Why is revegetation important?

Tree roots holding the soil.

Revegetation is critical to the success of restoration and enhancement efforts in the Las Vegas Wash. Over the past 30 years, wetland vegetation has decreased from approximately 2000 acres to nearly 200 acres. This is mostly due to increasing flows in the Wash, which have subsequently altered surface and subsurface hydrology and accelerated erosional processes. When lands are cleared for channel stabilization activities, opportunities are created for revegetating lands adjacent to these structures. Most often the adjacent lands are cleared of non-native invasive species, which also helps with long-term invasive management strategies in the Wash. These cleared areas are then planted with native wetland, riparian, and upland plants, thus further protecting the channel against erosion and enhancing wildlife habitat. So far, 181 acres of land has been revegetated along the Wash.

The Yellow-rumped Warbler is one of many birds that use the Wash during migration.

There are a variety of benefits of the revegetation program to the overall stabilization and enhancement effort on the Wash. First, revegetation is important because plant roots can hold on to soil particles that would otherwise erode downstream. Because plant roots can hold on to the soil, the ground becomes more stable. Plants can also serve as physical barriers slowing soil and water movement downstream.

Second, revegetation is important because it creates habitat for fish and wildlife. Over 300 species of fish and wildlife have been found using the Wash. Many of these animals are birds that are breeding in the Wash or periodically stopping over on their migration route. Approximately 80% of the U.S. breeding bird population and more than 50% of the protected migratory bird species in the U.S. rely on wetland and riparian habitats.

The yerba mansa is an example of one of the many emergent plants used.

Mature Cottonwood tree (Populus fremontii)

Emergent vegetation growing in the Demonstration Wetlands pond.

Third, revegetation is important because some plants can “polish” the water. Emergent plants are excellent at removing nutrients and other compounds from the water. Wetlands in the Wash act as a biological filter for all of the water draining from the Las Vegas Valley.

In addition to the environmental benefits of enhancing native vegetation in the Wash, most of the revegetation effort qualifies as mitigation under the U.S. Army Corps of Engineers 404 permit. The permit is required for the construction of grade control structures on the Wash and states that we must mitigate an acre for every acre of open water habitat that is impacted by weir construction activities. So far, 68 of the 181 acres we have planted qualify as mitigation. The Las Vegas Wash Capital Improvements Plan states that 176 acres will need to be revegetated to mitigate the impacts of the entire stabilization

Revegetation activities in the Wash don't just stop with areas that are slated for channel stabilization. Researchers are also studying how wetland vegetation might be able to “polish” water in the Wash by setting up outdoor experiments at Lake Mead and the City of Henderson Water Reclamation Facility. The Floating Wetland project that was conducted at Lake Mead and the Demonstration Wetlands project currently under way at the City of Henderson Water Reclamation Facility, are seeking to provide quantitative information on the effectiveness of plants to “polish” water in the Wash and Lake Mead.

The Las Vegas Wash riparian ecosystem:
development, degradation, and active rehabilitation (.pdf)