MIRES

Used especially in Europe to denote peatforming environments, mires include bog, fen, swamp and carr, and may also include moor. ‘Mire’ is allembracing: it includes the peat and peatland and the peat-forming vegetation. In this regard, it is a useful, though not precise, term; in the United States, the term peatland is more often used. Diplotelmic (two-layered) mires have an anaerobic catotelm below the acrotelm, which is aerobic.

classification of mires can be based on one or more of a range of features. Moore (1984: 2) considered these under seven headings: (1) floristics, (2) vegetation structure and physiognomy, (3) morphology, (4) hydrology, (5) stratigraphy, (6) chemistry and (7) peat characteristics, but noted that even such a classification of taxonomic criteria is far from perfect, for many of these features are themselves closely interrelated. This wide range of criteria has resulted in a diverse range of classifications, from detailed classifications based principally on phytosociology, such as those used in Central Europe and in Ireland, to the more generalised classification based on nutrient source, as is sometimes used in parts of northwest Europe, particularly by palaeoecologists (e.g. ombrotrophic mire or rheotrophic mire). The difficulty with phytosociological classifications of mires is that they are based on the current vegetation. This can be a rather static view of what is inherently a dynamic system. Such classifications might not always acknowledge a mire’s ontogeny, or what might be growing there naturally but for the considerable human influence over recent centuries or decades (as, e.g. the underrepresentation of carr habitats, the overrepresentation of depauperate blanket mire and the relative emphasis given to lowland wet heath in Britain’s National Vegetation Classification of mires and heathlands) or what might be able to grow there were the climate to shift perceptibly. It is clear from the analysis of peat stratigraphy that the surface vegetation of some mires has responded to climatic changes in the past and would be expected to do so in the future. A simpler classification, which was formerly used in Britain, is one based on trophic status: oligotrophic bogs and eutrophic fens. However, ‘poor fen’ vegetation is at best mesotrophic, whereas some valley and basin mires are mesotrophic but support ‘bog’ rather than ‘fen’ communities.

Mires are natural archives of environmental history and can be examined using a range of palaeoecological techniques, including pollen analysis, plant macrofossil analysis, analysis of testate amoebae (rhizopod analysis), stable isotope analysis and determination of peat humification, to give various proxy records of vegetation or climatic history, which assist in reconstructing the environmental changes of the Late Quaternary.

The major peat formers in circum-boreal mires of the Northern Hemisphere are the bog mosses (sphag-num spp.), ericaceous shrubs and graminoids, including members of the Cyperaceae (sedge) and Poaceae (grass) families. Further south, and particularly in Southern Hemisphere mires, a wider range of taxa may be major peat formers, including members of the Restionaceae. The peat of tropical bog forests may largely be composed of tree remains.

In some parts of northwest Europe, the deliberate land drainage of mires, the cutting of peat for fuel and for use in horticulture and the afforestation of bogs have led to a rapid and catastrophic loss of mire habitats. The loss of raised mire habitats through drainage was particularly great in The Netherlands—losses that accumulated over recent centuries and were paralleled in Britain to a lesser degree—but in the past 50 years, mechanised peat cutting has led to increased loss of raised mire habitats in both Britain and Ireland, such that mire conservation and restoration have become a major conservation issue, and there are growing concerns for mire habitats even in countries with abundant and extensive mires, such as Canada, Estonia and Finland. The fragility of mire vegetation is well recognised and there is increasing concern over the loss of wetland habitats worldwide.

...