Introduce nurse plants to aid focal non-woody plants: freshwater wetlands
Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 2
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.
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
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