Add below-ground organic matter before/after planting trees/shrubs: freshwater wetlands

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

Study locations

Key messages

  • One study evaluated the effects, on vegetation, of adding below-ground organic matter to freshwater wetlands planted with trees/shrubs. The study was in the USA.


  • Community composition (1 study): One replicated, randomized, paired, controlled study in a created wetland in the USA found that amongst plots planted with tree seedlings, those amended with large amounts compost contained a plant community characteristic of drier conditions, three years later, than the community in unamended plots. The lowest compost dose had no significant effect on this outcome.
  • Overall richness/diversity (1 study): The same study found that amongst plots planted with tree seedlings, those amended with a large amount of compost had lower plant species richness and diversity, three years later, than unamended plots. Lower compost doses had no significant effect on either outcome.


  • Overall abundance (1 study): One replicated, randomized, paired, controlled study in a created wetland in the USA found that amongst plots planted with tree seedlings, those amended with compost supported a similar overall vegetation biomass, three years later, to unamended plots.


  • Individual plant size (1 study): One replicated, randomized, paired, controlled study in a created wetland in the USA found that birch Betula saplings were larger, three years after planting seedlings, in plots amended with large amounts of compost than in unamended 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

  1. A replicated, randomized, paired, controlled study in 2002–2005 in a created freshwater wetland in Virginia, USA (Bailey et al. 2007) found that the effects of adding organic matter to plots planted with tree saplings depended on the dose added. Four different doses of organic matter were used. After approximately three years, plots receiving the three highest doses contained a plant community characteristic of drier – but still wetland – conditions than unamended plots (data reported as a wetland indicator index). In plots receiving the two highest doses, birch Betula spp. saplings were significantly larger than in unamended plots (size calculated as an index combining height, stem diameter and crown diameter; data not reported). Plots receiving the highest dose had lower plant species richness (5.3 species/m2) than unamended plots (7.4 species/m2). The same was true for plant diversity (data reported as a diversity index). In all other comparisons, there were no significant differences between amended and unamended plots (see original paper for data). Further, at all four doses, above-ground vegetation biomass did not significantly differ between amended plots (580–790 g/m2) and unamended plots (604 g/m2). Methods: In June 2002, twenty 14-m2 plots were established, in four sets of five, on an 8-year-old created wetland. All plots were cleared and tilled. In July, organic matter (dry wood and garden compost) was mixed into the surface of 16 plots (four random plots/set, each with a different dose: 56, 112, 224 or 336 Mg/ha). The remaining four plots (one random plot/set) received no organic matter. In December 2002, ten saplings (five birch, five pin oak Quercus palustris) were planted in each plot and fertilized. Vegetation was surveyed in 2005. Plant species and cover were recorded monthly April–October. Surviving birch saplings were counted in June. Vegetation samples were cut in August, then dried and weighed.

    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?

List of journals searched by synopsis

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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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