Remove vegetation that could compete with planted 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

50%
Certainty

25%
Harms

0%

Calculating overall effectiveness category

Background information and definitions

Removing other plants before or after planting desirable marsh or swamp plants could reduce competition for space, light and nutrients. Survival and growth of planted vegetation may be improved. Note that abundant competitors, and/or the absence of the vegetation to be introduced, could be symptoms of inappropriate physical conditions that may also need to be managed. Also note that existing vegetation may help to protect planted vegetation from extreme temperatures and sunlight, and protect the wetland surface from erosion.

To be clear, this action includes various specific actions that remove undesirable plants (e.g. physical removal, mowing, herbicide application) or kill undesirable seeds (e.g. burning, covering the soil with black plastic) in areas planted with desirable marsh or swamp plants. Management might be one-off or continuous. Evidence summarized for this action focuses on responses of the planted vegetation; studies that report responses of other vegetation are included in separate interventions elsewhere on this site.

Related actions: Introduce nurse plants before/after planting target marsh or swamp vegetation.

Study locations

Key messages

One study evaluated the effects, on emergent non-woody vegetation planted in brackish/saline wetlands, of removing competing plants. The study was in the USA.

VEGETATION COMMUNITY

VEGETATION ABUNDANCE

VEGETATION STRUCTURE

OTHER

Germination/emergence (1 study): One replicated, randomized, paired, controlled study in an estuarine salt marsh in the USA found that thinning cover of the dominant plant before sowing dwarf saltwort Salicornia bigelovii seeds had no significant effect on saltwort seedling density, over the following two months.
Survival (1 study): The same study found that thinning the dominant plant increased the survival rate of dwarf saltwort Salicornia bigelovii transplants over the first six months after planting.

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 thinning dominant pickleweed Salicornia virginica before sowing/planting dwarf saltwort Salicornia bigelovii did not significantly affect the density of saltwort seedlings, but did increase survival of planted saltwort. Two months after sowing/planting, the total density of saltwort seedlings did not significantly differ between thinned and unthinned plots (data not reported). However, after six months, the survival rate of planted saltwort seedlings was 2.4 times greater in thinned than unthinned plots (further data not reported). 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. In 36 plots (12 random plots/set), pickleweed had been thinned (stems cut and removed) to leave roughly 50% cover. The other plots were left unthinned (>75% pickleweed cover). Pickleweed cover remained lower in thinned than unthinned plots throughout the growing season. Half of the plots had also been lowered slightly (5–10 cm). 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
Add cover other than mulch before/after planting non-woody plants: freshwater wetlands Action Link	Unknown effectiveness (limited evidence)	1	Synopsis Link
Add cover other than mulch before/after planting non-woody plants: brackish/saline wetlands Action Link	No evidence found (no assessment)	0	Synopsis Link
Add upland topsoil before/after planting trees/shrubs: brackish/saline wetlands Action Link	No evidence found (no assessment)	0	Synopsis Link