Restoring the ecosystem services and functions of areas that hold or convey water is a widespread practice, often accompanied by evaluations of the success of that effort.
Invasive Species Density
One of the common issues in restored areas is the appearance of invasive plant species that may negatively affect the desired outcomes. In an effort to determine a level of invasive species presence that could be tolerated without impacting the overall restoration goals, a study evaluated 21 stream and 23 wetland restoration projects completed in Virginia, USA.1 The sites were evenly distributed across the Coastal Plain and Piedmont regions and ranged from one to 19 years since establishment. All sites fell under state and federal mitigation laws for non-tidal forested wetlands or stream restoration projects (Figure 1). The focus was on two invasive species common in constructed wetlands (Anthraxon hispidus and Typha spp.), two common in stream restoration sites (Lespedez cuneata and Lonicera japonica) and one common in both settings (Microstegium vimineum).
Transects were established from “completely invaded (>20%)” to “uninvaded” areas for each invasive species and plots were surveyed for plant species and cover. From these data, the amount of invasive plant cover that negatively impacted species richness could be estimated for each of the five target invasives. In the wetlands, all three invasive species negatively impacted community properties at the highest level of invasion, but the effects were less clear at lower levels. Often the highest richness occurred on the edge of the most invaded areas. A total of 194 plant species were identified in the wetland areas. The stream sites hosted 286 plant species with results similar to those of the wetlands study: species richness was negatively impacted in the highly invaded area but not in the moderately to uninvaded areas. Plots of invasive cover versus native richness suggested that the maximum values occurred at around 10% invasive cover. The authors suggest that efforts to remove invasive species at levels lower than 10% may be counterproductive given these results. However, they caution that continued monitoring is still important to know when these levels are being exceeded.
Effects of Flow Controls
The semiarid rangelands of the Gunnison Basin in Colorado, USA, were the focus of a study on the effects of erosion control structures on the surrounding vegetation.2 Land use over the years resulted in wagon tracks, stock ponds, roads and grazing that led to erosion in ephemeral and perennial stream channels.
To reduce this erosion, a variety of simple structures known as “Zeedyk structures” (See Resource) were installed to slow flow and to reconnect the channels with the surrounding floodplains. Aside from erosion control, these structures help to create wet meadows that host plants that are critical for wildlife, particularly the Gunnison sage-grouse, which is identified as a threatened species by the U.S. Fish and Wildlife Service. The 202,000-ha area has cold winters and warm summers with a highly variable average annual precipitation of 230 mm. Six of the study’s nine years were considered drought years.
The management objective for installing 900 structures in 11 drainageways was to increase obligate and facultative wetland species, including sedges, rushes and forbes, by 20% within five years. This was evaluated with plant surveys from 2012 to 2020 in 135 permanent transects in treated areas and thirty transects in untreated (no structures) areas of seven of these drainageways.
Overall, the 20% increase in wetland species was met in 75% of the ephemeral and 100% of the perennial stream areas, with a net cover gain of approximately 40% during the monitoring period. Areas with the least wetland plant cover tended to have the greatest increases. Among the 215 plant species present, 13 wetland species were relatively common, particularly Baltic rush (Juncus balticus) and western aster (Symphyotrichum ascendens). Forbs were increased modestly (4%/year) by the treatments, while grasses, mostly Kentucky bluegrass (Poa pratensis) and western wheatgrass (Pascopyrum smithii), increased only in the ephemeral stream areas. The authors conclude that these structures appear to be beneficial in creating wetland meadows, but that additional monitoring is needed to evaluate longer-term effects.
References
- DeBerry DA and Hunter, DM. 2024. Impacts of invasive plants on native vegetation communities in wetland and stream mitigation. Biology 13:275. https://doi.org/
- 10.3390/biology13040275.
- Rondeau, RJ, Austin G, Miller, RS, Parker A,
- Breibart S,Conner, Neely E, Seward NW, Vasquez MG, Zeedyk WD. 2024. Restoration of wet meadows to enhance Gunnison sage-grouse habitat and drought resilience in arid rangelands. Restoration Ecology 32:2, e14039. doi: 10.1111/rec.14039.
Resource
Zeedyk structures: https://lowtechpbr.restoration.usu.edu/resources/recipes/Rock/erosionControl.html.
About the Expert
Rich McLaughlin, Ph.D., received a B.S. in natural resource management at Virginia Tech and studied soils and soil chemistry at Purdue University for his master’s degree and doctoral degree. He has retired after 30 years as a professor and extension specialist in the Crop and Soil Sciences Department at North Carolina State University, specializing in erosion, sediment and turbidity control. He remains involved with the department as professor emeritus.
