Saltcedar
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 Introduction and Spread

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Introduction and Spread

Early Introduction

Appearing in the Bible under the name Eshel, and in ancient Arabic literature as Asul, the genus Tamarix appears to have originated in India then spread to Asia and the Middle East (Tellman 1997). Tamarix, often referred to collectively simply as Saltcedar, was introduced into North America from Europe and Asia. Eight species of saltcedar were first brought to North America in the 1800s from southern Europe or the eastern Mediterranean region (DiTomaso 1998). Saltcedar escaped early cultivation and is now common throughout the United States (Christensen 1962; DiTomaso 1998; Robinson 1965).

Bowser (1957) speculated that Spanish explorers and conquistadors may have brought saltcedar to the New World between 1540 and 1750, however, there are no references or herbarium specimens to confirm the authenticity of this claim (Harris 1966). Saltcedar was sold by the Old American Nursery in New York in 1823, by Bertram’s in Philadelphia in 1828, and in the 1830s by several other nurseries (Robinson 1965). The oldest record of saltcedar in the western United States is in a nursery catalog from California dated 1856 (Robinson 1965). Harris (1966) speculated that saltcedar planted as an ornamental in parks and gardens formed the original stock in the southwestern United States. By the early 1920s, the plant escaped and was common along most major drainage systems in the southwest (Clover and Jotter 1944; Harris 1966). Once established, saltcedar spread rapidly from 1935 to 1955 (Christensen 1962).

During the 20th century saltcedar gained widespread prominence within many watershed basins in the western United States (DiTomaso 1998, Brock 1994). Its distribution and growth along river ways is influenced by local elevation, soil, and topographic variants (Tomanek and Ziegler 1960). Typically, in the headwaters or upper reaches of stream corridors where cold temperatures limit growth at elevations above 6,800 ft (2,100 m), saltcedar infestations are light and plants are widely scattered (Everitt 1980 and Brotherson and Winkel 1986). At middle elevations or transitional zones, saltcedar often occurs as a narrow belt along river edges within the confines of steep canyons and ravines. On low lying floodplains saltcedar may grow densely in the under story of established native riparian forest or broadly across open areas as an impenetrable thicket (Crins 1989).

There are few river systems in Texas, Oklahoma, New Mexico, Arizona, Utah, Nevada, and California where saltcedar is not present (Brock 1994). Saltcedar is continuing to spread northward into Oregon, Washington, Idaho, Wyoming, Montana, Kansas, Nebraska, North and South Dakota, and Canada (DeLoach 1991; Swenson and Mullins 1985) and southward into Mexico (Glenn et al. 1998). Saltcedar is also found in Louisiana, Arkansas, Georgia, Mississippi, North and South Carolina, and Virginia (Rice 2003; USDA NRCS 2002).

Often overlooked, saltcedar is widespread in many upland landscape positions, such as along roadsides, railroad right-of-ways, residential areas, parks, rangeland etc. It is also common in other water situations such as irrigation canals, springs, seeps, lakes, playas, arroyos, and dirt stock tanks.

United States Spread

Precise estimates of saltcedar spread and acreage are complicated because while it is increasing in some natural areas, it is declining in others because of agricultural, municipal, or other development. Graf (1978) examined photo records of Canyonland National Park on the Colorado and Green River systems between 1925 and 1931 and estimated the saltcedar spread rate to be 12.5 mi per year (20 km per year), resulting in a 27% reduction in channel width. A similar estimate by Salas et al. (1996) using aerial photos over a 280-mi (451-km) stretch of the lower Colorado River indicated that saltcedar increased by 20% from 1981 to 1994 (about 1.3% per year).

Saltcedar was reported to occur on about 10,000 ac (4,000 ha) of riparian habitat in the southwestern United States in the 1920s (Robinson 1965). By the 1960s, nearly 900,000 ac (360,000 ha) were infested. Saltcedar continued to spread to an estimated 1.3 million ac (540,000 ha) in the 1970s (Gay and Fritschen 1979). It occupied at least 1.47 million ac (600,000 ha) by 1987 (Brotherson and Field 1987; DiTomaso 1998). Saltcedar spread rate from Oklahoma to southern California, and from Colorado to Sonora, Mexico, was estimated at 3 to 4% per year (DiTomaso 1998). Acreage with saltcedar in 2003 was estimated at about 3.3 million ac (1.3 million ha) in the 17 western states (Young et al. 2004).

The aggressive spread of saltcedar in New Mexico and other regions of the southwest is illustrated by its rapid expansion in the Pecos river valley. During a three-year period, saltcedar expanded from a few seedlings at Lake McMillan in 1912, to cover more than 600 ac (240 ha) along the watercourse by 1915. By 1925, infestations expanded to 12,300 ac (4,978 ha), and continued to increase to 57,000 ac (23,067 ha) by 1960 (Robinson 1965). Average spread rate per year in the Pecos River valley from 1912 to 1960 was about 25%. Saltcedar now occurs along the river’s edge and outer floodplains of the Pecos River from its junction at the Rio Grande northward nearly 800 miles (1,400 km) to the headwater area of Pecos, New Mexico (McDaniel et al. 2000).

Mechanisms of spread

A number of factors lead to the establishment and spread of saltcedar (DiTomaso 1998). There is considerable debate as to why saltcedar is such an invasive species (Young et al. 2004). It is likely that saltcedar spread is both the product of natural and anthropogenic changes in riparian communities, and the consequence of alterations over the last century to river hydrology (Lovich 2000). Saltcedar spread is associated with dramatic changes in geomorphology, ground water availability, soil chemistry, fire frequency, plant community composition, and wildlife diversity (Graf 1978, Busch 1995, Anderson 1996, Sala et al. 1996).

Rapid colonization and expansion of saltcedar most commonly occurs with flood events or water inundation. For example, the most dramatic spread of saltcedar within New Mexico’s Rio Grande floodplain occurred in the early 1940’s. During this period, rainfall was the highest recorded in the 20th century, resulting in massive flooding from 1 to 3 miles across the Rio Grande corridor. Saltcedar seed was carried in the river water and deposited onto moist soil substrates as flood waters receded. New plants successfully established and shortly thereafter greater attention was directed towards saltcedar control (Anonymous 1951). Due in part to this event, the Water Control Act of 1948 was passed, which gave the Corp of Engineers and the Bureau of Reclamation responsibility for construction of reservoirs, levees, and conveyance canals that acted to straighten and confine the river. This has lead to an isolation of the river from the remainder of the original floodplain. Thus today, saltcedar spreads quite differently inside and outside the confines of levees.

Habitats it can invade/site characteristics

Saltcedar prevails in monospecific thickets where native plants have been eliminated by wildfire (Busch and Smith 1995), intermixed with native plants in mature riparian forest, and in early successional habitats such as recently scoured sandbars or in post-burn floodplain communities (Brotherson and Field 1987; Frasier and Johnsen 1991). It is also widespread in areas away from river systems such as springs, seeps, lakes, playas, arroyos, dirt stock tanks, roadsides, railroad rights-of-way, residential areas, parks, and other upland situations (McDaniel and Taylor 2003). Vegetation or habitat types most susceptible to saltcedar invasion include floodplains, riparian communities, seasonal wetlands, and lake and river margins (Johnson 1986). Saltcedar density in riparian areas is generally higher than the densities of cottonwood-willow or screwbean mesquite that historically dominated riparian areas in the southwestern United States (Egan et al. 1993).

Saltcedar is a “facultative phreatophyte” meaning that although it grows best when there is an attainable source of groundwater, it can survive in arid areas without an abundance of surface moisture. Saltcedar occurs in a variety of alluvial (river influenced) mixed soils on floodplains (Taylor and McDaniel 1998b). The plant typically occupies sites with silt loams and silt clay loams high in organic matter, intermediate moisture, high water tables, and little erosion (Brotherson and Winkel 1986). Saltcedar can grow at elevations greater than 6,890 ft (2,100 m), but prefers saline soils below 1,640 ft (500 m) (DiTomaso 1998). Although there are no specific data on the range of temperature conditions in which saltcedar spp. survive, these species are found in hot, arid, desert environments to cold, high, mountain habitats.

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