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A variety of mire types in Carbajal Valley, Argentina.
Spatially regular net patterning of strings and hollows, arising from scale-dependent positive feedbacks.[1] Great Vasyugan Bog in western Siberia.
Avaste Fen, one of the largest fens in Estonia.

A mire is a wetland type, dominated by living, peat-forming plants. Mires arise because of incomplete decomposition of organic matter, due to waterlogging and subsequent anoxia. Like coral reefs, mires are unusual landforms in that they derive mostly from biological rather than physical processes, and can take on characteristic shapes and surface patterning.

There are four types of mire: bog, fen, marsh and swamp.[2] A bog is a mire that due to its location relative to the surrounding landscape obtains most of its water from rainfall (ombrotrophic), while a fen is located on a slope, flat, or depression and gets most of its water from soil- or groundwater (minerotrophic). Thus while a bog is always acidic and nutrient-poor, a fen may be slightly acidic, neutral, or alkaline, and either nutrient-poor or nutrient-rich.[3] Although marshes are wetlands within which vegetation is rooted in mineral soil, some marshes form shallow peat deposits: these should be considered mires. Swamps are characterized by their forest canopy and, like fens, are typically of higher pH and nutrient availability than bogs. Some bogs and fens can support limited shrub or tree growth on hummocks.

For botanists and ecologists, the term peatland is a more general term for any terrain dominated by peat to a depth of at least 30 cm (12 in), even if it has been completely drained (i.e., a peatland can be dry, but a mire by definition must be actively forming peat).

Mires are a kind of "...living relic... [A] living skin on an ancient body"[4] in which successive layers of regular plant growth and decay are preserved stratigraphically with a quality of preservation unknown in other wetland environments.

Global distribution

Wooded bog in Lahemaa National Park, Estonia. 65% of mires in Estonia have been strongly affected or damaged by human activity in recent years.[5]
Extraction of peat from derelict blanket bog, South Uist, Scotland. This old bog is no longer forming peat because the vegetation has been changed, and therefore it is not a mire.
Satellite image of burning tropical peat swamp, Borneo. In 1997 alone, 73000ha of swamp was burned in Borneo, releasing the same amount of carbon as 13-40% of the mean annual global carbon emissions of fossil fuels. The majority of this carbon was released from peat rather than overlying tropical rainforest.

Mires, although perhaps at their greatest extent at high latitudes in the Northern Hemisphere, are found around the globe. Mires occur wherever conditions are right for peat accumulation: largely where organic matter is constantly waterlogged. The distribution of mires therefore depends on topography, climate, parent material, biota and time.[6] The type of mire - bog, fen or swamp - depends also on each of these factors.

In polar regions, mires are usually shallow, because of the slow rate of accumulation of dead organic matter, and often contain permafrost. Very large swathes of Canada, northern Europe and northern Russia are covered by boreal mires. In temperate areas mires are typically more scattered due to historical drainage and peat extraction, but can cover large areas as blanket bog where precipitation is very high (e.g. in maritime climates inland near the coasts of the north-east and south Pacific, and the north-west and north-east Atlantic). In the sub-tropics, mires are rare and restricted to the wettest areas. In the tropics, mires can again be extensive, typically underlying tropical rainforest (e.g. in Kalimantan).

Mires are in rapid decline globally due to drainage for agriculture and forestry, and for peat harvesting. For example, more than 50% of original European mire area, more than 300000 km2, has been lost.[7]


Mires have unusual chemistry, which influences inter alia their biota and the chemistry of the water outflow. Peat has very high cation-exchange capacity due to its high organic matter content: cations such as Ca2+ are preferentially adsorbed onto the peat in exchange for H+ ions. Water passing through peat declines in nutrients and in pH. Therefore mires are typically nutrient-poor and acidic unless the inflow of groundwater (bringing in supplementary cations) is high.[8]


A valley mire creates a level ground surface in otherwise dramatic topography. Upper Bigo Bog, Rwenzori Mountains, Uganda.

Mires elevate the ground surface above the original topography. Mires can reach considerable heights above the underlying mineral soil or bedrock: peat depths of above 10m have been recorded in temperate regions (many temperate and most boreal mires were removed by ice sheets in the last Ice Age), and above 25m in tropical regions.[8] When the absolute decay rate in the catotelm (the lower, water-saturated zone of a mire) matches the rate of input of new peat into the catotelm, the mire will stop growing in height.[9] A simplistic calculation, using typical values for a Sphagnum bog of 1mm new peat added per year and 0.0001 proportion of the catotelm decaying per year, gives a maximum height of 10m. More advanced analyses incorporate expectable nonlinear rates of catotelm decay.

See also


  1. ^ Eppinga; et al. (2008). "Regular Surface Patterning of Peatlands: Confronting Theory with Field Data". Ecosystems. 11: 520–536. 
  2. ^ National Wetlands Working Group (1997). The Canadian wetland classification system (2nd ed.). University of Waterloo, Canada. 
  3. ^ Geist, Helmut (2006). Our Earth's Changing Land: An Encyclopedia of Land-Use and Land-Cover Change. 2. Greenwood. p. 463. ISBN 9780313327841. 
  4. ^ Goodwille, Roger (1981). "Peatlands: living relics". Naturopa. Strasbourg: European Information Centre for Nature Conservation of the Council of Europe (19). OCLC 605722266. 
  5. ^ Joosten H., Tanneberger F. & Moen, A., eds. (2015). Mires and Peatlands of Europe. Schweizerbart Science Publishers. Stuttgart. 
  6. ^ Gorham, Eville (1857). "The Development of Peat Lands". The Quarterly Review of Biology. 32 (2): 145–166. 
  7. ^ Joosten, H.; Clarke, D. (2002). Wise use of mires and peatlands. International Mire Conservation Group and International Peat Society. 
  8. ^ a b Rydin, Håkan; Jeglum, John (2006). The Biology of Peatlands (1st ed.). Oxford University Press. 
  9. ^ Clymo, R.S. (1984). "The limits to peat bog growth". Philosophical Transactions of the Royal Society of London B: Biological Sciences. 303: 605–654. Bibcode:1984RSPTB.303..605C. doi:10.1098/rstb.1984.0002. 

External links

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