Tamarisk
Tamarix spp.

Description: Most tamarisks, also known as saltcedars, are deciduous shrubs or small trees growing up to 15 feet tall and forming dense thickets. They are characterized by slender branches and gray-green foliage. The bark is reddish-brown on young branches, becoming brownish-purple and ridged with age. The leaves are scale-like, about 1/16 inch long, and overlap each other along the stem. They are often encrusted with salt secretions. From March to September, dense masses of pink to white flowers appear on 2 inch long spikes at the branch tips. One species of tamarisk, Tamarix aphylla, is an evergreen tree that can grow up to 50 feet tall and usually flowers during the winter. 1

Habitat: Tamarisk establishes in disturbed and undisturbed streams, rivers, bottomlands, washes and other areas where its seedlings can be exposed to extended periods of saturated soil. It can grow in highly saline soils, and will often increase the salinity of soils in areas where it has invaded.1

Total Range: The native range for tamarisk is in Eurasia and Africa. It was first introduced into the western United States in the early 1800's as a source of wood, shade and erosion control. It is now estimated that approximately one million acres within the United States have been infested with tamarisk. It occurs primarily in the southwestern states, including Arizona, but has spread as far north as Montana. 2

Threat to Native Species and/or Environments: The tamarisk is a major threat to native riparian woodlands, which support the greatest levels of biodiversity within desert ecosystems. It is a fire-adapted species, often increasing the frequency and intensity of fires that can severely burn native vegetation.1 It can also change the salinity of soils, which kills intolerant riparian plants such as the Fremont cottonwood (Populus fremontii) and Goodding's willow (Salix gooddingii). Tamarisks use great amounts of ground water which lowers groundwater tables, causing springs to dry up and other plants to perish. Their dense growth within washes and other watercourses can promote flooding by blocking the natural flow of water. 2 Native wildlife species, especially birds, have declined in numbers where tamarisks have invaded due to their small fruits and seeds, lack of insects, unpalatable foliage and unsuitable structure for cover and nesting.3

Tamarisk in Pima County: Tamarisk can be found along many of the major watercourses in Pima County. It is especially prevalent along the Santa Cruz River, where effluent flows provide a continual water source, and the San Pedro River.

A variety of methods have been employed to control infestation of this species, including mechanical, chemical and biological.1 It should be noted that once tamarisk has established itself in an area, its removal may not lead to a subsequent replacement by native plant species. In addition, the federally endangered Southwestern willow flycatcher (Empidonax traillii extimus) is known to utilize tamarisk in areas where it has replaced native willows normally used by the flycatcher for nesting.1

References

1 Native Plant Conservation Alliance, Alien Plant Working Group, March 2, 1999. www.nps.gov/plants/alien/fact/pese1.htm

2 Stein, Bruce A. and Stephanie R. Flack, eds. 1996. America's Least Wanted: Alien Species Invasions of U. S. Ecosystems. The Nature Conservancy, Arlington, Virginia.

3 DeLoach, C. J. January 1997. Saltcedar and biological controls. The Arizona Riparian Council newsletter. Vol. 10, No. 1, pp. 1 and 3.