Use cutting to control problematic large trees/shrubs: freshwater marshes

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

Effectiveness

60%
Certainty

32%
Harms

10%

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

Two studies evaluated the effects, on vegetation, of cutting down problematic large trees/shrubs in freshwater marshes. One study was in the UK and one was in the USA.

VEGETATION COMMUNITY

Overall extent (1 study): One study of a dune slack in the UK reported an increase in total vegetation coverage between one and two years after clearing scrub (by cutting and applying herbicide).
Overall richness/diversity (1 study): The same study reported a small increase in total plant richness between one and two years after clearing scrub (by cutting and applying herbicide).
Characteristic plant richness/diversity (1 study): The same study reported an increase in the number of slack-characteristic plant species present between one and two years after clearing scrub (by cutting and applying herbicide).
Native/non-target richness/diversity (1 study): The same study reported an increase in native plant richness between one and two years after clearing scrub (by cutting and applying herbicide).

VEGETATION ABUNDANCE

Individual species abundance (1 study): One study quantified the effect of this action on the abundance of individual plant species, other than the species being controlled. The site comparison study in the USA found that tussock sedge Carex stricta was less dense in a wet meadow restored by removing trees (along with other interventions, including planting sedges) than in nearby natural meadows, after 11–14 years.

VEGETATION STRUCTURE

Height (1 study): One site comparison study in the USA reported that sedge tussocks were shorter in a wet meadow restored by removing trees (along with other interventions, including planting sedges) than in nearby natural meadows, after 11–14 years.
Diameter/perimeter/area (1 study): The same study reported that sedge tussocks had a smaller perimeter in a wet meadow restored by removing trees (along with other interventions, including planting sedges) than in nearby natural meadows, after 11–14 years.
Basal area (1 study): The same study reported that the basal area of sedge tussocks was smaller in a wet meadow restored by removing trees (along with other interventions, including planting sedges) than in nearby natural meadows, after 11–14 years.

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 study in 2005–2007 of a dune slack in England, UK (Smith & Kimpton 2008) reported that after cutting grey willow Salix cinerea scrub (along with applying herbicide), ground vegetation recolonized. In 2006, approximately one year after removing willows, 80% of the site was covered with vegetation (mostly herbaceous). There were 108 vascular plant taxa, including 98 natives. Approximately 54 taxa were characteristic of dune slacks. In 2007, approximately two years after removing willows, 95% of the site was covered with vegetation (still mostly herbaceous). There were 111 vascular plant taxa, including 107 natives. Approximately 65 taxa were characteristic of dune slacks. Twenty-eight taxa recorded in 2006 were not present in 2007, but 31 new taxa had colonized the site. Methods: In November/December 2005, dense grey willow scrub in a dune slack (low-lying area amongst dunes) was controlled. Grey willows were cut at ground level, then herbicide (Roundup® Biactive Plus) was applied to the largest stumps. The study does not distinguish between the effects of these interventions. Cut material was burned on site. Vascular plant taxa and their overall coverage were surveyed in August/September 2006 and 2007.
Study and other actions tested
Referenced paper
Smith P.H. & Kimpton A. (2008) Effects of grey willow Salix cinerea removal on the floristic diversity of a wet dune-slack at Cabin Hill National Nature Reserve on the Sefton Coast, Merseyside, England. Conservation Evidence, 5, 6-11.
A site comparison study in 2008 of five sedge meadows in Illinois and Wisconsin, USA (Lawrence & Zedler 2013) found that a meadow restored by removing trees (and excess sediment, then planting tussock sedge Carex stricta) – contained more but smaller sedge tussocks than nearby natural meadows after 11–14 years. In four of four comparisons, the restored meadow contained a greater density of sedge tussocks (8.4 tussocks/m²) than natural meadows (4.5–5.6 tussocks/m²). Sedge tussocks were also smaller in the restored meadow than in the natural meadows. This was true in four of four comparisons for height (restored: 5 cm; natural: 11–18 cm), perimeter (restored: 39 cm; natural: 51–82 cm) and volume (restored: 560 cm³; natural: 2,342–6,604 cm³). The basal area of tussocks in the restored meadow was only 0.07 m²/m², compared to 0.12–0.23 m²/m² in the natural meadows (statistical significance not assessed). Methods: In 2008, sedge tussocks were surveyed in one restored and four natural sedge meadows (15–30 quadrats/meadow, each 1 m²). The restored meadow was formerly a wooded floodplain. Trees and accumulated sediment were removed, then plugs of tussock sedge planted 30 cm apart, between 1994 and 1997. The study does not distinguish between the effects of these interventions on any non-planted sedges.
Study and other actions tested
Referenced paper
Lawrence B.A. & Zedler J.B. (2013) Carbon storage by Carex stricta tussocks: a restorable ecosystem service? Wetlands, 33, 483-493.

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
Physically remove problematic plants: brackish/saline swamps Action Link	No evidence found (no assessment)	0	Synopsis Link
Use prescribed fire to control problematic plants: brackish/saline swamps Action Link	No evidence found (no assessment)	0	Synopsis Link
Use cutting/mowing to control problematic herbaceous plants: freshwater swamps Action Link	Unknown effectiveness (limited evidence)	2	Synopsis Link