Use fences or barriers to protect freshwater wetlands planted with non-woody plants
Overall effectiveness category Likely to be beneficial
Number of studies: 4
Background information and definitions
Plants introduced to wetlands may be vulnerable to physical damage from grazing, wind, waves or sediment. Barriers could be used to protect planted vegetation from such physical damage. Here, “barriers” is used quite broadly and includes sleeves, tree guards, fences and fine-meshed silt screens placed around planted vegetation, sticky oils or resins painted onto planted vegetation, and offshore walls or breakwaters. Some of these barriers may have incidental effects on temperature, humidity and sunlight intensity (but covers and screens whose main aim is to modify these factors are considered elsewhere). If the general area containing planted vegetation is fenced, rather than individual planted plants, other colonizing vegetation may benefit too.
Related actions: Use barriers to keep livestock off ungrazed marshes; Exclude or remove livestock from historically grazed marshes; Exclude wild vertebrates using physical barriers; Exclude wild invertebrates using physical barriers; Add surface mulch to complement planting; Add cover other than mulch to complement planting.
Supporting evidence from individual studies
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
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
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
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