The understory of the bosque developed as the Middle Rio Grande was dammed, channeled and controlled by levees, drainage systems and other flood control methods. Since there was no longer annual flooding and the river channel was contained within higher banks, many new plants began to gain a foothold underneath an aging cottonwood forest. The understory is a mixture of Tamarisk, Russian Olive, Siberian Elm and other introduced species that have thrived in a riparian habitat that no longer floods on a regular basis.