Remove vegetation that could compete with planted non-woody plants: freshwater wetlands

Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 3
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How is the evidence assessed?

Effectiveness

40%
Certainty

35%
Harms

3%

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

Three studies evaluated the effects, on emergent non-woody vegetation planted in freshwater wetlands, of removing competing plants. All three studies were in the USA. Two studies used the same experimental wet basins but planted different species.

VEGETATION COMMUNITY

VEGETATION ABUNDANCE

Herb abundance (1 study): One replicated, randomized, paired, controlled study in wet meadows in the USA found removing an invasive species with herbicide before sowing mixed grass and forb seeds increased the total biomass of sown species after 1–2 growing seasons, but that burning to remove the invasive species had no significant effect on sown species biomass.
Individual species abundance (1 study): One replicated, paired, controlled study in wet basins in the USA found that the effect of weeding to remove competitors on lake sedge Carex lacustris biomass and density, in the three years after planting, depended on the year and water level.

VEGETATION STRUCTURE

Height (2 studies): Two replicated, paired, controlled studies in wet basins in the USA examined the effect of weeding to remove competitors on the height of planted sedges. One of the studies found that weeding had no significant effect on the height of planted tussock sedge Carex stricta in three of three years. The other study found that weeding reduced the average height of lake sedge Carex lacustris in the first year after planting, but had no significant effect in the following two years.

OTHER

Survival (2 studies): Two replicated, paired, controlled studies in wet basins in the USA examined the effect of weeding to remove competitors on the survival of planted sedges Carex spp. Both studies found that weeding had no significant effect on sedge survival in at least two of three years. One of the studies found that weeding affected tussock sedge Carex stricta survival in the second year after planting, but that the direction of the effect depended on plot elevation.

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, before-and-after study in 1995–1997 in three recently excavated wet basins in Minnesota, USA (Budelsky & Galatowitsch 2000) found that weeding to remove competitors had no significant effect on survival of planted lake sedge Carex lacustris, but that effects on sedge abundance and height depended on other factors. The study generally does not report data for the comparisons in this summary. In each of three years, the survival rate of planted sedges was statistically similar in weeded and unweeded plots. The effect of weeding on sedge above-ground biomass, stem density and height depended on time since planting, elevation and/or water regime. For example, in all three years, weeding increased sedge biomass/m² in higher/drier plots but had no significant effect in lower, wetter plots. The average height of sedge shoots was lower in weeded than unweeded plots in the first year, but there was no significant difference between treatments in the second and third years. Methods: Forty-eight 5-m² plots were established, in 12 sets of four, across three wet basins (same as in Study 2). In May 1995, nursery-reared lake sedge was planted into each bare plot (10 or 45 plants/plot). Twenty-four plots (2 plots/set) were weeded (colonizing plants removed) throughout the study. The plots were situated at four different elevations, and each basin had a different water regime (falling, stable or rising through each growing season). Vegetation was surveyed through the 1995, 1996 and 1997 growing seasons.
Study and other actions tested
Referenced paper
Budelsky R.A. & Galatowitsch S.M. (2000) Effects of water regime and competition on the establishment of a native sedge in restored wetlands. Journal of Applied Ecology, 37.
A replicated, paired, controlled study in 1995–1997 in three recently excavated wet basins in Minnesota, USA (Budelsky & Galatowitsch 2004) found that weeding to remove competitors had no significant effect on the height of planted tussock sedge Carex stricta, and that effect on sedge survival depended on other factors. In each of three years, the height of planted sedges was statistically similar in weeded and unweeded plots (data not reported). Weeding had no significant effect on sedge survival in the first and third years after planting. In the second year, weeding increased planted sedge survival at high elevations (weeded: 100%; unweeded: 57%) but reduced sedge survival at low elevations (weeded: 38%; unweeded: 96%). The study also reported data on biomass/plant and shoot number/plant. The effect of weeding on these metrics depended on time since planting, elevation and/or water regime (see original paper). Methods: Forty-eight 5-m² plots were established, in 12 sets of four, across three wet basins (same as in Study 1). In May 1995, nursery-reared tussock sedge was planted into each bare plot (10 or 45 plants/plot). Twenty-four plots (2 plots/set) were weeded (colonizing plants removed) throughout the study. The plots were situated at four different elevations, and each basin had a different water regime (falling, stable or rising through each growing season). Vegetation was surveyed through the 1995, 1996 and 1997 growing seasons.
Study and other actions tested
Referenced paper
Budelsky R.A. & Galatowitsch S.M. (2004) Establishment of Carex stricta Lam. seedlings in experimental wetlands with implications for restoration. Plant Ecology (formerly Vegetatio 1948-1996), 175, 91-105.
A replicated, randomized, paired, controlled study in 2000–2004 in two wet meadows Minnesota, USA (Reinhardt Adams & Galatowitsch 2006) found that the effect of removing invasive reed canarygrass Phalaris arundinacea before sowing mixed grass and forbs seeds depended on the removal method. After 1–2 growing seasons, plots sprayed with herbicide contained more biomass of sown species (total: 0–70 g/m²) than unsprayed plots (total: 0 g/m²). Sprayed plots also contained less canarygrass biomass (10–480 g/m²) than unsprayed plots (420–880 g/m²). In contrast, burned plots contained a statistically similar overall biomass of sown species – and canarygrass – to unburned plots (data not reported). The pattern of results was the same for non-sown and total vegetation biomass (see Actions: Use prescribed fire to control problematic plants and Use herbicide to control problematic plants). Methods: In the early 2000s, one hundred and sixty 25-m² plots were established, in 40 sets of four, across two canarygrass-invaded wet meadows. One hundred and twenty plots (three random plots/set) were sprayed with herbicide (Roundup® Ultra): in May, August or September and in one or two years. Eighty plots (20 random sets) were burned in spring. Some plots therefore received neither, one, or both removal treatments. All plots were sown with a mixture of grass and forb seeds in the spring after the final removal treatment. Dry biomass samples were taken in August, 1–2 growing seasons after sowing.
Study and other actions tested
Referenced paper
Reinhardt Adams C. & Galatowitsch S.M. (2006) Increasing the effectiveness of reed canary grass (Phalaris arundinacea L.) control in wet meadow restorations. Restoration Ecology, 14, 441-451.

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
Actively manage water level before/after planting non-woody plants: brackish/saline wetlands Action Link	No evidence found (no assessment)	0	Synopsis Link
Actively manage water level before/after planting non-woody plants: freshwater wetlands Action Link	Unknown effectiveness (limited evidence)	3	Synopsis Link
Create mounds or hollows before planting non-woody plants: brackish/saline wetlands Action Link	Unknown effectiveness (limited evidence)	1	Synopsis Link