Add surface mulch: brackish/salt marshes
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 vegetation establishment and growth. Mulches can also help to manage acidification by excluding oxygen from sediments and stimulating microbial processes that neutralize the acidity (Baldwin 2011). Carbon-rich organic matter may also help to shift the competitive balance away from invasive species in polluted environments, enriched in certain nutrients (Reever Morghan & Seastedt 1999; Tilman et al. 1999; Perry et al. 2004). 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.
To be summarized as evidence for this action, studies must have added mulch that is largely free from plant propagules. The mulch should be used to help or manage existing vegetation, such as remnant patches of vegetation, or seedlings that germinate from seeds already present.
Baldwin D. (2011) National Guidance for the Management of Acid Sulfate Soils in Inland Aquatic Ecosystems, Environment Protection and Heritage Council and the Natural Resource Management Ministerial Council, Australia.
Perry L.G., Galatowitsch S.M. & Rosen C.J. (2004) Competitive control of invasive vegetation: a native wetland sedge suppresses Phalaris arundinacea in carbon-enriched soil. Journal of Applied Ecology, 41, 151–162.
Reever Morghan K.J. & Seastedt T.R. (1999) Effects of soil nitrogen reduction on nonnative plants in restored grasslands. Restoration Ecology, 7, 51–55.
Tilman E.A., Tilman D., Crawley M.J. & Johnston A.E. (1999) Biological weed control via nutrient competition: potassium limitation of dandelions. Ecological Applications, 9, 103–111.
Supporting evidence from individual studies
A replicated, paired, controlled study in 1999–2001, aiming to create a saltmarsh on a lagoon sandflat in New South Wales, Australia (Chapman & Roberts 2004) found that mulched plots were more likely to contain glasswort Sarcocornia quinqueflora than unmulched plots, but that mulching typically had no significant effect on glasswort biomass, glasswort cover or plant species richness (because of high variability between plots). After 20 months, glasswort was present in a significantly greater proportion of mulched plots (89%) than unmulched plots (56%). However, above-ground glasswort biomass was statistically similar in mulched (9–19 g/units not clear) and unmulched plots (8–11 g/units not clear). Over the two years following intervention, glasswort cover was statistically similar under each treatment in 6 of 10 comparisons (for which mulched: 4–43%; unmulched: 4–19%). In the other comparisons, mulching either increased glasswort cover or had variable effects across the site (see original paper). Meanwhile, plant species richness was similar under each treatment in 11 of 11 comparisons (mulched: 1–4 species/4 m2; unmulched: 1–3 species/4 m2). Methods: In October 1999, forty 4-m2 plots were established (in two sets of 20) on almost-bare sediment next to a patchy salt marsh. Twenty plots (10 plots/set) were mulched with seagrass and seaweed (5–10 cm layer). Mulch was reapplied when it thinned or was blown away. Plant species and cover were surveyed 10–11 times over two years after mulching. In June 2001, glasswort shoots were cut from 12 plots, then air-dried and weighed. Roughly half way through the study, some plots were damaged by motorbike riders (further details not reported).Study and other actions tested