Action: Restore ponds
- Fifteen studies investigated the effectiveness of pond restoration for amphibians.
- One replicated, before-and-after study in Denmark found that pond restoration had mixed effects on European tree frog population numbers depending on site. One replicated, controlled, before-and-after study in the UK found that pond restoration did not increase great crested newt populations. Six replicated, before-and-after studies (including one controlled and one site comparison study) in Denmark, Estonia, Italy and the UK found that pond restoration and creation increased numbers of amphibian species, maintained or increased populations, or increased pond occupancy and ponds with breeding success. One found that numbers of species did not increase. Two before-and-after studies (including one replicated study) in Estonia found that pond restoration, along with terrestrial habitat management, maintained or increased populations of natterjack toads. One systematic review in the UK found that there was no conclusive evidence that mitigation, which often included pond restoration, resulted in self-sustaining great crested newt populations.
- One small, replicated study in the USA found that pond restoration had mixed effects on spotted salamander hatching success depending on restoration method.
- One replicated, before-and-after study in the UK found that restoration increased the number of ponds used by breeding natterjack toads. One replicated study in Sweden found that following restoration green toads only reproduced in one of 10 ponds. Three before-and-after studies (including one replicated, controlled study) in Denmark and Italy found that restored and created ponds were colonized by 1–7 species, with 6–65% of ponds colonized and 35% used for breeding.
Ponds are often drained, left to dry or degraded during the development of agriculture or expansion of urban areas or other land uses. Although some amphibians are relatively tolerant of poor pond conditions, breeding is likely to be more successful in better quality ponds. Restoration of ponds may therefore help to increase populations of amphibians.
Studies included here investigated the restoration of ponds using a combination of interventions. Studies that investigated pond restoration using one specific action are discussed under the relevant intervention, i.e. ‘Deepen, de-silt or re-profile ponds’, ‘Add specific plants to aquatic habitats’, ‘Remove specific aquatic plants’ and ‘Remove canopy to reduce pond shading’. For removal or control of fish populations see ‘Threat: Invasive alien and other problematic species – Reduce predation by other species’.
Studies investigating the restoration of wetlands are discussed in ‘Restore wetlands’.
Supporting evidence from individual studies
A replicated, before-and-after study in 1983–1985 of 23 restored ponds on Borholm, Denmark (Fog 1988) considered that 14 were successful and two failed. European tree frogs Hyla arborea were found in 10 ponds. There were large tree frog population increases in two ponds, moderate increases in five, no change in one and declines in two ponds post-restoration. One of the failures was due to pollution, another to ducks and restoration had changed the community in a third pond. In 1983–1985, 23 ponds were restored on private land, primarily to improve European tree frog populations. Restoration involved activities such as dredging and tree cutting.
A before-and-after study in 1985–1987 of head-started European tree frogs Hyla arborea released into 20 restored and created ponds near Aarhus, Denmark (Skriver 1988) found evidence of breeding a year after release. In 1986, 17–21 males were heard calling in four ponds, but no females, eggs or tadpoles were recorded. In 1987, up to 50 males were heard calling in 13 ponds. Four egg masses were found in one pond and tadpoles in six ponds. One hundred and fifty egg masses were collected from the nearest natural population. These were captive-reared in hot houses. Over 6,000 metamorphs were released into nine created and 11 restored ponds (over 10 km2) in 1985–1986.
A replicated study in 1987–1993 of 10 ponds on the island of Samsø, Sweden (Amtkjær 1995) found that restoration only resulted in successful breeding by green toads Bufo viridis in one pond. A year after pond cleaning, breeding was recorded in one pond, only males in another and no toads in the third pond. Only one male was seen in one of the seven ponds that were enlarged and had fish removed. In winter 1987–1991, three ponds were cleaned due to eutrophication. Seven ponds had fish removed and were enlarged. Ponds were monitored by call and torch surveys and by counting tadpoles and metamorphs during 4–6 visits in April–September.
A replicated, before-and-after study in 1977–1996 of ponds on chalkland in England, UK (Beebee 1997) found that pond restoration and creation resulted in increased occupancy by amphibians but not species richness/pond. In 1996, 69% of ponds were used compared to 55% in 1977. Species richness was similar in 1977 and 1996 (all ponds: 1.1; used ponds: 1.9 vs 1.6 species). Occupancy increased from 1977 to 1996 for common frogs Rana temporaria (4 vs 9 ponds) and toads Bufo bufo (2 vs 4). However, occupancy decreased for smooth newts Triturus vulgaris (14 vs 10), palmate newts Triturus helveticus (6 vs 3) and great crested newts Triturus cristatus (9 vs 3). Despite restoration, 17 of 33 original ponds were lost by 1996. However, a higher proportion of surviving ponds (n = 26) were in good condition in 1996 (58%) compared with 1977 (24%). Ponds were within a 150 km2 area. Eleven of 33 ponds had been restored since 1977 and 13 created. Ponds were surveyed in spring 1995 or 1996 for species presence by egg counts, torchlight surveys and netting and trapping for newts.
A replicated, controlled, before-and-after study in 1986–1997 of 3,446 ponds restored and created for amphibians in Denmark (Fog 1997) found that pond management was effective for maintaining and increasing populations. Populations survived five years after restoration in 92% (74–100%) of cases, compared to just 40% (32–52%) of cases without restoration. A total of 175 (39%) restored ponds were naturally colonized by rare species and 28 colonized by released animals. Approximately 2,000 ponds were restored or created for rare species, over half of which were for the European tree frog Hyla arborea. The national population of the species doubled as a result. A questionnaire was sent to all those responsible for pond projects across Denmark to obtain data. Over a third of projects dredged existing ponds and 7% had other types of restoration. For a pond to be defined as ‘colonized’ a species had to be present but not breeding.
A replicated, before-and-after study in 1998–2000 of restored and created ponds in 12 natural parks in the Lombardy District, Italy (Gentilli et al. 2002) found that pond restoration and creation resulted in increases in some existing amphibian species populations and colonization by new species within two years. Existing populations increased at six sites (average: 1.5 species; range 1–4). Between one and seven species colonized ponds at each site (average: 1.7 species). Numbers of egg clumps increased in the second year. Ponds were created or were restored by methods such as deepening and were lined with clay or PVC if necessary. Other habitat management was also undertaken at some sites including increasing dead wood, excavating tributary canals and removing and excluding fish.
A replicated, before-and-after study in 1991–1999 in a reserve in Caerlaverock, Scotland, UK (Phillips, Patterson & Shimmings 2002) found that pond restoration increased the number of ponds used by breeding natterjack toads Bufo calamita. Out of 12 ponds restored in 1995–1998, 11 were used for breeding every year until 1999, compared to just four before restoration. Overall, breeding occurred one or two years after restoration in eight ponds that had not been used for breeding during the previous two or more years. All ponds used before restoration were still used for breeding and there was little change in use of unmanaged ponds. In 1995–1999, 17 ponds were restored by clearing aquatic vegetation, excavation and redefinition. Electric fences were installed around ponds during the summer to exclude cattle and sheep. Fences were removed after toadlet emergence. Ponds were visited at least four times in May–August 1991–1992 and 1994–1999 to count eggs, tadpoles and toadlets.
A replicated, before-and-after study in 1989–1997 of 25 restored and 23 created ponds on nine islands in Funen County, Denmark (Briggs 2003) found that there was a significant increase in the green toad Bufo viridis population. Overall, the population on the islands increased from 1,112 to 3,520 toads over the seven years. Numbers were similar on islands with just pond creation and restoration (1,020 to 952) and increased on the two where cattle grazing was also reintroduced (92 to 2,568). Overall, pond occupancy increased from 23 to 51 and the number of ponds with breeding success increased from nine to 15. In 1989–1997, ponds were created or restored by removing plants and dredging. On two of the islands, cattle grazing was also reintroduced to 73 ha of coastal meadows and abandoned fields. Populations were monitored annually in 1990–1997 during two or three call and visual surveys and dip-netting surveys. One population was also monitored in 1987–1989.
A replicated, before-and-after study in 1986–2004 of coastal meadows in Funen County, Denmark (Briggs 2004) found that pond restoration and creation, along with reintroduction of grazing, significantly increased green toad Bufo viridis and natterjack toad Bufo calamita populations. On 10 islands, green toads increased from 1,132 in 1988–1990 to over 10,000 adults in 2004. Numbers were similar on four islands with no management (512 to 510). Pond occupancy increased from 27 in 1988 to 61 in 1997 and ponds with breeding success from 11 to 22. Natterjack toads increased from 3,106 in 1998–1990 to 4,892 adults in 1997. Numbers of ponds with breeding success was similar (28 to 34). However, in 2000–2004, numbers dropped and small populations were lost due to insufficient grazing. Numbers of natterjacks declined on four islands with no restoration (270 to 170). From 1986–1991, 25 ponds were restored by reed removal and 23 created for green toads and six were restored and eight created for natterjacks on 16 islands. Cattle grazing was reintroduced on six and continued on ten islands. Green toad eggs were translocated to one island. Four populations were monitored annually and others less frequently during 2–3 call and visual surveys and dip-netting.
A before-and-after study in 1992–2004 of a coastal meadow on an islet in Estonia (Lepik 2004) found that pond and terrestrial habitat restoration maintained a population of natterjack toads Bufo calamita. A total of 17 natterjacks were counted in 1992 and seven in 2004, with numbers ranging from 1–17/year. It is considered by the author that without management the natterjack population may have declined or become extinct. Common toad Bufo bufo counts were eight in 1992 and four in 2004 and ranged from 3–40/year. Restoration involved reed and scrub removal, mowing (cuttings removed) and reintroduction of sheep grazing. Toads were counted along a 1 km transect.
A replicated, before-and-after study in 2001–2004 of three coastal meadows in Estonia (Rannap 2004) found that restoration of breeding ponds, along with terrestrial habitat management, increased numbers of natterjack toads Bufo calamita on one island and stopped a decline on the other two islands. In 2001–2004, habitats were restored on three coastal meadows where the species still occurred. Sixty-six breeding ponds and natural depressions were cleaned, deepened and restored. Restoration also included reed and scrub removal, mowing (cuttings removed) and implementation of grazing where it had ceased.
A replicated, before-and-after, site comparison study of 450 existing ponds, 22 of which were restored, and 208 created ponds in six protected areas in Estonia (Rannap, Lõhmus & Briggs 2009) found that within three years amphibian species richness was higher in restored and created ponds than unmanaged ponds (3 vs 2 species/pond). The proportion of ponds occupied also increased for common spadefoot toad Pelobates fuscus (2 to 15%), great crested newt Triturus cristatus (24 to 71%) and the other five amphibian species (15–58% to 41–82%). Breeding occurred at increasing numbers of pond clusters from one to three years after restoration and creation for great crested newt (39% to 92%) and spadefoot toad (30% to 81%). Prior to restoration and creation, only 22% of ponds were considered high quality for breeding. In 2005, 405 existing ponds were sampled by dip-netting. In autumn 2005–2007, 22 ponds were restored and 208 created for great crested newts and spadefoot toads in 27 clusters. Restoration included clearing vegetation, extracting mud, levelled banks, pond drying and ditch blocking (for fish elimination). Monitoring was undertaken by visual and dip-netting surveys during one visit in 2006–2008.
A small, replicated study in 2005–2007 of five restored forest ponds in Illinois, USA (Sacerdote & King 2009) found that spotted salamander Ambystoma maculatum hatching success increased following additional prescribed burning, but not canopy removal. Eggs failed to hatch in three restored ponds. However, hatching success of egg masses increased after a prescribed burn at the one pond (2005: 0%; 2006–2007: 30–54%). This was not the case following canopy thinning at another pond (0%). Restored ponds had similar hatching success to ponds with resident spotted salamanders in 2005–2006 (29 vs 30%), but significantly higher success in 2007 following additional restoration (62 vs 20%). Restoration started in 2000 and included destruction of drainage tiles, clearing of invasive plants and prescribed burning. An egg mass was placed in two mesh enclosures (56 x 36 x 36 cm) in each restored pond. Three enclosures with an egg mass were also placed in each of three ponds with existing spotted salamanders populations (different site). Eggs were monitored every five days.
A replicated, controlled, before-and-after study in 2008–2010 of nine restored ponds in a reserve in England, UK (Furnborough et al. 2011) found that dredging and vegetation clearance did not appear to significantly increase great crested newt Triturus cristatus numbers in the first two years. Results were difficult to interpret but suggested that complete restoration and partial manual restoration did not significantly change numbers of newts. Data suggested that partial mechanical restoration may have had resulted in slight increases in newts. In winter 2008–2009, three groups of four ponds had sediment and vegetation removed by: partial manual clearance, partial mechanical clearance with an excavator, complete mechanical clearance or no management (controls). Torchlight surveys were undertaken before restoration and in March–June 2009–2010. Survey effort varied between years.
A systematic review in 2011 of the effectiveness of mitigation actions for great crested newts Triturus cristatus in the UK (Lewis 2012) found that neither the 11 studies found or monitoring data from licensed mitigation projects showed conclusive evidence that mitigation, which often included pond restoration, resulted in self-sustaining populations or connectivity to populations in the wider countryside. Only 22 of 460 licensed projects provided post-development monitoring data and of those, 16 reported that small, three medium and one large population was sustained. Two reported a loss of the population. A total of 127 (41%) of English and 46 (30%) of Welsh licence files contained licence return (reporting) documents. Of those, only 9% provided post-development monitoring data and a further 7% suggested surveys were undertaken, but no data were provided. The review identified 11 published or unpublished studies together with 309 Natural England and 151 Welsh Assembly Government (licensing authorities) mitigation licence files. Mitigation measures were undertaken to reduce the impact of the development and included habitat management such as creating or restoring ponds, as well as actions to reduce deaths including translocations.
- Fog K. (1988) Pond restoration on Bornholm. Memoranda Societatis pro Fauna et Flora Fennica, 64, 143-145
- Skriver P. (1988) A pond restoration project and a tree-frog Hyla arborea project in the municipality of Aarhus Denmark. Memoranda Societatis pro Fauna et Flora Fennica, 64, 146-147
- Amtkjær J. (1995) Increasing populations of the green toad Bufo viridis due to a pond project on the island of Samsø. Memoranda Societatis pro Fauna et Flora Fennica, 71, 77-81
- Beebee T. (1997) Changes in dewpond numbers and amphibian diversity over 20 years on chalk downland in Sussex, England. Biological Conservation, 81, 215-219
- Fog K. (1997) A survey of the results of pond projects for rare amphibians in Denmark. Memoranda Societatis pro Fauna et Flora Fennica, 73, 91-100
- Gentilli A., Scali S., Barbieri F. & Bernini F. (2002) A three-year project for the management and the conservation of amphibians in Northern Italy. Biota, 3, 27-33
- Phillips R.A., Patterson D. & Shimmings P. (2002) Increased use of ponds by breeding natterjack toads, Bufo calamita, following management. Herpetological Journal, 12, 75-78
- Briggs L. (2003) Recovery of the green toad Bufo viridis Laurenti, 1768 on coastal meadows and small islands in Funen County, Denmark. Deutsche Gesellschaft für Herpetologie und Terrarienkunde, 14, 274-282
- Briggs L. (2004) Restoration of breeding sites for threatened toads on coastal meadows. Pages 34-43 in: Coastal meadow management - best practice guidelines. Ministry of the Environment of the Republic of Estonia, Tallinn.
- Lepik I. (2004) Coastal meadow management on Kumari Islet, Matsalu Nature Reserve. Pages 86-89 in: Coastal meadow management - best practice guidelines. Ministry of the Environment of the Republic of Estonia, Tallinn.
- Rannap R. (2004) Boreal Baltic coastal meadow management for Bufo calamita. Pages 26-33 in: Coastal meadow management - best practice guidelines. Ministry of the Environment of the Republic of Estonia, Tallinn.
- Rannap R., Lõhmus A. & Briggs L. (2009) Restoring ponds for amphibians: a success story. Hydrobiologia, 634, 87-95
- Sacerdote A.B. & King R.B. (2009) Dissolved oxygen requirements for hatching success of two Ambystomatid salamanders in restored ephemeral ponds. Wetlands, 29, 1202-1213
- Furnborough P., Kirby P., Lambert S., Pankhurst T., Parker P. & Piec D. (2011) The effectiveness and cost efficiency of different pond restoration techniques for bearded stonewort and other aquatic taxa. Report on the Second Life for Ponds project at Hampton Nature Reserve in Peterborough, Cambridgeshire. Froglife report.
- Lewis B. (2012) An evaluation of mitigation actions for great crested newts at development sites. PhD thesis. The Durrell Institute of Conservation and Ecology, University of Kent.