Natural mires store carbon and are valuable for biodiversity.
Mires are peat producing vegetation communities which consists mainly of wetland vegetation. Typical plants for mires include for example mosses, sedges and horsetails. Organic soil of mires, peat, is formed by remnants of dead plants. Depth of peat layer increases constantly due to wet conditions with low oxygen levels that make degradation processes to happen ineffectively. Peat layer increment is very slow though. In Finland, annual peat accumulation rate varies from fraction of a millimeter to a couple of millimeters.
Finnish mires have developed after the previous ice age via three different mechanisms: overgrowth of waters, forest land paludification or as a result of land uplift. There are tens of different mire types. Mires can be divided roughly into open and wooded types. Division can be made further based on site fertility. Open mire types range from poor open bogs to eutrophic fens. Wooded types have pine bogs in the poor end and spruce mires on nutrient-rich sites.
In international comparison, Finland is a country of peatlands. Over one fourth of the total land area of Finland consists of peatlands. Mires have undergone a significant transformation due to human activity. In southern parts of Finland almost 80 percent of original mire area has been ditched, the share being around 40 percent in the north. Silvicultural ditching is carried out to improve forest growth on peatlands. Mire conversion to agricultural land and peat production areas has also taken place.
Wide scale ditching projects, done during past decades, have improved the total growth of Finnish forests significantly. It has also led to the decrease of natural state mires. Hydrology is the key factor defining natural conditions and species composition of mire ecosystems. That’s why mires in natural or near natural hydrological state are important for biodiversity. In modern forestry first-time ditching is not done anymore. Natural state mires are left as set-aside areas to safeguard biodiversity.