Add surface mulch before/after planting non-woody plants: brackish/saline 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 1996–1997 in two degraded, intertidal, brackish marshes in Manitoba, Canada (Handa & Jeffries 2000) found that adding surface mulch increased the cover of one of two planted herb species, but did not significantly affect survival rates of either species or overall above-ground biomass. On all five survey dates across the second growing season after planting, creeping alkaligrass Puccinellia phryganodes cover was higher in mulched plots (1,820–5,400 mm2/m2) than unmulched plots (1,090–3,810 mm2/m2). However, cover of estuary sedge Carex subspathacea never significantly differed between treatments (mulched: 670–2,880 mm2/m2; unmulched: 720–2,600 mm2/m2). On all five dates, survival rates were statistically similar under each treatment for both alkaligrass (mulched: 87–100%; unmulched: 52–93%) and estuary sedge (mulched: 28–58%; unmulched: 23–50%). On at least two of three dates (results not clearly reported), live above-ground biomass was statistically similar under each treatment for both alkaligrass-dominated vegetation (mulched: 45–178 g/m2; unmulched: 29–122 g/m2) and sedge-dominated vegetation (mulched: 1–4 g/m2; unmulched: 1–4 g/m2). Methods: In June 1996, plugs of creeping alkaligrass and estuary sedge were transplanted from natural stands to 1-m2 plots within brackish marsh vegetation damaged by geese (one species/marsh; 12 plots/species; 42 plugs/plot). Two random quarters of each plot were mulched after planting (5 mm layer of peat from a nearby marsh). Half of each plot was also fertilized. All plots were fenced to exclude geese. Vegetation was surveyed in summer 1997. Survival and cover were monitored for planted plants in the centre of each plot. Vegetation samples were cut from the margins of each plot, then washed to remove dead biomass, dried and weighed.Study and other actions tested