TABLE 2. Differences in mires due to trophic conditions (after Laasimer & Masing, 1995). Characters
Eutrophic
Mesotrophic
Oligotrophic
Water sypply and trophic states
precipitation, ground, surface and flood water
precipitation, little influence of ground water
precipitation water only
Landform of the mire as a whole
flat or concave
flat
convex or flat
Microtopography
even or with grass(sedge) tussocks
cotton-grass tussocks and moss hummocks
a mosaic of moss hummocks and depressions
Tree layer
Betula pubescens, Alnus glutinosa, sparse Picea abies, seldom Pinus sylvestris
Betula pubescens and Pinus sylvestris only
Pinus sylvestris only, and/or sparse Betula pubescens
Shrub layer
Betula fruticosa, Myrica gale, Salix ssp.
Myrica gale, sparse Salix ssp.
absent
Dwarf shrub layer
absent
Calluna vulgaris, Ledum palustre, Andromeda polifolia, Chamaedaphne calyculata, Vaccinium uliginosum on hummocks
Grass and herb layer (field layer)
various grasses, herbs and forbs, especially Carex ssp.
in depressions eutrophic plants, often Potentilla palustris, Menyanthes trifoliata Trichophorum alpinum, Carex lasiocarpa
Moss layer
mainly Bryales
mainly Sphagnales, often Polytrichum strictum, Aulacomnium palustre
Peat
mainly sedge or woody peat suitable for fuel and fertilizing
mainly sedge peat suitable for fuel and litter
Eriophorum vaginatum, Trichophorum cespitosum, Rhynchospora alba, Rubus chamaemorus and Drosera ssp.
only sphagnum peat suitable for litter and gardening
Considering hydrochemical conditions and water sources as main principles for mire classification, the following system can be used (Masing, 1975, 1988): 1. minerotrophic mires, supplied by precipitation as well as by telluric water, derived from the ground: 1.1. soligenous mires, supplied by springs, 1.2. topogenous mires, supplied by ground water, 1.3. limnogenous mires, supplied by floods or forming through terrestrialization of waterbodies; 2. ombrotrophic mires, supplied exclusively by precipitation. Mixotrophic (transitional) mires represent an intermediate stage in mire development and they are often surrounding ombrotrophic (raised) bogs. Every landscape can be treated as a complex of developing bio- and geosystems which form parts of higher systems and at the same time can be divided into smaller sub-systems (Masing, 1982, 1984). Therefore, a site (especially a mire site) is a complex of microsites and can be described on the basis of its components (features); in mires, these include tussocks, hummocks and the depressions between them (hollows, hollowpools, funnels). Following this structural approach, the principles of Estonian bog sites classification can be represented according to Table 3.
ESTONIAN MIRES: INVENTORY OF HABITATS
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