Introduce nurse plants to aid focal non-woody plants: freshwater wetlands

How is the evidence assessed?
  • Effectiveness
    not assessed
  • Certainty
    not assessed
  • Harms
    not assessed

Study locations

Key messages

  • Two studies evaluated the effects, on vegetation, of introducing nurse plants to freshwater wetlands planted with emergent, non-woody plants. Both studies were on the same site in the USA, but used different experimental set-ups.

VEGETATION COMMUNITY

 

VEGETATION ABUNDANCE

  • Characteristic plant abundance (1 study): One replicated, randomized, paired, controlled, before-and-after study in an experimental wet basin in the USA found that sowing potential nurse plants alongside target sedge meadow species reduced the density of the target species overall, and of target grass-like species. Nurse plant addition sometimes affected the abundance of target forbs, depending on the presence of an invasive species and addition of sawdust to plots.
  • Individual species abundance (2 studies): Two replicated, randomized, paired, controlled, before-and-after studies in wet basins in the USA quantified the effect of this action on the abundance of individual plant species. One study reported that sowing potential nurse plants typically had no significant effect on – and sometimes reduced – the biomass of sown porcupine sedge Carex hystericina, after 1–2 growing seasons. The other study reported varying effects of potential nurse plants on the abundance of individual target plant species, depending on factors such as diversity of the nurse crop and addition of sawdust to plots.

VEGETATION STRUCTURE

 

OTHER

  • Germination/emergence (1 study): One replicated, randomized, paired, controlled study in an experimental wet basin in the USA found that the presence of a high-diversity nurse crop reduced the germination rate of sown sedge meadow species. A low-diversity nurse crop had no significant effect on their germination rate.

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

  1. A replicated, randomized, paired, controlled, before-and-after study in 1997–1999 in a wet basin in Minnesota, USA (Perry & Galatowitsch 2003) found that sowing two potential nurse plant species typically had no significant effect on above-ground biomass of sown porcupine sedge Carex hystericina, after 1–2 growing seasons. Amongst plots experimentally invaded with reed canarygrass Phalaris arundinacea, plots with and without nurse plants contained a statistically similar sedge biomass in 48 of 48 comparisons (with: 0–100 g/m2; without: 0–1 g/m2). Amongst plots that were not experimentally invaded, plots with and without nurse plants contained a statistically similar sedge biomass in 14 of 16 comparisons (with: 0–1,130 g/m2; without: 0–1,790 g/m2). In the other two comparisons, plots with nurse plants contained a lower sedge biomass (0 g/m2) than plots without (2–700 g/m2). Methods: In June 1997 and April 1998, four hundred and eighty 0.25-m2 plots were established (in five sets) in an experimental, vegetation-free wet basin. Porcupine sedge seeds were sown onto all 480 plots (500–5,000 seeds/m2). Seeds of one nurse plant species (either barnyardgrass Echinochloa crusgalli or nodding smartweed Polygonum lapathifolium) were sown onto 384 plots (125–5,000 seeds/m2). Reed canarygrass seeds were sown onto 336 plots (125–5,000 seeds/m2). Treatments were randomly allocated within sets of plots. Biomass was sampled from the centre of the plots – half after one growing season, half after two – then dried and weighed. This study used the same site as (2), but a different experimental set-up.

    Study and other actions tested
  2. A replicated, randomized, paired, controlled, before-and-after study in 2004–2005 in two wet basins in Minnesota, USA (Iannone & Galatowitsch 2008) found that sowing potential nurse species along with target sedge meadow species did not increase the germination rate or abundance of the target species after one growing season. Sixteen weeks after sowing, the germination rate was significantly lower in plots with a high-diversity nurse crop (33%) than plots with a low-diversity nurse crop (51%) or no nurse crop (61%). Plots with a nurse crop had a lower total density of the target species (with: 370–1,000; without: 980–1,300 shoots/m2) and target grass-like plants (with: 150–660; without: 660–780 shoots/m2). The effect of nurse crops on the total density of target forbs depended on presence of invasive reed canarygrass Phalaris arundinacea and addition of sawdust (see original paper for details). The study also reported data on the abundance of individual target species. Nurse crops had significant effect on 9 of 10 target species, although this sometimes depended on nurse crop diversity, canarygrass presence, sawdust addition and the outcome metric. For example, 6 of 10 target species had lower cover in plots with a high-diversity nurse crop than plots with no nurse crop (data reported as cover classes; see original paper for full details). Methods: In May 2005, seeds of 10 target sedge meadow species were sown onto seventy-two 1-m2 plots (total 2,250 seeds/m2) across two experimental, vegetation-free wet basins. The plots were grouped in six sets of 12. At the same time, a nurse crop was sown onto 48 plots (eight random plots/set; total 2,100 seeds/m2). This contained either five species (24 plots) or one species (24 plots). Some plots had also been amended with sawdust (October 2004) or sown with reed canarygrass (May 2005). Target vegetation was surveyed for 16 weeks after sowing. Seedlings were counted in five 100-cm2 subplots/plot. Shoot density and cover were monitored across the whole of each plot. This study used the same site as (1), but a different experimental set-up.

    Study and other actions tested
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.

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Marsh and Swamp Conservation

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Marsh and Swamp Conservation
Marsh and Swamp Conservation

Marsh and Swamp Conservation - Published 2021

Marsh and Swamp Synopsis

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