Add surface mulch before/after planting non-woody plants: 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 understory herbs increased their cover in one of the swamps, but had no significant effect in the other. Cover was monitored one year after planting. In one swamp, invaded by common reed Phragmites australis, mulched plots had higher cover of native understory herbs (26%) than unmulched plots (4%). The mulched plots also had lower reed cover (mulched: 40%; unmulched: 73%). In the other swamp, invaded by reed canarygrass Phalaris arundinacea, mulched plots had statistically similar cover of native understory herbs (3%) to unmulched plots (2%). Canarygrass cover was also similar between treatments (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/swamp) were mulched with eucalypt Eucalyptus sp. woodchips. All plots were then planted with native understory herbs (3 plants/m2; species not reported), plus shrubs (1 plant/m2) and tree seedlings (1 plant/2 m2). Vegetation was surveyed in March 2015, in five 1-m2 quadrats/plot.Study and other actions tested