Tamarisk Tree, Pink flowers on this tamarisk may be beautiful, but hard to enjoy once you realize that it is a destructive invasive plant. This large green shrub has feathery green branches with pink tips.
Invasive Plant Species: Tamarisk
In Arizona, however, the removal of old trees is controversial, in part because it has become a preferred nesting site for the endangered willow flycatcher (Empidonax traillii extimus). Tamarisk (Tamarix species), also known as salt cedar, is a tall tree with feathery green to bluish green foliage. As in Montana, South Dakota, Texas and Wyoming, it is listed as a harmful weed. In New Mexico, it is a nemesis, an invasive species similar to our buffalo grass.
How did it get here?
Tamarisk was introduced to our area for erosion control. Tamarisk can be planted as an ornamental tree or as a windbreak. It also reproduces vegetatively; broken plant parts (even tiny leaf scales) can take root and form new plants. And it multiplies by seed that travels with wind and water.
What is the threat?
Tamarisk is a thirsty plant with a high evaporation rate that absorbs a lot of water and releases it into the air. It competes with native plants and displaces coastal habitats. Other mature trees serve as nesting sites for southwest pastures and flycatchers, but tamarisks contribute little to food or other benefits for native animals. In the Saguaro National Park the tamarisks are well under control, but in other western states they can cause serious damage.
It grows quickly and forms thick stands, creating large areas of dense shade. This shadow increases the fire frequency, changes the hydrology, lowers the water table and increases the salinity of the soil. It also discourages native seedlings from trees and grasses and reduces the diversity of plants and animals in the ecosystem.
Several other national parks, such as the Grand Canyon, Canyonlands and Lake Mead National Recreation Area, also have significant tamarisk infestations that threaten natural resources and impair recreation.
Management goals and strategies
Our goal was to eradicate all tamarisks in the park. We used both manual and chemical controls. The park managed to conduct a survey and remove all the people we could find.
Small seedlings can be raised by hand. Ripe trees can be felled and herbicides applied to the trunk to prevent regrowth. Plants larger than one hand can easily be pulled up and removed by digging into the roots.
The salt cedar leaf beetle (Diorhabda elongata) has been used as a biological control in other states with astonishing success. However, it was not used in Arizona out of concern for the southwestern willow flycatcher. Its spread into the birds’ habitat has threatened the risk of unforeseen consequences and led to calls for a reduction in the insect’s use, a story captured in a Scientific American article. It has also depopulated tamarisk-infested areas, which requires active restoration.
Progress to date
Park biologists thought the tamarisk was extinct until a 100-year flood in 2006 brought seeds to parts of the Rincon Creek area, leading to thousands of seedlings. One or two unknown trees caused the infestation, and the biologists ignored the seeds. Biologists were concerned that they were not aware of any tamarisk trees in the drainage that flows into the Rincon Creek watershed.
Faced with thousands of seedlings and the possibility of catastrophe, the park applied for and received grants to survey the tamarisk and to remove drainage from the park and potential habitats for the tree. Crews searched and removed seedlings from trees to bring the tree under control. Surveying teams found some mature trees that had been washed away uncontrollably.
Tamarisk spreads upstream and downstream through wind and water. It is critical that the park and private property owners in the Rincon Creek catchment area work together to remove tamarisks. Read our Tamarisk Resource Letter, which summarises the work we have done to eradicate the tamarisks in the park.
How to Identify Tamarisk
The flowers appear in spikes and are often pink or pale pink, although some are cream white. Tamarisk species are large shrubs or trees with a feathery appearance. Depending on the species, they can be 15 to 50 feet tall and ripe and deciduous in winter. The pinnate branches are similar to those of cedars and junipers, with tiny triangular scaly leaves and fine branches.
How you can help
Tamarisk is not on the federal or state of Arizona’s list of harmful weeds, but it is available at some nurseries. Please inform the nursery management of your concerns about the use of tamarisks in our area.
Good alternatives for trees in your garden are desert willow (Chilopsis linearis), desert iron (Olneya tesota). Remove all tamarisks from your garden. Tamarisk seedlings should be removed from the yard and dug up as this increases the size of the tree and does not have to wait until the next season.