U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2006–3071

May 2006

Tamarisk Control, Water Salvage, and Wildlife Habitat 

Restoration Along Rivers in the Western United States 

Printed on recycled paper

In the latter part of the 19th century, species of the nonnative shrub tamarisk (also called saltcedar; for example, Tamarix 

ramosissima, T. chinensis) were introduced to the United States 

for use as ornamental plants and for erosion control. By 1877, 

some naturalized populations had become established, and by 

the 1960s, tamarisk was present along most rivers in the semiarid and arid parts of the West and was quite abundant along 

downstream reaches of the major southwestern rivers such 

as the Colorado, Rio Grande, Gila, and Pecos. The principal 

period of tamarisk invasion coincided with changing physical 

conditions along western rivers associated with the construction 

and operation of dams. In many cases, these altered physical 

conditions appear to have been more favorable for tamarisk 

than native riparian competitors like cottonwoods and willows 

(Populus and Salix; Glenn and Nagler, 2005). 

The great abundance of tamarisk along western rivers has 

led resource managers to seek to control it for various reasons, 

including a desire to (1) increase the flow of water in streams 

that might otherwise be lost to evapotranspiration (ET) (evapotranspiration is the combination of water lost as vapor from a 

soil or open water surface [evaporation] and water lost from the 

surface of the plant, usually from the stomata [transpiration]); 

(2) restore native riparian vegetation (here, “riparian” refers to 

the banks and flood plains of rivers, or shorelines of reservoirs 

or lakes); and (3) improve wildlife habitat.

Water Salvage

The concept of clearing riparian vegetation to increase 

streamflow and downstream water supply has been investigated 

by the U.S. Geological Survey (USGS), other Federal and State 

agencies, and academics since the 1950s. Simplistic estimates 

of potential increases in streamflow following tamarisk removal 

can be obtained by multiplying an evapotranspiration (ET) rate 

for tamarisk by the number of acres of a flood plain occupied 

by tamarisk. The estimates obtained from this product can be 

misleading because the ET values used are often overestimates 

(6-9 feet/year) based on studies of individual plants in wellwatered tanks. In field conditions, recent studies indicate that 

ET in tamarisk-dominated riparian vegetation is 2.5-4 feet/year 

(Dahm and others, 2002). In the 1970s and 1980s, the USGS 

conducted controlled studies of water budgets pre- and posttamarisk clearing along the Pecos and Gila Rivers. These studies suggest that measurable water salvage following tamarisk 

clearing is only 0-1.5 acre-feet/year due to ET of replacement 

vegetation, increased evaporation, loss to ground water, or other 

difficult-to-quantify “sinks” (Culler and others, 1982; Weeks 

and others, 1987; Shafroth and others, 2005). 

Riparian Restoration

Often, restoration of native vegetation is a primary or 

secondary objective when clearing nonnative tamarisk. 

Approaches to restoring riparian vegetation following tamarisk 

removal may be active (for example, planting potted native 

plants, irrigating, and so forth), passive (for example, removing a stressor, or restoring natural processes), or hybrids (for 

example, spreading native seed in conjunction with a controlled 

reservoir release). Problematic tamarisk invasions usually 

occur in situations where the natural processes that favor native 

vegetation have been altered, tipping the balance in favor of 

tamarisk. These processes include natural patterns and quantities of streamflow and associated sediment and landform 

dynamics. Therefore, restoration efforts are most successful and 

sustainable when the underlying conditions favoring tamarisk 

invasion are addressed. Merely removing tamarisk generally 

will not lead to sustainable restoration of native riparian plant 

communities. Often, tamarisk or other alien weeds will simply 

recolonize the site over time (Stromberg, 2001; Shafroth and 

others, 2005). 
Wildlife Habitat Implications

 Because native riparian forests in arid and semiarid parts 

of western North America are critical to the support of a variety 

of wildlife species, the purpose of riparian restoration is often 

to improve wildlife habitat. Although a number of studies have 

shown that many species (such as neotropical migratory birds) 

prefer native cottonwood and willow habitats to tamarisk, there 

are many taxa for which tamarisk provides suitable habitat 

(see Shafroth and others, 2005). The most prominent example 

is the federally listed southwestern willow flycatcher, which 

frequently nests in stands of tamarisk. Thus, the wildlife habitat 

implications associated with tamarisk control can be complex 

and controversial and can be closely linked to the restoration 

potential of a control site. In the absence of a carefully planned 

and executed restoration effort, the vegetation that is anticipated to replace tamarisk following removal may be an inferior 

substitute for many wildlife taxa. Further, flood-plain habitat 

conditions other than the vegetation alone may strongly influence wildlife populations, such as the frequency and magnitude 

of flooding and the complexity of different vegetation types and 

water sources throughout the flood plain. Simply removing 

tamarisk generally will not improve wildlife habitat. This must 

be accompanied by science-based restoration and monitoring 

plans to evaluate effectiveness. 

Control Techniques

Various methods have been used to attempt to control existing stands of tamarisk along western rivers, including chemical, 

mechanical, and biological controls. Chemical control can be 

used for site-specific removal (for example, application to cut 

stumps) or for larger areas (areal spraying). Mechanical control 

generally involves cutting or bulldozing the above-ground 

material, raking up the root crowns, and burning the slash. 

Because chemical and mechanical approaches tend not to result 

in 100 percent mortality, followup control efforts are usually 

required. If the control site is still suitable for establishment of 

new tamarisk seedlings, then followup efforts may be required 

indefinitely. Biological control agents (herbivorous insects from 

tamarisk’s native range in Asia) have recently been released at 

a number of field sites. The U.S. Department of Agriculture 

and partners are monitoring the results of these efforts, which 

are still at an early stage. Biological control is potentially more 

sustainable than other methods, but it is controversial because it 

involves introducing another nonnative organism, with potentially unforeseeable consequences. Long-term, sustainable 

control generally requires addressing the underlying causes of 

tamarisk invasion. 

Conclusions

Controlling tamarisk for water salvage, riparian vegetation 

restoration, and wildlife habitat improvement has great appeal 

to land and water managers and to the public. However, all 

of these post-tamarisk removal objectives can be difficult to 

achieve over the long term without the input of the best scientific information. Sound, interdisciplinary science conducted 

by experts within the USGS has contributed to the present state 

of knowledge and is continuing to contribute to new, innovative approaches. For example, USGS scientists are conducting 

research to investigate many of the remaining uncertainties 

surrounding the issue of tamarisk management. These include 

mapping and modeling the current and future distribution of 

tamarisk; understanding the environmental conditions and 

processes associated with tamarisk invasions; comparing insect 

and bird use of tamarisk and restored riparian vegetation; and 

developing novel restoration approaches, including streamflow 

management downstream from dams and active planting of dry 

riparian sites. 

Literature Cited

Culler, R.C., Hanson, R.L., Myrick, R.M., Turner, R.M., and 

Kipple, F.P., 1982, Evapotranspiration before and after clearing phreatophytes, Gila River flood plain, Graham County, 

Arizona: U.S. Geological Survey Professional Paper 655-P, 67 p. 

Dahm, C.N., Cleverly, J.R., Coonrod, J.E.A., Thibault, J.R., 

McDonnell, D.E., and Gilroy, D.J., 2002, Evapotranspiration at the land/water interface in a semi-arid drainage basin: 

Freshwater Biology, v. 47, p. 831-843.

Glenn, E.P., and Nagler, P.L., 2005, Comparative ecophysiology of Tamarix ramosissima and native trees in western U.S. 

riparian zones: Journal of Arid Environments, v. 61, p. 419-446. 

Shafroth, P.B., Cleverly, J.R., Dudley, T.L., Stuart, J., Taylor, 

J.P., van Riper, C., and Weeks, E.P., 2005, Control of Tamarix 

in the western U.S. - Implications for water salvage, wildlife 

use, and riparian restoration: Environmental Management, v. 

35, p. 231-246. 

Stromberg, J.C., 2001, Restoration of riparian vegetation in the 

south-western United States: importance of flow regimes and 

fluvial dynamism: Journal of Arid Environments v. 49, p. 17-34.

Weeks, E.P., Weaver, H.L., Campbell, G.S., and Tanner, B.D., 

1987, Water use by saltcedar and by replacement vegetation 

in the Pecos River floodplain between Acme and Artesia, 

New Mexico: U.S. Geological Survey Professional Paper 

491-G, 33 p.

For more information, contact:

Patrick B. Shafroth

USGS Fort Collins Science Center

2150 Centre Ave., Buillding C

Fort Collins, CO 80526

Phone: (970) 226-9327

e-mail: Pat_Shafroth@usgs.gov