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

Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 1
Share Tweet Email

View assessment score

How is the evidence assessed?

Effectiveness

40%
Certainty

30%
Harms

1%

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 brackish/saline wetlands planted with emergent, non-woody plants. The study was in Canada.

VEGETATION COMMUNITY

VEGETATION ABUNDANCE

Overall abundance (1 study): One replicated, randomized, paired, controlled study in intertidal brackish marshes in Canada found that adding surface mulch after planting wetland herbs typically had no significant effect on total live vegetation biomass, two growing seasons later.
Individual species abundance (1 study): The same study found that adding surface mulch increased the cover of one of two planted herb species (creeping alkaligrass Puccinellia phryganodes) but had no significant effect on cover of the other species (estuary sedge Carex subspathacea). Cover was monitored over the second growing season after planting/mulching.

VEGETATION STRUCTURE

OTHER

Survival (1 study): One replicated, randomized, paired, controlled study in intertidal brackish marshes in Canada found that adding surface mulch had no significant effect on the survival of two of two planted herb species, after two growing seasons.

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 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
Referenced paper
Handa I.T. & Jeffries R.L. (2000) Assisted revegetation trials in degraded salt-marshes. Journal of Applied Ecology, 37, 944-958.

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	Category
Remove vegetation that could compete with planted trees/shrubs: brackish/saline wetlands Action Link	No evidence found (no assessment)	Synopsis Link
Actively manage water level before/after planting non-woody plants: brackish/saline wetlands Action Link	No evidence found (no assessment)	Synopsis Link
Add cover other than mulch before/after planting non-woody plants: brackish/saline wetlands Action Link	No evidence found (no assessment)	Synopsis Link