Action: Introduce nurse plants (to aid focal peatland plants)
- Three studies examined the effect, on peatland vegetation, of introducing nurse plants to aid focal peatland plants. Two studies were in bogs. One was in a tropical peat swamp.
- Survival (1 study): One replicated, paired, controlled study in Malaysia reported that planting nurse trees had no effect on survival of planted peat swamp tree seedlings (six species).
- Cover (2 studies): Two replicated, randomized, paired, controlled, before-and-after studies in bogs in the USA and Canada found that planting nurse herbs had no effect on cover, after 2–3 years, of other planted vegetation (mosses/bryophytes, vascular plants or total cover).
Nurse or companion plants can be planted alongside focal plants to help the focal plants establish (Padilla & Pugnaire 2006). Nurse plants can bind together loose peat and reduce harsh environmental conditions (temperature fluctuations, desiccation and strong sunlight). Nurse plants must be able to tolerate these conditions, but invasive species (that spread easily) and species that may outcompete focal plants (physically or chemically) should be avoided. Instead, it is expected that nurse plants are eventually outcompeted by focal plants.
Herbs are common nurse plants in temperate peatlands, creating shelter for mosses. They may be directly planted or added as seed (the latter being a more efficient way to cover larger areas). Haircap moss Polytrichum strictum may act as a nurse plant for Sphagnum moss and vascular plant seedlings (based on a correlative study of natural colonization, and an experiment using non-peatland species; Groeneveld et al. 2007). In tropical peat swamps, light-tolerant trees can be used to shelter shade-loving trees.
To be included as evidence in this section, studies must have deliberately introduced nurse plants before planting focal peatland vegetation. Studies that planted peatland vegetation into existing nurse vegetation (e.g. Sliva & Pfadenhauer 1999), or examined natural colonization of nurse vegetation (e.g. Groeneveld et al. 2007) are not included.
Related intervention: introduce nurse plants as one of many combined interventions e.g. lime/seed/fertilizer; introduce nurse plants without introducing peatland vegetation.
Groeneveld E.V.G., Masse A. & Rochefort L. (2007) Polytrichum strictum as a nurse-plant in peatland restoration. Restoration Ecology, 15, 709–719.
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.
Sliva J. & Pfadenhauer J. (1999) Restoration of cut-over raised bogs in southern Germany – a comparison of methods. Applied Vegetation Science, 2, 137–148.
Supporting evidence from individual studies
A replicated, paired, controlled study in 1999–2000 in a degraded peat swamp forest in Malaysia (Ismail et al. 2001) reported that planting nurse trees had no effect on the survival of focal planted tree seedlings. No statistical tests were carried out. Six different tree species were planted. After 14 months, 82% of seedlings had survived in plots with nurse trees, compared to 83% of seedlings in plots without nurse trees (data not reported separately for each species). In June 1999, thirty-six plots in a degraded, open peat swamp were planted with peat swamp trees (16 seedlings/plot). There were three pairs of plots for each of six tree species. Eighteen plots (one plot/pair) were also planted with 2 m tall Hopea odorata as nurse trees. The other plots contained no additional trees. All plots were cleared of vegetation before planting and the planting holes were fertilized. Survival was recorded in August 2000.
A replicated, randomized, paired, controlled, before-and-after study in 1997–1999 in a historically mined bog in Minnesota, USA (Rochefort et al. 2003) found that planting nurse herbs before adding vegetation fragments had no effect on vegetation cover. After two growing seasons, plots with and without nurse herbs had similar cover of total vegetation (3–77% vs 1–71%), Sphagnum mosses (0–68% vs 0–73%), other mosses (<1% with or without nurse herbs) and vascular plants (1–3% with or without nurse herbs). In 1997–1998, forty-eight 1.5 x 1.5 m plots were established, in six blocks of eight. Twenty-four plots (four random plots/block) were planted with 16 fewseed sedge Carex oligosperma plants. The other 24 plots were left as bare peat. Then, all plots were sown with fresh vegetation fragments from the surface of natural bogs. Some plots with and without nurse sedges were also mulched with straw. In October 1999, vegetation cover was visually estimated in four 25 x 25 cm quadrats/plot.
A replicated, randomized, paired, controlled, before-and-after study in 2007–2010 in two historically disturbed bogs in Ontario, Canada (Corson & Campbell 2013) found that planting nurse herbs before sowing Sphagnum moss fragments had no effect on bryophyte cover. After three years, Sphagnum cover did not differ significantly between plots with nurse herbs (low density: 52%; high density: 51%) and without (38%). There was also no difference in total bryophyte cover between treatments (with nurse plants: 72–76%; without: 68%). In August 2007, eighteen 2 x 2 m plots were established, in six blocks of three, on historically disturbed bogs. Twelve plots (two random plots/block) were planted with cottongrass Eriophorum vaginatum tussocks as nurse plants: six at low density (50 cm apart) and six at high density (25 cm apart). The other six plots were left as bare peat. Then, all plots received fresh fragments of rusty bog moss Sphagnum fuscum and flat-topped bog moss Sphagnum fallax, and 30 g/m2 rock phosphate fertilizer. In August 2010, moss cover was estimated by eye in six random 12.5 x 12.5 cm subplots within each plot.
- Ismail P., Shamsudin I., Nik Muhamad N.M. & Faridah Hanum I. (2001) Rehabilitation of grassland areas in peat swamp forests in Peninsular Malaysia. Proceedings of the Asian Wetland Symposium, Penang, Malaysia, 57-64.
- Rochefort L., Quinty F., Campeau S., Johnson K. & Malterer T. (2003) North American approach to the restoration of Sphagnum dominated peatlands. Wetlands Ecology and Management, 11, 3-20
- Corson A. & Campbell D. (2013) Testing protocols to restore disturbed Sphagnum-dominated peatlands in the Hudson Bay Lowland. Wetlands, 33, 291-299