Non-native South American mesquites are a serious problem around much of Tucson. They are very weedy and sprout and grow quickly - see before half of image below. They are contamitaing the gene pool of the native velvet mesquite to the point where any mesquite that come up now on their own are either hybrids or mostly non-native genes. Velvet mesquite is a keystone tree of our region and is very important for everything from firewood to wildlife habitat. Due to many characteristics these South American varieties are not desirable.
The growth you see below is only ~6 months after the entire chicane had been clear-cut. These mesquites will outcompete most any other plant if there is extra water such as on First St.