Add surface mulch before/after planting non-woody plants: freshwater wetlands

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

Effectiveness

50%
Certainty

30%
Harms

0%

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 emergent, non-woody plants. The study was in Australia.

VEGETATION COMMUNITY

VEGETATION ABUNDANCE

Herb abundance (1 study): One replicated, randomized, paired, controlled study in floodplain swamps in Australia found that mulching with woodchips before planting native understory herbs either increased or 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 native understory herbs reduced the cover of one problematic species (common reed Phragmites australis) one year later, but had no significant effect on another (reed canarygrass Phalaris arundinacea).

VEGETATION STRUCTURE

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 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
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
Disturb soil/sediment surface before planting trees/shrubs: freshwater wetlands Action Link	No evidence found (no assessment)	0	Synopsis Link
Add cover other than mulch before/after planting trees/shrubs: freshwater wetlands Action Link	Unknown effectiveness (limited evidence)	1	Synopsis Link
Use fences or barriers to protect brackish/saline wetlands planted with non-woody plants Action Link	No evidence found (no assessment)	0	Synopsis Link