Story 3: Controlling Tamarisk Infestations Along Southern Nevada's Wetlands and Waterways
"Yes, it is everywhere!" This is the cry of Curt Deuser, Supervisory Restoration Biologist for the National Park Service Exotic Plant Management Team, in response to a question about the invasion of tamarisk (Tamarix spp.) in the Lake Mead National Recreation Area. Since the 1850's, tamarisk, also known as salt cedar, has been invading riparian areas and wetlands in the western United States. This deciduous shrub or small tree, native to Central Asia and the Mediterranean, was originally brought to this country as an ornamental, and was also used for erosion control and the creation of windbreaks. Proving highly compatible with the climate and soil of the western U.S., tamarisk has taken the place of native vegetation along many rivers and streams and is estimated to cover over 1 million acres of land.
The introduction of tamarisk in the Lake Mead area occurred at least 50 years ago after Hoover Dam was built when the plant probably escaped from ornamental plantings or isolated erosion control projects. Its spread along the Colorado River was accelerated by the dam, which altered stream flows, hindering native plant reproduction. Tamarisk has since spread into nearly all of the tributaries within the Colorado River watershed including areas with natural water flow regimes. In Curt's region, which includes Nevada, California, Arizona, Utah and Colorado, up to 90% of riparian areas, rivers, streams, washes and wetlands are affected.
The spread of Tamarisk creates huge problems for plant, animal and human inhabitants of the land it invades. It consumes much more water than the plants it displaces, and infestations in small isolated waterways can dry up or greatly reduce the amount of water available in an area. Tamarisk also reduces forage for grazing since it is not palatable to most animals and has little nutritional value for those who will eat it. The dense thickets formed by Tamarisk create access problems for hikers, campers, and animals, and also increase the danger of rapid spreading, high intensity wildfires. The lack of available water, poor grazing and limited physical access created by Tamarisk makes land unsuitable for ranching or tourist uses and significantly decreases its value. Curt notes that once land is invaded by tamarisk it is very expensive to control. The goal of Curt and the NPS is to maintain and restore native plant communities where possible in order to support both the ecological and economic health of the land, and to reduce human-related impacts in areas that are set aside for preservation.
The Lake Mead Exotic Plant Management Team uses a number of methods to combat tamarisk including mechanical removal by chainsaws or heavy equipment followed by a spot herbicide treatment, and prescribed burning followed by herbicide application. Sometimes hand pulling or heavy equipment removal is sufficient, omitting the need for herbicide treatment. Curt says that most of these methods have been successful and that the method employed depends on the scale or location of the infestation. Hand pulling or spot herbicide treatment has proven to be the best method for maintaining control once an area has been cleared. The fact that an endangered bird species, the Southwestern Willow Flycatcher, has adapted to nesting in tamarisk has complicated the biocontrol release process and the use of tamarisk-eating beetles may be the best and most cost effective long term control method.
The Lake Mead Exotic Plant Management Team remains unyielding in their fight to maintain and restore riparian plant communities throughout the southwestern U.S. Areas that have been cleared of Tamarisk are monitored once every 1-3 years for new infestations. Progress is being made, but the spread of tamarisk and the problems it causes remain serious. "Native plants represent our natural heritage, with many plants being unique to particular regions of the world," Curt says. "Native plants and wildlife evolved together to support a balanced, healthy environment, and non-native plants alter that balance." Fortunately, Curt and his team, along with many other governmental agencies and private citizens, have taken on the mission of ecologically restoring our western waterways and riparian areas by controlling the growth and spread of tamarisk.
See the Tamarisk species profile for more information.