Transplant wetland soil before/after planting non-woody plants: freshwater wetlands

Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 2
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How is the evidence assessed?

Effectiveness

56%
Certainty

33%
Harms

0%

Calculating overall effectiveness category

Background information and definitions

Loose soil can be transplanted from a healthy marsh or swamp to a one that is being created or restored. Soil could simply be added to a recipient site, or be used to replace material in the recipient site. Soil transplants can be useful to introduce a chemically and physically suitable substrate for growth of wetland vegetation, and a mixture of soil organisms such as bacteria, fungi and invertebrates (Anderson & Cowell 2004). Thus, soil transplants might be used to aid the initial survival and growth of introduced marsh or swamp plants. Soil transplants usually also contain a mixture of wetland plant seeds, roots, tubers or rhizomes, which could supplement the focal introduced vegetation to create a diverse, wetland-characteristic plant community.

Caution: This action inevitably causes damage to any donor site. Also, transplanted soil could contain invasive plants, animals or microorganisms. A possible solution to these problems is to use soil from healthy marshes or swamps that are earmarked for destruction. Using local donor sites could minimize the spread of invasive species, and make use of communities adapted to local conditions.

Other published names for this action include “salvaged marsh surface replacement”, transplanting “seed banks” and “mulching”. We restrict the latter term to the addition of organic matter that is largely free of plant propagules, e.g. domestic compost or seaweed, to the ground surface.

Related actions: Transplant or replace wetland soil, other than to complement planting; Add upland topsoil before/after planting.

^{Anderson C.J. & Cowell B.C. (2004) Mulching effects on the seasonally flooded zone of west-central Florida, USA wetlands. Wetlands, 24, 811–819.}

^{Brown S.C. & Bedford B.L. (1997) Restoration of wetland vegetation with transplanted wetland soil: an experimental study. Wetlands, 17, 424–437.}

Study locations

Key messages

Two studies evaluated the effects, on vegetation, of transplanting wetland soil to freshwater wetlands planted with emergent, non-woody plants. One study was in the USA and one was in Canada.

VEGETATION COMMUNITY

Community composition (1 study): One replicated, site comparison study of created freshwater marshes in the USA found that those amended with marsh soil developed plant communities characteristic of wetter conditions than unamended marshes. Most marshes had also been planted. All were ≥5 years old.
Overall richness/diversity (1 study): The same study found that marshes amended with marsh soil had similar (dry season) or lower (wet season) plant species richness and diversity to unamended marshes. Most marshes had also been planted. All were ≥5 years old.

VEGETATION ABUNDANCE

Overall abundance (1 study): One replicated, site comparison study of created freshwater marshes in the USA reported that amongst planted marshes, adding marsh soil had no significant effect on overall vegetation cover or biomass, after ≥5 years.
Characteristic plant abundance (1 study): One replicated, site comparison study of created freshwater marshes in the USA reported that amongst planted marshes, those also amended with marsh soil had greater cover of wetland-characteristic plants than unamended marshes, after ≥5 years.
Individual species abundance (1 study): One replicated, randomized, paired, controlled study in freshwater trenches in Canada found that adding peat-rich soil to pots of mine tailings before planting water sedge Carex aquatilis typically increased its above-ground biomass two growing seasons later.

VEGETATION STRUCTURE

OTHER

Survival (1 study): One replicated, randomized, paired, controlled study in freshwater trenches in Canada found that adding peat-rich soil to pots of mine tailings either increased or had no significant effect on survival of planted water sedge Carex aquatilis over 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, site comparison study in 1999–2000 of the ephemeral marsh zone in 33 created freshwater wetlands in Florida, USA (Anderson & Cowell 2004) found that adding marsh soil before planting marsh vegetation created a plant community characteristic of wetter conditions and had season-specific effects on plant species richness and diversity, but had no significant effect on overall vegetation abundance. Whilst amended and unamended marshes both developed a wetland-characteristic plant community, the community in amended marshes was characteristic of significantly wetter conditions (data reported as a wetland indicator index). Amended marshes had 44–75% cover of wetland-characteristic plants (vs unamended marshes: 32–58%; statistical significance not assessed). In the wet season, plant species richness and diversity were similar or lower in amended marshes than unamended marshes (amended: 9; unamended: 11 species/m²; and diversity reported as an index). In the dry season, these metrics were similar or higher in amended marshes than unamended marshes (amended: 8; unamended: 7 species/m²; diversity reported as an index). Both treatments had statistically similar overall vegetation cover (amended: 54–83%; unamended: 49–76%) and above-ground biomass (amended: 87; unamended: 80 g/m²). Cover of plant groups (e.g. grasses/reeds, mosses, and tree/shrub seedlings) was generally similar in amended and unamended marshes (see original paper for data). Methods: Vegetation was surveyed in the marshy, seasonally flooded zone of 33 excavated wetlands (≥5 years old). All but one wetland had been planted with marsh vegetation (details not reported). Marsh soil had been spread on the surface of 17 of the sites, in a layer 15–30 cm thick. In November 1999 (wet season) and June 2000 (dry season), plant species and cover were recorded in three 1-m² quadrats/marsh. In August 2000, vegetation was cut from three 0.25-m² quadrats/marsh, then dried and weighed.
Study and other actions tested
Referenced paper
Anderson C.J. & Cowell B.C. (2004) Mulching effects on the seasonally flooded zone of west-central Florida, USA wetlands. Wetlands, 24, 811-819.
A replicated, randomized, paired, controlled study in 2010–2011 in six experimental wetland trenches in Alberta, Canada (Roy et al. 2014) found that adding peat-rich soil to mine tailings did not reduce survival of planted water sedge Carex aquatilis over two growing seasons, and typically increased the biomass of surviving sedges. In two of four comparisons, pots of mine tailings mixed with peat-rich soil supported higher sedge survival (50–67%) than pots of raw mine tailings (24–44%). There was no significant difference between treatments in the other two comparisons (added peat: 74%; raw tailings: 54–69%). In three of four comparisons, the above-ground biomass of surviving sedges was higher in pots of mine tailings mixed with peat-rich soil (2.1–2.8 g/trench) than in pots of raw mine tailings (1.1–1.5 g/trench). There was no significant difference between treatments in the other comparisons (added peat: 2.2 g/trench; raw tailings: 2.2 g/trench). Methods: In June 2010, water sedges were collected from a natural marsh and randomly planted into 192 one-gallon pots (number of plants/pot not clearly reported). Half of the pots contained mine tailings mixed with peat-rich soil (1:2 parts). Half of the pots contained pure mine tailings (dense sediments, low in organic matter, rich in salts and metals). The pots were placed into six experimental wetland trenches: 16 peaty pots and 16 raw tailings pots/trench. Surviving plants were harvested at the end of the 2011 growing season. Biomass was dried before weighing.
Study and other actions tested
Referenced paper
Roy M.-C., Mollard F.P.O. & Foote A.L. (2014) Do peat amendments to oil sands wet sediments affect Carex aquatilis biomass for reclamation success? Journal of Environmental Management, 139, 154-163.

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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This Action forms part of the Action Synopsis:

Marsh and Swamp Conservation

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