has existed since January, 2000. Typically, 10-15 volunteers work mornings doing reconnaissance ("recon") every second Friday, and eradication ("rad") every third Saturday of each month. Volunteers are recruited through allied organizations such as the Arizona Native Plant Society and local schools with environmental education programs. Volunteer teams are also recruited from visiting college and university groups who are willing to provide labor in exchange for benefits such as camping privileges at Pima County's Gilbert Ray Campground. Other benefits of the volunteer program include networking and educational opportunities. Participants share knowledge concerning plant conservation issues and plant identification. Camaraderie naturally develops among the volunteers who share common interests related to Sonoran Desert natural history and conservation.

A typical Weedwacker morning begins and ends with a breakfast/brunch potluck. Following a hike or van transportation to a priority site, a "grass class" covers plant identification and bunch grass removal methods. The group methodically moves down through the washes or other selected site, cutting flower or seed heads off and removing individual plants using pry bars and mattocks. While roots may be lodged in rocks, the alluvial soil is loose enough to allow for fairly easy removal. Two strategies have been adopted to deal with the removed plants. Whole plants have been physically removed from the site in plastic bags. This method is preferred if the plant has already dispersed seeds which have become lodged into its own crown, and the site is easily accessible. A second method is to remove seed heads and place the uprooted plants on high ground to dry out and expire. Plants appear to regenerate only occasionally, but can be controlled by seedling removal during routine monitoring.

To date, the Weedwackers program has been successful in eliminating major infestations in the washes. As a result of this multi-institutional initiative, an aggressive program has been developed that actively protects native desert habitats. Over 500 volunteers have cleared an estimated 8,000 acres of buffelgrass and fountain grass infestations in the Tucson Mountains. These volunteers have manually removed over 600 bags, or the equivalent of 12,000 pounds of weeds. The results of removing buffelgrass and fountain grass have been remarkable. Biological diverse populations of native plants have become established once again. Ultimately, the Weedwacker program will provide training to volunteers county-wide, who in turn can implement exotic weed eradication programs throughout the Sonoran Desert region.

Site after Weedwackers have cleared buffelgrass

Barb Skye Siegel is currently working for SASI.