Retain/restore/create vegetation around freshwater marshes
Overall effectiveness category Likely to be beneficial
Number of studies: 4
Background information and definitions
Management of the watershed or catchment (the area of land which drains into a wetland) can be a critical part of wetland conservation.
Maintaining, restoring or creating vegetation in the watershed could reduce the amount of pollution reaching focal marshes (amongst other benefits; Ma 2016). Vegetated slopes or buffer zones may retain sediment and nutrients better than bare soil (Skagen et al. 2008; Smith et al. 2016). Perennial, deep-rooted plants in catchments can also soak up water and prevent salinization (due to rising water tables) in areas with salty soils (NSW Government 2019). Artificial wetlands may be built in the catchment of a focal marsh or swamp, and planted with vegetation that can remove or break down pollutants (Brix 2003). Vegetation could be retained around development, or could be introduced to degraded land around focal sites. Vegetation in watersheds could be carefully harvested, providing income to support conservation (Wantzen et al. 2006).
To be summarized as evidence for this action, studies must have reported the effect of vegetation near/around a focal marsh on the vegetation within the marsh. The surrounding vegetation may be permanent (e.g. planting forests) or temporary (e.g. planting cover crops in farmland). The scope of this action does not include (a) studies of water quality only, or (b) studies of the surrounding habitat, even if it is also a marsh, since this habitat is sacrificed to protect the focal site.
Brix, H. (2003) Plants used in constructed wetlands and their functions. Proceedings of the 1st International Seminar on the Use of Aquatic Macrophytes for Wastewater Treatment in Constructed Wetlands, 8–10 May 2003, Lisbon, Portugal, 81–109.
Ma M. (2016) Riparian buffer zone for wetlands. In: C.M. Finlayson, M. Everard, K. Irvine, R.J. McInnes, B.A. Middleton, A.A. van Dam, N.C. Davidson (eds.) The Wetland Book I: Structure and Function, Management, and Methods. Springer, Dordrecht. Accessed 28 October 2019.
NSW Government (2019) Type of Salinity and their Prevention. Available at https://www.environment.nsw.gov.au/topics/land-and-soil/soil-degradation/salinity/type-of-salinity-and-their-prevention. Accessed 30 December 2020.
Skagen S.K., Melcher C.P. & Haukos D.A. (2008) Reducing sedimentation of depressional wetlands in agricultural landscapes. Wetlands, 28, 594–604.
Smith C., DeKeyser E.S., Dixon C., Kobiela B. & Little A. (2016) Effects of sediment removal on prairie pothole wetland plant communities in North Dakota. Natural Areas Journal, 36, 48–58.
Wantzen K.M., Siqueira A., da Cunha C.N. & de Sá M.d.F.P. (2006) Stream-valley systems of the Brazilian Cerrado: impact assessment and conservation scheme. Aquatic Conservation: Marine and Freshwater Ecosystems, 16, 713–732.
Supporting evidence from individual studies
A replicated, paired, site comparison study of 261 ephemeral freshwater marshes (playas) in the Great Plains of the USA (O’Connell et al. 2012) found that marshes within revegetated cropland had greater plant species richness, plant biomass and cover of wetland-characteristic plants than marshes within current cropland, and similar richness and cover of wetland-characteristic plants to marshes within natural grassland. Compared to marshes within current cropland, restored-catchment marshes had greater plant species richness (reported as statistical model results), greater above-ground plant biomass (restored: 420; cropland: 200 g/m2) and typically greater cover of wetland-characteristic plant species (two of three comparisons, for which restored: 22–27%; cropland: 11–15%). Compared to marshes within natural (never ploughed) grassland, restored-catchment marshes had similar plant species richness (reported as statistical model results) and typically similar cover of wetland-characteristic plant species (two of three comparisons, for which restored: 22–27%; natural: 22–26%). However, restored-catchment marshes had greater above-ground plant biomass (420 g/m2) than marshes within natural grassland (240 g/m2). The study also reported that restored-catchment marshes were dominated by Great-Plains-native perennial plants, like natural marshes, but had greater cover of non-native plants than both natural and cropland marshes (see original paper for data). Methods: In summer (year not reported), vegetation was surveyed within 261 playa wetlands. These were arranged in 87 sets of three. In each set, one wetland was within former cropland now planted with a perennial cover crop, one was within extant cropland, and one was within natural grassland. Surveys included crop plants within wetlands. Biomass was dried before weighing. Most of the sites in this study were also studied in (2).Study and other actions tested
A replicated, site comparison study of 258 ephemeral freshwater marshes in central USA (O’Connell et al. 2013) reported that marshes within revegetated cropland contained a different plant community to natural marshes (surrounded by permanent grassland) and degraded marshes (surrounded by cropland), with lower cover of perennial wetland plants and fewer perennial wetland species than the natural marshes. Results summarized for this study are not based on assessments of statistical significance. After 1–20 years, the overall plant community composition differed between restored-catchment, natural and degraded marshes (data reported as a graphical analysis). Perennial wetland species were underrepresented in restored-catchment marshes (30% cover; 3.5 species/marsh) compared to natural marshes (47% cover; 5.0 species/marsh). However, restored-catchment marshes had greater cover of these species than degraded marshes (7% cover; species richness not reported). Annual wetland species were overrepresented in restored-catchment marshes compared to natural marshes in terms of abundance (data reported as a graphical analysis only). However, there was a similar number of these species in restored-catchment marshes (5.2 species/marsh) and natural marshes (5.4 species/marsh). Methods: Around 2010, vegetation was surveyed in 258 ephemeral playa marshes (along two transects crossing each marsh, in both the cool and warm seasons). Of these marshes, 86 were undergoing restoration under the Conservation Reserve Program (former cropland in catchment replanted to grassland 1–20 years previously; no intervention within the marshes), 86 were in natural catchments, and 86 were in degraded, farmed catchments. This study used a subset of the sites from (1).Study and other actions tested
A before-and-after study in 2008–2014 of a lakeshore freshwater marsh in southern China (Liu et al. 2016) found that after planting herbs into a polluted river feeding it (and planting directly into the marsh), plant species richness increased. Statistical significance was not assessed. The marsh contained 14 plant species before planting but 26 plant species five years after. Methods: In May 2009, the river feeding a lake was planted with pollution-reducing vegetation: bur-reed Sparganium simplex, mare’s tail Hippuris vulgaris and yellow floating heart Nymphoides peltatum. The river water quality had recently declined, due to inputs of nutrients and domestic sewage. Some herbs were also planted directly into the lakeshore marsh (number of species not reported). The study does not distinguish between the effects of these interventions on any non-planted vegetation. Lakeshore vegetation (emergent, floating and submerged) was surveyed before (July 2008) and for approximately five years after (July 2009–2014) planting (details not fully reported).Study and other actions tested
A replicated, site comparison study in 2010 of 20 prairie pothole wetlands in North Dakota, USA (Smith et al. 2016) found that potholes amongst restored perennial vegetation contained a different marsh and wet meadow plant community to nearby natural marshes, with greater cattail cover and sometimes greater horizontal vegetation cover. The overall plant community composition in both the marsh and wet meadow zones significantly differed between potholes surrounded by restored perennial upland vegetation and nearby natural potholes (data reported as a graphical analysis). Across both zones, the potholes in restored areas had greater cover of hybrid cattail Typha x glauca (19%) than natural potholes (5%). In the marsh zone – but not the wet meadow zone – visual obstruction was greater in potholes in restored areas than in natural potholes (data reported as a visual obstruction index). Methods: In summer 2010, vegetation was surveyed in the marsh (seasonally flooded) and wet meadow (occasionally flooded) zones of 20 prairie potholes (10 quadrats/zone/pothole). Eleven potholes used to be surrounded by cropland, but this had been restored to perennial vegetation cover (details and dates not reported, but probably around 2–7 years previously). However, these potholes likely contained excess sediment that had washed off the cropland. The other nine potholes were surrounded by land that was not, and had never been, cultivated.Study and other actions tested