Biological Changes: Plants

The introduction of non-native plants and animals has also had a significant impact on the native communities. Two species of introduced plants, saltcedar or tamarisk (Tamarix chinensis) and Russian olive (Elaeagnus angustifolia), have spread throughout the valley, due in large part to certain aspects of their biology. For example, saltcedar can produce seeds as early as its first year, and seeds are typically produced from early spring to late fall. This allows saltcedar to become established over a much broader window of time than cottonwoods and to take advantage of later summer thunderstorms and flooding.

Unlike cottonwoods or saltcedar, Russian olive is shade tolerant and so can spread within the established forest. Both of these exotics can form dense thickets that stabilize the riverbank and decrease the likelihood of flooding, further contributing to the decline of cottonwoods. A number of other exotics, such as Siberian elm (Ulmus pumila), white mulberry (Morus alba), tree of heaven (Ailanthus altissima), sweet clover (Melilotus alba) and Johnson grass (Sorghum halapense), are now common in the bosque. In many places along the Middle Rio Grande Valley, these exotic plants now dominate the riverside forest. Predictions are that if water management continues as it has in the past, introduced plants will soon dominate the Valley bosque.