Two centuries ago, the United States bet on the tamarisk as a solution to river erosion. This tree, resilient and capable of growing in saline soils, seemed ideal for stabilizing riverbanks in arid regions. However, this species has transformed the landscape of the western part of the country, affecting native ecosystems.
From environmental solution to western invader
In the 19th century, the tamarisk was imported from Asia and first used as an ornamental plant. It was then promoted to control erosion due to its tolerance to drought and heat. However, as the 20th century progressed, the perception changed drastically. Research, such as that by historian Matthew K. Chew, indicates that this plant became the scapegoat for water scarcity and river degradation.
The tamarisk thrived due to changes in the natural flows of rivers, caused by the development of dams and water diversions. These changes favored its expansion to the detriment of native species such as poplars and willows, which require seasonal flooding to germinate.
The belief that the tamarisk consumed enormous amounts of water led to its eradication, with the hope of recovering water flows. However, recent studies by the USGS indicate that its consumption is similar to or less than that of other native woody plants, questioning the effectiveness of its removal.
Furthermore, a synthesis of more than two decades of data suggests that water use by plant communities varies according to climate and location. In warmer regions, water demand is higher due to a prolonged growing season.
In 2001, the tamarisk leaf beetle was introduced as a biological control alternative to traditional methods. Although it has reduced tamarisk coverage, its full effects on the ecosystem are still under study, with varied results in reducing evapotranspiration.
The tamarisk has also adapted as a habitat for endangered bird species, such as the southwestern willow flycatcher. The removal of Tamarix without an adequate replacement plan could harm these species.
The lesson from the tamarisk is that the elimination of invasive species does not guarantee the restoration of an ecosystem. Current restoration projects aim to recover natural processes and promote the growth of native species to achieve sustainable environmental balance.
According to the dataset published in Hydrological Processes and collected in ScienceBase Catalog, the complexity of river management shows that an invasive species can be both a symptom and a catalyst of environmental problems in altered rivers.
