Physically remove problematic plants: freshwater marshes
Overall effectiveness category Likely to be beneficial
Number of studies: 5
Background information and definitions
This action considers complete physical removal of problematic plants, i.e. pulling up or digging up entire plants, or scraping living vegetation from the marsh surface. Removal may be targeted to individual organisms, or applied to the whole plant community. The most appropriate removal method will depend on the species to be removed, and the site conditions (e.g. Tobias et al. 2016).
If plants are completely removed, including roots where applicable, immediate regrowth will be prevented (although long-term recolonization from the seed bank or from neighbouring sites is possible). For some species, disposing of the problem plants off-site may help to prevent regrowth, but disposal should be done carefully to avoid causing an invasion elsewhere (Stevens et al. 1997).
For this action, “vegetation” refers to overall or non-target vegetation. Studies that only report responses of target problematic plants have not been summarized.
Related actions: Remove surface soil/sediment, including any plants on it.
Stevens K.J., Peterson R.L. & Stephenson G.R. (1997) Vegetative propagation and the tissues involved in lateral spread of Lythrum salicaria. Aquatic Botany, 56, 11–24.
Tobias V.D., Block G. & Laca E.A. (2016) Controlling perennial pepperweed (Lepidium latifolium) in a brackish tidal marsh. Wetlands Ecology and Management, 24, 411–418.
Supporting evidence from individual studies
A before-and-after, site comparison study in 1984–1986 in an ephemeral freshwater marsh invaded by knotgrass Paspalum distichum in northwest India (Middleton et al. 1991) reported that an area cleared of vegetation developed similar vegetation cover to uncleared areas within nine months, but with different dominant species. Statistical significance was not assessed. Before intervention, the marsh had 69–70% total vegetation cover, 49–51% cover of knotgrass, <1% cover of water snowflake Nymphoides indicum and 2–4% cover of algae. After nine months, and at the same time of year, cleared areas had developed 68% total vegetation cover. This included <1% knotgrass cover, 29% water snowflake cover and 24% algal cover. Meanwhile, uncleared areas had 64% total vegetation cover, 49% knotgrass cover, 1% water snowflake cover and 6% algae cover. Methods: In June 1985, knotgrass-invaded vegetation was cleared, using bulldozers, from a marshy area in Keoladeo National Park. Comparable estimates of vegetation cover were made before clearance (March 1984 and 1985; ≥638 quadrats across whole marsh in each survey) and after clearance (March 1986; 55 quadrats in cleared area and ≥638 quadrats across rest of marsh). All quadrats were 1 m2.Study and other actions tested
A replicated, randomized, paired, controlled, before-and-after study in 1988–1991 in two wet meadows invaded by purple loosestrife Lythrum salicaria in New York State, USA (Morrison 2002) found that physically removing all vegetation had no significant effect on vegetation richness, diversity or overall cover three years later, but increased cover of grass-like plants and reduced cover of forbs. After three years and in both meadows, cleared and uncleared plots had statistically similar plant species richness (cleared: 8; uncleared: 7–8 species/m2), plant diversity (data reported as a diversity index) and overall vegetation cover (cleared: 79%; uncleared: 78–117%). However, cleared plots were dominated by grass-like plants (73–74% cover) and had little cover of forbs (overall: 6–9%; purple loosestrife: 2%), whereas uncleared plots had little cover of grass-like plants (26–39%) and had high cover of forbs (overall: 41–92%; purple loosestrife: 31–78%). Note that these differences were only statistically significant in one of the two meadows. For data on the cover of other individual plant species, see original paper. Before intervention and within each meadow, plots destined for each treatment had statistically similar total vegetation cover (99–153%), plant species richness (8–10 species/m2). plant diversity, grass-like plant cover (11–67%) and loosestrife cover (18–82%). In one meadow, overall forb cover was lower in plots destined for clearance (25%) than plots not destined for clearance (121%). Methods: In 1988, six pairs of 1-m2 plots were established across two loosestrife-invaded wet meadows. In September, all vegetation was dug up and removed from one random plot in each pair. These plots were also used in (3). Vegetation was not removed from the other plots. Plant species and their cover were surveyed before removal (August 1988) and three years after (September 1991).Study and other actions tested
A replicated, randomized, paired, controlled, before-and-after study in 1988–1991 in two wet meadows that had been cleared of vegetation in New York State, USA (Morrison 2002) found that controlling regrowth of invasive purple loosestrife Lythrum salicaria (by pulling up seedlings and applying herbicide to large shoots) had no significant effect on plant species richness, diversity or vegetation cover. After three years, plots with and without control of loosestrife regrowth had statistically similar plant species richness (control: 7; no control: 8 species/m2), plant diversity (data reported as a diversity index), total vegetation cover (control: 67–82%; no control: 79%), grass-like plant cover (control: 60–75%; no control: 70–73%) and forb cover (control: 5–20%; no control: 8–10%). Purple loosestrife cover was 0% in plots where regrowth had been controlled, but still only 2% in plots where regrowth had not been controlled. For data on the cover of other individual plant species, see original paper. Before intervention and within each meadow, plots destined for each treatment had statistically similar plant species richness (8–9 species/m2), plant diversity, total vegetation cover (103–143%), grass-like plant cover (16–58%), forb cover (25–56%) and purple loosestrife cover (23–63%). Methods: In 1988, six pairs of 1-m2 plots were established across two loosestrife-invaded wet meadows. In September, all vegetation was dug up and removed from the plots. In six of the plots (one random plot/pair), loosestrife regrowth was controlled twice/year thereafter (pulling up seedlings and painting large shoots with glyphosate; the study does not distinguish between the effects of these interventions). In the other plots loosestrife regrowth was not controlled. These plots were also used in (2). Plant species and their cover were surveyed before initial removal (August 1988) and three years after (September 1991).Study and other actions tested
A controlled, before-and-after study in 2001–2003 in an ephemeral freshwater wetland dominated by compact rush Juncus conglomeratus in southern France (Félisiak et al. 2004) reported that removing the vegetation increased the number of plant species characteristic of Mediterranean temporary marshes over the following two years. Statistical significance was not assessed. The number of characteristic plant species increased in stripped plots, from zero in the year before intervention to 3–4 in the two years after (units not reported). The number of characteristic plant species was relatively stable in unmanaged plots (before: 2–4; after: 3–6). Methods: Four plots were established in rush-dominated vegetation near a reservoir. In autumn 2001, one plot was stripped of vegetation (including the root mat), exposing bare soil. The other three plots were left undisturbed. Plant species were recorded in the year before intervention (2001) and for two years after (2002 and 2003).An example of management by removalStudy and other actions tested
Referenced paperFélisiak D., Duborper E. & Yavercovski N. (2004) An example of management by removal of vegetation: lac des Aurèdes (Var, France). Pages 84pp in: P. Grillas, P. Gauthier, N. Yavercovski & C. Perennou (eds.) Mediterranean Temporary Pools Volume 1 – Issues Relating to Conservation, Functioning and Management. Station Biologique de la Tour du Valat, Arles.
A replicated, randomized, paired, controlled, before-and-after study in 2011–2013 in a freshwater marsh invaded by hybrid cattail Typha x glauca in Michigan, USA (Lishawa et al. 2015) found that physically removing the cattail-dominated vegetation changed the plant community composition and increased plant species richness and diversity. In the two years following vegetation removal, the overall plant community composition significantly differed between cleared and uncleared plots (data reported as a graphical analysis). Cleared plots had lower relative cover of hybrid cattail (cleared: 21–26%; uncleared: 87% of total cover). They also contained less hybrid cattail biomass (cleared: 29–51; uncleared: 500–700 g/m2). In both years, cleared plots contained more plant species (cleared: 13–14; uncleared: 8 species/16 m2) and had greater plant diversity (reported as a diversity index). Before intervention, plots destined for each treatment contained statistically similar plant communities with similar relative cover of cattail (84–87%), cattail biomass (data not reported), species richness (5–7 species/16 m2) and diversity. Methods: Sixteen 4-m2 plots were established in two areas of a freshwater marsh that had been invaded by hybrid cattail (one for >30 years, one for <20 years). In August 2011, vegetation was removed from eight plots (four random plots/area): vegetation was cut and removed, then rhizomes (underground horizontal stems) were dug up and removed. No vegetation was removed from the other eight plots. Roots and rhizomes were cut around the edge of each plot. Vegetation was surveyed in July before (2011) and for two years after (2012–2013) intervention. Dry above-ground biomass was estimated, after intervention only, from the height of cattail stems.Study and other actions tested