Forests of a single tree species are more vulnerable to damage. Stands with mixed species are thus a good way to improve forests’ resilience to damage and help them adapt to a changing climate. Another excellent way to improve the climate resilience of forests is the mixed cultivation of both spruce and pine on a suitable site. This reduces the risks that especially spruce faces due to the increasingly common droughts. However, spruce increases growth density, which is necessary for pines in terms of moose damage. The tree species best suited to the site type can be chosen during young stand management, and some of the naturally generated broadleaved trees can also be left in place.
We consider the fertility of the site in decisions on mixed cultivation. For example, a forest predominated by pine is sought for more barren site types. In areas that grow bilberries or that are lusher, the goal is a mix of coniferous trees and approximately 10 per cent of broadleaved trees.
Metsä Group’s updated guidelines for young stand management address mixed cultivation from early cleaning onward. In practice, this means leaving a few random silver birch grown from seed in a stand of conifers during early cleaning, which ensures that the silver birch are not taller than the conifers. The silver birch can be used for premium plywood in the future.
If all broadleaved trees were cut in early cleaning, the broadleaved trees left in place during thinning would derive from shoots and would thus be of a poorer quality. During early cleaning, all broadleaved trees that are clearly ahead in growth or derive from sprouts are removed. Other tree species are left in place, especially in empty spots, and their density is kept in check. A good rule of thumb is to ensure that the number of tree species is the same before and after young stand management.
The choices made in young stand management pave the way for the future mixed forest. If all the broadleaved trees are removed during young stand management, it is difficult to increase their share during the remaining forest cycle. In other words, now is the time to begin preparing for the changing climate. A mix of different species safeguards forest diversity, offers a range of alternatives and improves the climate resilience of forests. This is why mixed forests are an investment in the future.