Use cutting to control problematic large trees/shrubs: brackish/salt marshes

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

Effectiveness

60%
Certainty

30%
Harms

0%

Calculating overall effectiveness category

Background information and definitions

This action involves cutting off above-ground parts of mature shrubs and trees: plants that are too large to mow. Note that vegetation may resprout from roots or stumps that are left in place. Cutting may be done manually or with machinery, depending on the species to be cut and the site conditions. Cuttings may be removed from the site, or left in place to rot down.

Locally, it may be desirable to remove all trees/shrubs from open marshes to prevent them from developing into swamps. However, note that encroachment of woody vegetation into marshes may be necessary for habitat migration and conservation of swamps at a regional or global scale (Saintilan et al. 2014). Within swamps, it may be desirable to remove individual trees/shrubs to maintain the vegetation structure or composition.

For this action, “vegetation” refers to overall or non-target vegetation. Studies that only report responses of target problematic plants have not been summarized.

^{Saintilan N., Wilson N.C., Rogers K., Rajkaran A., & Krauss K.W. (2014) Mangrove expansion and salt marsh decline at mangrove poleward limits. Global Change Biology, 20, 147–157.}

Study locations

Key messages

One study evaluated the effects, on vegetation, of cutting down problematic large trees/shrubs in brackish/salt marshes. The study was in the USA.

VEGETATION COMMUNITY

Community composition (1 study): One controlled, before-and-after study in a salt marsh in the USA reported that in seven of nine cases, the overall plant community composition varied more across plots from which mangrove trees had been removed than a plot from which mangrove trees had not been removed. Vegetation was surveyed after two years of continual tree removal.

VEGETATION ABUNDANCE

Overall abundance (1 study): One controlled, before-and-after study in a salt marsh in the USAreported that removing >50% of invading mangrove trees increased total cover of salt marsh vegetation two years later, but that removing <50% of invading mangrove trees had no clear effect.

VEGETATION STRUCTURE

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 controlled, before-and-after study in 2012–2014 in a salt marsh colonized by mangrove trees in Texas, USA (Guo et al. 2017) reported that clearing patches of mangrove vegetation increased cover of salt marsh vegetation (when >50% was cleared) and increased variation in plant community composition (when any amount was cleared). Statistical significance was not assessed. Before intervention, all plots were dominated by black mangrove Avicennia germinans, with <1–19% total cover of salt marsh plant species. After two years, plots where more than half of the mangrove vegetation had been cleared developed greater total cover of salt marsh plant species (28–80%) than an uncleared plot (16%). Plots where less than half of the mangrove vegetation had been cleared retained similar total cover of salt marsh plant species (3–21%) to the uncleared plot. In seven of nine cleared plots, the variation in plant community composition between quadrats was greater than in the uncleared plot – with particularly high variation when 80–90% of the mangrove vegetation was cleared (data reported as a similarity index). Methods: Ten 1,008-m² plots were established in a degraded coastal salt marsh. In summer 2012, mangrove trees were cut and removed from a variable number of 9-m² cells within each plot, leaving 0–100% of the mangrove vegetation remaining. The cells were re-cut every 3–4 months. Cover of every plant species was visually estimated along a transect (1 m wide) spanning the length of each plot, before mangrove cutting began (June 2012) and approximately two years after (August 2014).
Study and other actions tested
Referenced paper
Guo H., Weaver C., Charles S.P., Whitt A., Dastidar S., D'Odorico P., Fuentes J.D., Kominoski J.S., Armitage A.R. & Pennings S.C. (2017) Coastal regime shifts: rapid responses of coastal wetlands to changes in mangrove cover. Ecology, 98, 762-772.

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

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