Mire is a water-saturated land (ecosystem), in which organic (vegetative) matter is accumulated faster than it is decomposed. This sediment is called peat.
Peat is an unconsolidated, organogenic and organic sediment consisting mainly of humified remains of helophytic (subordinately, aquatic) plants. The plant remains (stems and roots of sedges and reeds, dead trees, leaves, fruits, pollen) become partly decomposed under waterlogged, anoxic conditions. In the mire, the new plants grow upon the old. Inorganic mineral matter washed or blown into the mire, also contributes to peat formation. Peat has a brownish to black colour. It constitutes the precursor of coal, since coal derives from peat through coalification.
Peatland is a peat deposit with significant thickness of peat beds.
Depending on the morphology and their forming conditions, mires and peatlands can be distinguished into three main classes: fens, bogs, and transitional mires.
Fens form in low-lying areas occupied by stagnant water for long time every year. Since their formation depends on the topographic conditions, they are also called topogenous mires. The fens are supplied with ground and surface waters, rich in ions; therefore, the conditions are eutrophic, and the helophytic flora is very luxuriant.
Bogs form in areas with humid climatic conditions. Their formation depends only on the precipitation; therefore, they are also called ombrogenous mires and the conditions are oligotrophic. Respectively, the helophytic vegetation is restricted to mosses, Sphagnum spp. and lichens, in northern latitudes, with a few tree species in the tropical zone.
Transitional mires have an intermediate position between fen and bog. They are called ombrominerotrophic, since ground and surface waters and precipitation feed them. The flora thriving in transitional mires includes both fen and bog elements.
