No, this isn't a post about illegal aliens. Arizona has long been the site of a different kind of invasion, foreign plants. One of the most invasive species is the tamarisk. Native of Africa and Eurasia, these sturdy plants can spread both vegetatively, by adventitious roots or submerged stems, and sexually, by seeds. There are over fifty species of tamarisks with eight now found in the U.S. The Tamarix was introduced to the United States as an ornamental shrub, a windbreak, and a shade tree in the early 1800s. In the 1930s, during The Great Depression, tree-planting was used as a tool to fight soil erosion on the Great Plains, and the trees were planted by the millions.Wikipedia
As the photo above illustrates, stands of this non-native plant have spread along most of the waterways in Arizona. Although there is some controversy over whether or not the tamarisks displace native species, it is my own observation that they grow so thickly along the rivers and streams that nothing else can live. The USGS has a research program "Changes in Riparian Vegetation in Arizona Repeat Photography at Gaging Stations." One set of photos, along the Virgin River at Littlefield, dramatically shows the effects of the tamarisk invasion. This first photo was taken in 1942:
The second photo was taken in 2000 at exactly the same location:
It is interesting to watch so-called western movies, many times the scenery and plant life in the movies will be anachronistic with the time period depicted, merely because of the presence of foreign plant invaders.
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