Create mounds or hollows before planting non-woody plants: brackish/saline wetlands

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

Effectiveness

35%
Certainty

24%
Harms

13%

Calculating overall effectiveness category

Background information and definitions

This action involves creating discrete mounds (e.g. by adding blocks of soil, bundles of sticks, other coarse woody debris) or hollows (e.g. by excavation) before planting marsh or swamp vegetation. The scale of this action falls somewhere between reprofiling/relandscaping (large-scale landscape features, tens of metres wide) and disturbing the ground surface (which may create small scale mounds or hollows, millimetres or a few centimetres wide/deep).

Often, this action aims to mimic the natural microtopography of marshes or swamps, which can be created by sediment accumulation, erosion, tree fall, root growth or animal activity (Vivian-Smith 1997, Bruland & Richardson 2005). Microtopography can increase plant diversity, because the different microclimates or microelevations may support different species (Vivian-Smith 1997). Planting into mounds can be useful if seedlings would otherwise be flooded too deeply or for too long (Zamith & Scarano 2010). Large woody debris will also add nutrients and organic matter to a site as it decomposes.

Studies that examine the effects of planting into existing microtopographic features (e.g. mounds), even if they compare effects between different kinds of features, are not summarized as evidence here (e.g. Raulings et al. 2007; Sleeper & Ficklin 2016).

Related actions: Create mounds or hollows, other than to complement planting; Reprofile/relandscape before planting; Disturb soil/sediment surface before planting without creating discrete mounds and/or hollows.

^{Bruland G.L. & Richardson C.J. (2005) Hydrologic, edaphic, and vegetative responses to microtopographic reestablishment in a restored wetland. Restoration Ecology, 13, 515–523.}

^{Raulings E.J., Boon P.I., Bailey P.C., Roache M.C., Morris K. & Robinson R. (2007) Rehabilitation of swamp paperbark (Melaleuca ericifolia) wetlands in south-eastern Australia: effects of hydrology, microtopography, plant age and planting technique on the success of community-based revegetation trials. Wetlands Ecology and Management, 15, 175–188.}

^{Sleeper B.E. & Ficklin R.L. (2016) Edaphic and vegetative responses to forested wetland restoration with created microtopography in Arkansas. Ecological Restoration, 34, 117–123.}

^{Vivian-Smith G. (1997) Microtopographic heterogeneity and floristic diversity in experimental wetland communities. Journal of Ecology, 85, 71–82.}

^{Zamith L.R. & Scarano F.R. (2010) Restoration of a coastal swamp forest in southeastern Brazil. Wetlands Ecology and Management, 18, 435–448.}

Study locations

Key messages

One study evaluated the effects, on vegetation, of creating mounds or hollows in brackish/saline wetlands before planting emergent, non-woody plants. The study was in the USA.

VEGETATION COMMUNITY

VEGETATION ABUNDANCE

Individual species abundance (1 study): One replicated, randomized, paired, controlled study in an estuarine salt marsh in the USA found that amongst plots sown/planted with dwarf saltwort Salicornia bigelovii, those that had been excavated into depressions had lower cover of dominant pickleweed Salicornia virginica – over the first growing season – than plots left at ground level.

VEGETATION STRUCTURE

OTHER

Germination/emergence (1 study): One replicated, randomized, paired, controlled study in an estuarine salt marsh in the USA found that there were no more (sometimes fewer) dwarf saltwort Salicornia bigelovii seedlings in excavated depressions than in level plots, two months after sowing saltwort seeds.

Survival (1 study): The same study found that the survival rate of dwarf saltwort Salicornia bigelovii transplants was not greater (sometimes lower) in excavated depressions than in level 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

A replicated, randomized, paired, controlled study in 2006 in an estuarine salt marsh in California, USA (Varty & Zedler 2008) found that excavating depressions before sowing/planting dwarf saltwort Salicornia bigelovii did not increase saltwort seedling density or transplant survival, but did reduce density of the initially dominant succulent. Two months after sowing/planting, there were fewer dwarf saltwort seedlings in 10-cm depressions (3 seedlings/0.25 m²) than on level plots (10–14 seedlings/0.25 m²), with no significant difference between 5-cm depressions (9 seedlings/0.25 m²) and level plots. The same was true for survival of dwarf saltwort transplants after six months (10-cm depressions: <40%; 5-cm depressions: 70%; level plots: 70%). However, depressions had lower cover of pickleweed Salicornia virginica in 12 of 12 comparisons over the whole growing season (10-cm depressions: 41–59%; 5-cm depressions: 49–65%; level plots: 58–78%). Methods: In March 2006, dwarf saltwort was planted and sown into seventy-two 0.25-m² plots (three sets of 24) on a pickleweed-dominated salt marsh. Four seedlings and 1.25 ml of seed were added to each plot. Thirty-six plots (12 random plots/set) had been lowered by 5 cm or 10 cm before planting, by removing subsurface sediment. The other plots remained at ground level. Some pickleweed was cut and removed from half of the plots. Vegetation was surveyed between May and September 2006.
Study and other actions tested
Referenced paper
Varty A.K. & Zedler J.B. (2008) How waterlogged microsites help an annual plant persist among salt marsh perennials. Estuaries and Coasts, 31, 300-312.

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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This Action forms part of the Action Synopsis:

Marsh and Swamp Conservation

Related Actions

Actions	Effectiveness	Studies	Category
Remove vegetation that could compete with planted trees/shrubs: brackish/saline wetlands Action Link	No evidence found (no assessment)	0	Synopsis Link
Introduce nurse plants to aid focal non-woody plants: freshwater wetlands Action Link	Unknown effectiveness (limited evidence)	2	Synopsis Link
Remove vegetation that could compete with planted trees/shrubs: freshwater wetlands Action Link	Likely to be beneficial	5	Synopsis Link