Remove plant litter: freshwater marshes

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

Effectiveness

50%
Certainty

30%
Harms

0%

Calculating overall effectiveness category

Background information and definitions

Accumulation of dead plant matter, or litter, can cause undesirable changes to marsh plant communities. Litter can affect temperature, light and nutrient availability (Weltzin et al. 2005) and act as a barrier to seedlings from below and seeds from above (Facelli & Pickett 1991). Litter removal may be necessary after abandonment or suppression of disturbance.

Caution: Litter accumulation is an important process in some wetlands, contributing organic matter to the soil. Where it is desirable to remove litter, removal by hand may cause less damage to soils and vegetation than using heavy machinery. Be aware that seeds of desirable plants may be removed along with the litter.

To be summarized as evidence for this action, studies must have examined the effect of litter removal alone (not, for example, the effect of removing litter from mown plots, or the combined effect of mowing and litter removal).

Related actions: Cut/mow herbaceous plants to maintain or restore disturbance and Use prescribed fire to maintain or restore disturbance, both of which could help to clear plant litter.

^{Facelli J.M. & Pickett S.T.A. (1991) Plant litter: its dynamics and effects on plant community structure. The Botanical Review, 57, 1–32.}

^{Weltzin J.F., Keller J.K., Bridgham S.D., Pastor J., Allen P.B. & Chen J. (2005) Litter controls plant community composition in a northern fen. Oikos, 110, 537–546.}

Study locations

Key messages

One study evaluated the effects, on vegetation, of removing plant litter from freshwater marshes. The study was in the USA.

VEGETATION COMMUNITY

Community composition (1 study): One replicated, paired, controlled study in rewetted marshes in the USA found that plots cleared of plant litter contained a plant community characteristic of wetter conditions than uncleared plots after one growing season – but not after two.
Overall richness/diversity (1 study): The same study found that plots cleared of plant litter contained a similar number of wetland plant species to uncleared plots, after 1–2 growing seasons.

VEGETATION ABUNDANCE

Overall abundance (1 study): One replicated, paired, controlled study in rewetted marshes in the USA found that plots cleared of plant litter had greater cover of wetland plants than uncleared plots after one growing season – but not after two.

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 replicated, paired, controlled study in 1992–1993 in five freshwater marshes undergoing restoration in New York State, USA (Brown & Bedford 1997) found that plots cleared of plant litter contained a more wetland-characteristic plant community and greater cover of wetland plant species than uncleared plots after one growing season, but that these effects disappeared after two growing seasons. After one growing season, cleared plots contained a plant community more characteristic of wetland conditions than uncleared plots (data reported as a wetland indicator index). Cleared plots also had greater total cover of wetland plants (cleared: 24%; uncleared: 19%). The number of wetland plant species did not significantly differ between treatments (cleared: 2.4; uncleared: 2.0 species/plot). After two growing seasons, all metrics were statistically similar under both treatments: community composition, wetland plant cover (cleared: 67%; uncleared: 54%) and wetland plant richness (cleared: 3.7; uncleared: 2.8 species/plot). Methods: In May 1992, twenty 0.25-m² plots were established across five recently rewetted sites (drained for ≥40 years previously). In five plots (one plot/site), all surface litter and plant stems were removed. Litter was left in the other 15 plots (three plots/site). Plant species and cover were recorded in autumn 1992 and 1993.
Study and other actions tested
Referenced paper
Brown S.C. & Bedford B.L. (1997) Restoration of wetland vegetation with transplanted wetland soil: an experimental study. Wetlands, 17, 424-437.

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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