Mature forest provides wood for many purposes.
When a forest stand gets mature, its growth slows down. Older trees with weakened vital functions are more vulnerable to natural damages brought on by weather, fungi and insects. In commercial forests, forest regeneration should be started when the yearly growth of mature forest has declined but trees are still healthy. The right timing ensures the best economic outcome for forest owners and the harvest of high-quality raw material for wood products.
The age at which a forest stand matures and is ready for regeneration depends on factors such as the latitude, the tree species and the type of soil. Regeneration age in Finland is usually between 60 and 120 years. Forests in more southern locations and with broadleaf tree species reach maturity earlier compared to those in northern latitudes and conifers. In Finland, regeneration areas are relatively small in size, just around 1,5 hectares on the average.
In natural forests, two factors trigger forest regeneration: small-scale dynamics via canopy openings caused by the death of single trees; and large disturbances where a forest stand dies as a result of natural damage. In commercial forests, the same ecological rule applies: to be able to regenerate, existing trees must first fall. Thus, regeneration starts with harvesting.
The most common methods of regeneration felling are clear-cutting and seed-tree cutting. During clear-cutting, all trees except retention trees, deadwood and other protected trees are harvested. The soil is then prepared for planting seedlings or sowing seeds. In the seed-tree method, trees from the previous generation (20 – 100 per hectare, depending on species) are left at the harvesting site to produce seeds. The soil only needs to be lightly prepared and regeneration occurs naturally over the next couple of years.
Small-scale clear-cuttings and strip harvestings are useful methods for sites with special needs. They can be used where there is high recreational value, landscape planning needs, special environmental targets or if successful forest regeneration would be expensive and difficult with other methods.
Forests can also be grown as a continuous cover stands. In this case there’s no actual final felling and regeneration occurs naturally when dominant layer trees are harvested. The undergrowth already present is utilised. To create continuous forest cover, harvesting must be intense enough to create suitable conditions for new trees to grow. Continuous cover forestry must meet some prerequisites regarding the site and existing forest structure for it to be silviculturally and economically viable.
Planting is the starting point for new forest growth.
In thinning, growing space for best trees is created.
Deadwood is one of the key elements for biodiversity.