Action: Use prescribed fire to maintain or restore disturbance
- Three studies examined the effects on peatland vegetation of using prescribed fire to maintain or restore disturbance. Two studies were in fens and one was in a bog. N.B. Prescribed burning in peatlands with no history of disturbance is considered as a separate action.
- Characteristic plants (1 study): One replicated before-and-after study in a fen in the UK reported that burning (along with other interventions) had no effect on cover of fen-characteristic mosses or herbs.
- Herb cover (2 studies): One replicated, controlled study in a fen in the USA reported that burning reduced forb cover and increased sedge/rush cover, but had no effect on grass cover. In contrast, one replicated before-and-after study in a fen in the UK reported that burning (along with other interventions) reduced grass/sedge/rush cover.
- Tree/shrub cover (2 studies): Two replicated studies in fens in the USA and the UK reported that burning (sometimes along with other interventions) reduced tree/shrub cover.
- Overall plant richness/diversity (3 studies): Two replicated, controlled studies in a fen in the USA and a bog in New Zealand found that burning increased plant species richness or diversity. However, one replicated before-and-after study in a fen in the UK reported that burning (along with other interventions) typically had no effect on plant species richness and diversity.
Regular disturbance may maintain vegetation in a desirable, semi-natural state – particularly in fen meadows and some fens (Middleton 2012). Disturbance can clear dominant plants, maintain light availability and control nutrient levels. This can favour a plant community rich in plant species and/or peatland characteristic species. Therefore, conservationists may sometimes want to actively maintain or restore disturbance. Prescribed burns might be one way to do this.
Burning itself may be the disturbance that has been reduced, as a result of land abandonment or because landscape changes (such as roads or ditches) create fire breaks. Historically, some North American fens burned annually due to lightning fires or intentional burning by humans (Middleton et al. 2006). Burning on some bogs helps to clear dominant vegetation (Norton & De Lange 2003).
Caution: Disturbance is not desirable on all peatlands. Fen meadows and some fens may benefit from disturbance. Many other fens, bogs and peat swamps will not. Natural fires in bogs and tropical peat swamps are rare, occurring every few centuries (Lindsay et al. 2011; Page & Hooijer 2016). Further risks specific to prescribed fires include the difficulty of controlling their intensity, duration and area. Uncontrolled burns can damage seed banks, Sphagnum mosses and the peat itself. Prescribed burns may be best carried out in the winter, when the peat is cold and wet (sometimes frozen), to avoid setting the peat on fire and reduce the risk of fire spreading beyond the prescribed area. Also note that burning might produce apparently desirable changes in vegetation over the short term (e.g. less heather cover and increased herb cover), followed by a rapid return to a degraded state.
Middleton B.A. (2012) Rediscovering traditional vegetation management in preserves: trading experiences between cultures and continents. Biological Conservation, 158, 750–760.
Middleton B., Holsten B. & van Diggelen R. (2006) Biodiversity management of fens and fen meadows by grazing, cutting and burning. Applied Vegetation Science, 9, 307–316.
Lindsay R., Birnie R. & Clough J. (2011) Burning. IUCN UK Peatland Programme Briefing Note No. 8.
Norton D.A. & De Lange P.J. (2003) Fire and vegetation in a temperate peat bog: implications for the management of threatened species. Conservation Biology, 17, 138–148.
Page S.E. & Hooijer A. (2016) In the line of fire: the tropical peatlands of South East Asia. Philosophical Transactions of the Royal Society B, 371, 20150176.
Supporting evidence from individual studies
A replicated, controlled study in 1998–2000 in a degraded, shrubby sedge meadow in Wisconsin, USA (Middleton 2002) found that burned plots contained more plant species than unburned plots, and had greater sedge/rush cover, but lower tree/shrub and forb cover and similar grass cover. The cover results were not tested for statistical significance. Over two subsequent years, species richness was higher in burned plots (7.1 species/0.2 m2) than unburned plots (6.5 species/0.2 m2). Burned plots also had greater cover of sedges/rushes (burned: 15–39%; unburned: 10–28%), but lower tree/shrub cover (burned: 0–11%; unburned: 6–12%) and lower forb cover (burned: 11–28%; unburned: 18–35%). Grass cover was similar in burned (1–12%) and unburned plots (0–9%). The cover results were not tested for statistical significance. Fifty-six 20 x 20 m plots were established in a degraded sedge meadow (historically burned and, in parts, grazed). Sedge meadows are sedge-dominated peatlands, fed by ground water. In December 1998, 33 plots were burned whilst 23 were not. In August 1999 and 2000 cover and height of every species were recorded, in one 0.2 m2 quadrat/plot.
A replicated, controlled, before-and-after study in 1994–1998 in a bog in New Zealand (Norton & De Lange 2003) found that burned plots contained a different plant community to unburned plots, with greater plant species richness, diversity and cover. Before intervention, all plots contained a similar overall plant community. After four years, burned and unburned plots contained different communities (data reported as a graphical analysis; difference not tested for statistical significance). Also, burned plots experienced significant increases in foliage cover (from 103% before burning to 171% four years after), plant species richness (from 8 to 14 species/4 m2) and plant diversity (data reported as a diversity index). In unburned plots, these measures declined (cover: from 104 to 100%; richness: from 9 to 6 species/4 m2). In July (winter) 1994, twelve 2 x 2 m plots in a fire-suppressed bog were burned. Twelve control plots remained unburned. Cover of every plant species was recorded in all plots immediately before burning, and at intervals until September 1998.
A replicated before-and-after study in 2010–2012 in a degraded fen in Wales, UK (Birch et al. 2015) reported that burning (along with other interventions) reduced grass/sedge/rush and shrub cover, but typically had no effect on fen-characteristic plant cover and overall diversity, and had mixed effects on vegetation height. In both managed plots, there were decreases in total grass/sedge/rush cover (before burning: 97–98%; two years after: 70–74%) and shrub cover (before: 7–81%; after: 10–13%). Cover of purple moor grass Molinia caerulea decreased significantly in one plot with a similar trend in the other (before: 4–64%; after: 0–3%). There was no significant change in cover of fen-characteristic mosses (<1% before and after), fen-characteristic herbs (before: <2%; after: <1%), or plant species richness/diversity (in three of four comparisons). Vegetation height decreased in one plot but did not change in the other. Two 20 x 20 m plots were established in an abandoned fen. In September 2011, both plots were burned. After burning, one plot was mown and both plots were lightly grazed by cattle. The study does not distinguish between the effects of these interventions and burning. Cover of every plant species was estimated before burning (August 2008) and two years after (autumn 2013), in five 4 m2 quadrats/plot.
- Middleton B. (2002) Winter burning and the reduction of Cornus sericea in sedge meadows in southern Wisconsin. Restoration Ecology, 10, 723-730
- Norton D.A. & De Lange P.J. (2003) Fire and vegetation in a temperate peat bog: implications for the management of threatened species. Conservation Biology, 17, 138-148
- Birch K.S., Guest J.E., Shepherd S., Milner P., Jones P.S. & Hanson J. (2015) Responses of rich-fen Annex I and related habitats to restoration and management undertaken as part of the Anglesey & Lyn Fens LIFE Project. Technical Report No. 7. LIFE Project: Anglesey & Llyn Fens.