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Tending options for seedling stands
On this site, we demonstrate the establishment of spruce-birch mixed forest in the juvenile stand management and compare the later development of mixed stands with that of pure spruce and untreated spruce stands.
The seedling stand is growing on fertile site (OMT). The stand was clearcut in November 2016, mounded in June 2017, planted with Norway spruce in September 2017, and early cleaned in October 2019. In June 2024, four treatment areas were established in the seedling stand: no treatment, a pure spruce stand, and two spruce-birch mixtures where birches as tall as or taller than spruces were left to grow. Outside these treatment areas, the seedling stand was managed according to the Metsähallitus practices.
At the seedling stage, birches can be slightly taller than spruces, ensuring good crown development and diameter growth in mixed stands. During precommercial thinning, it is important to monitor the density of the remaining trees to ensure that birches supplement, rather than increase, the overall density. Furthermore, protective thickets and important tree species such as aspen, alder, rowan and willows should be preserved as individual trees or groups of trees. Adjacent to the precommercial thinning site is the tree species diversification site, where a variety of tree species have been planted to enhance biodiversity. These species include oak (Quercus robur), alder (Alnus glutinosa), larch (Larix sibirica), Douglas fir (Pseudotsuga menziesii) and maple (Acer platanoides).
Tree species diversification
Diversification of tree species selection increases climate resilience of forests
Regeneration tree species are selected based on site fertility and soil type to ensure optimal use of the land's productive capacity for forest growth. To enhance biological diversity and climate resilience, forest regeneration focuses on diversifying the tree species suitable for the site. Our three main tree species—Scots pine, Norway spruce, and silver birch—offer good opportunities for this, except on infertile sites suitable only for pine. Species diversity can be enhanced by using different tree species in various regeneration areas, different parts of the regeneration area, or as mixtures.
Planting spruce is a common method of forest regeneration as it gives good results, and planting pine and silver birch involves the risk of browsing damage. However, climate change makes spruce more susceptible to drought and other causes of damage. To adapt to climate change, it is essential to increase the diversification of tree species selection in forests and to select species that are suitable for the site.
In addition to the main tree species, planting less-used tree species is an option if the site is suitable. For example, planting alder on wet sites is a good alternative to planting spruce. Even individual trees or groups of trees can contribute to the variety of tree species and enhance the overall diversity of the forest.
PUUVA test sites and tending options for seedling stands
On this site, we demonstrate how less-used tree species diversify the forest's tree species selection and compare in growth to Norway spruce (Picea abies).
The stand is growing on fertile site (OMT) characterized by fine sand mineral soil. In February 2023, a coniferous mixed forest of about 60 years old on this site was clearcut. The regeneration area was mounded by an excavator in May 2023.
On the regeneration area, circular plots (900 m2) were planted with oak (Quercus robur), alder (Alnus glutinosa), larch (Larix sibirica) and Douglas fir (Pseudotsuga menziesii) in June 2023. The intermediate areas between the circular plots were planted with spruce seedlings in June 2024. The species-specific planting densities were: larch 1300 trees/ha, spruce, alder and Douglas fir 1800 trees/ha and oak 2000 trees/ha. Additionally, small groups of maple (Acer platanoides) were planted.
