Reprofile/relandscape: freshwater swamps
Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 2
Background information and definitions
This action involves large-scale reprofiling or landscaping, aiming to restore or create swamps. This includes excavating large basins (>8 ha or >280 m diameter), moving soil/sediment from the site into levees/berms/impoundments, removing unnatural hills or levees, filling in deep depressions and altering the elevation/slope of coastal areas. In other words, this action aims to restore wetland hydrology (how wet the soil is and when it is wet/flooded) by adjusting the ground surface relative to the water table or sea. Soil from existing marshes or swamps might be imported as part of relandscaping efforts, but we consider this as a separate action.
Caution: Heavy machinery is usually needed for this intervention. Heavy vehicles can churn and compress wetland soils (Campbell et al. 2002).
Related actions: Raise water level to restore degraded swamps; Raise water level to restore/create swamps from other land uses; Facilitate tidal exchange to restore degraded swamps; Facilitate tidal exchange to restore/create swamps from other land uses; Excavate pools; Create mounds or hollows; Remove surface soil/sediment; Deposit soil/sediment to form physical habitat structure; Reprofile/relandscape before planting.
Campbell D.A., Cole C.A. & Brooks R.P. (2002) A comparison of created and natural wetlands in Pennsylvania, USA. Wetlands Ecology and Management, 10, 41–49.
Supporting evidence from individual studies
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.Study and other actions tested
A replicated, site comparison study in 2000 of 11 freshwater swamps in Virginia, USA (Snell-Rood & Cristol 2003) found that created swamps – reprofiled then planted with trees/shrubs – had a similar proportion of habitat-characteristic vegetation and similar horizontal vegetation cover to similar-aged swamps recovering naturally from logging, but contained shorter woody vegetation with a lower basal area and density. After 7–11 years, created and naturally recovering swamps contained statistically similar proportions of tree species characteristic of four soil moisture classes (from “highly saturated” to “partially saturated”), had statistically similar vegetation cover (both ground and canopy) and contained herbs of statistically similar height (data not reported). However, woody vegetation in created swamps was shorter (created: 2.0 m; natural: 4.4 m) and had a lower basal area (created: 59 cm2/100 m2; natural: 519 cm2/100 m2). Finally, created swamps had lower horizontal vegetation cover, both 1 m and 2 m above the ground (created: 26–45%; natural: 83–92%). Methods: In summer 2000, vegetation was surveyed in 11 swamps of similar age, water level and surrounding land use. Six swamps had been created by reprofiling upland sites to increase soil moisture, then planting a mix of wetland trees/shrubs (and in one case, adding wetland soil). The study does not distinguish between the effects of these interventions on non-planted vegetation. Five swamps were recovering naturally after clearcut logging.Study and other actions tested