Add lime (before/after planting)
Overall effectiveness category Likely to be ineffective or harmful
Number of studies: 6
Background information and definitions
Peatland plant survival and growth is partly determined by the acidity of a peatland, or pH (Rydin & Jeglum 2013). Fen plants grow in alkaline to weakly acidic peat (approximately pH 6–8, similar to saliva, tap water or sea water). Bog plants grow in more acidic peat (approximately pH 4–5, similar to tomato juice or coffee). The acidity of a peatland also determines the availability of nutrients. For example, phosphorous becomes locked away in acidic soils (Weil & Brady 2016).
Lime (calcium and/or magnesium-rich chemicals) can be added to peatlands to reduce acidity and modify nutrient availability, potentially increasing survival or growth of peatland vegetation. To be included as evidence in this section, studies must have reported the response of peatland vegetation, not just nurse plants (e.g. Caporn et al. 2007).
Caution: The benefits and harms of liming are very context specific. Liming is mostly used in fens and fen meadows, but is sometimes used in extremely polluted, exceptionally acidic bogs. Lime could damage most bogs by reducing natural acidity.
Caporn S., Sen R., Field C., Jones E., Carroll J. & Dise N. (2007) Consequences of lime and fertilizer application for moorland restoration and carbon balance. Moors for the Future Research Report.
Rydin H. & Jeglum J.K. (2013) The Biology of Peatlands, Second Edition. Oxford University Press, Oxford.
Weil R.R. & Brady N.C. (2016) The Nature and Properties of Soils, Fifteenth Edition. Pearson, USA.
Supporting evidence from individual studies
A controlled, before-and-after study in 1991 in a historically mined raised bog in England, UK (Money 1995) found that liming reduced growth of one planted Sphagnum species and had no effect on another. The growth rate of recurved bog moss Sphagnum recurvum was 12–50% lower in limed pools than in unlimed pools. The effect of liming was especially strong in pools that were also fertilized. The growth rate of feathery bog moss Sphagnum cuspidatum was not significantly lower (only 4–8% less) in limed pools than in unlimed pools. In 1991, individual Sphagnum plants (cut to 5 cm length) were submerged (30 cm deep) in 4 m3 pools dug in the bog (number of plants and pools not reported). After 10 days, four treatments were applied: lime with fertilizer, liming only, fertilization only, or none. Limed pools received 80g calcium carbonate. Fertilized pools received 30 g sodium phosphate. The length of all plants was measured after 20 weeks.Study and other actions tested
A replicated, controlled study in 1994–1995 in a degraded fen meadow in the Netherlands (van Duren et al. 1998) reported that liming typically reduced survival of planted herbs. Three species were planted: carnation sedge Carex panicea, tawny sedge Carex hostiana and meadow thistle Cirsium dissectum. In four of six comparisons, survival after two growing seasons was lower in limed plots (8–20%) than in unlimed plots (15–32%). In one comparison, survival was no different in limed and unlimed plots (72%). In the final comparison, survival was higher in limed plots (88%) than in unlimed plots (80%). After one growing season, lime had little effect on survival (>92% in all plots). In May 1994, twenty 1 m2 plots were each planted with 15 plants (five of each species). Ten plots were limed (450–510 g/m2) and ten were not. All plots had been rewetted and were mown every August. Half had been stripped of topsoil. In August 1994 and 1995, survival of all plants was recorded.Study and other actions tested
A replicated, randomized, paired, controlled, before-and-after study in 2004–2005 in a degraded fen in Sweden (Mälson & Rydin 2007) found that liming increased survival and spread of sown fen mosses. After one growing season, moss survival was significantly higher in plots that had been limed (60–93% of plots contained live moss shoots) than in unlimed plots (4–48%). After two growing seasons, moss cover was significantly higher in limed plots (8–34%) than in unlimed plots (<1–10%). In June 2004, ninety-six 9 cm2 plots were established, in four equal blocks, on rewetted (historically drained) bare peat. Fragments of four fen-characteristic moss species were added (16 fragments of a single species in 9 cm2 subplots) to 24 plots (625 cm2). Twelve of these had been limed before planting (1.2 kg/m2, raising pH from 4.9 to 6.3). Some plots were also covered (with sedge litter or plastic gauze) after planting. Moss survival was assessed after one growing season. Moss cover was visually estimated after two growing seasons.Study and other actions tested
A replicated, controlled, before-and-after study in a greenhouse in Sweden (Mälson & Rydin 2007) found that liming increased the growth rate of planted fen mosses. After five months, shoots of all four planted moss species were longer in limed trays (42–91 mm) than in unlimed trays (29–61 mm). When planted, fragments were 10 mm long. Four trays of peat (19 x 56 cm) were each planted with 160 moss fragments: ten clusters of four fragments, for each of four species. In two of the trays, lime had been mixed into the peat before planting (128 g/tray). All trays were covered with clear plastic lids, kept in controlled light conditions, watered and systematically rearranged every 10 days. After five months, the length of all planted fragments was measured.Study and other actions tested
A replicated, randomized, controlled, before-and-after study in 2011 in a nursery in Indonesia (Yuwati et al. 2014) found that liming typically had no effect on growth of planted tree seedlings. Seedlings of 22 peat swamp tree species were studied. Limed and unlimed seedlings showed similar height growth for 15 species, similar growth of stem diameter for 14 species, and similar increase in dry mass for 19 species. The remaining species showed mixed responses: liming increased growth of some but reduced growth of others. In June 2011, 10 random seedlings of each species were limed (36.8 mg dolomitic lime twice/week) and 10 were not. Seedlings were grown in pots of soil and rice husk, from seed or transplanted from the wild. The duration of the experiment was not reported.Study and other actions tested
Referenced paperYuwati T.W., Rachmanadi D., Santosa P.B., Rusmana . & Graham L.L.B. (2014) Response of peat swamp forest species to macronutrients. Pages 46-63 in: F.R.U. Banjarbu, . FORDA & L.L.B. Graham (eds.) Tropical Peat Swamp Forest Silviculture in Central Kalimantan. Kalimantan Forests and Climate Partnership, Indonesia.
A replicated, randomized, paired, controlled study in 2011–2013 in a historically mined bog in Quebec, Canada (Rochefort et al. 2016) found that liming plots sown with vegetation fragments had no effect on vegetation cover. After two years, there was no significant difference between limed and unlimed plots for total vegetation cover (limed: 25%; unlimed: 21%), vascular plant cover (limed: 21%; unlimed: 18%) or bryophyte cover (limed: 4%; unlimed: 3%). In winter 2009/2010, nine pairs of 20 m2 plots were sown with mixed vegetation fragments from a donor fen. The plots were on a historically mined bog, but the aim of this study was to create a fen because the post-mining peat chemistry was more fen-like than bog-like. In July 2012, dolomitic lime was added to one plot/pair (15 g/m2). The other plots were not limed. In July 2014, vegetation cover was estimated in six quadrats/plot: vascular plants in three 1 x 1 m quadrats and bryophytes in three 50 x 50 cm quadrats.Study and other actions tested