There are many kinds of forests, and a single cultivation method is not the right choice everywhere. In the cultivation of different kinds of forests, there is room for both continuous cover and periodic cover forestry.
The former, continuous cover forestry, is the subject of lively debate. Depending on one’s perspective, it is considered either the only sustainable method of forest management or a serious threat to the sustainability of forests. And sustainability is, of course, a key principle of forest management, although a demanding one. The goals of its various aspects – financial, ecological and social sustainability – are hard to reconcile without compromises. The sometimes even sharply polarised differences of opinion are largely about how each of us understands the word “sustainability”.
Continuous cover forestry involves diverse management methods. Selection cutting is best suited for forests dominated by spruce. In this method, the biggest trees in the forest are removed, while the cover is retained across the entire management area. However, the felling is done with a heavy hand, so that the naturally regenerating seedlings in the undergrowth are provided with enough light and room to develop.
Group-selection and strip felling are basically small-scale continuous cover cultivation. They involve the making of small gaps in the forest which, according to current practice, are allowed to regenerate naturally. According to the law, regeneration is not mandatory if this gap is less than 0.3 hectares in size.
The most important prerequisite for sustainable wood production is ensuring the regeneration of the growing stock. There is strong research-based evidence suggesting that natural regeneration and seedling growth without forest management measures are more uncertain and slow in continuous cover forestry than in managed, even-aged plantations. As yet, there is not enough research data to show whether regeneration in continuous cover forestry is sufficient in replacing the amount of trees removed during the cuttings in the long run.
After selection cutting, the growing stock is visibly sparser and grows at a slower pace than in even-aged thinning stands. According to various studies, wood output in continuous cover forestry is 15–25 per cent lower than in periodic cover forestry. The greatest risk for wood production is posed by the root rot of spruce stands, and continuous cover forestry creates lamentably favourable conditions for the spread of this.
Biodiversity must be looked after. A forest’s biodiversity cannot be safeguarded by either continuous cover or periodic cover forestry itself without the necessary nature management measures. Sturdy decaying wood and a mixture of deciduous trees are particularly important structural features for the biodiversity of forests. Similarly, big and old trees are valuable and should be retained, regardless of the cultivation method. Continuous cover forestry favours species for which the continuous cover of a forest and the undergrowth in such forests is important.
Paying attention to forests’ carbon binding is increasingly important. In pine barrens, the intensity of the felling has the strongest impact on the volume of the growing stock and on carbon binding, regardless of the management method. In peatlands, most of the carbon storage is in the soil. Nutrient-rich, drained peatland forests release large amounts of carbon into the atmosphere as the peat decomposes. In such forests, continuous cover forestry allows for increasing the soil’s carbon storage and carbon binding.
The predominant forestry method in Finland is periodic cover forestry, which has been studied here for a long time. In recent years, diverse data has also been accumulated on continuous cover forestry. However, data on long-term measurements is still lacking, which is why the long-term impacts continue to involve a great deal of uncertainty.
Nevertheless, the studies have already enabled the identification of sites best suited for different forestry methods and charted the strengths and weaknesses of each. It is indeed clear that the best result in terms of sustainable forest management is achieved by choosing the method depending on the site’s characteristics – in other words, “both”, rather than “either/or”.
Natural Resources Institute Finland (Luke)