During the 20th century Finnish forestry gradually introduced a form of forest management in which the forest is managed in cycles called rotation periods, ending in forest regeneration. The purpose of this is to simulate the natural development of a forest, called succession, during which several succession stages and habitats follow each another.
The rotation period ends in a regeneration felling, which is also considered the beginning of forest regeneration. A regeneration felling may include the removal of all or almost all trees (clear cutting or clear felling) depending on the guidelines of forestry management, but seedling trees or mother trees (seedling felling) or shelterwood (shelterwood felling) may also be left unfelled.
Clear cutting or clear felling means the felling of all or nearly all trees in a forest, depending on the guidelines of forestry management. According to PEFC-certification, 5–10 trees are left permanently standing in connection with clear felling. Their purpose is to promote biodiversity.
Leaving seedling and shelterwood trees unfelled means that the regeneration is called natural, because the new trees are seedled naturally. In a seedling felling, 50 to 150 seedling trees are left per hectare. The seeds from these trees will grow into a new forest after the final felling.
Shelterwood felling is used when felling spruce, if the intention is to generate a new spruce stand on the site. In shelterwood felling, 200 to 400 shelter trees per hectare are normally left, to protect the spruce seedlings, which prefer shade.
After a final felling the forest is either cultivated – which means either sowing or planting – or allowed to regenerate naturally, in the case of seedling felling. Once the stand has become stabilised, the seedling trees and shelterwood are removed in a cutting of hold-overs. The first trees to spread naturally onto a felling site are called pioneer trees. In connection with regeneration, the soil is often prepared.
The normal rotation period in Southern Finland is 60 to 80 years. At the end of the rotation period, the forest is called mature or regeneration-ready. During the rotation period of a forest area, seedling stands are tended and thinnings are carried out.