Canyon Sketches Vol 24 - March 2012

Grand Canyon National Parks Marks National Invasive Species Awareness Week

Allyson Mathis

Electrofishing for trout.

In 1916, Congress directed the National Park Service to conserve natural and cultural resources unimpaired for the benefit of future generations. Invasive and other exotic (or non-native) species impair park resources by disrupting the canyon's complex ecosystems, frequently reducing biodiversity, modifying or degrading wildlife habitat, and jeopardizing endangered species, such as humpback chub, one of the four remaining species of native fish in the Colorado River in Grand Canyon.

National Invasive Species Awareness Week provides an opportunity to explore management issues related to invasive species at Grand Canyon and to mark successful efforts to control or reduce the impacts non-native species have on the park's natural systems.


National Invasive Species Awareness Week is coordinated by the National Invasive Species Council which is co-chaired by the Secretaries of Interior, Agriculture and Commerce. The Council was established by Executive Order 13112 to ensure that federal programs and activities to prevent and control invasive species are coordinated, effective and efficient. Invasive species are exotic species that degrade the environment, impact native species, cause economic impacts, and threaten human health and well-being.

New Zealand Mudsnail
New Zealand mudsnail

U.S. Geological Survey

Grand Canyon National Park faces serious threats from invasive plants, non-native fish species, aquatic nuisance species such as the New Zealand mudsnail, as well as brown-headed cowbirds and non-native bison/cattle hybrids on the North Rim. Invasive plants that threaten park ecosystems include tamarisk, Sahara mustard, diffuse knapweed, cheatgrass, and other species.

Chief of Science and Resource Management Martha Hahn said, "Invasive and exotic plants, animals and invertebrate species present a myriad of threats to Grand Canyon's native and endemic species. Hence, controlling invasive species is one of the emphasis areas for Science and Resource Management. We focus on controlling species that have the most adverse impacts and where our efforts can have the most positive outcomes for native species. Our goal is to ultimately restore ecological balance throughout Grand Canyon."


Invasive Plants

Removing tamarisk.
Removing tamarisk.

To date, 196 exotic plant species have been documented within park boundaries. These species represent about 11% of the total number of plant species that occur in the park, and managers estimate that non-native plants may occur in nearly 50% of the park, vastly altering the canyon's natural plant communities.

Vegetation Program Manager Lori Makarick said, "The task of preserving park ecosystems from invasive plants feels daunting at times, but we have a highly skilled staff directing the program and there are a large number of volunteer stewards who are willing to work hard and get dirty to assist in our efforts.

Controlling invasive plant species is intensive work. We have made some important advances towards reducing the impacts of exotic plants, but there is always the threat of new invasions of harmful plants."

Invasive plant survey.
Invasive plant survey.
The park's invasive plant management program has two main emphasis areas: surveying for new occurrences of invasive plants and controlling non-native plants that are already established in the park.

Staff survey for new arrivals each year, focusing on roadways, boundaries, trails, park entrances, the river corridor and developed areas where new invasive species are likely to occur through the inadvertent spreading by visitors.
In 2011, park staff identified four new exotic arrivals, one of which, yellow bluestem, is an aggressive grass that appears to be spreading rapidly in Arizona.
2011 tamarisk removal Havasu Creek
Havasu Creek tamarisk removal.
During control projects in 2011, crews removed 664,811 individual non-native plants from nearly 6,500 infested acres. This accomplishment was possible because of the large number of volunteers who contributed more volunteer hours to the Vegetation Program than ever before.

Last year, the park began a new program to help control invasive plants in established campsites along the Colorado River. In the Adopt-a-Camp program, professional river guides removed high priority invasive plants from selected river campsites following protocols provided by the park.
Applying tamarisk herbicide.

Control of invasive tamarisk in tributaries is a major component of the park's invasive plants program and has been ongoing since 2002. The project has focused on tributaries and side canyons, which contain high quality desert riparian habitat and retain their natural hydrology. To date, more than 290,000 tamarisk trees have been removed from at least 130 tributaries.

Makarick said, "The tamarisk program has been really successful, but the return of native diversity in the side canyons after the tamarisk trees are removed is a slow process. It is difficult, expensive, and sometimes not feasible to try to re-create a native habitat, community or ecosystem once it has been lost, so the project has reinforced how important it is to control invasive species, or prevent their establishment before they take over and dominate."

Himalaya blackberry before removal. (1999)
One of the park's other successes in controlling invasive plant species is the removal of Himalaya blackberry plants from the Indian Garden area. By 1999, this plant dominated the stream-side habitat along Garden and Pipe Creek and was threatening to reach the Colorado River and spread throughout the river corridor.

The next year, the park began an aggressive project to eradicate Himalaya blackberry at Indian Garden that was complemented by planting native vegetation to replace the exotic plants, eliminating this threat to the park's riparian ecosystems. Arizona grape, cattail, red bud, coyote willow, and other native species now thrive along Garden Creek, providing food and shelter to a myriad of wildlife species.

Invasive Animals

large trout from Bright Angel Creek
Trout from Bright Angel Creek

Non-native fish, especially rainbow and brown trout, have become abundant in the altered aquatic ecosystem of the Colorado River, and in some tributaries. Today, at least 13 species of non-native fish are found in the park, and only four of the eight native species remain. Non-native fish species prey on and/or compete with native fish. Brown trout are particularly voracious predators of native fish.

Grand Canyon National Park is conducting a multi-year project to reduce the number of brown and rainbow trout in Bright Angel Creek in order to restore the drainage's native fish community, to the extent feasible. Learn more about this project...

Bright Angel Creek once supported large numbers of native fish, including the endangered humpback chub. Today, Bright Angel Creek is the main spawning site in Grand Canyon for non-native brown trout, and it is hoped that this project will also benefit native species in the Colorado River as well.

Biologist operating the weir in Bright Angel Creek.
Checking the weir in Bright Angel Creek.

Biologists are using two methods for capturing and removing non-native trout from Bright Angel Creek during the fall and winter months: a weir, or fish trap, and electro-fishing. The weir captures adult trout that live in the Colorado River as they enter Bright Angel Creek to spawn.

Electro-fishing allows fisheries biologists to monitor and assess the fish population of the creek and also remove non-native trout that live in the stream.

Fisheries Program Manager Brian Healy said, "The purpose of the Bright Angel Creek Trout Reduction Project is to benefit endangered humpback chub and other native fish species in the Colorado River, and to restore and enhance, to the extent possible, the native fish community that once flourished in Bright Angel Creek."

Bision in an open field.
Bison on the North Rim.
Threats to the park resources are not only caused by non-native plants and fish. Invasive bison/cattle hybrids are adversely impacting natural resources on the North Rim, particularly sensitive water sources, vegetation and fragile soils.

Bison were brought to U.S. Forest Service land on the Kaibab Plateau in 1906 in an effort to breed them with cattle to produce hybrids, an experiment that was not economically successful. Today, the herd that resulted from this breeding effort is managed by the Arizona Game and Fish Department with the House Rock Valley Wildlife Area designated as bison range.
bison impact on the North Rim.
Bison impact on the North Rim.
Since 2000, bison began traveling to the Kaibab Plateau and into Grand Canyon National Park. The herd now numbers more than 300 head, with the majority staying within park boundaries year round. An interagency management group is currently determining what steps to take to reduce or eliminate the negative impacts to park resources that the bison are causing.

These efforts to eliminate or reduce the impacts caused by the invasive and/or exotic tamarisk, blackberry, trout, and bison are not the only management actions taken by the Division of Science and Resource Management in Grand Canyon National Park.

The park contains at least 196 species of non-native plants, four species of non-native mammals, six non-native bird species, and 13 species of non-native fish, all of which threaten the canyon's natural ecosystems. Furthermore, there is always the possibility that other invasive species will enter the park and pose new threats to the park's native plants and animals.

Chief of Science and Resource Management Martha Hahn said, "Control of invasive species is one of many resource management issues that require integrated planning. We are working at the watershed and landscape level, actively engaging with park neighbors, keeping the public informed, and enlisting the assistance of volunteers to protect Grand Canyon from the damage caused by invasive species. We are proud to celebrate our invasive species mitigation accomplishments during National Invasive Species Awareness Week, and are also taking this opportunity to reflect on our commitment to protecting Grand Canyon's biological diversity from the threats posed by exotic species."


To learn more about volunteer opportunities to help control invasive plants in Grand Canyon:

To learn more about the Bright Angel Creek Trout Reduction Project:

To learn more about National Invasive Species Council:

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Last updated: February 24, 2015

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