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

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

Effectiveness

29%
Certainty

30%
Harms

20%

Calculating overall effectiveness category

Background information and definitions

Nurse plants, also known as companion plants or pioneer plants, can be planted alongside focal plants to help the focal plants establish (Padilla & Pugnaire 2006). Nurse plants may benefit focal plants in variety of ways, including: trapping and stabilizing sediments, trapping propagules, mitigating harsh environmental conditions (e.g. temperature fluctuations and strong sunlight), attracting pollinators, deflecting herbivory away from focal species, and/or limiting weed establishment.

Caution: Nurse plant species must be chosen carefully. Species that spread easily or are very strong competitors can cause more harm than good. For example, the non-native mangrove apple Sonneratia apetala has been used to restore Chinese mangroves, but has spread into neighbouring forests (Ren et al. 2009). Use of non-native nurse plants may not always be ethically acceptable.

To be summarized as evidence for this action, studies must have (a) deliberately introduced nurse plants before planting target marsh or swamp vegetation, and (b) reported the effects of the nurse plants on other vegetation, not just the survival or growth of the nurse plants. Studies must have explicitly planted vegetation for its nursing effect. Studies are not summarized as evidence here if they planted target vegetation into existing nurse vegetation (e.g. Egerova et al. 2003; McKee et al. 2007), or examined spontaneous colonization amongst planted nurse vegetation.

Related actions: Introduce nurse plants without introducing target marsh or swamp vegetation.

^{Egerova J., Proffitt C.E. & Travis S.E. (2003) Facilitation of survival and growth of Baccharis halimifolia L. by Spartina alterniflora Loisel. in a created Louisiana salt marsh. Wetlands, 23, 250–256.}

^{McKee K.L., Rooth J.E. & Feller I.C. (2007) Mangrove recruitment after forest disturbance is facilitated by herbaceous species in the Caribbean. Ecological Applications, 17, 1678–1693.}

^{Padilla F.M. & Pugnaire F.I. (2006) The role of nurse plants in the restoration of degraded environments. Frontiers in Ecology and the Environment, 4, 196–202.}

^{Ren H., Lu H., Shen W., Huang C., Guo Q., Li Z. & Jian S. (2009) Sonneratia apetala Buch.Ham in the mangrove ecosystems of China: an invasive species or restoration species? Ecological Engineering, 35, 1243–1248.}

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

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
Referenced paper
Perry L.G. & Galatowitsch S.M. (2003) A test of two annual cover crops for controlling Phalaris arundinacea invasion in restored sedge meadow wetlands. Restoration Ecology, 11, 297-307.
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
Referenced paper
Iannone B.V. & Galatowitsch S.M. (2008) Altering light and soil N to limit Phalaris arundinacea reinvasion in sedge meadow restorations. Restoration Ecology, 16, 689-701.

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?

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This Action forms part of the Action Synopsis:

Marsh and Swamp Conservation

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