Add surface mulch before/after planting trees/shrubs: freshwater wetlands

Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 1
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How is the evidence assessed?

Effectiveness

39%
Certainty

30%
Harms

3%

Calculating overall effectiveness category

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.

Related actions: Add surface mulch, other than to complement planting; Add cover other than mulch to complement planting.

Study locations

Key messages

One study evaluated the effects, on vegetation, of mulching freshwater wetlands planted with trees/shrubs. The study was in Australia.

VEGETATION COMMUNITY

VEGETATION ABUNDANCE

Tree/shrub abundance (1 study): One replicated, randomized, paired, controlled study in floodplain swamps in Australia found that mulching with woodchips before planting native shrubs had no significant effect on their overall cover, one year later.
Individual species abundance (1 study): The same study found that mulching with woodchips before planting swamp gum Eucalyptus camphora seedlings had no significant effect on swamp gum cover, one year later. Mulching reduced cover of the problematic herb species in one of two swamps, but had no significant effect in the other.

VEGETATION STRUCTURE

Height (1 study): One replicated, randomized, paired, controlled study in floodplain swamps in Australia found that planted swamp gum Eucalyptus camphora seedlings reached a similar height, after one year, in mulched and unmulched plots.

About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

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
Referenced paper
Greet J., King E. & Stewart-Howie M. (2016) Plastic weed matting is better than jute or woodchips for controlling the invasive wetland grass species Phalaris arundinacea, but not Phragmites australis. Plant Protection Quarterly, 31, 19-22.

Please cite as:

Taylor N.G., Grillas P., Smith R.K. & Sutherland W.J. (2021) Marsh and Swamp Conservation: Global Evidence for the Effects of Interventions to Conserve Marsh and Swamp Vegetation. Conservation Evidence Series Synopses. University of Cambridge, Cambridge, UK.

Where has this evidence come from?

List of journals searched by synopsis

All the journals searched for all synopses

This Action forms part of the Action Synopsis:

Marsh and Swamp Conservation

Related Actions

Actions	Effectiveness	Studies	Category
Use fences or barriers to protect freshwater wetlands planted with non-woody plants Action Link	Likely to be beneficial	4	Synopsis Link
Bury surface soil/sediment (before planting) Action Link	No evidence found (no assessment)	0	Synopsis Link
Add upland topsoil before/after planting non-woody plants: brackish/saline wetlands Action Link	No evidence found (no assessment)	0	Synopsis Link