The relation between the occurrence of forest site types and swamp types was studied using data collected in the national line survey of Finnish forests carried out in 1921‒1924. The majority of peatlands in Finland has been formed by forest land becoming paludificated. When the peat layer is thin, the fertility of the peatland depends on the underlying mineral soil, consequently, good swamp types occur on fertile subsoil and poor types on poor subsoil. When the peat layer becomes thicker, the relationship weakens. The surrounding mineral soils influence the quality of the peatland by the runoff from the catchment area. The direct comparison of forest site and swamp types is not possible, because for one forest site type there are several swamp types that have different levels of humidity. According to the study, a very distinct mutual relation can be seen between occurrence of forest site types and swamp types.
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