An Unwelcome Guest

photo: Salt Creek Canyon with (left) and without (right) tamarisk. Tamarisk often forms dense groves that block out other species. Notice the greater abundance of surface water and variety of plants in the right hand photo.
Salt Creek Canyon with (right) and without (left) tamarisk. Tamarisk often forms dense groves that block out other species. Notice the greater abundance of surface water and variety of plants in the left-hand photo.

NPS Photos by Neal Herbert


Not everything you observe during your visit to Canyonlands is meant to be here. In fact, you’ll probably come across many unwelcome guests as you explore the park. But don’t look to your fellow visitors: the culprits are non-native plants.

Non-native plants are one of the greatest threats facing Canyonlands and much of the American west. These plants can alter ecosystems, food chains and nutrient cycles by out-competing native organisms in their own habitat. They accomplish this by changing soil chemistry, natural fire frequency, as well as the availability of water, space, nutrients and light. As a result, populations of native plants like cottonwood, willow and many grasses have declined significantly in the last few decades.

In Canyonlands, cheatgrass (Bromus tectorum), an annual grass from Eurasia, can be found almost everywhere there is soil. Tamarisk (Tamarix spp.) and Russian knapweed (Centaurea repens), have invaded the rivers, springs and wetlands. Nearly 100 different non-native weeds have been documented in the park. Just as gardeners and landscapers deal with weeds around their homes and yards, park managers confront weeds in Canyonlands, but on a much larger scale.

Canyonlands has taken an active approach to weed control for years. The first tamarisk control project began in 1984 in Horseshoe Canyon. Present efforts focus on the removal of tamarisk in Horse, Wooden Shoe, Lost and Salt Creek canyons in the Needles, and Shafer and Lathrop canyons at the Island in the Sky. Russian Knapweed control is being conducted along the Green River. The park also attempts to control invasive weeds like field bindweed (Convolvulus arvensis), diffuse knapweed (Centaurea diffusa), Russian olive (Elaeagnus angustifolia) and puncturevine (Tribulus terrestris).

Teams equipped with shovels, chainsaws and backpack sprayers perform most weed control in the park. Trees like tamarisk are cut and the slash is piled for burning. Stumps are sprayed with herbicide to prevent re-sprouting. Park staff, regional Exotic Plant Management Teams and volunteer groups like the Sierra Club and the Wilderness Volunteers have all assisted in this effort.

During the summer of 2003, National Park Service and Utah State University crews began mapping non-native weeds in the park. This inventory program will measure the extent of the weed problem and determine the focus of future weed management goals at Canyonlands.

Scientists are searching for better ways to manage non-native plants. The United States Geological Survey studies many aspects of non-native plants, including whether soil chemistry can be altered to suppress cheatgrass while favoring native plants. They are also developing methods to predict where cheatgrass might invade next. This would allow land managers to focus on undisturbed areas for early detection and even prevent new cheatgrass invasions.

During your visit to Canyonlands, you can help manage our weed problem. Prevent the spread of weeds by ensuring that you do not disperse seeds to new areas. Check your camping equipment, shoes and the undercarriage of your vehicle for plant stems, roots and seed before leaving an area. If you recognize non-native weed infestations the park should know about, fill out an observation card at any visitor center. Be sure to include the name of the weed, its location and size of the infestation.

When you return home, you can further your education by learning about the non-native weeds in your community. Knowledge of these weeds will enable you to reporting infestations to local weed managers.

Last updated: December 15, 2022

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