Use fences or barriers to protect planted brackish/saline wetlands planted with trees/shrubs
Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 1
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 swamps; Exclude or remove livestock from historically grazed swamps; 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 1997–1998 in four sandy coastal sites in Florida, USA (Salgado Kent & Lin 1999) reported that planted red mangrove Rhizophora mangle propagules within full-length plastic shelters – but not full-length bamboo shelters or below-ground plastic shelters – had higher survival rates than unprotected propagules, and found that seedlings within full-length shelters grew taller than seedlings in the other treatments. After 4–8 months, the survival rate was 76–100% for propagules/seedlings within translucent plastic shelters that extended above and below ground (vs 0–2% within similar shelters made from bamboo; 0% within plastic shelters that extended below ground only; and 0–6% without shelter; statistical significance not assessed). After 22–129 days, seedlings within full-length plastic shelters were significantly taller than unprotected seedlings in three of four comparisons (other comparison no significant difference, because no propagules had developed into seedlings) and significantly taller than seedlings in the other types of shelters in four of four comparisons (see original paper for data). Methods: In August and November 1997, a total of 796 red mangrove propagules were planted, around the high tide level, in four exposed, sandy, coastal sites. There were 13–35 propagules/site/season for each of the four shelter treatments. Shelters differed in material and height (see above) but were all 3.8 cm internal diameter and had a slit running down them to allow water exchange. Propagules (or the seedlings they became) were monitored twice a month for up to eight months after planting.Study and other actions tested