birch stand Molinia caerulea, Calamagrostis canescens, C. epigeios, Deschampsia cespitosa, C. vaginata and C. nigra prevail. Filipendula ulmaria, Peucedanum palustris, Potentilla erecta, Lysimachia thyrsiflora and L. vulgaris are also common. The moss layer is discontinuous. On hummocks around the tree bases Pleurozium schreberi and Hylocomium splendens grow, while between hummocks Aulacomnium palustre, Calliergonella cuspidata and Sphagnum spp. are more common.
4.1.4.2 Poor paludifying forests Forests growing on overmoistened soils with rather thick litter of the moor type belong to this site type group. Recent soils often have compact humus-illuvial spodic horizon at the boundary of the capillary fringe. Polytrichum site type forests grow all over Estonia on sands where Gleyic, Carbic and Histic Podzols occur. The total thickness of ground litter and peat layers is 10–30 cm, and according to the decomposition rate it can be divided into 2–3 subhorizons. The leading tree species is pine (60%); birch (21%) and spruce (17%) occur less often. The undergrowth is sparse or absent. There can grow Frangula alnus, Salix cinerea, S. rosmarinifolia and Sorbus aucuparia. Ground vegetation consists of a few species only and Vaccinium myrtillus dominates. The coverage of Vaccinium uliginosum, V. vitis-idaea, Ledum palustre and Calluna vulgaris is smaller. Other typical species are: Carex globularis, Molinia caerulea, Equisetum sylvaticum, E. palustre, E. fluviatile, Calamagrostis canescens, Carex nigra, C. lasiocarpa, C. echinata, Dryopteris carthusiana, etc. The moss layer is vigorous, with abundant quantities of ordinary Polytrichum commune, Sphagnum spp., Pleurozium schreberi, Dicranum polysetum, D. scoparium and Aulacomnium palustre. Vaccinium uliginosum site type forests are characterized by well-developed dwarf shrub and moss layer, which contains considerable amount of sphagna and hair moss. These habitats are widespread everywhere in Estonia inducing podzolisation, often with a humus illuviation in the condition of groundgleying on sands that are poor in most chemicals. Carbic, Gleyic and Histic Podzols are typical. Total thickness of ground litter and peat is 10–30 cm, and according to the decomposition rate it can be divided into 2–3 subhorizons. The scarce tree layer is formed by pines alone, but in regrowth some spruce or birch can grow as well. The bush layer is almost lacking or represented by sparse junipers, Frangula alnus and/or willows (Salix cinerea, S. myrtilloides, S. rosmarinifolia, S. lapponum, S. aurita). Dwarf shrubs such as Vaccinium uliginosum, V. myrtillus, V. vitis-idaea, Calluna vulgaris, Ledum palustre, Empetrum nigrum and Andromeda polifolia dominate in the ground vegetation. Some grasses or herbs grow also there, such as Molinia caerulea, Eriophorum vaginatum, Rubus chamaemorus and Melampyrum pratense. The moss layer is continuous and Sphagnum spp. form the majority of the cover.
4.1.5 Peatland forests Though peatland forests sensu lato include paludifying forests as well, in the present publication the term ‘peatland forest’ is only used for forests which peat horizon thickness is at least 30 cm. According to the development stage, as well as the botanical, nutrient and water content of peat, peatland forests are divided as minerotrophic, mixotrophic and ombrotrophic ones.
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