Restore or create wetlands

How is the evidence assessed?
  • Effectiveness
  • Certainty
  • Harms

Study locations

Key messages

  • Four studies evaluated the effects on mammals of restoring or creating wetlands. Three studies were in the USA and one was in the UK.


  • Community composition (1 study): A site comparison study in the USA found that the composition of mammal species present differed between a created and a natural wetland.
  • Richness/diversity (2 studies): Two site comparison studies (one replicated) in the USA, found that mammal species richness did not differ between created and natural wetlands.


  • Abundance (1 study): A before-and-after study in the USA found that following marshland restoration, muskrat abundance increased.
  • Survival (1 study): A replicated, controlled, before-and-after study in the UK, found that water voles persisted better in wetlands that were partially restored using mechanical or manual methods than they did in wetlands undergoing complete mechanical restoration.


About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

Supporting evidence from individual studies

  1. A before-and-after study from the 1960s to 1981 of a marshland alongside Lake Erie, Ohio, USA (Kroll & Meeks 1985) found that marshland restoration was associated with increased numbers of muskrat Ondatra zibethicus. Population trends were not tested statistically. Four to five years after marsh restoration started, the average number of muskrat pelts collected in the annual harvest (3,657–5,583) was higher than four years prior to restoration (376). The number of pelts was similar to that 10 years prior to restoration, before the marshland was degraded by high water levels (3,681 pelts). Muskrat pelt prices did not significantly affect harvest size. Marsh was restored by reconstructing dikes to facilitate water level control. Muskrat harvest figures were obtained from trappers, who traditionally trapped the same areas each year. The harvest was not directly regulated.

    Study and other actions tested
  2. 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.

    Study and other actions tested
  3. A replicated, site comparison study in 1999–2000 of 17 wetlands in South Dakota, USA (Juni & Berry 2001) found that mammal species richness was similar in created, restored and enhanced wetlands compared to in natural wetlands. There was no significant difference in the average number of species found in created (2.7 species), restored (2.4 species) and enhanced wetlands (1.9 species) and in natural wetlands (1.4 species). Four created, four restored, four enhanced and five natural wetlands were sampled. Wetland creation involved either impounding a small stream or excavating a basin. Restoration included plugging drainage ditches or breaking sub-surface drainage tiles. Enhancement included manipulating water levels to increase wetland size or changing vegetation structure. Wetland creation, restoration and enhancement was carried out within the previous 10 years. Monitoring was undertaken in spring and autumn in 1999–2000. Sampling at each site included live-trapping (four transects, each with five traps spaced 5 m apart), complemented with pitfall traps and sightings.

    Study and other actions tested
  4. A replicated, controlled, before-and-after study in 2008–2010 on a wetland near Peterborough, UK (Furnborough et al. 2011), found that partial pond restoration using mechanical or manual methods led to greater persistence of water voles Arvicola amphibius than did complete mechanical restoration. No statistical analyses were performed. After management, the number of pond visits (out of 12: four visits to each of three ponds) revealing water vole presence at partial manual restoration ponds (nine) and partial mechanical restoration ponds (nine) was greater than at full mechanical restoration ponds (two) and similar to that at unmanaged ponds (10). Before management, water voles were present at all ponds set to undergo restoration and at two of three unmanaged ponds. Pond restoration took place between October 2008 and January 2009, on a 126-ha site. Four ponds were restored by complete mechanical excavation of edge and bottom vegetation, four by mechanical clearance of 15 m of pond edge, four by manual clearance of 15 m of pond edge and four were unmanaged. Ponds were in three replicate clusters. Monitoring entailed searches for water vole feeding signs or latrines in autumn 2008 (pre-restoration) and in June, September and October 2009 and March 2010 (post-restoration).

    Study and other actions tested
Please cite as:

Littlewood, N.A., Rocha, R., Smith, R.K., Martin, P.A., Lockhart, S.L., Schoonover, R.F., Wilman, E., Bladon, A.J., Sainsbury, K.A., Pimm S. and Sutherland, W.J. (2020) Terrestrial Mammal Conservation: Global Evidence for the Effects of Interventions for terrestrial mammals excluding bats and primates. Synopses of Conservation Evidence Series. University of Cambridge, Cambridge, UK.

Where has this evidence come from?

List of journals searched by synopsis

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Terrestrial Mammal Conservation

This Action forms part of the Action Synopsis:

Terrestrial Mammal Conservation
Terrestrial Mammal Conservation

Terrestrial Mammal Conservation - Published 2020

Terrestrial Mammal Conservation

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What Works in Conservation provides expert assessments of the effectiveness of actions, based on summarised evidence, in synopses. Subjects covered so far include amphibians, birds, mammals, forests, peatland and control of freshwater invasive species. More are in progress.

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