Peatlands are ecosystems where the production of biomass exceeds its decomposition. The result is the accumulation of organic matter coming from plant debris and especially Sphagnum mosses that dominate peatland vegetation. This more or less decomposed plant biomass forms the peat. Sphagnum mosses grow a few centimetres a year in height, but because of the subsequent decomposition and compaction processes of the plant material, the rate of accumulation of peat is only about 0.5 - 1 mm per year. Thus, deep peat deposits are the result of thousands of years of accumulation of plant debris. Therefore, it is clear that restoration will not regenerate peat at a rate that would permit peat extraction in the near future.
Peatlands can develop by two processes: 1) terrestrialization or infilling of shallow lakes; or 2) paludification of poorly drained land, which is the formation of peat directly on mineral soil. With time, the accumulation of plant debris changes the environmental conditions of the substrate, causing a shift from aquatic to semi-aquatic habitats to fen that can then evolve to a bog environment with increasing peat thickness.
Fens are a type of peatland that are fed by precipitation and surface runoff water. Because runoff water comes in contact with mineral soil, it is enriched in base cations. For this reason fens are also called minerotrophic peatlands. Fen vegetation communities vary a lot, but they are often dominated by sedges that are the origin of sedge peat. With the accumulation of peat, peatlands slowly become higher than the surrounding ground and reach a point where they are only fed by water from precipitation. From this moment, plants cannot have access to mineral rich water coming from adjacent lands and this triggers the change toward a bog environment: minerals availability decreases significantly, acidic conditions develop and Sphagnum dominated plant communities capable of supporting such conditions replace sedge vegetation.