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Providing evidence to improve practice

Action: Use prescribed fire to control problematic plants Peatland Conservation

Key messages

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  • Six studies evaluated the effects on peatland vegetation of using prescribed fire to control problematic plants: five in bogs and one in fens. Four studies were based on the same experimental set-up in the UK. N.B. Prescribed burning in historically disturbed peatlands is considered as a separate action.
  • Moss cover (4 studies): One replicated, paired, controlled study in bogs in Germany found that burning increased moss/lichen/bare ground cover in the short term (2–7 months after burning). Three replicated, paired studies (based on the same experimental set-up) in one bog in the UK found that moss cover (including Sphagnum) was higher in plots burned more often.
  • Herb cover (4 studies): Of two replicated, paired, controlled studies in bogs in Germany and the UK, one found that burning had no effect on cottongrass cover after 2–7 months but the other found that burning increased cottongrass cover after 8–18 years. Two replicated, paired studies in the same bog in the UK reported that cottongrass cover was similar in plots burned every 10 or 20 years. The study in Germany also found that burning reduced purple moor grass cover but had mixed effects, amongst sites, on cover of other grass-like plants and forbs.
  • Tree/shrub cover (5 studies): Three replicated, paired studies in a bog in the UK found that heather cover was lower in plots burned more often. One replicated, paired, controlled study in bogs in Germany found that heather cover was lower in burned than unburned plots. Two replicated, controlled studies in the bogs in Germany and fens in the USA found that burning (sometimes along with other interventions) did not affect cover of other shrubs.
  • Vegetation structure (1 study): One replicated, paired, controlled study in a bog in the UK found that plots burned more frequently contained more biomass of grass-like plants than plots burned less often, but contained less total vegetation, shrub and bryophyte biomass.
  • Overall plant richness/diversity (2 studies): Two replicated, controlled studies (one also randomized and paired) in the fens in the USA and a bog in the UK found that burning reduced or limited plant species richness. In the USA, burning was carried out along with other interventions.

Supporting evidence from individual studies

1 

A replicated, randomized, paired, controlled study in 1954–1973 in a blanket bog in England, UK (Rawes & Hobbs 1979) found that repeatedly burned plots developed less heather Calluna vulgaris cover and greater cover of some mosses than once-burned plots, but that cover of cottongrasses Eriophorum spp. was similar under both treatments. After 18 years, twice-burned plots consistently had less heather cover (19–30%) than once-burned plots (67–82%). Twice-burned plots also had greater cover of rusty swan-neck moss Campylopus flexuosus in 3 of 4 comparisons (for which twice-burned: 38–46%; once-burned: 11–22%) and Sphagnum mosses in 2 of 4 comparisons (when sheep were excluded; twice-burned: 19%; once-burned: 5%). All plots had similar cover of six other moss species (see original paper) and cottongrasses (twice-burned: 8–67%; once-burned: 6–62%). Mixed responses to burning were reported for 26 other plant groups. In 1954, four areas (each containing six 1,000 m2 plots) in a historically grazed bog were burned. Within each area, two random plots were burned again in 1965 whilst four plots were not burned again. Half of the plots were also fenced to exclude sheep. In 1972, vegetation cover was estimated by recording, in each plot, plants touching 250 randomly placed pins.

2 

A replicated, paired study in 1954–1980 in a blanket bog in England, UK (Hobbs 1984) reported that burned plots became dominated by cottongrasses Eriophorum spp. within 3–5 years, and that burning more often reduced cover of heather Calluna vulgaris but typically increased moss and liverwort cover. These results were not tested for statistical significance. All plots were burned in 1954 and 1975. In 1978–1980, the plots were dominated by cottongrass (sheathed cottongrass Eriophorum vaginatum cover: 46–84%; common cottongrass Eriophorum angustifolium cover: 3–28%). Half of the plots were also burned in 1965. In 1978–1980, these plots had less cover of heather (shoots: 6–26%; stems: 2–17%) than plots that were not burned in 1965 (shoots: 22–70%; stems: 17–59%). The more frequently burned plots also had greater moss cover (Sphagnum in 5 of 6 comparisons; other mosses in 14 of 18 comparisons) and liverwort cover (in 22 of 33 comparisons) but similar cottongrass cover. In 1954, four pairs of 1,000 m2 plots were established on a grazed bog. All plots were burned in 1954 and 1975. Four plots (one plot/pair) were also burned in 1965. Vegetation cover was estimated in August 1978–1980, in 128 quadrats/plot, (each 10 x 10 cm and arranged along a transect). This study was based on the same experimental set-up as (1), (4) and (6).

3 

A replicated, paired, controlled study in 2003 in four degraded raised bogs in Germany (Hochkirch & Adorf 2007) found that burned plots consistently had less cover than unburned plots of purple moor grass Molinia caerulea (25 vs 40%) , but more moss/lichen/bare ground cover (36 vs 8%). Meanwhile, burned and unburned plots had similar cover of cottongrass Eriophorum vaginatum (12 vs 16%) and cross-leaved heath Erica tetralix (2 vs 6%). Vegetation height, and cover of other minor forbs and grass-like plants, responded inconsistently to burning across the four bogs (see original paper). Between February and May 2003, 4–45 ha of four grassy/shrubby bogs were burned. Two fires were prescribed and two were wild. The study does not analyze the effects of these separately. Between July and September 2003, vegetation cover and height were recorded along a 100 m transect in each bog, spanning the burned area and an adjacent unburned area.

4 

A replicated, paired, controlled study in 1954–2004 in a blanket bog in England, UK (Ward et al. 2007) found that repeatedly burned plots contained less total vegetation, shrub and bryophyte biomass than once-burned plots, but more biomass of grass-like plants. After 50 years, repeatedly burned plots contained less above-ground vegetation biomass (134 g/m2) than once-burned plots (297 g/m2). This included less biomass of shrubs (repeatedly burned: 236; once-burned: 116 g/m2) and bryophytes (repeatedly burned: 5; once-burned: 53 g/m2). In contrast, biomass of grass-like plants was significantly higher in repeatedly burned plots (13 g/m2) than once-burned plots (8 g/m2). In 1954, sixteen 1,000 m2 plots were established, in four blocks of four, in a historically grazed bog. All plots were burned once in 1954. Thereafter, eight plots (two plots/block) were burned every 10 years. The other plots were not burned again. Additionally, half of the plots were fenced to exclude sheep. In 2003–2004, live above-ground vegetation was cut from one 25 cm2 quadrat/plot, then dried and weighed. Samples were taken in spring, summer, autumn and winter. This study was based on the same experimental set-up as (1), (2) and (6).

5 

A replicated, controlled, before-and-after study in 1986–2000 in two shrub-invaded fens in Ohio, USA (Barry et al. 2008) found that burning shrubs (along with cutting and herbicide application) altered plant community composition and prevented increases in plant species richness, but had no effect on shrub cover. The overall plant community composition changed significantly over time along transects with and without shrub control, but they accumulated different sets of species (data reported as a graphical analysis). Plant species richness was stable in the fen with shrub control (before: 12.8; after 14 years: 12.7 species/m2) but increased in the fen without shrub control (before: 12.5; after 14 years: 14.6 species/m2). Woody plant cover increased similarly in fens with shrub control (before: 46%; after 11 years: 62%) and without shrub control (before: 20%; after: 28%). From 1986, encroaching shrubs were managed using ad hoc burning, cutting and herbicide application. The study does not distinguish between the effects of these interventions. Three of four transects were managed in one fen (‘with shrub control’). Only one of four transects were managed in the other fen (‘without shrub control’). In summer 1986 (before shrub control began), 1999 and 2000, vegetation cover was estimated in 1 m2 quadrats along the eight transects. Shrub cover was estimated from aerial photographs.

6 

A replicated, randomized, paired, controlled study in 1954–2001 in a blanket bog in England, UK (Lee et al. 2013) found that repeated burning prevented development of heather-dominated vegetation and increased Sphagnum moss cover (with a short time between burns) but reduced total plant species richness. At first measurement in 1972, all plots had similar liverwort-rich vegetation. After 29 years, burned plots had greater cover of cottongrasses Eriophorum spp. than unburned plots, but less cover of heather Calluna vulgaris (data reported as graphical analyses). Averaged over the entire experimental period, plots burned every 10 years (but not plots burned every 20 years) had greater cover of Sphagnum moss than unburned plots (data not reported). There were significantly fewer plant species in burned plots (15.5–16.6/plot) than in unburned plots (17.3/plot). The effects of burning were similar in grazed and ungrazed plots. In 1954–1955, four 60 x 90 m areas were burned in a historically grazed bog. Within each area, two random plots were left unburned for the rest of the study period, two plots were burned every 10 years, and two plots burned every 20 years. Under each treatment, half of the plots were grazed by sheep. Vegetation cover was measured in 1972, 1982, 1991 and 2001 by recording, in each plot, plants touching 100 randomly placed pins. This study was based on the same experimental set-up as (1), (2) and (4).

Referenced papers

Please cite as:

Taylor N.G., Grillas P. & Sutherland W.J. (2018) Peatland Conservation. Pages 329-392 in: W.J. Sutherland, L.V. Dicks, N. Ockendon, S.O. Petrovan & R.K. Smith (eds) What Works in Conservation 2018. Open Book Publishers, Cambridge, UK.