Collected Evidence: Collected Evidence: Raise water level to restore degraded freshwater marshes Five studies evaluated the effects, on vegetation, of raising the water level to restore degraded freshwater marshes. There were three studies in the USA and one in each of the Netherlands and Japan. VEGETATION COMMUNITY Overall extent (1 study): One before-and-after study of a floodplain in Japan reported that the area covered by marsh vegetation was higher five years after dechannelizing a river than 10 years before. Community types (1 study): One before-and-after study of a floodplain in Japan reported changes in the area covered by different marsh plant communities over five years after dechannelizing a river compared to 10 years before. Community composition (1 study): One replicated study of dune slacks in the Netherlands reported changes in the overall plant community composition after stopping groundwater extraction (along with other interventions). Overall richness/diversity (2 studies): One replicated, site comparison study of dune slacks in the Netherlands reported that overall plant species richness was greater in restored slacks (groundwater extraction stopped five years previously, along with other interventions) than in mature unmanaged slacks. One replicated, before-and-after study of floodplain marshes in the USA reported that total plant species richness tended to be lower over nine years after raising the water table than before, but that there was no significant difference for diversity. Characteristic plant richness/diversity (1 study): One replicated study of dune slacks in the Netherlands simply quantified the richness of characteristic plant species – typical of dune slacks or nutrient-rich marshes – over five years after stopping groundwater extraction (along with other interventions). VEGETATION ABUNDANCE Overall abundance (3 studies): One replicated, before-and-after study of floodplain marshes in the USA reported that total vegetation cover tended to be lower over nine years after raising the water table than before. One replicated, randomized, paired, controlled, before-and-after study of freshwater marshes in the USA found that damming to raise the water table prevented increases in understory vegetation cover over the following year. One replicated study of dune slacks in the Netherlands simply quantified total vegetation over five years after stopping groundwater extraction (along with other interventions). Cover never exceeded 50%. Herb abundance (1 study): One replicated, randomized, paired, controlled, before-and-after study of freshwater marshes in the USA found that damming to raise the water table had no significant effect on cover of sedges Carex There were similar increases in dammed and undammed marshes over one year. Characteristic plant abundance (1 study): One replicated, before-and-after study of floodplain marshes in the USA reported changes in the cover of wetland- and habitat-characteristic plant species over nine years after raising the water table. Individual species abundance (3 studies): Three studies quantified the effect of this intervention on the abundance of individual plant species. For example, one replicated, before-and-after study in the USA reported that rewetted floodplain marshes became dominated by a non-native wetland shrub, approximately 4–9 years after raising the water table. One replicated study of a freshwater wetland in the USA reported that the effects of reflooding on the density of emergent plant species depended on the species and water level. VEGETATION STRUCTURECollected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3026https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3026Wed, 31 Mar 2021 14:47:11 +0100Collected Evidence: Collected Evidence: Facilitate tidal exchange to restore degraded brackish/salt marshes Seven studies evaluated the effects, on vegetation, of facilitating tidal exchange to restore degraded brackish/salt marshes. Six studies were in the USA. One study included sites in both the USA and Canada. VEGETATION COMMUNITY Overall extent (1 study): One before-and-after study in the USA reported that over 10 years after improving tidal exchange in a degraded marsh, the area of salt marsh vegetation increased – but not quite to historical, pre-degradation levels. Community types (1 study): One before-and-after study in the USA reported that 3–10 years after improving tidal exchange in a degraded marsh, the area of salt marsh community types differed from historical, pre-degradation levels. Community composition (3 studies): Three before-and-after studies in the USA found that in the four years after improving tidal exchange in degraded brackish/salt marshes, the overall plant community composition significantly differed to that present before intervention. However, in one of the studies this was only true in one of two marshes (the most degraded before intervention). One of the studies also reported that the overall plant community composition became more similar to adjacent natural brackish/salt marshes over two growing seasons after intervention. Overall richness/diversity (1 study): One replicated, before-and-after, site comparison study in the USA/Canada found that overall plant species richness was similar in ≥3-year-old tidally restored salt marshes and nearby natural salt marshes. However, there was also no significant difference between degraded marshes (before tidal restoration) and the natural marshes. Characteristic plant richness/diversity (1 study): One study of a coastal marsh in the USA reported that over three years after restoring tidal exchange (along with a prescribed burn), the number of salt-tolerant plant species increased, whilst the number of freshwater plant species decreased. VEGETATION ABUNDANCE Overall abundance (1 study): One replicated, site comparison study of salt marshes in the USA found that tidally restored areas had a lower overall plant stem density, after 13–54 years, than natural salt marshes. Characteristic plant abundance (2 studies): Two before-and-after studies of coastal marshes in North America reported that within three years of restoring tidal exchange (sometimes along with other interventions), total cover of fresh/brackish plant species decreased. In one study the total cover of salt-tolerant plant species increased, but in the other study it did not. One of the studies also found that tidally restored marshes had lower cover of salt-tolerant plants than nearby natural marshes. Individual species abundance (5 studies): Five studies quantified the effect of this action on the abundance of individual plant species. All five studies were in brackish/salt marshes in the USA. Three before-and-after studies reported increases in cover or frequency of smooth cordgrass Spartina alterniflora in the four years after improving tidal exchange. One replicated, site comparison study found that smooth cordgrass cover was lower in tidally restored areas than in natural salt marshes, 13–54 years after tidal restoration. Two before-and-after studies reported no clear change in frequency or cover of saltmeadow cordgrass Spartina patens in the four years after improving tidal exchange, but one before-and-after study reported an increase in saltmeadow cordgrass cover over two growing seasons after improving tidal exchange. Four studies reported declines in cover or frequency of less salt-tolerant species such as common reed Phragmites australis and cattails Typha spp. in the four years after improving tidal exchange (sometimes along with other interventions). One replicated, site comparison study found that common reed cover was similarly low (<1%) in tidally restored areas and natural salt marshes, 13–54 years after tidal restoration. VEGETATION STRUCTURE Vegetation height (3 studies): Two before-and-after studies of brackish/salt marshes in the USA found that common reed was shorter 1–4 years after improving tidal exchange than before. One replicated, site comparison study in the USA found that the maximum vegetation height was similar in tidally restored salt marshes and natural salt marshes, 13–54 years after tidal restoration. Collected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3035https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3035Wed, 31 Mar 2021 19:34:00 +0100Collected Evidence: Collected Evidence: Cut/mow herbaceous plants to maintain or restore disturbance: brackish/salt marshes Six studies evaluated the effects, on vegetation, of cutting/mowing to maintain or restore disturbance in brackish/salt marshes. Two studies were in France. There was one study in each of the USA, Denmark, South Africa and Estonia. VEGETATION COMMUNITY Community composition (1 study): One replicated, randomized, controlled, before-and-after study in brackish wet grasslands in Estonia found that annual cutting affected overall plant community composition, with significant differences between cut and uncut plots after four years. Overall richness/diversity (3 studies): Two replicated, site comparison studies in France found that cut and uncut reedbeds had similar overall plant species richness. One replicated, randomized, controlled, before-and-after study in brackish wet grasslands in Estonia found that cut and uncut plots typically had similar plant species richness and diversity over four years. VEGETATION ABUNDANCE Overall abundance (1 study): One replicated, site comparison study in France found that cut and uncut reedbeds had similar cover of plants other than common reed Phragmites australis. Individual species abundance (5 studies): Five studies quantified the effect of this action on the abundance of individual plant species. For example, two replicated, randomized, controlled, before-and-after studies in brackish marshes or grasslands in South Africa and Estonia found that cutting had mixed effects on the abundance of common reed Phragmites australis after 1–4 years, depending on the water level of the plots. One site comparison study in Denmark found that a fresh/brackish reedbed cut two years previously contained fewer “tall” common reed stems than a reedbed cut seven years previously. Two replicated, site comparison studies in France found that cut reedbeds contained a similar number (and, in one study, biomass) of live reed stems than uncut reedbeds, but far fewer dead stems. VEGETATION STRUCTURE Height (4 studies): Two controlled studies (one also replicated, randomized, before-and-after) in brackish marshes in the USA and South Africa reported that rushes or reeds were shorter in cut plots than in uncut plots, for up to one year after cutting. Two replicated, site comparison studies in France found that live reed stems were a similar height in cut and uncut reedbeds. Diameter/perimeter/area (3 studies): Two site comparison studies (one replicated) in fresh/brackish reedbeds in Denmark and France found that common reed Phragmites australis stems were a similar diameter in cut and uncut reedbeds. One replicated, randomized, controlled, before-and-after study in a brackish marsh in South Africa found that cutting reduced the diameter of common reed stems present one year later. Basal area (1 study): One site comparison study in a fresh/brackish marsh in Denmark found that the basal area of common reed Phragmites australis stems was smaller in a reedbed cut two years previously than in a reedbed cut seven years previously. Only “tall” stems were sampled. Collected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3045https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3045Thu, 01 Apr 2021 15:21:23 +0100Collected Evidence: Collected Evidence: Use grazing to maintain or restore disturbance: freshwater marshes Five studies evaluated the effects, on vegetation, of using grazing to maintain or restore disturbance in freshwater marshes. Two studies were in the UK. There was one study in each of the Netherlands, Germany and the USA. VEGETATION COMMUNITY Community types (2 studies): One study of a riparian wet meadow in Germany reported changes in the area of plant community types over four years of grazing (after cutting trees/shrubs). One replicated, before-and-after study of dune slacks in the UK reported that the plant community type within plots remained stable over 16 years of grazing. Community composition (3 studies): Two replicated, randomized, paired, controlled, studies in freshwater marshes/wet meadows in the UK and the USA reported that the overall plant community composition was similar in grazed and ungrazed plots after 2–9 years. One replicated study of dune slacks in the Netherlands simply reported changes in the overall plant community composition after resuming grazing (along with other interventions). Overall richness/diversity (4 studies): Two studies (one replicated, before-and-after) in wetlands in Germany and the UK reported that after resuming grazing (and cutting trees/shrubs in one study), there were increases in total plant species richness and/or diversity. One replicated, randomized, paired, controlled, before-and-after study in the UK reported that grazing had no significant effect on overall plant species richness in wet grassland and flush vegetation: there were similar declines over nine years in grazed and ungrazed plots. One replicated study of dune slacks in the Netherlands simply quantified total plant species richness over three years after resuming grazing (along with other interventions). Characteristic plant richness/diversity (2 studies): One replicated, before-and-after study in dune slacks in the UK reported that after resuming grazing, the number of dune-slack indicator species increased. One replicated study of dune slacks in the Netherlands simply quantified the richness of characteristic plant species – typical of dune slacks or nutrient-rich marshes – over three years after resuming grazing (along with other interventions). VEGETATION ABUNDANCE Overall abundance (2 studies): One replicated, randomized, paired, controlled, before-and-after study in freshwater marshes/wet meadows in the USA found that grazing typically had no significant effect on overall vegetation biomass after 1–2 years. One replicated study of dune slacks in the Netherlands simply quantified total vegetation cover over three years after resuming grazing (along with other interventions). Cover never exceeded 50%. Herb abundance (1 study): One replicated, randomized, paired, controlled, before-and-after study in the UK reported that grazing had no significant effect on the cover of forbs or grass-like plants in wet grassland and flush vegetation: there were similar declines over nine years in grazed and ungrazed plots. Tree/shrub abundance (1 study): One study of a riparian wet meadow in Germany reported that some trees/shrubs regrew over four years of grazing (after cutting trees/shrubs). Bryophyte abundance (1 study): One replicated, randomized, paired, controlled, before-and-after study in the UK reported that grazing had no significant effect on bryophyte cover in wet grassland and flush vegetation: there were similar changes over nine years in grazed and ungrazed plots. Individual species abundance (1 study): One replicated study of dune slacks in the Netherlands simply quantified the cover of individual species present over three years after resuming grazing (along with other interventions). Only two species had >1% cover in any slack. VEGETATION STRUCTURE Height (2 studies): One site comparison study of a riparian wet meadow in Germany reported that an area grazed by cattle (after cutting trees/shrubs) contained shorter vegetation than an adjacent unmanaged area. One replicated, randomized, paired, controlled study in wet grassland and flush vegetation in the UK found that the maximum vegetation height was typically similar, over four years, in plots grazed by cattle and plots from which cattle were excluded. OTHER Survival (1 study): One study of a riparian wet meadow in Germany reported that 20% of black alder Alder glutinosa trees were still alive after being cut back and grazed for four years. Collected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3050https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3050Thu, 01 Apr 2021 19:34:04 +0100Collected Evidence: Collected Evidence: Physically remove problematic plants: freshwater marshes Five studies evaluated the effects, on vegetation, of physically removing problematic plants from freshwater marshes. Three studies were in the USA, one was in India and one was in France. Two of the studies in the USA were in the same site and shared some plots. VEGETATION COMMUNITY Community composition (1 study): One replicated, randomized, paired, controlled, before-and-after study in the USA found that physically removing all vegetation from a cattail-invaded marsh altered the overall plant community composition, over the following two years. Overall richness/diversity (3 studies): One replicated, randomized, paired, controlled, before-and-after study in the USA found that removing all vegetation from a cattail-invaded marsh increased overall plant species richness 1–2 years later. Two replicated, randomized, paired, controlled, before-and-after studies in wet meadows in the USA found that physically removing vegetation had no significant effect on overall plant species richness or diversity three years later. One of the studies removed all vegetation, whilst the other controlled regrowth of the invasive species (by physical removal along with herbicide application). Characteristic plant richness/diversity (1 study): One controlled, before-and-after study in a temporary marsh in France reported that stripping all vegetation increased the number of habitat-characteristic plant species present in the following two years. VEGETATION ABUNDANCE Overall abundance (3 studies): Three before-and-after studies (two also replicated, randomized, paired, controlled) in freshwater marshes/wet meadows in India and the USA found that physically removing vegetation had no clear or significant effect on overall vegetation cover, nine months or three years later. Two of the studies removed all vegetation, whilst one controlled regrowth of the invasive species (by physical removal along with herbicide application). Herb abundance (2 studies): Of two replicated, randomized, paired, controlled, before-and-after studies in loosestrife-invaded wet meadows in the USA, one reported that removing all vegetation increased the cover of grass-like plants, and reduced the cover of forbs, three years later. The other study found that controlling regrowth of the invasive species – by physical removal and applying herbicide – had no significant effect on cover of grass-like plants or forbs after three years. Algae/phytoplankton abundance (1 study): One before-and-after, site comparison study in India reported that removing all vegetation from a knotgrass-invaded marsh increased the cover of algae nine months later. Individual species abundance (3 studies): Three studies quantified the effect of this action on the abundance of individual plant species, other than the target problematic species. For example, one before-and-after, site comparison study in India reported that removing all vegetation from a knotgrass-invaded marsh increased the cover of some other common herb species nine months later. VEGETATION STRUCTURECollected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3091https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3091Sat, 03 Apr 2021 14:59:31 +0100Collected Evidence: Collected Evidence: Physically damage problematic plants: freshwater marshes Five studies evaluated the effects, on vegetation, of physically damaging problematic plants in freshwater marshes. There were two studies in Australia and two in Costa Rica. In each country, the two studies were based in one study area but used different experimental set-ups. The final study was in Mexico. VEGETATION COMMUNITY Overall extent (1 study): One controlled, before-and-after study in a freshwater marsh in Costa Rica reported that crushing (and burning) cattail stands reduced the area of live vegetation present 5–22 months later. Community composition (1 study): One replicated, randomized, paired, controlled study in a marsh in Costa Rica found that plots in which cattail-dominated vegetation was crushed had a different overall plant community composition, over the following 15 months, to plots in which vegetation was not crushed. Overall richness/diversity (3 studies): Two controlled studies (one also replicated, randomized, paired) in one freshwater marsh in Costa Rica reported that in plots where cattail-dominated vegetation was crushed (sometimes along with burning), plant species richness and diversity were not lower than in plots where vegetation was not crushed (or burned). Vegetation was surveyed 2–22 months after intervention. One replicated, randomized, paired, controlled study in a freshwater marsh in Mexico found that disking after cutting grass-invaded vegetation increased overall plant diversity, after 4–8 months, compared to cutting alone. However, disking had no significant effect on plant richness. VEGETATION ABUNDANCE Overall abundance (2 studies): One controlled, before-and-after study in a freshwater marsh in Costa Rica reported that crushing (and burning) cattail stands reduced live vegetation cover 5–22 months later. One replicated, randomized, paired, controlled study in a freshwater marsh in Mexico found that disking after cutting grass-invaded vegetation typically had no significant effect on overall plant density, after 4–8 months, compared to cutting alone. Herb abundance (1 study): One study of a floodplain marsh in Australia simply reported grass/sedge cover for up to four years after crushing mimosa-invaded vegetation (along with other interventions). Native/non-target abundance (2 studies): One replicated, randomized, paired, controlled, before-and-after study in a mimosa-invaded wetland in Australia reported that crushing mimosa stands did not reduce – and often increased – cover of non-mimosa vegetation one year later. One study of a floodplain marsh in Australia simply reported non-target vegetation cover for up to four years after crushing mimosa-invaded vegetation (along with other interventions). Individual species abundance (2 studies): Two studies quantified the effect of this action on the abundance of individual plant species, other than the species being controlled. One replicated, randomized, paired, controlled study in a freshwater marsh in Costa Rica found that plots in which cattail-dominated vegetation was crushed supported a greater abundance of individual plant species other than cattail, over the following 15 months, than plots in which vegetation was not crushed. One replicated, randomized, paired, controlled study in a freshwater marsh in Mexico found that disking after cutting grass-invaded vegetation increased the cover of two of five common native plant species, after 4–8 months, compared to cutting alone. VEGETATION STRUCTURECollected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3095https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3095Sat, 03 Apr 2021 16:05:22 +0100Collected Evidence: Collected Evidence: Use herbicide to control problematic plants: brackish/salt marshes Seven studies evaluated the effects, on vegetation, of using herbicide to control problematic plants in brackish/salt marshes. Six studies were in the USA. One study was in South Africa. Two studies shared part of the same experimental set-up. VEGETATION COMMUNITY Relative abundance (1 study): One site comparison study of brackish marshes in the USA found that a marsh sprayed with herbicide for nine years (and burned for three) and a nearby natural marsh supported a similar relative abundance of the dominant plant species, smooth cordgrass Spartina alterniflora. Overall richness/diversity (1 study): One site comparison study of brackish marshes in the USA reported that a marsh sprayed with herbicide for nine years (and burned for three) contained more plant species than an unburned and unsprayed marsh – but also more plant species than a nearby natural marsh. Native/non-target richness/diversity (2 studies): One replicated, randomized, paired, controlled, before-and-after study in a pepperweed-invaded marsh in the USA found that applying herbicide did not increase the richness of non-pepperweed species over two years after intervention. The precise effect depended on the herbicide used. One study of an intertidal area in the USA simply counted the number of native salt marsh plant species that colonized after treating smooth cordgrass Spartina alterniflora stands with herbicide. VEGETATION ABUNDANCE Native/non-target abundance (5 studies): Three replicated, randomized, paired, controlled, before-and-after studies in pepperweed-invaded marshes in the USA found that applying herbicide typically did not increase cover of non-pepperweed vegetation, in the two years following intervention. The precise effect depended on the herbicide used. Two studies on the coasts of South Africa and the USA simply quantified the abundance of native salt marsh vegetation that colonized after treating smooth cordgrass Spartina alterniflora stands with herbicide. Individual species abundance (4 studies): Four studies quantified the effect of this action on the abundance of individual plant species, other than the species being controlled. For example, one site comparison study of brackish marshes in the USA reported that a marsh sprayed with herbicide for nine years (and burned for three) contained more smooth cordgrass Spartina alterniflora than an unburned and unsprayed marsh, and a similar amount of smooth cordgrass to a nearby natural marsh. One replicated, paired, controlled, before-and-after study in a pepperweed-invaded marsh in the USA reported that applying herbicide typically reduced cover of dominant native species over two years. The precise effect depended on the herbicide used. VEGETATION STRUCTURE Height (1 study): One site comparison study of brackish marshes in the USA found that in a marsh sprayed with herbicide for nine years (and burned for three), the dominant plant species (smooth cordgrass Spartina alterniflora) grew to a similar height as in a nearby natural marsh. Collected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3121https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3121Sun, 04 Apr 2021 17:19:16 +0100Collected Evidence: Collected Evidence: Exclude wild vertebrates: brackish/salt marshes Seven studies evaluated the effects, on vegetation, of physically excluding wild vertebrates from brackish/salt marshes. Five studies were in the USA. The other studies were in France and Sweden. In five studies, the problematic vertebrates were mammals. In the other two studies, they were birds. Two of the studies were conducted in the same area, but with different experimental set-ups. VEGETATION COMMUNITY Overall richness/diversity (3 studies): Two replicated, paired, controlled studies in brackish marshes in the USA found that fencing to exclude nutria Myocastor coypus had no significant effect on total plant species richness: fenced and open plots contained a similar number of plant species after 1–2 growing seasons. One replicated, randomized, paired, controlled, before-and-after study in brackish marshes in the USA reported that excluding mammals typically had no significant effect on changes in plant species richness over two years. VEGETATION ABUNDANCE Overall abundance (5 studies): Five replicated, paired, controlled studies involving brackish marshes in France and the USA found that fencing to exclude medium-large vertebrates maintained or increased overall vegetation abundance. Vegetation cover or biomass were compared between fenced and open plots, after 1–2 growing seasons or over the winter after fencing. Individual species abundance (6 studies): Six studies quantified the effect of this action on the abundance of individual plant species. The six replicated, controlled studies in brackish and salt marshes in France, Sweden and the USA reported that fencing to exclude medium-large mammals typically maintained or increased the abundance of the dominant herb species over 1–4 growing seasons. Four of the studies found that fenced and open plots contained a similar abundance (biomass, cover or density) of cordgrasses Spartina spp. Three of the studies found that bulrushes Schoenoplectus spp./Scirpus spp. were more abundant in fenced than open plots. However, one study reported no clear difference in bulrush abundance between treatments and one study reported mixed effects depending on moisture levels and which mammals were excluded. VEGETATION STRUCTURE Height (3 studies): One replicated, paired, controlled study in a brackish marsh in France found that overall vegetation height increased over two years in plots fenced to exclude medium-large mammals, compared to a decline in plots left open. Two replicated, controlled studies in brackish and salt marshes in Sweden and the USA found that vertebrate exclusion did not reduce (i.e. maintained or increased) the height of dominant herb species over 2–4 growing seasons. Collected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3133https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3133Mon, 05 Apr 2021 12:16:03 +0100Collected Evidence: Collected Evidence: Build barriers to protect littoral brackish/salt marshes from rising water levels and severe weather Five studies evaluated the effects, on vegetation, of building barriers to protect littoral brackish/salt marshes from rising water levels and severe weather. Three studies were in the USA, one was in Italy and one was in the Netherlands. VEGETATION COMMUNITY Overall extent (3 studies): Two controlled studies (one also replicated, randomized, paired) in Italy and the USA found that protecting salt marshes with offshore structures had no significant effect on the seaward limit of emergent vegetation, after 17–27 months. It was similar, or retreated at a similar rate, in protected and unprotected marshes. One replicated, randomized, paired, controlled study in the USA found that brackish marshes protected with oyster shell reefs receded less, over one year, than unprotected marshes. Community composition (1 study): One replicated, site comparison study in the Netherlands reported that marshes protected with low sea walls had a similar overall plant community composition to nearby natural salt marshes, 15–22 years after the walls were built. Overall richness/diversity (2 studies): One controlled study in Italy reported that a salt marsh protected with an offshore fence contained more plant species, after 17 months, than an unfenced marsh. One replicated, site comparison study in the Netherlands recorded 85 plant and algal species across two salt marshes that had developed behind low sea walls, over 15–22 years, compared to 155 species recorded across multiple natural marshes in the region. VEGETATION ABUNDANCE Overall abundance (2 studies): Two controlled studies (one also replicated, randomized, paired) in Italy and the USA found that brackish/salt marshes protected with offshore structures contained a similar total amount of vegetation to unprotected marshes. This was true for cover and biomass. Individual species abundance (2 studies): One replicated, paired, site comparison study in the USA found that salt marshes protected with offshore breakwaters (and planted with cordgrasses Spartina spp.) typically contained less smooth cordgrass S. alterniflora, after 2–3 growing seasons, than nearby natural marshes. One replicated, site comparison study in the Netherlands reported that in marshes protected with low sea walls for 15–22 years and nearby natural salt marshes, the same plant species were the most frequent. VEGETATION STRUCTURE Height (1 study): One replicated, paired, site comparison study in the USA found that salt marshes protected with offshore breakwaters (and planted with cordgrasses Spartina spp.) contained shorter smooth cordgrass S. alterniflora plants, after 2–3 growing seasons, than nearby natural marshes. Collected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3182https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3182Tue, 06 Apr 2021 16:13:45 +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%2Fconservationevidencejournal.com%2Factions%2F3191https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3191Wed, 07 Apr 2021 07:28:08 +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%2Fconservationevidencejournal.com%2Factions%2F3193https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3193Wed, 07 Apr 2021 12:22:32 +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%2Fconservationevidencejournal.com%2Factions%2F3195https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3195Wed, 07 Apr 2021 13:41:27 +0100Collected Evidence: Collected Evidence: Excavate freshwater pools Seven studies evaluated the effects, on vegetation within pools or surrounding marshes/swamps, of excavating freshwater pools. Five studies were in the USA, one was in Guam and one was in Canada. Two of the studies in the USA were based on the same set of pools. VEGETATION COMMUNITY Relative abundance (2 studies): One replicated, paired, site comparison study in a freshwater marsh in Canada reported that a smaller proportion of individual plants around excavated pools were wetland-characteristic species, compared to the proportion around natural pools. The excavated pools were 1–3 years old. One replicated study in the USA reported that excavated pools became dominated by non-native plant species over eight years. Overall richness/diversity (3 studies): One replicated, paired, site comparison study in a freshwater marsh in Canada found that overall plant species richness and diversity were similar around excavated pools and natural pools, 1–3 years after excavation. Two studies involving freshwater marshes in Guam and the USA simply quantified plant species richness 12–18 months after excavation (along with other interventions). VEGETATION ABUNDANCE Overall abundance (1 study): One replicated, site comparison study in the USA found that excavated and natural pools had similar cover of emergent vegetation, seven years after excavation. The same was true for submerged vegetation. Characteristic plant abundance (2 studies): Two replicated studies in the USA reported the abundance of native pool-characteristic species over 3–8 years after excavating pools. One of the studies was also a site comparison and reported that these species were less abundant in the excavated pools than nearby natural pools. Shrub abundance (2 studies): One replicated, site comparison study in the USA found that excavated and natural pools had similar cover of shrubby vegetation after seven years. One replicated study in the USA simply quantified shrub abundance over five years after excavating pools/potholes (along with other interventions). Algae/phytoplankton abundance (1 study): One replicated, site comparison study in the USA found that excavated and natural pools contained a similar biomass of surface-coating algae and phytoplankton, after seven years. The same was true for phytoplankton after eight years. Individual species abundance (5 studies): Five 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 excavated and natural pools had similar cover of loosestrife Lythrum sp. seven years after excavation, but that excavated pools had greater cover of duckweed Lemna sp., cattails Typha spp. and common reed Phragmites australis. VEGETATION STRUCTURECollected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3211https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3211Fri, 09 Apr 2021 08:47:38 +0100Collected Evidence: Collected Evidence: Reprofile/relandscape: brackish/saline swamps Five studies evaluated the effects, on vegetation, of reprofiling/relandscaping to restore or create brackish/saline swamps. Three studies were in the USA. Two of these shared a study site. There was one study in Singapore and one in Thailand. VEGETATION COMMUNITY Overall extent (1 study): One study of a coastal site in the USA reported that the area of mangrove vegetation increased between 6 and 14 years after reprofiling (and planting propagules). Relative abundance (2 studies): Two site comparison studies in the USA and Singapore reported that areas of reprofiled coastal land (sometimes also planted with propagules) supported a different relative abundance of tree species to natural forests, after roughly 3–15 years. Overall richness/diversity (1 study): One site comparison study in Singapore reported that an area of reprofiled coastal land colonized by mangrove vegetation had higher plant species richness, after three and a half years, than an adjacent mature mangrove patch. Tree/shrub richness/diversity (3 studies): Two replicated, site comparison studies in the USA, reported that where mangrove forests developed on reprofiled (and planted) sites, they contained a similar number of tree species to nearby mature forests after 7–30 years. One study in a former shrimp pond in Thailand simply reported the number of mangrove tree species that spontaneously colonized in the six years after reprofiling (along with other interventions). VEGETATION ABUNDANCE Overall abundance (1 study): One site comparison study in Singapore reported that an area of reprofiled coastal land colonized by mangrove vegetation had a higher density of individual plants, after three and a half years, than an adjacent mature mangrove patch. Tree/shrub abundance (3 studies): Two replicated, site comparison studies in the USA, reported that where mangrove forests developed on reprofiled (and planted) sites, they contained a greater density of trees than nearby mature forests after 17–30 years. One study in a former shrimp pond in Thailand simply reported the number of mangrove trees that spontaneously colonized in the six years after reprofiling (along with other interventions). Individual species abundance (1 study): One study in a former shrimp pond in Thailand reported the number of mangrove trees, by species, that spontaneously colonized in the six years after reprofiling (along with other interventions). VEGETATION STRUCTURE Overall structure (1 study): One replicated, site comparison study in the USA reported that where mangrove forests developed on reprofiled (and planted) sites, they had a different overall structure to nearby mature forests after 17–30 years. Height (2 studies): One replicated, site comparison study in the USA, reported that where mangrove forests developed on reprofiled (and planted) sites, they had a shorter canopy than nearby mature forests after 17–30 years. One site comparison study in Singapore reported that in an area of reprofiled coastal land colonized by mangrove vegetation, most plants were in a similar height category to those in an adjacent mature mangrove patch, but that the maximum plant height was lower. Vegetation was surveyed three and a half years after reprofiling. Diameter/perimeter/area (2 studies): Two site comparison studies in the USA reported that mangrove forests that developed on reprofiled (and planted) coastal areas contained thinner trees, on average, than mature natural forests, after 7–18 years. Basal area (3 studies): Three site comparison studies in the USA compared mangrove forests that developed on reprofiled (and planted) coastal areas to mature natural forests. Two of the studies reported that restored forests had a smaller basal area than mature natural forests, after 7–18 years. The other study reported that restored forests had a similar basal area to mature natural forests, after 17–30 years. Collected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3216https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3216Fri, 09 Apr 2021 09:10:45 +0100Collected Evidence: Collected Evidence: Remove surface soil/sediment: freshwater marshes Six studies evaluated the effects, on vegetation, of removing surface soil/sediment to restore or create freshwater marshes. Four studies were in the USA. One study was in the Netherlands. One study was in Japan. VEGETATION COMMUNITY                              Community composition (3 studies): Two replicated, site comparison studies in the USA reported that freshwater marshes being restored by removing excess soil/sediment (along with other interventions) typically contained a different overall plant community, after 1–12 years, to both degraded and natural marshes nearby. One replicated study of dune slacks in the Netherlands simply reported changes in the overall plant community composition over four years after stripping topsoil (along with other interventions). Overall richness/diversity (4 studies): One replicated, site comparison study of dune slacks in the Netherlands reported that overall plant species richness was greater in restored slacks (topsoil stripped five years previously, along with other interventions) than in mature unmanaged slacks. One replicated, site comparison study in the USA reported that freshwater marshes being restored by removing topsoil (along with other interventions) contained fewer wetland plant species, after 1–12 years, than nearby natural marshes. Two studies (including one site comparison) in freshwater marshes in the USA and Japan reported that the effect of removing topsoil on overall plant species richness depended on the amount removed. Characteristic plant richness/diversity (2 studies): One replicated, site comparison study of a floodplain marsh in Japan found that where stripped plots were colonized by plants within two growing seasons, they contained more wetland-characteristic species than an adjacent unstripped area. One replicated study of dune slacks in the Netherlands simply reported the number of characteristic plant species present over five years after stripping topsoil (along with other interventions). VEGETATION ABUNDANCE Overall abundance (3 studies): Three studies (two replicated) in the Netherlands, the USA and Japan simply quantified the overall abundance of vegetation that colonized – within five years – freshwater wetlands stripped of topsoil (sometimes along with other interventions). Characteristic plant abundance (2 studies): Two studies (one replicated) in freshwater marshes in the USA and Japan simply quantified the abundance of wetland-characteristic plant species that colonized – within five years – areas stripped of topsoil. Individual species abundance (5 studies): Five 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 pothole wetlands restored by removing excess sediment (sometimes along with planting herbs) had lower hybrid cattail Typha x glauca cover than unrestored wetlands after 2–7 years, and similar hybrid cattail cover to nearby natural wetlands. One replicated study of dune slacks in the Netherlands simply quantified the cover of individual species present over five years after stripping topsoil (along with other interventions). Only two species had >1% cover in any slack. VEGETATION STRUCTURE Overall structure (1 study): One study in a freshwater marsh in the USA reported that the effect of removing topsoil on the abundance of tall vegetation depended on the amount removed. Visual obstruction (1 study): One replicated, site comparison study of pothole wetlands in the USA found that the effect of removing excess sediment (sometimes along with planting herbs) on horizontal vegetation cover, 2–7 years later, depended on the elevation/vegetation zone. Height (1 study): One site comparison study in the USA reported that sedge tussocks were shorter in a wet meadow restored by removing excess sediment (along with other interventions, including planting sedges) than in nearby natural meadows, after 11–14 years. Diameter/perimeter/area (1 study): One site comparison study in the USA reported that sedge tussocks had a smaller perimeter in a wet meadow restored by removing excess sediment (along with other interventions, including planting sedges) than in natural meadows, after 11–14 years. Basal area (1 study): One site comparison study in the USA reported that the basal area of sedge tussocks was smaller in a wet meadow restored by removing excess sediment (along with other interventions, including planting sedges) than in nearby natural meadows, after 11–14 years. Collected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3221https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3221Fri, 09 Apr 2021 13:07:41 +0100Collected Evidence: Collected Evidence: Add sediment: brackish/salt marshes Five studies evaluated the effects, on vegetation, of adding sediment to existing brackish/salt marshes. All five studies were in the USA. Two studies were based on one experimental set-up and two studies were based on another. VEGETATION COMMUNITY Relative abundance (1 study): One replicated, site comparison study in the USA found that salt marshes amended with sediment typically supported a greater relative abundance of smooth cordgrass Spartina alterniflora than degraded marshes after two years, but that this typically remained lower than in natural marshes. Overall richness/diversity (1 study): The same study found that salt marshes amended with sediment typically had greater plant species richness than degraded marshes, and statistically similar richness to natural marshes, after two years. VEGETATION ABUNDANCE Overall abundance (1 study): One replicated, site comparison study in the USA found that salt marshes amended with sediment typically had greater total vegetation cover than degraded marshes, and statistically similar cover to natural marshes, after two years. Individual species abundance (4 studies): Four studies quantified the effect of this action on the abundance of individual plant species. For example, all four studies (including two replicated, randomized, paired, controlled) of salt marshes in the USA found that adding sediment typically increased the abundance of smooth cordgrass Spartina alterniflora, over approximately 1–5 years. This is based on total biomass, density and/or cover. One of the studies reported that adding sediment increased the cover of three other species after one year. VEGETATION STRUCTURE Height (1 study): One replicated, randomized, paired, controlled study in a salt marsh in the USA found that the height of the dominant plant species, smooth cordgrass Spartina alterniflora, did not significantly differ between plots amended with sediment and unamended plots. Height was measured 16 months after sediment amendment began. Collected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3231https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3231Fri, 09 Apr 2021 14:26:47 +0100Collected Evidence: Collected Evidence: Introduce fragments of non-woody plants: freshwater wetlands Five studies evaluated the effects, on vegetation, of introducing fragments of emergent, non-woody plants to freshwater wetlands. Three studies were in the USA. Two studies were in one marsh in Australia, but used different experimental set-ups. VEGETATION COMMUNITY   VEGETATION ABUNDANCE Overall abundance (2 studies): Two replicated, randomized, paired, controlled, before-and-after studies in a floodplain marsh in Australia found that plots planted with wick grass Hymenachne acutigluma had similar overall vegetation cover to unplanted plots after one year. One of the studies continued for longer, and found that planted plots had greater overall vegetation cover than unplanted plots after three years. Herb abundance (1 study): One replicated, randomized, paired, controlled, before-and-after study in a floodplain marsh in Australia found that plots planted with wick grass Hymenachne acutigluma had similar overall sedge/grass cover to unplanted plots after one year. Individual species abundance (4 studies): Four studies quantified the effect of this action on the abundance of individual plant species. For example, of two replicated, randomized, paired, controlled, before-and-after studies in a floodplain marsh in Australia, one found that wick grass Hymenachne acutigluma was more frequent and had greater cover, after 1–3 years, in plots where its runners had been planted than where they had not been planted. The other study reported that wick grass cover was present, with approximately 1% cover, in 5 of 10 plots where its runners had been planted. This study monitored vegetation one year after planting. VEGETATION STRUCTURE   OTHER Germination/emergence (1 study): One replicated, randomized, paired, controlled study in a floodplain marsh in Australia found that planting wick grass Hymenachne acutigluma had no significant effect on the germination rate of invasive mimosa Mimosa pigra over three years. Survival (5 studies): Two replicated studies planted sedge Carex fragments into freshwater wetlands in the USA. One study reported 38–79% survival of planted tubers over one growing season, whilst the other study reported 0–73% survival of planted rhizomes after 1–9 months. One replicated study in a tidal freshwater marsh in the USA reported that 6–31% of planted California bulrush Schoenoplectus californicus rhizomes had produced shoots after three months. For two other species, all planted rhizomes died within three months. Two replicated, randomized, paired, controlled, before-and-after studies in a floodplain marsh in Australia reported absence of planted wick grass Hymenachne acutigluma from 17–50% of plots after one year. Collected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3260https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3260Sat, 10 Apr 2021 13:28:02 +0100Collected Evidence: Collected Evidence: Introduce seeds of non-woody plants: brackish/saline wetlands Eight studies evaluated the effects, on vegetation, of introducing seeds of emergent, non-woody plants to brackish/saline wetlands. There were three studies in the USA, two in the Netherlands and two in China. The other study was a global systematic review. VEGETATION COMMUNITY   VEGETATION ABUNDANCE Individual species abundance (4 studies): Four replicated studies quantified the effect of this action on the abundance of individual plant species. One study in an estuary in China also gave a before-and-after comparison, and reported higher density and biomass of seablite Suaeda salsa five months after sowing its seeds than on the bare sediment present before sowing. VEGETATION STRUCTURE Height (1 study): One replicated study on a mudflat in the Netherlands reported that the average height of surviving common cordgrass Spartina anglica plants increased, between one and six months after sowing cordgrass seeds. OTHER            Germination/emergence (5 studies): Five replicated studies in the Netherlands, the USA and China quantified germination rates of seeds sown into intertidal areas. Some seeds germinated in all five studies, at a rate of <1% to 25%. Two studies reported that no seeds germinated for some species and/or in some environments. Survival (3 studies): One replicated study in a salt marsh in the Netherlands quantified survival rates of individual germinated seedlings: 0–83% over their first growing season, depending on species and site conditions. Another replicated study in a salt marsh in the Netherlands reported that after two growing seasons, common cordgrass Spartina anglica was absent from 90% of plots in which had been sown. One global systematic review reported variable survival of herbs sown (or planted) in salt marshes: 0% to ≥95% after 20 days to 13 years, depending on the study. Collected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3265https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3265Sat, 10 Apr 2021 15:35:13 +0100Collected Evidence: Collected Evidence: Add inorganic fertilizer before/after planting non-woody plants: brackish/saline wetlands Seven studies evaluated the effects, on vegetation, of adding inorganic fertilizer to brackish/saline wetlands planted with emergent, non-woody plants. Four studies were in the USA. Two of these were based in the same marsh, but used different experimental set-ups. Two studies were in Canada. One study was in China. VEGETATION COMMUNITY   VEGETATION ABUNDANCE Overall abundance (2 studies): One replicated, randomized, paired, controlled study in intertidal brackish marshes in Canada found that adding fertilizer when planting wetland herbs typically had no significant effect on total live vegetation biomass, after two growing seasons. One replicated, paired, controlled, before-and-after study in salt-contaminated bogs in Canada found that overall vegetation biomass and cover were greater in fertilized than unfertilized plots, one year after introducing salt marsh vegetation. Individual species abundance (6 studies): Six studies quantified the effect of this action on the abundance of individual plant species. For example, three replicated, randomized, paired, controlled studies in intertidal areas in the USA found that the abundance of cordgrasses Spartina spp. was typically similar in fertilized and unfertilized plots, 1–2 growing seasons after planting. This was true for density, biomass and/or cover. However, one controlled study on former borrow pits in the USA found that cordgrass Spartina spp. biomass was typically greater in fertilized than unfertilized plots, one growing season after planting. This study also found that fertilization typically reduced black rush Juncus roemarianus biomass, one growing season after planting. VEGETATION STRUCTURE Height (6 studies): Five replicated, controlled studies (four also paired, three also randomized) in brackish/saline wetlands in the USA, China and Canada found that adding fertilizer had no significant effect on the height of planted/sown wetland herbs after 1–2 growing seasons. One controlled study on former borrow pits in the USA found that fertilized smooth cordgrass Spartina alterniflora was taller than unfertilized smooth cordgrass, two growing seasons after planting. OTHER Survival (4 studies): Three replicated, randomized, paired, controlled studies in intertidal areas in the USA and Canada found that adding fertilizer had no significant effect on the survival of planted wetland herbs over 1–2 growing seasons. One controlled study on former borrow pits in the USA reported that adding standard fertilizer to planting holes reduced the survival of planted big cordgrass Spartina cynosuroides, after one growing season. Collected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3305https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3305Sun, 11 Apr 2021 08:57:23 +0100Collected Evidence: Collected Evidence: Add below-ground organic matter before/after planting non-woody plants: freshwater wetlands Seven studies evaluated the effects, on vegetation, of adding below-ground organic matter to freshwater wetlands planted with emergent, non-woody plants. All seven studies were in the USA. Two of the studies were in a greenhouse. VEGETATION COMMUNITY Overall richness/diversity (1 study): One replicated study of marshes alongside a stream in the USA found that adding compost before planting wetland herbs typically reduced overall plant species richness over the following three growing seasons. Richness was negatively related to the amount of soil organic matter in plots. VEGETATION ABUNDANCE Overall abundance (1 study): One replicated study of marshes alongside a stream in the USA found that adding compost before planting wetland herbs had no significant effect on total vegetation biomass after three growing seasons. Biomass was not significantly related to the amount of soil organic matter in plots. Characteristic plant abundance (1 study): One replicated, randomized, paired, controlled, before-and-after study in an experimental wet basin in the USA found that adding sawdust to plots before sowing a mixture of target sedge meadow species had no significant effect on the density of target species overall or target grass-like species. Adding sawdust sometimes affected the density of target forbs, depending on the presence/diversity of a nurse crop. Individual species abundance (2 studies): Two replicated, randomized, paired, controlled studies in wetlands in the USA quantified the effect of this action on the abundance of individual plant species. One study found that incorporating woodchips into soil mounds before planting tussock sedge Carex stricta reduced total tussock sedge cover after two growing seasons. The other study reported varying effects of sawdust addition on the abundance of individual plant species, depending on factors such as the species and presence/diversity of a nurse crop. VEGETATION STRUCTURE Individual plant size (4 studies): Three replicated, controlled studies (one also paired) in the USA found that mixing compost into the substrate before planting tussock sedge Carex stricta seedlings typically increased the biomass and/or number of shoots they developed over 2–3 months. However, in one of the studies, compost typically had no significant effect on top of other soil amendments. One replicated, randomized, paired, controlled study in a wetland in the USA found that incorporating woodchips into soil mounds had no significant effect on the biomass of planted tussock sedge Carex stricta, over two growing seasons. OTHER Germination/emergence (1 study): One replicated, randomized, paired, controlled study in an experimental wet basin in the USA found that seeds of mixed sedge meadow species had a similar germination rate, over 16 weeks after sowing, in plots with or without added sawdust. Survival (2 studies): One replicated, randomized, controlled study in an excavated wetland in the USA found that planted lurid sedge Carex lurida tubers had a higher survival rate, after one year, in plots that had been amended with leaf litter than in unamended plots. One replicated, randomized, paired, controlled study in a wetland in the USA found that incorporating woodchips into soil mounds increased survival of planted tussock sedge Carex stricta in a drier area, but reduced its survival in a wetter area. Growth (1 study): One replicated, randomized, paired, controlled study in a wetland in the USA found that incorporating woodchips into soil mounds had no significant effect on the growth rate of planted tussock sedge Carex stricta, over two growing seasons. Collected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3308https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3308Sun, 11 Apr 2021 09:50:48 +0100Collected Evidence: Collected Evidence: Add below-ground organic matter before/after planting non-woody plants: brackish/saline wetlands Six studies evaluated the effects, on vegetation, of adding below-ground organic matter to brackish/saline wetlands planted with emergent, non-woody plants. Five studies were in the USA and one was in China. Two studies were in the same marsh, but used different experimental set-ups. VEGETATION COMMUNITY   VEGETATION ABUNDANCE Individual species abundance (5 studies): Three replicated, randomized, controlled studies in the USA found that adding organic matter before/after planting cordgrasses Spartina spp. typically had no significant effect on cordgrass abundance (biomass and/or density) after 1–2 growing seasons. One replicated, paired, controlled study in an estuary in the USA found that mixing kelp compost into the sediment before planting California cordgrass Spartina foliosa increased its density, three growing seasons later. One replicated, controlled, before-and-after study in an estuary in China found that mixing reed debris into the sediment before sowing seablite Suaeda salsa increased its biomass, but not its density, five months later. VEGETATION STRUCTURE Individual plant size (1 study): One replicated, randomized, paired, controlled study in an estuary in the USA found that tilling compost into plots before planting salt marsh vegetation typically increased the overall size of plants surviving after 1–2 growing seasons. Size was reported as a combination of height and lateral spread. Height (5 studies): Four replicated, controlled studies in the USA and China found that adding organic matter before/after introducing salt marsh plants (cordgrasses Spartina spp. or seablite Suaeda salsa) had no significant effect on their height after 1–2 growing seasons. One replicated, paired, controlled study in an estuary in the USA found that mixing kelp compost into the sediment before planting California cordgrass Spartina foliosa increased its height, three growing seasons later. OTHER Survival (1 study): One replicated, randomized, paired, controlled study in an estuary in the USA found that plots amended with kelp compost supported a higher survival rate of planted salt marsh vegetation over 1–2 growing seasons, with a similar but typically insignificant trend for survival rates of individual species. Growth (1 study): One replicated, randomized, controlled study in a greenhouse in the USA found that adding alginate after planting cordgrasses had no significant effect on the average number of shoots per plant, nine weeks later. Collected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3309https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3309Sun, 11 Apr 2021 09:50:58 +0100Collected Evidence: Collected Evidence: Use fences or barriers to protect freshwater wetlands planted with trees/shrubs Five studies evaluated the effects, on vegetation, of using fences or barriers to protect freshwater wetlands planted with trees/shrubs. Four studies were in the USA and one was in Australia. VEGETATION COMMUNITY   VEGETATION ABUNDANCE Tree/shrub abundance (1 study): One replicated, paired, controlled study in a floodplain swamp clearing in the USA found that amongst plots sown with tree seeds, fencing to exclude deer had no significant effect on total tree seedling density after three years. VEGETATION STRUCTURE Height (2 studies): One replicated, paired, controlled study in a floodplain swamp clearing in the USA found that amongst plots sown with tree seeds, those also fenced to exclude deer contained taller tree seedlings, after three years, than those left unfenced. One replicated, paired, controlled study in created freshwater wetlands in the USA found that the average height of white cedar Thuja occidentalis saplings typically increased by a similar amount, between two and five years after planting, in plots fenced to exclude deer and plots left unfenced. OTHER Survival (3 studies): One replicated, paired, controlled study in floodplain swamps in Australia reported that planted swamp gum Eucalyptus camphora seedlings had a much higher survival rate, over one year, in plots fenced to exclude mammals than in open plots. Two replicated, paired, controlled studies in freshwater wetlands in the USA reported that exclusion fencing sometimes increased survival of planted tree seedlings but sometimes had no clear or significant effect. This depended on factors such as the season of planting, seedling elevation, and site. Growth (1 study): One replicated, randomized, controlled study in a nutria-invaded wetland in the USA found that planted baldcypress Taxodium distichum seedlings grew more, over one growing season, when protected than when left unprotected. Plastic guards increased height and diameter growth rates. Sticky, insect-repellent oil increased the growth rate for height, but not diameter. Collected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3330https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3330Sun, 11 Apr 2021 13:15:05 +0100Collected Evidence: Collected Evidence: Remove vegetation that could compete with planted trees/shrubs: freshwater wetlands Five studies evaluated the effects, on trees/shrubs planted in freshwater wetlands, of removing competing plants. Four studies were in the USA. Two of these took place in the same swamp, but with different experimental set-ups. One study was in Australia. VEGETATION COMMUNITY   VEGETATION ABUNDANCE   VEGETATION STRUCTURE Height (3 studies): Three replicated, controlled studies (two also randomized, two also paired) in a wet meadow in Australia and a degraded swamp in the USA found that clearing vegetation before planting tree/shrub seedlings typically had no clear or significant effect on their height, after 1–4 growing seasons. However, one of the studies in the USA found that planted baldcypress Taxodium distichum seedlings were taller, after three growing seasons, when planted amongst cut woody vegetation than below an uncleared canopy. Diameter/perimeter/area (1 study): One replicated, randomized, paired, controlled study in a wet meadow in Australia found that clearing vegetation, before planting tree/shrub seedlings, typically had no significant effect on the diameter of these seedlings nine months later. OTHER Germination/emergence (1 study): One replicated, randomized, paired, controlled study in a wet meadow in Australia found that there were more seedlings in plots that had been cleared of vegetation before sowing tree/shrub seeds, than in plots that had not been cleared before sowing. Seedlings were counted two months after sowing. Survival (4 studies): Three replicated, controlled studies (two also randomized, two also paired) in a wet meadow in Australia and a degraded swamp in the USA found that clearing vegetation before planting tree/shrub seedlings typically had no clear or significant effect on their survival, after 1–4 growing seasons. However, one of the studies in the USA found that planted baldcypress Taxodium distichum seedlings had a lower survival rate, after three growing seasons, when planted amongst cut woody vegetation than below an uncleared canopy. One replicated, randomized, paired, controlled study in degraded swamps in the USA found that removing reed canarygrass Phalaris arundinacea before planting tree/shrub seedlings never significantly reduced their survival rate over 1–2 growing seasons, and often increased it. Growth (1 study): One replicated, randomized, controlled study in the USA found that baldcypress Taxodium distichum seedlings planted into a marsh grew more in diameter, but less in height, when planted into plots cleared of vines than when planted into uncleared plots. Collected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3334https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3334Sun, 11 Apr 2021 14:09:05 +0100Collected Evidence: Collected Evidence: Chill seeds of non-woody plants before sowing: freshwater wetlands Six studies evaluated the effects – on emergent, non-woody plants typical of freshwater wetlands – of chilling their seeds before sowing. All six studies were in the USA. Five of the studies were in laboratories or greenhouses. VEGETATION COMMUNITY   VEGETATION ABUNDANCE   VEGETATION STRUCTURE   OTHER Germination/emergence (6 studies): All six replicated, controlled studies in the USA found that chilling (at 1–10°C) seeds of herbaceous plants before sowing either increased or had no significant effect on their germination rate. Within studies, the direction and/or size of the effect depended on factors such as the duration of chilling, species, conditions (light/temperature) after sowing, and sowing site (restored vs natural meadows). One replicated, randomized, controlled study in the USA found that freezing sawgrass Cladium jamaicense seeds before sowing reduced their germination rate. Collected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3367https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3367Mon, 12 Apr 2021 07:33:28 +0100Collected Evidence: Collected Evidence: Treat seeds of non-woody plants with chemicals before sowing: freshwater wetlands Six studies evaluated the effects – on emergent, non-woody plants typical of freshwater wetlands – of treating their seeds with chemicals before sowing. All six studies were in greenhouses or laboratories in the USA. VEGETATION COMMUNITY   VEGETATION ABUNDANCE   VEGETATION STRUCTURE   OTHER Germination/emergence (6 studies): Of six replicated, controlled studies in greenhouses or laboratories in the USA, five identified chemicals that sometimes increased, and did not significantly reduce, the germination rate of herb seeds: potassium nitrate, nitric acid and bleach. The effect of these chemicals depended on factors such as the age of the seeds, the species and other pre-sowing treatments. Two of the studies identified chemicals that never had a significant effect on the germination rate of herb seeds: a plant hormone and sulfuric acid. Collected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3380https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3380Mon, 12 Apr 2021 08:30:30 +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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