Removing invasive riparian plants from 13 Southwest national parks

Three shrub and tree species, Siberian elm, tamarisk and Russian olive, show up again and again in the National Park Service's work on streams and rivers in the Southwest, and they use a lot of water in drier riparian areas. An NPS article from August 2024, written by an NPS science communication specialist working on the Inflation Reduction Act (IRA) projects, explains how the service is removing them across 13 parks.

Giant Pedestal at White Sands National Park, where tamarisk grows through the top of a dune. The article says tamarisk is found in riparian areas across New Mexico and consumes over 200 gallons of water daily, which lets it outcompete native vegetation. NPS photo, David Bustos.

The threat

Invasive species are non-native organisms that spread rapidly, harm national parks and can outcompete native species. An NPS restoration biologist said they spread because they tolerate a wide range of habitat conditions and disturbances, produce a lot of viable seed and can sometimes produce several generations in one growing season. They also have no local predators to keep them in check. In water-rich riparian ecosystems they alter habitats, reduce food for native wildlife and can do long-term damage.

Invasive plants are causing trouble in parks in Arizona, New Mexico, Texas, Colorado and Utah. The Riparian Area Restoration Project spans 13 parks that received IRA funding in 2023, working with partners and the NPS Invasive Plant Management Teams (IPMTs) to eradicate invasives and restore native vegetation. At park after park, the biologist said, the usual response is to remove the invasives and plant natives.

Canyon de Chelly National Monument near Chinle, Arizona, during the development of a removal plan for tamarisk and Russian olive, the two invasives this project targets most heavily. NPS photo.

What the field has taught

The project is led by the natural resource program manager at Bandelier National Monument. The restoration biologist said that removing shrubs such as tamarisk and Canada thistle by hand is possible and necessary but often ends up spreading them more widely across an ecosystem. Most shrub species need a combination of manual labor and herbicide to be controlled and eradicated, whether thistle, tamarisk or Siberian elm. The article says herbicide goes directly onto the stumps or roots, which in time lets water return to riparian ecosystems and gives native plants a healthy, uninfested place to repopulate.

Each park has its own challenges, so the management differs:

Water hyacinth, a common riparian invasive at San Antonio Missions National Historical Park. NPS photo, Liz Marchio.

Partners and choices

Conservation youth crews, including the Southwest Conservation Corps and the Ancestral Lands Conservation Corps, were set to help with removal at Bandelier starting that fall. The program manager said many parks use youth agreements with groups such as Ancestral Lands, friends groups and similar organizations, and that Bandelier put money into Ancestral Lands for three years. The Park Service, the manager said, benefits from engaging underrepresented Indigenous youth in projects that reconnect them with the land and their heritage while protecting natural and cultural resources. The crews also give young people career training in natural resource management and add capacity for work that current staffing could not finish.

The biological resource program manager said climate change is accelerating the spread of invasives, that the work must move swiftly while respecting Tribal lands and relationships, and that three species, Siberian elm, tamarisk and Russian olive, are the consistent ones from park to park.

The usual path is hand crews cutting down the trees and shrubs, then treating with herbicide. After that it differs. Some parks stop there and let native plants return; others plant willows and other fast-growing natives to build resilience. Parks have the flexibility to use agreements with Tribal partners or conservation crews, or, depending on the area to be treated, the existing IPMTs, which treat the area themselves or train park staff on what to do, when and why.

The road ahead

The article calls the effort a long-term commitment that needs continuous work and adaptation. Funding fluctuates and new challenges emerge, and the program managers and restoration biologists agree that adaptive management and ongoing learning are the top priority. The IRA gives a crucial boost, but the on-the-ground work of manual removal, replanting and monitoring takes persistence. The program manager said that with the right support and strategies, these ecosystems and the parks' natural heritage can be restored and preserved for future generations.

The article notes that the IRA gives the Park Service an historic chance to address ecosystem resilience, restoration and environmental planning needs, with projects in every corner of the country, from Alaska to Florida to Maine. It lists Bandelier, Canyon de Chelly, Canyonlands, Great Sand Dunes, Hovenweep and Lake Meredith among the places it concerns.

Sources

• National Park Service article "Restoring Balance: The Battle Against Invasive Riparian Plant Species," August 2024, by an NPS science communication specialist (https://www.nps.gov/articles/imr-riparian-ecosystems.htm); the map credited to NASA DEVELOP is left out because it is drawn on a non-NPS satellite image; rewritten in hubnx's own words.