Forests can be grown by periodic cover forestry as an even-aged forest, or by continuous cover forestry as an uneven-aged forest. The choice of a suitable silvicultural method is influenced by the structure of the forest and the characteristics of the soil, as well as the goals of the forest owner in managing the forest property.
Periodic cover forestry
In periodic cover forestry, there is a distinction between the growth phase and the regeneration phase in forest development. In the growth phase, the main emphasis of forest management is on the management of growing stands through tending of seedling stand and thinning, and finally there is a regeneration felling. The regeneration phase ensures that the felled stand is replaced by new seedlings naturally or as a result of cultivation, that is, by seeding or planting. Periodic cover forestry ensures the continuity of rotted trees over tree generations and broadleaved tree mixture starting from the establishment of the seedling stand.
Continuous cover forestry
In continuous cover forestry, the forest is not regenerated and grown as a single, even generation of trees, but there are trees of many sizes and ages. When felling, part of the forest is removed by selection cuttings and small-scale clearcuttings. The felling cycle is repeated in the forest approximately every 15–20 years. Small trees account for the largest share of the trunks. A prerequisite for continuous cover forestry is that new seedlings are born naturally and new trees develop from the undergrowth reserve. The trees must be healthy.
The aim of intermediate felling, or thinning, is to accelerate the growth, thickening and strengthening of the remaining stands of trees, by increasing their room to grow, thereby promoting the growth of the healthiest, most economically valuable, and highest quality trees. Thinning operations affect tree species composition, maintain the health of the forest, reduce natural loss and generate income. The profitability of thinnings and the further development of the forest can be affected by thinning methods, which are low thinning, high thinning, quality thinning and line thinning.
It is important to do the first thinning in time so that the growth condition of the forest does not deteriorate. In the absence of growing room, the tops of the trees shrink and the growth slows down. A suitable time can be deduced from the crown of the tree. The share of a connecting crown for pines should be 40 per cent, for spruce 60 per cent and for birches 50 per cent of the length of the tree. Depending on the place of growth and the tree species, the first thinning is done when the stands are 10–16 m long.
Quite often, the next thinning is done about 10 to 20 years after the first thinning, when logs are also obtained from the forest. The need for thinning is assessed on the basis of stand growth and its density.
Thinning models specific for certain tree species have been prepared for each habitat type in Southern, Central and Northern Finland. Spruce and birches are often thinned twice before the regeneration, and pines can have three thinnings. In spruce forests contaminated by Annosum root rot, only one thinning is recommended before the regeneration felling.
In thinnings, biodiversity and wildlife management can be promoted by leaving dense bush growth for forest animals in addition to retention trees and by favouring broadleaved trees.
From the Metsään.fi service you can check the felling possibilities of your own forest. Before commencing the measures, a forest use notification should be made to the Finnish Forest Centre about the felling operations.