Add surface mulch: brackish/salt marshes

How is the evidence assessed?
  • Effectiveness
  • Certainty
  • Harms

Study locations

Key messages

  • One study evaluated the effects, on vegetation, of using organic mulch to restore or create brackish/salt marshes. The study was in Australia.


  • Overall richness/diversity (1 study): One replicated, paired, controlled study on a sandflat in Australia found that mulched and unmulched plots had similar plant species richness over two years.


  • Herb abundance (1 study): One replicated, paired, controlled study on a sandflat in Australia found that mulched plots were more likely to contain glasswort Sarcocornia quinqueflora than unmulched plots, after 20 months. However, mulching had no significant effect on glasswort biomass after 20 months, and typically had no significant effect on glasswort cover over two years.


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

  1. 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
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?

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Marsh and Swamp Conservation

This Action forms part of the Action Synopsis:

Marsh and Swamp Conservation
Marsh and Swamp Conservation

Marsh and Swamp Conservation - Published 2021

Marsh and Swamp Synopsis

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