A large-scale habitat type, which includes our paludifying forests, (true) fen forests, and swamp forests. They all grow on flat land, in flat depressions, or at the foot of slopes where groundwater is close to the ground. The groundwater level is variable: in spring, it is high, often reaching the surface, while in summer, it drops deeper.
In paludifying forests, the thickness of the peat horizon does not reach 30 centimetres; in fen and swamp forests, the moderately or well-decomposed peat is thicker. The low-mobility groundwater of fen forests is rather poor in terms of minerals; the more mobile groundwater of swamp forests contains more minerals. In the initial stage of paludification, spruce and white birch dominate in places in the tree layer, whereas the moor birch dominates in fen forests and the black alder and the moor birch dominate in swamp forests.
There are paludifying and fen forests everywhere, but they are more abundant in Central and North-Western Estonia, while swamp forests grow more in North-Eastern, Central, and South-Western Estonia.
Includes the following habitat type groups according to Paal: 131 (rich paludified forests) and 141 (minerotrophic swamp forests).