Part I
At the 'Forest Arena' event organised by the Natural Resources Institute Finland (Luke) in Helsinki at the beginning of October, Professor Jari Hynynen and Senior Scientist Sauli Valkonen reported on the differences in silviculture between continuous-cover forests and periodic-cover forests.
Even when avoiding clear-cutting, a forest requires specific management if we wish to preserve biodiversity.
When comparing clear-cutting and non-clear-cutting methods, no significant difference was found in their impact on mitigating climate change factors. According to information provided by the Natural Resources Institute Finland, there is a significant difference in the volume of timber harvested, which leans in favour of clear-cutting.
A group of 12 scientists from the Natural Resources Institute Finland studied the differences between non-clear-cut and clear-cut silviculture. The study took into account eight indicators: forest regeneration, the volume of timber produced, forest harvesting and log supply, profitability, the risk of forest damage, biodiversity, forestry in peatlands, and activities related to the protection of other ecosystems and the climate.
The summary was prepared by Professor Jari Hynynen and Senior Scientist Sauli Valkonen. The research data was collected for all types of non-clear-cut forestry, such as selective logging, thinning from below (i.e., only harvesting the thickest logs), and small-gap harvesting, where the clear-cut area is 700-5000 square metres.
The data obtained were compared with stand thinning and regeneration felling indicators in clear-cut forestry, including complete harvesting and the seeding, planting, or natural regeneration of a new forest.
Clear-felling creates a favourable environment for species that inhabit thinned forests, while non-clear-cut forestry is preferable for species that inhabit high-density stands.
According to biodiversity researcher Juha Siitonen, non-clear-cut forestry is better for species that do not thrive in thinned forests. This includes bilberries and species that feed on bilberries, as well as species that feed on decaying wood.
Currently, there are few natural environments with dense forest cover in Finland, which suggests that the area of forest managed using continuous-cover silviculture needs to be increased. There are fewer problems with species that can also survive in open areas.
However, if the areas managed by continuous-cover forestry increase or if this method becomes mandatory, the situation will change. In reality, the continuous-cover forestry method has not proven to be more effective at preserving biodiversity compared to clear-cut forestry.
Furthermore, if you want to make a good profit from your forest, it may be necessary to harvest intensively at short intervals. Continuous removal of the oldest and largest trees will create a forest with fewer broadleaved trees and will not allow for intensive accumulation of deadwood.
This is precisely why nature conservation must not be forgotten in continuous-cover forestry.
Trees retained during felling must be left standing, and natural assets that form an ecologically significant habitat must be protected.
As for climate change mitigation, there are no significant differences between the two silvicultural methods. The fact applies to both methods: the more timber is harvested, the lower the standing stock, and therefore, the lower the carbon stocks in the forest.
Is natural forest regeneration a sensible method?
The Finnish Forest Act stipulates that a forest owner must establish a new forest stand after regeneration felling. This can be achieved by seeding or planting, or by leaving enough uncut trees in the felling area so that they naturally begin the regeneration of a new forest.
In continuous-cover forestry, the regeneration process occurs naturally. This is an essential component for the method to be profitable, as savings in resources are achieved by avoiding soil preparation, seeding, planting, and other silvicultural operations.
Therefore, it is crucial for this method that natural regeneration proceeds successfully. Judging by the results of the study, it may work for now, but in the long term, it is not guaranteed.
The study proved that in southern Finland, a sufficient quantity of spruce seedlings forms naturally after selective harvesting. Most of them grow into large trees and reduce losses from harvesting or natural causes.
However, there are empty patches in the new growth areas, and the seedlings have a tendency to grow in tight clusters. They grow slowly – it can take 40-60 years for a sapling to reach a height of 1.3 metres, whereas in a periodic-cover forest, trees of that age have reached almost log size and can soon be harvested.
Growth can be accelerated by thinning the clusters, which, however, will reduce timber production. Harvesting small-diameter trees leads to variable seedling yields.
To be continued.
Figure 1. Professor Jari Hynynen and Senior Scientist Sauli Valkonen at the 'Forest Arena' event organised by the Natural Resources Institute Finland in Helsinki at the beginning of October, reporting on the differences in silviculture between continuous-cover forests and periodic-cover forests. Photograph by Antti Ranki.
Figure 2. The diagram illustrates selective logging, where the largest trees are harvested while the others are left to grow to construction timber size. Photo by Juha Varhi (Metsäkustannus).