Continuous cover forestry

Due to the different starting points of forests, some sites are better suited for continuous cover forestry than others. Healthy and vibrant forests, which have an existing spruce understorey, or which are already of diverse structures, are best suited for continuous cover forestry. Other suitable sites for continuous cover forestry include:

• Fertile mineral soils and lush, drained peatland forests (spruce mires on bilberry and grass peat soils). Spruces sprout in such soil very naturally.
• Forests with existing healthy undergrowth.
• Tension zones of mires and heaths, as well as the marginal zones of fields and water bodies bounded by forests. In these, the tree stock is often already layered.
• Other special forest management sites where the aim is to maintain tree cover, such as recreational and landscape forests.

Continuous cover forestry is not recommended on sites where a high presence of Heterobasidion root rot is observed. Through root connections, the root rot easily spreads to naturally regenerated seedlings. Read more about root rot

Also, over-dense, unmanaged and spindly forests are not recommended for continuous cover forestry, as smaller trees are usually in poor condition at these sites.

In terms of regeneration, it is essential that the soil condition is such that sprouting is easy and natural. A thick layer of mor humus, the raw humus layer of peatlands and abundant grass vegetation hamper natural regeneration of seedlings. Light tilling can improve regeneration at sites where the conditions are unfavourable to natural regeneration.

Selection cutting is a felling method used in continuous cover forestry to maintain the diversity of forest structure. In selection cutting, the largest log-sized trees are removed first, and dense groups of trees are thinned so that a target number of trees remains in the forest. Damaged and poor-quality trees are also removed in selection cutting, unless they are left as retention trees.

Selection cuttings spare some of the largest dominant log trees to produce seeds for new saplings, also healthy co-dominant trees are retained to develop into future dominant trees. When the existing stand allows it, a variety of tree species is retained in the forest. Pines and deciduous trees let light into the ground layer well, which promotes sapling growth. 

Selection cutting also spares nature sites valuable for biodiversity, nesting trees for birds, deadwood and protective thickets. In addition, permanent retention tree groups are spared, which will also be preserved in future felling operations.

Transferring from an even-aged commercial forest to continuous cover forestry calls for transition cuttings, which alters the even-aged structure of the tree stand towards an uneven-aged structure. The variation in trees can be promoted through group selection felling. Small gaps accelerate the growth of existing sapling groups and the regeneration of deciduous trees and pines. In continuous cover forestry, the size of an individual small gap may not exceed 0.3 ha, and they are part of the continuous cover forestry management area. During felling operations, the surface area of the trees left to grow on the site must be safeguarded, in order to achieve the target denseness in the whole area.

On mineral soils, roots competing for space and the shade from the marginal trees interfere with sprouting around the gap edges. Therefore, leaving elongated, narrow small gaps in mineral soil forests should be avoided. The diameter of a small gap should be at least 20 metres. In the lush growth sites in Southern Finland, grass growing in the small gaps may interfere with sapling growth. In this case, the diameter of the gap should not exceed 30–40 metres in order to keep ground vegetation in check. In small gaps with a diameter of 40 metres, saplings in the middle have good opportunities for growing rapidly, and light-demanding species have good opportunities to thrive. Once the saplings in the middle of the small gap have developed, the small gaps can be expanded in the following cuttings, and new small gaps can be established. 

Group selection fellings in peatland forests are particularly well suited for spruce forests that already have plenty of spruce saplings in the understorey. On peatlands, small gaps and narrow felled strips do not need to be wider than 10–20 metres to create good preconditions for spruce saplings. Pine is a light-demanding species and needs open areas for regeneration, so group selection felling and narrow felled strips are also suitable for continuous cover forestry of bog pine forests.

The continuous cover forestry method suitable for pine stands is overstorey management, which is implemented through seed-tree, strip and selection cuttings. At barren growth sites, the structure of the pine stand is often already uneven-aged, which enables uneven-aged forest management with selection cuttings. Particularly in Northern Finland, there are plenty of pine-dominated forests suitable for selection cuttings. 

Seed-tree cuttings aiming at overstorey management leave seed trees more densely (50–150 trunks/hectare) than even-aged forest management. Slight disturbance of the soil surface promotes seedling establishment at sites where the conditions are unfavourable to natural regeneration. Seed trees are not removed after seedling establishment, but they are thinned several times in future fellings, and some are left as retention trees. By regulating the density of the overstorey, it is possible to create a tree stand with varying structure.