Collected Evidence: Collected Evidence: Abandon cropland: allow freshwater marshes or swamps to recover without active intervention Four studies evaluated the effects, on vegetation, of abandoning cropland with the expectation that freshwater marshes or swamps would recover spontaneously. There was one study in each of Spain, South Korea, China and Japan. The studies involved former rice fields, soybean fields or pastures. VEGETATION COMMUNITY Community composition (2 studies): Two site comparison studies in South Korea and Japan reported that the overall plant community composition in abandoned cropland became more like natural swamps and/or marshes over time. Overall richness/diversity (2 studies): One site comparison study on a floodplain in Japan found that pastures abandoned for 5–25 years contained a higher richness of vascular, wetland plant species than pastures that remained in use. One study in South Korea simply reported the number of plant species in abandoned rice paddies increased over time. Characteristic plant richness/diversity (1 study): One site comparison study on a floodplain in Japan found that pastures abandoned for 5–25 years typically contained more marsh-indicator and swamp-indicator species than pastures that remained in use. VEGETATION ABUNDANCE Overall abundance (2 studies): One site comparison study in China found that vegetation biomass in abandoned soybean fields was lower than in natural wet meadows after three years, similar to natural wet meadows after six years, and higher than in natural wet meadows after 12 years. One study in Spain simply quantified the peak biomass and density of vegetation in rice fields abandoned for up to six years. Biomass, but not density, increased with time since abandonment. VEGETATION STRUCTURE Height (1 study): One site comparison study in China found that soybean fields abandoned for 3–12 years contained vegetation of a similar height to natural wet meadows. Diameter/perimeter/area (1 study): One site comparison study in South Korea reported that rice fields abandoned for 10 years contained thinner-stemmed Japanese alder Alnus japonica than mature alder forests. Collected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F2952https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F2952Mon, 22 Mar 2021 13:41:02 +0000Collected Evidence: Collected Evidence: Reduce intensity of livestock grazing: freshwater marshes Three studies evaluated the effects, on vegetation, of reducing livestock grazing intensity in freshwater marshes (without stopping grazing entirely). Two studies were in the USA and the other was in Ireland. In all three studies, livestock were cattle. VEGETATION COMMUNITY Community composition (1 study): One site comparison study in Ireland found that lightly and heavily grazed wet meadows contained a similar overall mix of plant species. Relative abundance (1 study): One replicated, randomized, paired, controlled study in the USA found that seasonally and continuously grazed ephemeral pools had similar cover of grasses relative to forbs. Overall richness/diversity (1 study): One site comparison study in Ireland found that lightly and heavily grazed wet meadows had similar overall plant species richness. Native plant richness/diversity (1 study): One replicated, randomized, paired, controlled study in the USA found that seasonally and continuously grazed ephemeral pools experienced similar changes in native plant species richness over three years. VEGETATION ABUNDANCE Overall abundance (1 study): One site comparison study in Ireland reported that lightly and heavily grazed wet meadows had similar overall vegetation cover. Herb abundance (1 study): One replicated, randomized, paired, controlled, before-and-after study in the USA found that lightly and moderately grazed springs/creeks had similar herb cover. Individual species abundance (1 study): One study quantified the effect of this action on the abundance of individual plant species. The site comparison study in Ireland reported, for example, that lightly grazed wet meadows had greater cover of black sedge Carex nigra, and lower cover of creeping bent Agrostis stolonifera, than more heavily grazed wet meadows. VEGETATION STRUCTURE Height (1 study): One site comparison study in Ireland found that lightly grazed wet meadows contained taller vegetation than heavily grazed wet meadows. Vegetation was measured in the summer, during the grazing season. Collected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F2970https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F2970Thu, 25 Mar 2021 14:15:51 +0000Collected Evidence: Collected Evidence: Change season/timing of livestock grazing: freshwater marshes Three studies evaluated the effects, on vegetation, of grazing freshwater marshes in different seasons or at different times. Two studies were in the USA and one was in Canada. In all three studies, the livestock were cattle. VEGETATION COMMUNITY Community composition (1 study): One replicated, randomized, paired, controlled, before-and-after study of freshwater marshes and wet meadows in the USA reported that plots grazed in the summer and autumn experienced similar changes in overall plant community composition over a year. Relative abundance (1 study): One replicated, randomized, paired, controlled study of ephemeral pools in the USA found that pools grazed in the dry or wet seasons had similar cover of grasses relative to forbs over three years. Overall richness/diversity (1 study): One replicated, site comparison study of freshwater marshes in Canada found that in summer, marshes grazed in the summer/autumn contained more plant genera than marshes grazed in the spring/summer. Native/non-target richness/diversity (1 study): One replicated, randomized, paired, controlled study of ephemeral pools in the USA found that pools grazed in the dry and wet seasons experienced similar changes in native plant richness over three years. VEGETATION ABUNDANCE Overall abundance (1 study): One replicated, randomized, paired, controlled, before-and-after study of freshwater marshes and wet meadows the USA found that, in three of four habitat types, summer- and autumn-grazed plots experienced similar changes in live vegetation biomass over one year. VEGETATION STRUCTURE Height (1 study): One replicated, site comparison study of freshwater marshes in Canada found that in summer, marshes grazed in the summer/autumn contained taller emergent vegetation than marshes grazed in the spring/summer. Collected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F2974https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F2974Thu, 25 Mar 2021 14:17:41 +0000Collected Evidence: Collected Evidence: Change type of livestock grazing: brackish/salt marshes Three studies evaluated the effects, on vegetation, of allowing different types of livestock to graze brackish/salt marshes. There was overlap in the sites used in the studies, which all compared cattle and horse grazing on one salt marsh in the Netherlands. VEGETATION COMMUNITY Community types (1 study): One replicated, randomized, paired, controlled, before-and-after study on a salt marsh in the Netherlands found that plots experienced similar changes in the area of a couch-grass-dominated community, over four years, whether grazed by cattle or horses. Community composition (1 study): One replicated, randomized, paired, controlled, before-and-after study on a salt marsh in the Netherlands found that plots grazed by cattle and plots grazed by horses experienced a similar turnover of plant species over six years, and had a similar overall plant community composition after six years. Overall richness/diversity (2 studies): Two replicated, randomized, paired, controlled studies on one salt marsh in the Netherlands found that plots grazed by cattle and plots grazed by horses had similar plant species richness after 1–6 years. One of the studies also reported similar increases in species richness over six years, whether plots were grazed by cattle or horses. VEGETATION ABUNDANCE Individual species abundance (1 study): One replicated, randomized, paired, controlled, before-and-after study on a salt marsh in the Netherlands3 found that plots grazed by cattle and plots grazed by horses experienced similar changes in the cover of two salt marsh herb species, over six years. VEGETATION STRUCTURE Height (2 studies): Of two replicated, paired, controlled studies on one salt marsh in the Netherlands, one found that horses maintained shorter late-summer vegetation than cattle after two years of grazing. The other study found that horses and cattle maintained late-summer vegetation of a similar height, over four years. The first study also examined variation in height between vegetation patches, and found no significant difference between horse- and cattle-grazed plots. Collected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F2979https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F2979Thu, 25 Mar 2021 15:05:17 +0000Collected Evidence: Collected Evidence: Backfill canals or trenches: freshwater marshes Three studies evaluated the effects, on vegetation, of backfilling canals or trenches in freshwater marshes. All three studies were in the USA. There was overlap in the canals used in two of the studies. VEGETATION COMMUNITY Overall extent (3 studies): Three replicated studies in freshwater marshes in the USA reported coverage of emergent marsh vegetation between 6 months and 25 years after backfilling. All three studies reported that coverage was greater on former spoil areas alongside canals than within the partly filled canal channels. Relative abundance (1 study): One replicated, paired, site comparison study in a freshwater marsh in the USA reported that in levelled former spoil areas alongside backfilled canals, the relative abundance of some key plant species differed from natural marshland. Vegetation was surveyed three years after backfilling. VEGETATION ABUNDANCE   VEGETATION STRUCTURECollected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F2987https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F2987Thu, 25 Mar 2021 21:10:33 +0000Collected Evidence: Collected Evidence: Backfill canals or trenches: brackish/salt marshes Four studies evaluated the effects, on vegetation, of backfilling canals or trenches in brackish/salt marshes. All four studies were in the USA. There was overlap in the canals used in three of the studies. All studies included some freshwater areas in some analyses, but all results are based predominantly on canals in brackish or saline marshes. VEGETATION COMMUNITY Overall extent (4 studies): One paired, site comparison study in marshes in the USA reported that emergent vegetation coverage was typically lower in backfilled canals, after four years, than in adjacent undisturbed marsh. Three other studies in marshes in the USA simply reported coverage of emergent marsh vegetation between 6 months and 25 years after backfilling canals. All four studies reported that coverage was greater on former spoil areas alongside canals than within the partly filled canal channels. Two of the studies also reported the frequency of submerged/floating vegetation after 6–60 months, and one reported coverage of upland plant species on spoil banks that had not been completely levelled after 6–11 years. Overall richness/diversity (2 studies): One replicated, site comparison study in marshes in the USA reported that former spoil areas alongside backfilled canals had greater plant species richness than nearby natural marsh, due to the presence of upland species on unlevelled areas. One other study of a backfilled canal in predominantly brackish and saline marshes in the USA simply quantified richness of submerged vegetation four years after backfilling. VEGETATION ABUNDANCE   VEGETATION STRUCTURECollected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F2988https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F2988Thu, 25 Mar 2021 21:10:50 +0000Collected Evidence: Collected Evidence: Reduce frequency of vegetation harvest: freshwater marshes Three studies evaluated the effects, on vegetation, of reducing the frequency of harvest in freshwater marshes (or harvesting at different frequencies). There was one study in each of the USA, Belgium and Italy. VEGETATION COMMUNITY Overall richness/diversity (1 study): One replicated, paired, controlled, before-and-after study in wet grasslands in Belgium reported that overall plant species richness was similar in plots harvested once or twice/year. VEGETATION ABUNDANCE Overall abundance (1 study): One replicated, paired, controlled, before-and-after study in wet grasslands in Belgium reported that the effect of harvesting twice/year (in July and October) on total above-ground biomass was intermediate between the effects of harvesting once/year in July or October. Individual species abundance (3 studies): All three studies quantified the effect of this action on the abundance of individual plant species. For example, one replicated, paired, controlled study in freshwater marshes in the USA reported that cattail Typha biomass was greater, nine months after the last harvest, in plots harvested every six weeks than in plots harvested every three weeks. One paired, controlled, before-and-after study in reedbeds in Italy found that the common reed Phragmites australis biomass was similar in plots harvested once or twice/year, when measured at least five months after the last harvest. VEGETATION STRUCTURECollected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F2997https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F2997Wed, 31 Mar 2021 13:15:36 +0100Collected Evidence: Collected Evidence: Change season/timing of vegetation harvest: freshwater marshes Three studies evaluated the effects, on vegetation, of harvesting vegetation from freshwater marshes in different seasons or at different times. There was one study in Switzerland, one in Belgium and one in Japan. VEGETATION COMMUNITY Community composition (1 study): One replicated, randomized, paired, controlled study in wet meadows in Switzerland reported that summer-harvested and winter-harvested plots experienced similar changes in their overall plant community composition, over 3–4 years. Overall richness/diversity (1 study): One replicated, paired, controlled study of wet grasslands in Belgium reported that the effect of a single harvest between June and November on overall plant species richness depended on the month of harvesting. VEGETATION ABUNDANCE Overall abundance (1 study): One replicated, paired, controlled study of wet grasslands in Belgium reported that the effect of a single harvest between June and November on overall vegetation abundance (including litter) depended on the month of harvesting. Individual species abundance (3 studies): All three studies quantified the effect of this action on the abundance of individual plant species. The studies all reported that individual species’ abundances responded differently to harvesting in different seasons. For example, the controlled, before-and-after study in Japan reported that harvesting in June reduced the abundance of common reed Phragmites australis, in the following summer, more than harvesting in July. VEGETATION STRUCTURE Overall structure (1 study): One replicated, randomized, paired, controlled study in wet meadows in Switzerland reported that summer-harvested and winter-harvested plots both experienced a shift in vegetation cover towards lower vegetation layers, over 3–4 years. Diameter/perimeter/area (1 study): The same study reported that summer harvesting and winter harvesting had opposite effects on the diameter of common reed Phragmites australis shoots: they became thinner over four years of summer harvests but thicker over three years of winter harvests. Collected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3005https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3005Wed, 31 Mar 2021 13:33:45 +0100Collected Evidence: Collected Evidence: Facilitate tidal exchange to restore degraded brackish/saline swamps Four studies evaluated the effects, on vegetation, of facilitating tidal exchange to restore degraded brackish/saline swamps. Three studies were in Mexico and one was in India. VEGETATION COMMUNITY Overall extent (2 studies): Two before-and-after studies on the coasts of India and Mexico reported that the area of mangrove forest in each site was greater 5–6 years after restoring tidal exchange (sometimes along with planting mangrove seedlings) than in the years before. Community composition (1 study): One before-and-after study of a mangrove forest in Mexico reported that the tree community composition was identical before and five years after restoring tidal exchange: the same three tree species were present at both times. Community types (1 study): One before-and-after study of a mangrove forest in Mexico reported that the relative coverage of stands dominated by each of three tree species was similar before and five years after restoring tidal exchange. Tree/shrub richness/diversity (2 studies): One site comparison study in Mexico reported that a tidally restored mangrove forest contained a similar number of tree species to nearby natural mangroves, after 10–11 years. One before-and-after study in Mexico reported identical tree species richness in a mangrove forest before and five years after restoring tidal exchange. VEGETATION ABUNDANCE Tree/shrub abundance (2 studies): Two site comparison studies in Mexico reported that tidally restored mangrove forests contained a lower density of trees or seedlings than nearby natural mangroves. Individual species abundance (1 study): One site comparison study in Mexico compared the abundance of three mangrove tree species in a tidally restored area and nearby natural forests (see original paper for data). VEGETATION STRUCTURE Height (2 studies): One site comparison study in Mexico reported that trees in a tidally restored mangrove forest were a similar height to trees in nearby natural mangroves, after 10–11 years. Another replicated, site comparison study in Mexico reported that seedlings in a tidally restored mangrove forest were taller than seedlings in a nearby natural mangrove. Diameter (1 study): One site comparison study in Mexico reported that trees in a tidally restored mangrove forest had a similar diameter to trees in nearby natural mangroves, after 10–11 years. Basal area (1 study): One site comparison study in Mexico reported that trees in a tidally restored mangrove forest had a smaller basal area than trees in natural mangroves, after 10–11 years. Collected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3037https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3037Wed, 31 Mar 2021 19:34:43 +0100Collected Evidence: Collected Evidence: Cut large trees/shrubs to maintain or restore disturbance: freshwater marshes Four studies evaluated the effects, on vegetation, of cutting large trees/shrubs to maintain or restore disturbance in freshwater marshes. Three studies were in the USA. One was in Germany. VEGETATION COMMUNITY Community types (1 study): One study of a riparian wet meadow in Germany reported changes in the area of plant community types over four years after cutting trees/shrubs (along with grazing). Community composition (1 study): One replicated, randomized, controlled, before-and-after study aiming to restore freshwater marshes in the USA found that cutting trees (along with other interventions) significantly affected the overall plant community composition over the following five years. Overall richness/diversity (1 study): One study of a riparian wet meadow in Germany reported that plant species richness increased over four years after cutting trees/shrubs (along with grazing). VEGETATION ABUNDANCE Overall abundance (2 studies): Of two replicated, randomized, paired, controlled, before-and-after studies in the USA, one found that cutting and removing woody plants from a degraded wet prairie had no significant effect on overall vegetation cover three years later. The other study was in wet patches of a pine forest and found that understory vegetation cover increased more, over one year, where trees were thinned than where they were not thinned. Characteristic plant abundance (1 study): One replicated, randomized, controlled, before-and-after study of overgrown freshwater marshes in the USA reported that of 26 plant taxa that became more frequent after cutting trees (along with other interventions), 16 were obligate wetland taxa. Herb abundance (1 study): One replicated, randomized, paired, controlled, before-and-after study in wet patches of a pine forest in the USA found that cover of sedges Carex increased more, over one year, where trees were thinned than where they were not thinned. Tree/shrub abundance (2 studies): One replicated, randomized, paired, controlled, before-and-after study of a wet prairie in the USA found that woody plant cover declined, over three years, in plots where trees/shrubs were cut – but increased in plots where trees/shrubs were not cut. One study of a riparian wet meadow in Germany simply reported that some trees/shrubs regrew over four years after cutting trees/shrubs (along with grazing). Individual species abundance (1 study): One study quantified the effect of this action on the abundance of individual plant species. The replicated, randomized, paired, controlled, before-and-after study of a wet prairie in the USA found, for example, that cutting trees and shrubs had no significant effect on cover of the dominant herbaceous plant, tussock grass Deschampsia cespitosa, three years later. VEGETATION STRUCTURE Height (1 study): One site comparison study of a riparian wet meadow in Germany reported that an area in which trees/shrubs were cut back (along with reinstating cattle grazing) contained shorter vegetation than an adjacent unmanaged area. OTHER Survival (2 studies): One replicated, randomized, paired, controlled study in a wet prairie in the USA found that cutting woody plants did not significantly affect their survival in the following year. One study of a riparian wet meadow in Germany simply 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%2F3046https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3046Thu, 01 Apr 2021 19:06:56 +0100Collected Evidence: Collected Evidence: Use grazing to maintain or restore disturbance: brackish/salt marshes Four studies evaluated the effects, on vegetation, of using grazing to maintain or restore disturbance in brackish/salt marshes. The studies were in the UK, Denmark, France and the USA. VEGETATION COMMUNITY Community composition (1 study): One replicated, paired, controlled, before-and-after study of brackish marshes in France reported that the overall plant community composition diverged, over five years, in plots where grazing was maintained and plots where grazing ceased. The precise effect depended on the flooding regime. Overall richness/diversity (2 studies): One controlled study on a salt marsh in Denmark reported that an area where grazing was maintained had identical plant species richness, after six years, to an area where grazing had ceased. One replicated, paired, controlled, before-and-after study of brackish marshes in France reported that the effect of continued grazing on plant species richness depended on the flooding regime. VEGETATION ABUNDANCE Overall abundance (3 studies): Two controlled studies on salt marshes in the UK and Denmark reported that areas where grazing was maintained contained less vegetation overall, after 2–6 years, than areas where grazing ceased. This was measured in terms of biomass or cover. One replicated, randomized, paired, controlled, before-and-after study in alkali marshes in the USA found that grazing had no significant effect on total vegetation biomass after 1–2 years. Individual species abundance (3 studies): Three studies quantified the effect of this action on the abundance of individual plant species. For example, one replicated, paired, controlled, before-and-after study of brackish marshes in France reported that continued grazing strongly limited colonization by common reed Phragmites australis over five years. VEGETATION STRUCTURECollected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3051https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3051Thu, 01 Apr 2021 19:35:04 +0100Collected Evidence: Collected Evidence: Reduce frequency of cutting/mowing: freshwater marshes Four studies evaluated the effects, on vegetation, of reducing the frequency of cutting/mowing in freshwater marshes (or cutting/mowing them at different frequencies). There was one study in each of USA, the Netherlands, Belgium and Italy. VEGETATION COMMUNITY Community composition (1 study): One replicated, randomized, paired, controlled study of farmland ditches in the Netherlands found that marshy areas cut once, twice or three times/year had a similar overall plant community composition, when surveyed in July. Overall richness/diversity (2 studies): Two replicated, paired, controlled studies in farmland ditches in the Netherlands and wet grasslands in Belgium reported that overall plant species richness was similar in plots cut once or twice/year (and three times/year in the Netherlands). VEGETATION ABUNDANCE Overall abundance (1 study): One replicated, paired, controlled, before-and-after study in wet grasslands in Belgium reported that the effect of cutting twice/year (in July and October) on total above-ground biomass was intermediate between the effects of cutting once/year in July or October. Individual species abundance (4 studies): All four studies quantified the effect of this action on the abundance of individual plant species. For example, one replicated, paired, controlled study in freshwater marshes in the USA reported that cattail Typha spp. biomass was greater, nine months after the last cut, in plots cut every six weeks than in plots cut every three weeks. One paired, controlled, before-and-after study in reedbeds in Italy found that common reed Phragmites australis biomass was similar in plots mown once or twice/year, when measured at least five months after the last cut. VEGETATION STRUCTURECollected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3066https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3066Fri, 02 Apr 2021 13:14:38 +0100Collected Evidence: Collected Evidence: Change season/timing of cutting/mowing: freshwater marshes Four studies evaluated the effects, on vegetation, of cutting/mowing freshwater marshes in different seasons or at different times. There was one study in each of Switzerland, the Netherlands, Belgium and Japan. VEGETATION COMMUNITY Community composition (2 studies): Two replicated, randomized, paired, controlled studies in wet meadows in Switzerland and farmland ditches in the Netherlands reported that cutting vegetation in different seasons typically had similar effects on the overall plant community composition, over 1–4 years. Overall richness/diversity (2 studies): One replicated, randomized, paired, controlled study in farmland ditches in the Netherlands found that marshy areas cut in May and areas cut in November typically contained a similar number of plant species, when surveyed in July. One replicated, paired, controlled study of wet grasslands in Belgium reported that the effect of a single mow between June and November on overall plant species richness depended on the month of mowing. VEGETATION ABUNDANCE Overall abundance (1 study): One replicated, paired, controlled study of wet grasslands in Belgium reported that the effect of a single mow between June and November on overall vegetation abundance (including litter) depended on the month of mowing. Individual species abundance (4 studies): All four studies quantified the effect of this action on the abundance of individual plant species. The studies all reported that the abundance of some plant species responded differently to cutting in different seasons. The controlled, before-and-after study in Japan, for example, reported that cutting in June reduced the abundance of common reed Phragmites australis in the following summer more than cutting in July. VEGETATION STRUCTURE Overall structure (1 study): One replicated, randomized, paired, controlled study in wet meadows in Switzerland reported that summer-mown and winter-mown plots both experienced a shift in vegetation cover towards lower vegetation layers, over 3–4 years. Diameter/perimeter/area (1 study): The same study reported that summer-mowing and winter-mowing had opposite effects on the diameter of common reed Phragmites australis shoots: they became thinner over four years of summer mowing but thicker over three years of winter mowing. Collected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3070https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3070Fri, 02 Apr 2021 13:38:46 +0100Collected Evidence: Collected Evidence: Use grazing to control problematic plants: freshwater marshes Three studies evaluated the effects, on vegetation, of using grazing to control problematic plants in freshwater marshes. Two studies were in the USA. One study was in Costa Rica. VEGETATION COMMUNITY Community composition (1 study): One replicated, randomized, paired, controlled study in Costa Rica found that amongst plots where cattail-dominated vegetation had been crushed, grazing had no significant effect on the overall plant community composition over 15 months. Relative abundance (1 study): One replicated, paired, controlled, before-and-after study in a canarygrass-invaded marsh in the USA found that grazing had no significant effect on the relative abundance of the invader: over two years, it declined similarly in grazed and ungrazed plots. Overall richness/diversity (3 studies): Of three replicated, paired, controlled studies in invaded marshes/wet meadows in the USA and Costa Rica, two found that grazing typically had no significant effect on plant species richness and/or diversity over approximately two years. The other study found that grazed areas had higher plant species richness than ungrazed areas after two months. VEGETATION ABUNDANCE Overall abundance (1 study): One replicated, paired, controlled, before-and-after study in a canarygrass-invaded marsh in the USA found that grazing had no significant effect on total vegetation cover at the ground surface, over two years. Native/non-target abundance (1 study): One replicated, paired, controlled, before-and-after study in an invaded wet meadow in the USA found that two months of grazing increased cover of non-invasive grass-like plants. VEGETATION STRUCTURECollected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3112https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3112Sun, 04 Apr 2021 15:42:11 +0100Collected Evidence: Collected Evidence: Use prescribed fire to control problematic plants: freshwater marshes Four studies evaluated the effects, on vegetation, of using prescribed fire to control problematic plants in freshwater marshes. Two studies were in the USA. There was one study in each of Australia and Costa Rica. VEGETATION COMMUNITY Overall extent (1 study): One controlled, before-and-after study in a freshwater marsh in Costa Rica reported that burning (and physically damaging) cattail stands reduced the area of live vegetation present 5–22 months later. Overall richness/diversity (2 studies): One controlled study in a freshwater marsh in Costa Rica found that plots in which cattail stands were managed (burned and physically damaged) had greater overall plant species richness than unmanaged plots, 11–22 months after intervention. One replicated, randomized, controlled study in a marsh in the USA found that the effect of prescribed burning on plant species richness in the following autumn depended on the season of burning. VEGETATION ABUNDANCE Overall abundance (2 studies): One controlled, before-and-after study in a freshwater marsh in Costa Rica reported that burning (and physically damaging) cattail stands reduced live vegetation cover 5–22 months later. One replicated, randomized, controlled study in a marsh in the USA found that the effect of prescribed burning on overall vegetation cover in the following autumn depended on the season of burning. Herb abundance (1 study): One study of a floodplain marsh in Australia simply reported grass/sedge cover for up to four years after burning mimosa-invaded vegetation (along with other interventions). Native/non-target abundance (2 studies): One replicated, randomized, paired, controlled study in canarygrass-invaded wet meadows in the USA found that prescribed burning had no significant effect on the biomass of plants other than the invasive species, 2–3 growing seasons later. One study of a floodplain marsh in Australia simply reported non-target vegetation cover for up to four years after burning mimosa-invaded vegetation (along with other interventions). Individual species abundance (1 study): One study quantified the effect of this action on the abundance of individual plant species, other than the species being controlled. The replicated, randomized, controlled study in a marsh in the USA found that the effect of prescribed burning on the cover of dominant species in the following autumn depended on the season of burning. VEGETATION STRUCTURECollected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3116https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3116Sun, 04 Apr 2021 16:05:02 +0100Collected Evidence: Collected Evidence: Use prescribed fire to control problematic plants: brackish/salt marshes Four studies evaluated the effects, on vegetation, of using prescribed fire to control problematic plants in brackish/salt marshes. All four studies were in the USA. Two studies were based on the same experimental set-up. VEGETATION COMMUNITY Overall richness/diversity (4 studies): Two replicated, randomized, paired, controlled studies in brackish and salt marshes in the USA reported that burned and unburned plots had similar plant species richness over the following 1–3 years. Two studies in saltgrass- or reed-dominated marshes in the USA reported that burned areas had greater plant species richness than unburned areas, after approximately 1–3 years. In one of the studies, burned areas had also been sprayed with herbicide for nine years – and contained more plant species than a nearby natural marsh. VEGETATION ABUNDANCE Overall abundance (3 studies): Three replicated, randomized, paired, controlled studies in brackish and salt marshes in the USA evaluated the effect of prescribed burning on vegetation cover. One study found that autumn-burned plots had lower overall vegetation cover than unburned plots after 11 months, but one found that winter-burned plots had similar overall vegetation cover to unburned plots after one year. Two of the studies reported that winter-burned plots had less standing dead vegetation cover than unburned plots in the following summer or winter. Individual species abundance (4 studies): All four studies quantified the effect of this action on the abundance of individual plant species, other than a species being controlled. For example, three replicated, randomized, paired, controlled studies in brackish and salt marshes in the USA reported mixed effects of burning on cover of saltgrass Distichlis spicata: higher in burned than unburned plots in the following summer, lower in burned than unburned plots in the following winter, or mixed effects amongst marsh types. Two replicated, randomized, paired, controlled studies in brackish and salt marshes in the USA reported that burning did not reduce cover of saltmeadow cordgrass Spartina patens, compared to cover in unburned plots, over the following 1–3 years. One site comparison study of brackish marshes in the USA reported that a marsh that had been burned for three years (and sprayed with herbicide for nine) contained more smooth cordgrass Spartina alterniflora than an unburned and unsprayed marsh, and a similar amount of smooth cordgrass to a nearby natural marsh. VEGETATION STRUCTURE Visual obstruction (1 study): One replicated, randomized, paired, controlled study in brackish and salt marshes in the USA found that the visual obstruction caused by vegetation (combination of height and horizontal cover) was similar in burned and unburned plots, after 11 months. Height (1 study): One site comparison study of brackish marshes in the USA found that in a marsh burned for two years (and sprayed with herbicide for nine), 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%2F3117https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3117Sun, 04 Apr 2021 16:05:16 +0100Collected Evidence: Collected Evidence: Use herbicide to control problematic plants: freshwater swamps Four studies evaluated the effects, on vegetation, of using herbicide to control problematic plants in freshwater swamps. All four studies were in the USA. VEGETATION COMMUNITY Overall richness/diversity (2 studies): One replicated, randomized, paired, controlled study aiming to restore canarygrass-invaded swamps in the USA found that plots sprayed with herbicide typically had greater plant species richness and diversity than unsprayed plots, after 1–2 growing seasons. One replicated, randomized, controlled study in a petunia-invaded floodplain swamp in the USA found that plots sprayed with herbicide had similar overall plant species richness to unsprayed plots over 15 months after spraying. Native/non-target richness/diversity (3 studies): Three replicated, controlled studies (also paired and/or randomized) in invaded freshwater swamps in the USA found that applying herbicide typically had no significant effect on native plant species richness, over 3–24 months after spraying. VEGETATION ABUNDANCE Tree/shrub abundance (2 studies): Two replicated, controlled studies in the USA evaluated the effects, on tree/shrub abundance, of managing canarygrass-invaded vegetation by applying herbicide. One study found that plots sprayed with herbicide contained more non-planted tree seedlings than unsprayed plots, after 1–2 growing seasons. The other study found that managed plots (cut, disked and sprayed with herbicide) contained more non-planted tree seedlings than unmanaged plots, after 1–3 years. Native/non-target abundance (2 studies): Two replicated, controlled studies in swamps in the USA reported that spraying invaded vegetation with herbicide (sometimes along with other interventions) typically had no clear or significant effect on native/non-target vegetation cover 1–3 years later. Cover was typically similar to unmanaged plots or before intervention. Individual species abundance (1 study): One replicated, randomized, paired, controlled study aiming to restore a canarygrass-invaded swamp in the USA reported that spraying the vegetation with herbicide affected the abundance of some individual plant species – other than the target problematic species – two growing seasons later. VEGETATION STRUCTURECollected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3122https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3122Sun, 04 Apr 2021 17:19:27 +0100Collected Evidence: Collected Evidence: Retain/restore/create vegetation around freshwater marshes Four studies evaluated the effects, on vegetation in freshwater marshes, of retaining/restoring/creating vegetation around them. Three studies were in the USA and one was in China. Two studies were largely based on the same sites. VEGETATION COMMUNITY Community composition (2 studies): Two replicated, site comparison studies in the USA reported that freshwater marshes surrounded by restored upland vegetation contained a different overall plant community, after 1–20 years, to nearby marshes surrounded by natural vegetation. One of the studies also reported differences between marshes in restored vs degraded catchments. Overall richness/diversity (3 studies): One replicated, paired, site comparison study in the USA found that marshes surrounded by restored upland vegetation had greater overall plant species richness than marshes within cropland, and similar richness to marshes within natural grassland. One replicated, site comparison study in the USA reported that freshwater marshes surrounded by restored upland vegetation contained fewer wetland plant species, after 1–20 years, than nearby marshes surrounded by natural vegetation. One before-and-after study of a lakeshore marsh in China reported that after revegetating a polluted input river (along with planting directly into the marsh), overall plant species richness increased. VEGETATION ABUNDANCE Overall abundance (1 study): One replicated, paired, site comparison study in the USA found that marshes surrounded by restored upland vegetation contained more plant biomass than marshes within cropland, but also more plant biomass than marshes within natural grassland. Characteristic plant abundance (1 study): One replicated, paired, site comparison study in the USA found that marshes surrounded by restored upland vegetation typically had greater cover of wetland-characteristic plants than marshes within cropland, and similar cover of these species to marshes within natural grassland. Individual species abundance (1 study): One replicated, site comparison study of pothole wetlands the USA found that wetlands surrounded by restored upland vegetation had greater cover of hybrid cattail Typha x glauca, after 2–7 years, than nearby natural wetlands. VEGETATION STRUCTURE Visual obstruction (1 study): One replicated, site comparison study of pothole wetlands in the USA found that parts of wetlands surrounded by restored upland vegetation created more visual obstruction, after 2–7 years, than the corresponding zone of nearby natural wetlands. Collected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3145https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3145Mon, 05 Apr 2021 15:14:57 +0100Collected Evidence: Collected Evidence: Deposit soil/sediment to form physical structure of brackish/salt marshes Four studies evaluated the effects, on vegetation, of depositing soil/sediment to form the physical structure of brackish/salt marshes (without introducing vegetation). Three studies were in the USA and one study was in Italy. Two studies took place in the same marsh, but in different areas. VEGETATION COMMUNITY Overall extent (1 study): One replicated study in a lagoon in Italy quantified the area of vegetation on sediment deposited up to 19 years previously (average six years four months, with 61% vegetation coverage). Community types (2 studies): Two replicated studies in coastal wetlands in the USA and Italy quantified the coverage of brackish or salt marsh plant communities on sediment deposited up to 19 years previously. Community composition (1 study): One replicated, site comparison study on the coast of the USA reported that the composition of the plant community that developed on deposited sediment depended on the time since deposition and the elevation of the sediment. Areas of sediment that were of a similar elevation to natural marshes (or slightly lower) developed (or were developing) a similar overall plant community composition to the natural marshes. Overall richness/diversity (1 study): One replicated study in an estuary in the USA reported that 1–2 plant species had colonized areas of deposited sediment after 4–8 years. VEGETATION ABUNDANCE   VEGETATION STRUCTURECollected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3236https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3236Fri, 09 Apr 2021 15:02:12 +0100Collected Evidence: Collected Evidence: Introduce fragments of non-woody plants: brackish/saline wetlands Three studies evaluated the effects, on vegetation, of introducing fragments of emergent, non-woody plants to brackish/saline wetlands. Two studies were in one bog in Canada. One study was in China. VEGETATION COMMUNITY   VEGETATION ABUNDANCE Overall abundance (2 studies): Two replicated, paired, controlled, before-and-after studies in salt-contaminated bogs in Canada found that plots planted with rhizomes or sown with fragments of salt marsh herbs had similar overall vegetation biomass, after one year, to plots that had not been planted or sown. Herb abundance (1 study): One replicated, paired, controlled, before-and-after studies in salt-contaminated bogs in Canada found that plots sown with fragments of salt marsh herbs had greater overall cover of the introduced species, after one year, to unsown plots. However, biomass of the introduced species did not significantly differ between sown and unsown plots. Individual species abundance (2 studies): Two replicated studies (one also before-and-after) in brackish/saline wetlands in Canada and China simply quantified the abundance of herb species, over one year or growing season after planting herb fragments. VEGETATION STRUCTURE   OTHER Germination/emergence (1 study): One replicated study on a tidal flat in China reported that at least 25% of bulrush Scirpus mariqueter corms (bulb-like organs) produced shoots within the first growing season after planting. Collected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3261https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3261Sat, 10 Apr 2021 13:28:14 +0100Collected Evidence: Collected Evidence: Transplant or replace blocks of vegetation: freshwater marshes Four studies evaluated the effects, on vegetation, of transplanting or replacing blocks of freshwater marsh vegetation. Three studies were in the USA. One study was in the UK. VEGETATION COMMUNITY Community composition (1 study): One replicated, paired, controlled study in rewetted marshes in the USA found that plots of transplanted marsh vegetation contained a plant community characteristic of wetter conditions than plots without transplants after one growing season – but not after two. Overall richness/diversity (2 studies): One replicated, before-and-after study in the UK reported that plant species richness within transplanted freshwater marsh vegetation was similar before transplanting and six years later. There was a temporary increase in richness after one year. One replicated, paired, controlled study in rewetted freshwater marshes in the USA found that plots of transplanted marsh vegetation contained more wetland plant species than plots without transplants after one growing season – but that there was no significant difference after two. VEGETATION ABUNDANCE Overall abundance (1 study): One replicated, paired, controlled study in rewetted freshwater marshes in the USA found that plots of transplanted marsh vegetation had greater cover of wetland plants than plots without transplants, after 1–2 growing seasons. Individual species abundance (2 studies): One replicated, site comparison study in a wet prairie in the USA found that after three growing seasons, the density of prairie cordgrass Spartina pectinata stems was lower in transplanted sods than in pristine or source prairies. One before-and-after study of transplanted freshwater marsh vegetation in the UK reported changes in the frequency of individual plant species from before to six years after transplanting. VEGETATION STRUCTURE Height (1 study): One replicated, site comparison study in a wet prairie in the USA found that after three growing seasons, prairie cordgrass Spartina pectinata was shorter in transplanted sods than in pristine or source prairies. Diameter/perimeter/area (2 studies): Two studies (one replicated) in wet prairies in the USA found that the average area of small transplanted sods (≤0.28 m2 initial size) increased over 3–4 growing seasons. One of the studies transplanted larger sods (0.65 m2 initial size) and reported that their average area decreased over 3–4 growing seasons. OTHER Survival (2 studies): Two studies (one replicated) in wet prairies in the USA reported ≥90% survival of transplanted sods of wet prairie vegetation after 3–4 growing seasons. Collected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3268https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3268Sat, 10 Apr 2021 15:36:31 +0100Collected Evidence: Collected Evidence: Actively manage water level before/after planting non-woody plants: freshwater wetlands Three studies evaluated the effects, on vegetation, of actively managing water levels in freshwater wetlands planted with emergent, non-woody plants. All three studies were in the USA. Two studies used the same experimental wet basins but planted different species. VEGETATION COMMUNITY Overall richness/diversity (1 study): One study in a freshwater marsh in the USA found that amongst plots amended with wetland soil, those flooded for longer contained fewer emergent plant species over the rest of the growing season following drawdown. Characteristic plant richness/diversity (1 study): The same study found that amongst plots amended with wetland soil, those flooded for longer contained fewer wetland-characteristic plant species over the rest of the growing season following drawdown. VEGETATION ABUNDANCE  Overall abundance (1 study): One study in a freshwater marsh in the USA found that amongst plots amended with wetland soil, those flooded for longer developed more submerged vegetation biomass before drawdown, but developed less emergent vegetation (biomass and stem density) over the rest of the growing season after drawdown. Individual species abundance (2 studies): Two studies quantified the effect of this action on the abundance of individual plant species. For example, one controlled, before-and-after study in wet basins in the USA found that the effect of mimicking a natural (falling) water regime on lake sedge Carex lacustris biomass and density, in the three years after planting, depended on the year and various environmental factors (e.g. planting density, elevation and weeding of competitors). VEGETATION STRUCTURE Height (2 studies): Two controlled studies in wet basins in the USA examined the effect of mimicking a natural (falling) water regime, compared to a stable or rising regime, on the height of sedges over three years after planting. One of the studies found no significant effect on the height of tussock sedge Carex stricta in three of three years. The other study found that the effect on the height of lake sedge Carex lacustris varied within and between years. OTHER Survival (2 studies): Two controlled studies in wet basins in the USA examined the effect of mimicking a natural (falling) water regime, compared to a stable or rising regime, on the survival of sedges Carex over three years after planting. The precise effect depended on the year and/or plot elevation. In the first year, sedge survival was typically lower under the falling regime. Collected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3281https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3281Sat, 10 Apr 2021 17:15:30 +0100Collected Evidence: Collected Evidence: Add inorganic fertilizer before/after planting non-woody plants: freshwater wetlands Four studies evaluated the effects, on vegetation, of adding inorganic fertilizer to freshwater wetlands planted with emergent, non-woody plants. Two studies were in the USA, one was in the Netherlands and one was in Ireland. One of the studies in the USA was in a greenhouse. VEGETATION COMMUNITY   VEGETATION ABUNDANCE Individual species abundance (1 study): One replicated, paired, controlled study of lakeshores planted with bulrushes Scirpus spp. in the Netherlands found that fertilized and unfertilized plots contained a similar amount (density and biomass) of each bulrush species over three growing seasons. VEGETATION STRUCTURE Individual plant size (2 studies): Two replicated, controlled studies (one also paired) in the USA found that adding fertilizer to mineral soil increased the biomass and/or number of shoots of tussock sedge Carex stricta seedlings, 2–3 months after planting. However, in both studies, adding fertilizer had no significant or clear effect on sedge size in plots amended with compost and/or topsoil. OTHER Growth (1 study): One replicated, paired, controlled, before-and-after study in tubs of mining waste in Ireland found that adding fertilizer increased growth of planted sweetgrass Glyceria fluitans in one case but had no significant effect in another. Collected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3304https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3304Sun, 11 Apr 2021 08:57:08 +0100Collected Evidence: Collected Evidence: Use fences or barriers to protect freshwater wetlands planted with non-woody plants Four studies evaluated the effects, on vegetation, of using fences or barriers to protect freshwater wetlands planted with emergent, non-woody plants. There was one study in each of Canada, the Netherlands, Israel and the USA. VEGETATION COMMUNITY Community composition (1 study): One replicated, site comparison study in the USA found that amongst planted/sown lakeshores, those protected with fences or wave breaks contained different wetland plant communities, after 1–6 years, than those without fences or wave breaks. VEGETATION ABUNDANCE Individual species abundance (1 study): One replicated, controlled study at the edge of a freshwater lake in the Netherlands found that amongst plots planted with lakeshore bulrush Scirpus lacustris, those from which wildfowl had been excluded contained a greater density and biomass of lakeshore bulrush, after 1–2 years, than those that remained open to wildfowl. VEGETATION STRUCTURE   OTHER Survival (2 studies): Two replicated, paired, controlled studies in freshwater wetlands in Canada and Israel reported that protecting emergent herbs, with silt screens or herbivore fencing, increased survival rates over 12–18 months after planting. Collected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3328https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3328Sun, 11 Apr 2021 13:14:37 +0100Collected Evidence: Collected Evidence: Designate protected area Four studies evaluated the overall effects, on vegetation or human behaviour, of designating protected areas involving marshes or swamps. There were two studies in China, one in Malaysia and one in Puerto Rico. VEGETATION COMMUNITY Overall extent (4 studies): Two studies (one replicated, one before-and-after) in China reported that the area of marsh, swamp or unspecified wetland in protected areas declined over 6–12 years. One replicated, site comparison study in Puerto Rico reported that protection had no clear effect on mangrove forest area, with similar changes over 25 years in protected and unprotected sites. One study of a mangrove forest in Malaysia reported that it retained at least 97% of its forest area over 98 years of protection as a forest reserve. VEGETATION ABUNDANCE   VEGETATION STRUCTURE Overall structure (2 studies): One replicated study in China reported “degradation” of the landscape structure of protected wetlands over 12 years. One before-and-after study in China reported fragmentation of wetland habitat within a protected area, but that this meant its structure became more like it had been 10–40 years previously. Collected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3384https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F3384Mon, 12 Apr 2021 08:40:54 +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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