Collected Evidence: Collected Evidence: Restore/create freshwater marshes or swamps (specific action unclear) Twenty-five studies evaluated the effects, on vegetation, of restoring/creating freshwater marshes or swamps using unclear or incompletely described actions. Twenty-three studies were in the USA. Two were in Canada. Two of the studies used the same set of wetlands. VEGETATION COMMUNITY Community types (1 study): One replicated, site comparison study in the USA reported that created wetlands had greater coverage of herbaceous vegetation after 7–8 years than natural wetlands, but lower coverage of forest and shrubby vegetation. Community composition (17 studies): Four replicated, site comparison studies in the USA found that the overall plant community composition in created freshwater wetlands differed from the community in natural wetlands, after 1–21 years. Two replicated, site comparison studies in the USA and Canada reported mixed effects of freshwater marsh restoration/creation on overall algal or plant community composition, depending on the habitat and use of mining waste during creation. Of four replicated, site comparison studies in the USA and Canada, three reported lower quality vegetation in restored/created wetlands than in natural wetlands, but one reported similar vegetation quality in created and natural wetlands. Two replicated, site comparison studies in the USA found that created marshes developed a plant community characteristic of similar wetness to natural marshes within 4–21 years – but in one study, this was only true for created marshes >10 years old. Seven replicated studies in the USA simply quantified the composition, quality or wetness of the plant community up to 22 years after wetland restoration/creation. Overall richness/diversity (17 studies): Eleven replicated studies, in the USA and Canada, compared overall plant richness/diversity in created/restored and natural/unmanaged freshwater wetlands. Five of the studies found that created/restored wetlands typically had similar plant taxonomic richness to natural/unmanaged wetlands. Three of the studies reported lower species richness in created than natural wetlands after 1–18 years. Two of the studies reported higher species richness in created than natural wetlands after 1–21 years. The final study reported mixed effects of marsh creation on plant species richness, depending on the vegetation zone and use of mining waste during creation. Two of the studies reported identical results for plant diversity as for richness (similar or greater in created vs natural wetlands) but one study found that the effect of management on plant diversity depended on the timing of drawdown. Six replicated studies in the USA simply quantified overall plant species richness and/or diversity over 1–16 years after wetland restoration/creation. Native richness/diversity (3 studies): Of two replicated, site comparison studies of freshwater wetlands in the USA, one found that restored/created wetlands contained more native plant species than natural wetlands after 1–11 years. The other found that restored wetlands contained fewer native plant species than natural wetlands after 2–8 years. One replicated study of swamp restoration sites in the USA simply quantified native plant richness over 1–8 years after intervention. VEGETATION ABUNDANCE Overall abundance (7 studies): Six replicated studies, all in the USA, compared overall vegetation abundance in created/restored and natural wetlands. Four of the studies found that created/restored freshwater wetlands contained less vegetation (cover or biomass) than natural wetlands after 1–18 years. Two of the studies found that created and natural fresh/brackish/saline wetlands contained a similar amount of vegetation (overall cover and density; wetland plant cover) after >1 year. One of these studies reported that restored wetlands had lower vegetation cover than natural marshes – but this reflected management goals. One replicated study in the USA simply quantified total vegetation cover and biomass 3–10 years after marsh creation. Herb abundance (2 studies): One replicated, site comparison study in the USA reported that created wetlands had greater overall cover of herb species, after 7–8 years, than natural wetlands. One replicated study in the USA simply quantified herb biomass in wetland restoration sites after 7–22 years. Tree/shrub abundance (1 study): One replicated study in the USA simply quantified the density of woody vegetation in wetland restoration sites after 7–22 years. Algae/phytoplankton abundance (1 study): One replicated, site comparison study in the USA found that ≤15-year-old restored freshwater marshes contained a similar phytoplankton biomass to natural marshes. Individual species abundance (9 studies): Nine studies quantified the effect of this action on the abundance of individual plant species. For example, one replicated, site comparison study in the USA found that created and natural freshwater marshes supported a similar abundance of pickerelweed Pontederia cordata after 1–11 years. VEGETATION STRUCTURECollected Evidencehttps%3A%2F%2Fwww.conservationevidence.com%2Factions%2F3190https%3A%2F%2Fwww.conservationevidence.com%2Factions%2F3190Wed, 07 Apr 2021 07:27:57 +0100Collected Evidence: Collected Evidence: Restore/create brackish/saline marshes or swamps (specific action unclear) Seven studies evaluated the effects, on vegetation, of restoring/creating brackish/saline marshes or swamps using unclear or incompletely described actions. Four studies were in the USA. There was one study in each of Australia, Canada and Indonesia. VEGETATION COMMUNITY Community composition (4 studies): Three replicated, site comparison studies in the USA and Australia reported that the overall plant or algal community composition in restored/created marshes typically became more like natural reference marshes over time. One replicated, site comparison study of fresh/brackish wetlands in Canada reported that the overall plant community was lower quality in restored/created sites than natural sites, after ≥3 years. Overall richness/diversity (1 study): One replicated, site comparison study of salt marshes in the USA found that created marshes had similar overall plant diversity, after 1–14 years, to natural marshes. Created marshes had lower plant species richness than natural marshes on average, but richness became more similar to natural marshes with time since creation. Algae/phytoplankton richness/diversity (1 study): One replicated, paired, site comparison study of brackish/saline marshes in the USA reported that restored and natural marshes contained a similar number of algal species, and found that they had similar algal diversity, after 1–28 years. VEGETATION ABUNDANCE Overall abundance (2 studies): One replicated, site comparison study of salt marshes in the USA found that created marshes contained less overall plant biomass, after 1–14 years, than natural marshes – but that biomass increased with time since creation. One replicated, site comparison study of fresh/brackish/saline marshes in the USA found that created (but not restored) marshes had similar overall vegetation cover to natural marshes. Both created and restored marshes had similar cover of wetland vegetation to natural marshes. Herb abundance (2 studies): One replicated, paired, site comparison study of brackish/saline marshes in the USA reported that restored marshes contained a greater density of cordgrasses Spartina than natural marshes in six of eight comparisons. Vegetation was surveyed 1–28 years after restoration, which involved planting cordgrasses. One replicated, paired site comparison study in the USA reported that created intertidal wetlands contained more smooth cordgrass Spartina alterniflora than nearby natural mangrove forests for around 13 years. Tree/shrub abundance (2 studies): One replicated, paired site comparison study in the USA reported that created intertidal wetlands contained fewer adult mangrove trees than nearby natural mangrove forests for up to 20 years – but predicted equivalence within 55 years. One replicated study in Indonesia simply quantified the density of tree seedlings three years after restoration of former mangrove ponds. Algae/phytoplankton abundance (1 study): One paired, site comparison study of brackish/saline marshes in the USA reported that older restored marshes (≥26 years old) contained a similar or greater abundance of algae to natural marshes, whereas younger restored marshes (<13 years old) contained less algae than natural marshes. VEGETATION STRUCTURE Diameter/perimeter/area (1 study): One replicated, paired site comparison study in the USA reported that created intertidal wetlands contained thinner adult mangrove trees than nearby natural mangrove forests for up to 20 years – but predicted equivalence within 25 years. Collected Evidencehttps%3A%2F%2Fwww.conservationevidence.com%2Factions%2F3191https%3A%2F%2Fwww.conservationevidence.com%2Factions%2F3191Wed, 07 Apr 2021 07:28:08 +0100Collected Evidence: Collected Evidence: Restore/create freshwater marshes or swamps (multiple actions) Seventeen studies evaluated the effects, on vegetation, of using >3 combined actions to restore/create freshwater marshes or swamps. Fourteen studies were in the USA. There was one study in each of Canada, the UK and East Africa. There was overlap in the sites used in three studies. VEGETATION COMMUNITY Overall extent (1 study): One before-and-after study in Canada reported that the area of emergent vegetation in a marsh was greater after 5–6 years of intervention than in the year before. Community composition (5 studies): Two replicated, site comparison studies in the USA found that restored/created freshwater wetlands contained different overall plant communities to natural or reference wetlands, after 1–8 years. Two site comparison studies in the USA reported similarity in species composition between restored/created and natural wetlands. Similarity ranged from 35% to 79% after 1–5 years. One study in the USA simply quantified the plant community composition of different pools within a marsh, two years after its creation. Overall richness/diversity (16 studies): Three studies (including one replicated, before-and-after, site comparison) of freshwater wetlands in the USA and Canada reported that multiple restoration actions increased overall or emergent plant species richness over 1–6 years. Another replicated, before-and-after, site comparison study in the USA reported that the effect of restoration on plant species richness varied between years. Two replicated, site comparison studies in the USA found that restored/created wetlands had similar plant species richness to natural or reference wetlands, after 1–8 years. One site comparison study in the USA reported that a created wetland contained fewer plant species than nearby natural marshes, after two years. Nine studies (four replicated, one before-and-after) in the USA and the UK simply quantified overall plant species richness and/or diversity approximately 1–10 years after intervention. Characteristic plant richness/diversity (6 studies): One replicated, before-and-after, site comparison study of freshwater wetlands in the USA reported that multiple restoration actions increased the richness of wetland-characteristic plant species over three subsequent years. Five studies (two replicated) in the USA simply quantified wetland-characteristic plant richness up to 10 years after intervention. VEGETATION ABUNDANCE Overall abundance (4 studies): Two replicated, before-and-after studies (one also a site comparison) of freshwater wetlands in the USA reported that multiple restoration actions reduced overall vegetation cover over the five subsequent years. Two replicated studies in the USA simply quantified overall vegetation cover for up to six years after intervention. Characteristic plant abundance (3 studies): Two replicated, before-and-after studies (one also a site comparison) of freshwater wetlands in the USA reported that multiple restoration actions did not increase the cover of wetland-characteristic vegetation over three subsequent years. One of the studies also monitored in the fifth (wetter) year after restoration, and reported greater cover of wetland-characteristic vegetation than before restoration. One replicated study on the same set of wetlands in the USA simply quantified wetland-characteristic vegetation cover for up to three years after intervention. Herb abundance (3 studies): One replicated, site comparison study in the USA found that restored wet prairies had similar grass and forb cover to remnant prairies after 3–8 years. Another replicated, site comparison study in the USA reported that created dune slacks had greater cover of annual herbs after three years than mature natural slacks, but similar cover of perennial herbs and floating aquatic herbs. One replicated, before-and-after study in the USA reported greater herb cover 1–5 years after restoration of freshwater wetlands than before. Tree/shrub abundance (3 studies): One replicated, site comparison study in the USA reported that created dune slacks had similar cover of trees and shrubs, after three years, to mature natural slacks. One replicated, before-and-after study in the USA reported lower cover of woody vegetation 1–5 years after restoration of freshwater wetlands than before. One replicated study in the USA simply quantified woody plant cover 1–2 years after intervention. Individual species abundance (10 studies): Ten studies quantified the effect of this action on the abundance of individual plant species. For example, the replicated, site comparison study in East Africa reported that the biomass of papyrus Cyperus papyrus in created marshes was within the range of natural marshes in the region after 18 months. VEGETATION STRUCTURECollected Evidencehttps%3A%2F%2Fwww.conservationevidence.com%2Factions%2F3192https%3A%2F%2Fwww.conservationevidence.com%2Factions%2F3192Wed, 07 Apr 2021 12:22:17 +0100Collected Evidence: Collected Evidence: Restore/create brackish/saline marshes or swamps (multiple actions) Eight studies evaluated the effects, on vegetation, of using >3 combined actions to restore/create brackish/saline marshes or swamps. Six studies were in the USA. One was in Singapore. One was in Indonesia. Three studies were based on the same experimental set-up. VEGETATION COMMUNITY Overall extent (1 study): One study of a coastal site in the USA reported that the coverage of mangrove vegetation increased, and the coverage of herbaceous vegetation declined, over five years after intervention (intended to restore mangrove forest). Overall richness/diversity (3 studies): Three studies of one salt marsh restoration site in the USA simply quantified plant species richness for up to 13 growing seasons after intervention. Tree/shrub richness/diversity (1 study): One site comparison study in Indonesia reported that a restored aquaculture pond contained a similar number of mangrove species to nearby reference forests, just 6–7 months after intervention. Some trees may have been present before intervention. VEGETATION ABUNDANCE Overall abundance (4 studies): One replicated, paired, site comparison study of salt marshes in the USA found that restored marshes had similar overall vegetation cover to natural marshes after 9–20 years. Three studies of one salt marsh restoration site in the USA simply quantified overall vegetation abundance for up to 13 growing seasons after intervention. Tree/shrub abundance (3 studies): One replicated, paired, site comparison study of salt marshes in the USA found that restored marshes had similar, limited shrub cover to natural marshes after 9–20 years. One site comparison study of mangrove forests in Singapore reported that a created mangrove forest supported lower above-ground biomass than mature natural forests after ≥15 years. One study in Indonesia simply counted the number of mangrove trees present 6–7 months after intervention. Individual species abundance (4 studies): Four studies in estuaries in the USA simply quantified the abundance of individual plant species for up to 13 growing seasons after intervention. VEGETATION STRUCTURE Overall structure (1 study): One replicated, paired, site comparison study of salt marshes in the USA found that restored marshes had less cover of short vegetation and greater cover of medium-height vegetation than natural marshes after 9–20 years. Restored and natural marshes had similar cover of tall vegetation. Height (2 studies): One study of a created mangrove forest in Singapore reported that the average height of surviving mangrove saplings increased over five years. One study of a salt marsh restoration site in the USA reported that maximum vegetation height did not clearly increase between the third and twelfth/thirteenth growing seasons after intervention. Collected Evidencehttps%3A%2F%2Fwww.conservationevidence.com%2Factions%2F3193https%3A%2F%2Fwww.conservationevidence.com%2Factions%2F3193Wed, 07 Apr 2021 12:22:32 +0100Collected Evidence: Collected Evidence: Deposit soil/sediment and introduce vegetation: freshwater marshesWe found no studies that evaluated the combined effects, on vegetation, of depositing soil/sediment to form the physical structure of freshwater marshes and introducing vegetation.   ‘We found no studies’ means that we have not yet found any studies that have directly evaluated this action during our systematic journal and report searches. Therefore we have been unable to assess whether or not the action is effective or has any harmful impacts. Please get in touch if you know of such a study for this action.Collected Evidencehttps%3A%2F%2Fwww.conservationevidence.com%2Factions%2F3194https%3A%2F%2Fwww.conservationevidence.com%2Factions%2F3194Wed, 07 Apr 2021 13:40:54 +0100Collected Evidence: Collected Evidence: Deposit soil/sediment and introduce vegetation: brackish/salt marshes Six studies evaluated the combined effects, on vegetation, of depositing soil/sediment to form the physical structure of brackish/salt marshes and introducing vegetation. All six studies were in the USA. Several sites, and even the same data from some sites, were used in multiple studies. VEGETATION COMMUNITY Overall extent (2 studies): Two replicated, site comparison studies of salt marshes in the USA compared the overall area of emergent vegetation in marshes created by depositing sediment and planting vs natural marshes. One study found that created and natural marshes had similar vegetation coverage after 2–23 years. The other study reported that created marshes had slightly lower vegetation coverage than nearby natural marshes after 2–4 years. Community types (1 study): One replicated, site comparison study in the USA found that four of four plant community types had similar coverage in created and natural salt marshes after 3–15 years. For most marshes, creation involved depositing sediment and planting herbs. Community composition (1 study): One replicated, before-and-after, site comparison study in the USA reported that the overall plant community in salt marshes created by depositing sediment and planting herbs/shrubs was <36% similar to nearby natural salt marshes, after 2–4 years. VEGETATION ABUNDANCE Overall abundance (1 study): One paired, site comparison study in the USA found that salt marshes created by depositing sediment and planting/sowing herbs typically contained at least as much vegetation (biomass and density) as natural marshes, after 1–4 years. Individual species abundance (4 studies): Four studies quantified the effect of this action on the abundance of individual plant species. For example, two studies (one review, one site comparison) in the USA found that salt marshes created by depositing sediment and introducing vegetation typically contained a similar amount (density and/or biomass) of cordgrasses Spartina spp. to nearby natural marshes, after 1–9 years. Meanwhile, one paired, site comparison study in the USA reported that whether created marshes contained a higher, lower or similar cordgrass density to natural marshes depended on plot elevation. VEGETATION STRUCTURE Overall structure (2 studies): One replicated, site comparison study in the USA found that salt marshes created (mostly) by depositing sediment and planting herbs contained larger patches of vegetation with straighter edges than natural marshes, after 3–15 years. One replicated, paired, site comparison study in the USA reported that created salt marshes contained a similar proportion of edge habitat to nearby natural salt marshes, after 2–23 years. Height (2 studies): Two site comparison studies in the USA compared the height of cordgrasses Spartina sp. in created and nearby natural marshes. One study (also paired) found that created marshes typically contained cordgrass of similar height to natural marshes, after 1–4 growing seasons. The other study reported that cordgrass was shorter in created than natural marshes, after 7–9 years. Collected Evidencehttps%3A%2F%2Fwww.conservationevidence.com%2Factions%2F3195https%3A%2F%2Fwww.conservationevidence.com%2Factions%2F3195Wed, 07 Apr 2021 13:41:27 +0100Collected Evidence: Collected Evidence: Deposit soil/sediment and introduce vegetation: freshwater swampsWe found no studies that evaluated the combined effects, on vegetation, of depositing soil/sediment to form the physical structure of freshwater swamps and introducing vegetation.   ‘We found no studies’ means that we have not yet found any studies that have directly evaluated this action during our systematic journal and report searches. Therefore we have been unable to assess whether or not the action is effective or has any harmful impacts. Please get in touch if you know of such a study for this action.Collected Evidencehttps%3A%2F%2Fwww.conservationevidence.com%2Factions%2F3196https%3A%2F%2Fwww.conservationevidence.com%2Factions%2F3196Wed, 07 Apr 2021 13:41:44 +0100Collected Evidence: Collected Evidence: Deposit soil/sediment and introduce vegetation: brackish/saline swampsWe found no studies that evaluated the combined effects, on vegetation, of depositing soil/sediment to form the physical structure of brackish/saline swamps and introducing vegetation.   ‘We found no studies’ means that we have not yet found any studies that have directly evaluated this action during our systematic journal and report searches. Therefore we have been unable to assess whether or not the action is effective or has any harmful impacts. Please get in touch if you know of such a study for this action.Collected Evidencehttps%3A%2F%2Fwww.conservationevidence.com%2Factions%2F3197https%3A%2F%2Fwww.conservationevidence.com%2Factions%2F3197Wed, 07 Apr 2021 13:41:58 +0100
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What Works in Conservation

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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