Controlling the Aliens:
Ravenna Grass in Grand Canyon

   The National Park Service is controlling a non- native grass population in the Colorado River corridor. Ravenna grass (Poaceae: Saccharum ravennae) was identified during Glen Canyon Environmental Studies Phase II. Populations of this large (3 m tall), Eurasian bunchgrass dramatically increased in the Grand Canyon from 1987 to 1992. First documented near Lees Ferry in 1981, NAU plant taxonomist Tina J. Ayers and I identified 55 populations between Lees Ferry and Diamond Creek in 1992. Ravenna grass was planted as an ornamental around Wahweap Bay on Lake Powell and the NPS is beginning eradication efforts there. It may have originally arrived at Lees Ferry on a motorboater’s bumper in the late 1970’s.

   Ravenna grass germinates in a wide variety of soil and canopy cover conditions, is highly competitive, and provides little bird and wildlife cover, all of which make it a threat to riparian habitats in the Grand Canyon. Although the threat of ravenna grass invasion to the mainstream riparian zone is significant, the real ecological danger is that this species could invade the Canyon’s pristine tributary and hanging garden habitats.

   With support from the river subdistrict and logistical support from Canyon R.E.O., a team of Prescott College volunteers armed with shovels and come-alongs mechanically removed more than 1,300 plants in 50 populations during a river trip in March, 1993. Fortunately the root masses are relatively easy to excavate and return visits to removal sites this summer show that excavation is highly successful as a control method.

   This species is not yet fully eradicated. We are decapitating this year’s seed heads on the few remaining plants to limit dispersal until we conduct the next control trip. Even after all populations are removed (hopefully by next March), we will continue monitoring the river corridor to detect new recruits. So as you cruise the Canyon, if you happen to notice any ravenna grass clumps, please jot down the mile and side and contact the NPS either at GCES or at the Grand Canyon (602 556-7457).

Larry Stevens