Use fences or barriers to protect freshwater wetlands planted with non-woody plants

How is the evidence assessed?
  • Effectiveness
    not assessed
  • Certainty
    not assessed
  • Harms
    not assessed

Study locations

Key messages

  • 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.

About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

Supporting evidence from individual studies

  1. A replicated, paired, controlled study in 1993–1994 in a freshwater marsh in Ontario, Canada (Chow-Fraser & Lukasik 1995) reported that silt screens increased survival of emergent vegetation one year after planting. Statistical significance was not assessed. In deep water (>40 cm at planting), 100% of planted arrowheads Sagittaria latifolia survived in a plot surrounded by a silt screen (vs 0% in a plot without a silt screen). In shallow water (15 cm at planting), the survival rate of planted broadleaf cattails Typha latifolia was more than twice as high in a screened plot than an unscreened plot (precise data not reported). Methods: In August 1993, two pairs of plots (one shallow-water, one deep-water) were established in Cootes Paradise Marsh. Each 6-m2 plot was planted with 90 plants: 30 arrowhead, 30 cattails and 30 submerged plants. All plots were fenced to exclude muskrats Ondatra zibethicus. Two plots (one plot/pair) were also surrounded by a finer-mesh silt screen. Vegetation was surveyed in August 1994. The study does not report full results from all plots.

    Study and other actions tested
  2. A replicated, controlled study in 1987–1989 at the edge of a freshwater lake in the Netherlands (Clevering & van Gulik 1997) found that protecting plots planted with lakeshore bulrush Scirpus lacustris ssp. lacustris (using fences or wire netting) increased bulrush density and biomass after 1–2 years. In summer, fenced plots contained 300–360 bulrush shoots/m2 with above-ground biomass of 1,250–1,550 g/m2. Plots covered with wire netting contained 60–90 bulrush shoots/m2 with above-ground biomass of 110–280 g/m2. In unprotected plots, bulrush was not present. The pattern of results was similar, although density and biomass lower, in spring (see original paper). Methods: Twenty 6- or 16-m2 plots were established behind breakwaters at the edge of a lake. In May 1987, lakeshore bulrush was transplanted into all plots (12 plants/m2). Eight plots were then fenced to exclude wildfowl (12 cm wire mesh, 1.2 m tall). Six plots were covered in wire netting (2 cm holes) at ground level, to protect the roots from wildfowl. The final six plots were not protected. Lakeshore bulrush shoots were counted and measured in spring and summer 1988 and 1989. Above-ground dry biomass was estimated from length-mass relationships.

    Study and other actions tested
  3. A replicated, paired, controlled study in the mid-1990s in a reflooded freshwater wetland in Israel (Kaplan et al. 1998) reported that fencing off planted emergent vegetation to protect it from herbivores increased its survival. Statistical significance was not assessed. In four of four comparisons, protected plants had higher survival rates (17–75%) than unprotected plants (0–10%) after 12–18 months. Methods: Emergent wetland plants were introduced to recently rewetted cropland. Yellow flag iris Iris pseudacorus was planted into peat soils flooded with 30 cm of water. Sixteen iris plants were protected and 50 were not. Papyrus Cyperus papyrus was planted into wet, saturated or flooded mineral soils. Seventy-two papyrus plants were protected and 72 were not. Protection involved fencing with wire mesh (5 x 5 cm holes) and plastic netting (mesh size not reported), primarily to exclude nutria Myocastor coypus.

    Study and other actions tested
  4. A replicated, site comparison study in 2005–2006 of 22 lakeshore restoration sites in Minnesota, USA (Vanderbosch & Galatowitsch 2010) reported that protecting planted lakeshores with fences or wave breaks affected the plant community composition 1–6 years later. Data were reported as graphical analyses and statistical significance was not assessed. In the seasonally flooded zone, protected sites developed communities of native perennial species such as Canadian reedgrass Calamagrostis canadensis and swamp milkweed Asclepias incarnata. Exposed sites were sparsely vegetated by annuals and weedy perennials. In the permanently flooded zone, protected sites generally developed emergent vegetation whilst exposed sites were dominated by submerged and floating vegetation. In two of five sites protected with wave breaks, all planted vegetation died. Methods: In summer 2005 and spring 2006, plant species and their cover were surveyed in 22 urban lakeshore restoration projects. Native vegetation (mostly emergent wetland herbs) had been planted or sown between 1999 and 2004. Protection involved onshore fences, offshore fences and/or wave breaks. Some fences completely enclosed sites and some partially enclosed sites. In eight sites, protection was only in place for the first growing season after planting.

    Study and other actions tested
Please cite as:

Taylor N.G., Grillas P., Smith R.K. & Sutherland W.J. (2021) Marsh and Swamp Conservation: Global Evidence for the Effects of Interventions to Conserve Marsh and Swamp Vegetation. Conservation Evidence Series Synopses. University of Cambridge, Cambridge, UK.

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Marsh and Swamp Conservation

This Action forms part of the Action Synopsis:

Marsh and Swamp Conservation
Marsh and Swamp Conservation

Marsh and Swamp Conservation - Published 2021

Marsh and Swamp Synopsis

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