Impacts

Native Vegetation -

• Tamarisk populations develop in dense thickets, with as many as 3,000 plants per acre, which can prevent the establishment of native vegetation (e.g., cottonwoods, willows, sage, grasses, and forbs).
• Due to their extensive root systems that are unselective in their uptake of ions, tamarisk draw more salts from the groundwater than native vegetation. These salts are excreted through tamarisk leaf glands and deposited on the ground with the leaf litter. This may result in a substantial rise in soil salinity and prevent the germination of many native plants. However there is some debate over the extent to which tamarisk contributes to soil surface salinity. Some researchers argue that altered river conditions are largely responsible for elevated soil salinity and that tamarisk now occupies areas that are too saline for native plants.

Wildfire -

• The large amount of leaf litter that tamarisk produces increases the intensity of riparian wildfires and may increase their frequency. These intense fires kill native vegetation such as cottonwoods and willows that are not adapted to them, but stimulate tamarisk growth.

Wildlife and Livestock -

• The effect of tamarisk on terrestrial wildlife depends on the species being considered, however tamarisk monocultures likely support a lower diversity of wildlife than a more diverse native plant community.
• Dense tamarisk stands affect livestock by reducing forage and preventing access to surface water.
• Tamarisk seeds and leaves are of little nutritional value to most wildlife and livestock.
• Dense tamarisk stands on stream banks accumulate sediment in their extensive root systems, gradually narrowing stream channels and increasing flooding potential. These changes in stream morphology can impact critical habitat for endangered fish.

People -

• Aesthetic values of the stream corridor are degraded by solid stands of tamarisk that exclude diverse vegetation and limit wildlife and bird viewing opportunities.
• Tamarisk block access to streams for recreation (e.g., boating, fishing, hunting, bird watching).
• Dense tamarisk stands on stream banks accumulate sediment in their extensive root systems, gradually narrowing stream channels and increasing flooding potential.

Water -

• Tamarisk may use either more or less water than native vegetation depending on the identity of the native species, stand densities and environmental and site conditions such as depth to groundwater and salinity. For instance tamarisk likely uses about that same amount of water as other phreatophytes such as willow or cottonwood, but tamarisk also invades more upland areas where it replaces non-phreatophytes which use much less water.

For a more extensive discussion and references please refer to the Colorado River Basin Tamarisk and Russian Olive Assessment.