My Story 6: Joining Forces to Fight Tamarisk in Nevada
The state of Nevada is currently fighting an infestation of invasive non-native plants, and has almost four-dozen species on its noxious weeds list. According to Tina Kadrmas, coordinator for Cooperative Weed Management Areas in Nevada, "the problem is very large and could turn into a catastrophe if we do not recognize that weeds are more than a rural problem". As real estate development and recreational land use have expanded in recent years, weed infestations have become common in every county and city in Nevada (especially in Washoe and Clark Counties). One weed in particular, tamarisk (Tamarix spp.) also known as salt cedar, is causing significant problems with water resources throughout the state.
Unlike many invasive plants which entered the U.S. accidentally through contaminated seed supplies or in shipping materials, tamarisk was intentionally introduced in the southwestern U.S as a windbreak and shade tree beginning in the late 1800's. Well adapted to Nevada's soil conditions and hot, dry climate, tamarisk soon spread outside the landscape areas where it was originally planted and established itself along river corridors and in riparian areas where it poses a serious threat to native plant species.
Tamarisk is known for its enormous consumption of water, a critical concern in an area like Nevada where water is scarce. It is estimated that a single mature tamarisk plant can consume 200 to 300 gallons of water per day leaving insufficient water to support the native under story plants essential to a healthy riparian environment. In addition, tamarisk exudes salt from its leaves which changes the chemistry of the surrounding soil, making it even more difficult for under story plants to establish, compete, and survive. Ultimately tamarisk squeezes out other species altogether and creates a plant monoculture in the infested area.
The economic impact of tamarisk infestations can be extensive. In Nevada, tamarisk is present on the Walker, Carson, Humboldt, Virgin and Colorado Rivers, which all supply water for agricultural and other uses in the state. Farmers in the Great Basin area report that river and ground water levels have fallen as a result of tamarisk infestations. Therefore, Nevadans not only pay for the direct cost of controlling and monitoring tamarisk infestations, they also pay dearly through the loss of water, a valuable and scarce resource.
Because tamarisk is usually found near waterways, stump-cut treatment and biological control are the most common methods for managing tamarisk. For stump-cut treatments, the plant is cut and then chemicals are applied directly to the fresh cut stump. These chemicals quickly seep into the wood reducing the chances of them trickling into the waterway. This method has been successful in controlling tamarisk, but is very labor intensive. Biological control using defoliating leaf beetles (Diorhabda elongate) has also been reasonably successful, although research has shown these beetles to be less effective at lower latitudes, making this approach less useful in southern Nevada than it has been in northern areas of the state. Foliar application of herbicides is also common and has been successful in test plots in New Mexico.
Once tamarisk has been successfully removed from an area, the land must be replanted with other species in order to restore and maintain its health. Like many land managers, Tina believes that reestablishing native plants is the ideal for land restoration. Unfortunately, the use of natives is not always possible due to a low seed bank and the high cost of seed. In cases where native species for replanting are not available, non-native plants which are able to hold soil and adapt to Nevada's arid climate without becoming invasive must be used. Tina notes that replanting in areas where weeds have been eradicated is critical in order to minimize the likelihood of reinfestation.
Success in controlling weeds can be unpredictable for land managers. "We as land managers struggle with the word 'successful' because a project cannot be deemed a success until years later when habitat is restored and healthy enough to combat weeds on its own", says Tina. Fortunately, progress has been made fighting tamarisk in southern Nevada, and organizations like the National Park Service and the Southern Nye County Cooperative Weed Management Area (CWMA) are serious about controlling the plant. Tina notes that the Southern Nye CWMA has received funding for habitat restoration (which includes tamarisk eradication) and that "this group is fighting tamarisk with the cut stump treatment in the Amargosa Valley of southern Nevada one tree at a time."
Tina is encouraged by the widespread cooperation between private citizens (CWMAs) and public agencies banding together to fight tamarisk infestations in Nevada, but still sees challenges ahead. It can be difficult to keep people excited about weed management projects because the management process can be tedious and there are usually long delays in seeing results. Maintaining adequate funding for weed control is also a challenge. Grants can be difficult to obtain and some have requirements that impede project funding. "The land is very dynamic and Mother Nature is surprisingly resilient", says Tina, "but weeds decrease the chances of Mother Nature recovering on her own". Tina would like to change that.
See the Tamarisk species profile for more information.