Tamarisk, or salt cedar, is a highly invasive plant that was introduced into this country in the 1800s from Eurasia, and it's caused plenty of problems along waterways in the West. A test project to control the pest with the tamarisk leaf beetle has been underway since 2001 in parts of the country, but a few of the beetles have turned up unexpectedly in the upstream end of Grand Canyon National Park. Will this prove to be a case of "Oh, my," or "Oh, me"?
If you've spent any amount of time along the Colorado River, odds are much of the greenery you've seen along the shoreline was tamarisk. The dense stands of the shrubby trees provide shade, attractive flowers and even some fall color in the desert. So, what's the problem? According to information from NPS publications:
A single, large tamarisk can transpire up to 300 gallons of water per day. In many areas where watercourses are small or intermittent and tamarisk has taken hold, it can severely limit the available water, or even dry up a water source. Because of its ability to spread, its hardiness, its high water consumption, and its tendency to increase the salinity of the soil around it, the tamarisk has often completely displaced native plants in wetland areas.
The leaves, twigs and seeds are extremely low in nutrients, so …very few insects or wildlife will use them. In one study … tamarisk stands supported less than 1% of the winter bird life that would be found in a native plant stand. Because of the tamarisk's ability to eliminate competition and form single-species thickets, wildlife populations have dropped dramatically.
Tamarisk also poses an increased wildfire risk where it grows in dense stands.
What's being done about the problem? Grand Canyon National Park and a number of partners began a concerted tamarisk control project in 2000.
The effort focuses on the park’s side canyons and tributaries ... To date, approximately 270,000 trees have been removed from over 6,000 acres in the park. Park biologists and volunteers continue to maintain those areas, and have documented the important recovery of native vegetation.
That work is time and labor intensive, and scientists around the country have been searching for natural controls. One which has shown promising results is the tamarisk leaf beetle (Diorhabda spp.) which feeds specifically on tamarisk. It was approved for release as a biological control agent in certain areas of the west in 2001.
Researchers previously thought that this species of the tamarisk leaf beetle would restrict its range to above the 38th parallel, which is near the upper end of Lake Powell. The beetles were not approved for release within 200 miles of southwestern willow flycatcher habitat, an endangered species which is known to nest in tamarisk.
Biologists and ecologists from the National Park Service and the Tamarisk Coalition, based in Grand Junction, Colorado, recently found the first tamarisk leaf beetle in Grand Canyon National Park.
Tamarisk beetle monitoring along the Colorado River in Grand Canyon National Park was conducted from August 9-24. During monitoring, small numbers of beetle larvae were found on tamarisk trees along both sides of the river corridor beneath Navajo Bridge and ... at Brown’s Inscription, twelve miles downstream of Lees Ferry. National Park Service biologists found adult beetles six miles downstream of Lees Ferry in September.
Tamarisk leaf beetles are now causing defoliation of tamarisk trees further south than originally anticipated. According to Dr. Dan Bean of the Colorado Department of Agriculture, the small population of beetles recently documented in Grand Canyon National Park is unlikely to overwinter successfully. However, it appears likely that as beetle numbers increase a viable reproducing population will be established in Grand Canyon within the next several years.
Lori Makarick, the Vegetation Program Manager at Grand Canyon, says the park plans to continue their current program of tamarisk control, but the project may take on a different dimension in future years.
"We have people removing tamarisk from the park’s backcountry this week." She added, "Now that the tamarisk beetle has been found in the park, we also need to make sure we are prepared to move forward with active native plant restoration efforts in the Colorado River Corridor in the next few years."
Contrary to what the name may suggest, an organization called The Tamarisk Coalition is not an advocacy group for the plants; it's working on ways to control the pest. It
provides education and technical assistance for the restoration of riparian lands in the west. That group and the Colorado Department of Agriculture are collaboratively monitoring the tamarisk beetle in Colorado, Utah and Arizona. They are tracking its dispersal, establishment, and expansion and providing information on impacts of the beetle on riparian native and non-native plant ecology and wildlife habitat.
Tim Carlson, Tamarisk Coalition Research and Policy Director, notes that,
"Monitoring of beetle movement and vegetative response are critically important, not only to understand the direct and indirect impacts of the beetle on riparian ecosystems, but in order to implement adaptive management activities aimed at re-establishing native vegetation."
According to Lori Makarick at Grand Canyon,
this will become increasingly important in areas along the Colorado River corridor that provide critical habitat for threatened and endangered species.
The continued spread of the tamarisk leaf beetle throughout the Colorado River in Grand Canyon National Park may have dramatic impacts on the canyon’s complex riparian ecosystems. Growing infestations of the tamarisk leaf beetle in Grand Canyon may defoliate and kill tamarisk trees that now dominate the river corridor.
While the demise of this nonnative invader is welcome, it will pose new management challenges such as: how to remove the standing dead trees, how to assess rapid changes in wildlife habitat, and how to successfully restore native plant communities.
Although Grand Canyon was not participating in the test project with the beetles, the staff recognizes the park doesn't exist in a vacuum. Martha Hahn, Chief of Science and Resource Management at the park, stated,
This is a situation where there are no boundaries and we will need to work with all land management agencies within the greater Colorado River watershed so that wildlife habitat and sensitive species planning is integrated into all of our planning efforts and decisions.
Grand Canyon Superintendent Steve Martin emphasized the long-range goal of all of the various beetle control projects is the return of native habitat along the river.
"Park resource management staff, as well as staff from other federal land management agencies and partner organizations has been very successful in controlling tamarisk in the park’s side canyons. With continued coordination and stakeholder involvement, we should be successful in actively restoring native plant communities and wildlife habitat in the river corridor."
Will introduction of the beetles prove to be a successful solution to the tamarisk problem, and lead to restoration of more natural conditions, or will hindsight find it was a case of "it seemed like a good idea at the time"? The answer may hinge on efforts by resource managers to speed the return native species to areas that have been dominated by the invasive plants for decades.
Check back in a few years for the answer.