These trees are considered a nonnative, invasive tree. They grow in abundance in the Middle East, Asia and parts of Africa with harsh conditions and little rain. For a long time they were thought to suck up the water and to squeeze out the willows and cottonwoods along the rivers in the Southwest where they helped prevent erosion. It has been a much maligned tree. Click here for a very interesting article about how scientific research has pretty much debunked these beliefs .