Tamarisk - a Noxious Western Tree

Saltcedar is one of several common names for an invasive non-native tree that is spreading rapidly through the intermountain region of the western United States, through the Colorado River Canyons, the Great Basin, California, and Texas. Other common names include tamarisk and salt cedar.

The tamarisk is degrading the rarest of habitats in the desert southwest - the wetlands. Salt cedar invades springs, ditches, and streambanks. The tree has taken over more than 1 million acres of the precious Western riparian resource.

Rapid Growth Rate

Under good conditions, the opportunistic tamarisk can grow 9 to 12 feet in a single season. Under drought conditions, saltcedar survives by dropping its leaves. This ability to survive under harsh desert conditions has given the tree an edge over more desirable native species and causing a sharp decline in cottonwood populations.

Regenerative Ability

Mature plants can survive flooding for up to 70 days and can quickly colonize moist areas due to the constant availability of seeds. The plant's ability to exploit suitable germinating conditions over a long time period gives saltcedar a considerable advantage over native riparian species.

Habitat

Mature tamarisk can also resprout vegetatively after fire, flood, or treatment with herbicides and can adapt to wide variations in soil condition. Saltcedar will grow at elevations up to 5,400 feet and prefers saline soils. They typically occupy sites with intermediate moisture, high water tables, and minimal erosion.

Adverse Impacts

The serious direct impacts of saltcedar are numerous. This invasive tree is now taking over and displacing native plants, specifically cottonwood, using its aggressive growth advantage in areas where natural native communities have been damaged by fire, flood or some other disturbance. Native plants have proven to be more valuable in retaining moisture on wetlands than tamarisk. The loss of these native species to tamarisk eventually leads to a net loss of water.

A Water Hog

The tamarisk has an extremely rapid evapotranspiration rate. There is a fear that this rapid loss of moisture could possibly cause serious depletion of groundwater. There is also an increased deposition of sediments in tamarisk-infested streams which causes a blockage. These sediment deposits encourage dense clumps of saltcedar growth which then promotes flooding during periods of heavy rain.

Controls

There are essentially 4 methods to control tamarisk - mechanical, biological, competition, and chemical. The complete success of any management program depends on the integration of all methods.

Mechanical control, including hand-pulling, digging, use of weed eaters, axes, machetes, bulldozers, and fire, may not be the most efficient method for removal of saltcedar. Hand labor is not always available and is costly unless it is volunteered. When heavy equipment is used, the soil is often disturbed with consequences that may be worse than having the plant.

In many situations, control with herbicides is the most efficient and effective method of control for removal of tamarisk. The chemical method allows regeneration and/or re-population of natives or re-vegetation with native species. The use of herbicides can be specific, selective and fast.

Insects are being investigated as potential biological control agents for saltcedar. Two of these, a mealybug (Trabutina mannipara) and a leaf beetle (Diorhabda elongata), have preliminary approval for release. There is some concern over the possibility that, due to the environmental damage caused by tamarisk, native plant species may not be able to replace it if the biological control agents succeed in eliminating it.