Wetlands mitigation: partnership between an electric power company and a federal wildlife refuge

Create or restore wetlands

A site comparison study in 1995–1996 of two forested wetlands in Maryland, USA (Perry et al. 1996) found that some reptiles colonised a created forested wetland. Black rat snakes Elaphe obsoleta were seen basking and several snapping turtles Chelydra serpentina laid eggs in a created forested wetland. A single five-lined skink Eumeces fasciatus was trapped in the adjacent natural wetland but none were trapped in the created wetland. As mitigation for loss of wetland, a 9 ha wetland was constructed in 1994, of which 5.5 ha was forested wetland. Reptiles were captured in pitfall and funnel traps along drift-fencing within the created and adjacent natural forested wetland. Trapping was conducted several times in 1995–1996.

(Summarised by: Katie Sainsbury)

Reprofile/relandscape: freshwater swamps

A study in 1994–1995 in Maryland, USA (Perry et al. 1996) reported that approximately 1–2 years after reprofiling and planting trees/shrubs, the site contained mostly herbaceous vegetation. The created wetland had 67–69% grass cover, 17–19% cover of other herbs, and 1% cover of woody plants. Methods: In winter 1993/1994, around 5.5 ha of a former firing range was reprofiled to wetland elevations. In spring/summer 1994, a mixture of tree and shrub species (6,327 individuals) were planted into the reprofiled site. Vegetation was surveyed in August 1994 and 1995. Cover of all plant species was recorded in 120 quadrats, each 1 m². The study does not distinguish between the effect of reprofiling and planting on non-planted vegetation.

(Summarised by: Nigel Taylor)

Create wetland

A site comparison study in 1994–1996 of a created forested wetland in a Research Refuge in Maryland, USA (Perry, Sibrel & Gough 1996) found that the created wetland supported a similar number of amphibian species to an adjacent natural forested wetland. Ten species were captured in the created wetland (284 individuals) and 11 in the adjacent natural wetland (87 individuals). Spotted salamander Ambystoma maculatum was only found in the created site and wood frog Rana sylvatica and marbled salamander Ambystoma opacum only in the natural wetland. As mitigation for loss of wetland, a 9 ha wetland was constructed in 1994, of which 5.5 ha was forested wetland. Amphibians were captured in pitfall and flannel traps along drift-fencing within the created and adjacent natural forested wetland. Trapping was conducted several times during the year.

Restore or create wetlands

A site comparison study in 1994–1995 of two forested wetlands in Maryland, USA (Perry et al. 1996) found that a created forested wetland had the same mammal species richness as a nearby natural site, but different species composition. No statistical analyses were performed. Four mammal species were recorded both on the created site and the natural site. Meadow vole Microtus pennsylvanicus was more abundant at the created site (0.17–0.58 individuals/trap/day) than at the natural site (0 individuals/trap/day). The same pattern was seen for House mouse Mus musculus, and domestic cat Felis catus (no data reported). White-footed mouse Peromyscus leucopus was less abundant at the created site (0–0.17 individuals/trap/night) than at the natural site (0.14–0.67 individuals/trap/night). Pine vole Pitymys pinetorum, gray squirrel Sciurus carolinensis and opossum Didelphis virginiana were found only in the natural site. Forest wetland (5.5 ha) was created on a former firing range. The site was graded in December 1993 and planted with native vegetation in spring and summer 1994. Mammals were live-trapped from November 1994 to March 1995 on the created site and adjacent natural forest wetland, using Sherman traps and larger box traps. Tracks were monitored in sand pits in summer 1995.

(Summarised by: Nick Littlewood)

Directly plant trees/shrubs: freshwater wetlands

A study in 1994–1995 a reprofiled and planted freshwater wetland in Maryland, USA (Perry et al. 1996) reported that the majority of planted trees/shrubs survived for one year, but there was little other change in vegetation cover and structure. Statistical significance was not assessed. After approximately one year, 83% of planted shrubs and 91% of planted trees were still alive. Survival varied between species, but was never lower than 69% (for highbush blueberry Vaccinium corymbosum). Over the year after planting, the average diameter of surviving trees increased from 11 to 15 mm. There was little other change in vegetation cover (grasses: 67–69%; other herbs: 17–19%; woody plants: 1%) or structure (tree height: 147–149 cm; tree canopy diameter: 29–33 cm; shrub height: 101 cm; shrub canopy diameter: 31–36 cm). Methods: In spring/summer 1994, a mixture of tree and shrub species (6,327 individuals) were planted into 5.5 ha of a former firing range, which had been reprofiled to manage water levels. Vegetation was surveyed in August 1994 and 1995. Tree/shrub survival, and diameter of surviving trees/shrubs, were monitored in twelve 25 x 25 m plots. Cover of all plant species was recorded in 120 quadrats, each 1 m². The study does not distinguish between the effect of planting trees/shrubs and reprofiling on non-planted vegetation.

(Summarised by: Nigel Taylor)