Add surface mulch before/after planting trees/shrubs: freshwater wetlands
Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 1
Background information and definitions
Organic mulches (i.e. remains or waste products of living organisms) can be placed on the surface of wetlands to stabilize temperatures and humidity, and provide shade to germinating plants. This may create a more hospitable environment for establishment and growth of planted vegetation. Examples of substances than can be used as mulches include compost, straw, seagrass leaves and seaweed (macroalgae).
Caution: It may be necessary to sterilize mulch before applying it, with heat or radiation, to kill propagules of undesirable plants. Adding organic matter as a mulch may be less labour intensive than mixing it into the soil or sediment, but increases the risk of the material being washed away.
Supporting evidence from individual studies
A replicated, randomized, paired, controlled study in 2014–2015 in two degraded floodplain swamps in Victoria, Australia (Greet et al. 2016) found that mulching plots with woodchips before planting native shrubs and tree seedlings had no significant effect on their cover or height. One year after planting, mulched and unmulched plots had statistically similar cover of native shrubs (mulched: 5–14%; unmulched: 4–8%) and swamp gum Eucalyptus camphora (mulched: 6–20%; unmulched: 7–11%). Swamp gum saplings were a statistically similar height in mulched and unmulched plots (data not reported). Mulching reduced the cover of problematic common reed Phragmites australis in one swamp (mulched: 40%; unmulched: 73%) but had no significant effect on the cover of problematic reed canarygrass Phalaris arundinacea in the other (mulched: 96%; unmulched: 99%). Methods: In February–March 2014, four 100-m2 plots were established in each of two floodplain wetlands. All plots had been recently cut and sprayed with herbicide (to control common reed or reed canarygrass) and fenced to exclude large animals. Four plots (two random plots/site) were mulched with eucalypt Eucalyptus sp. woodchips. All plots were then planted with native shrubs (1 plant/m2; species not reported), swamp gum seedlings (1 plant/2 m2) and understory herbs (3 plants/m2). Vegetation was surveyed in March 2015, in five 1-m2 quadrats/plot.Study and other actions tested