I am walking around a forest regeneration site. As I often do, I count the number of tree species in an individual forest stand. I arrive at nine, so we are fairly far south and on a fertile, exceptionally representative site. Spruce and pine have been planted on an area of just over one hectare, but silver birch, downy birch, aspen and rowan have also regenerated there naturally. In addition, black alders grow, as they typically do, in the buffer zone left along waterways. Just as typically, a couple of goat willows grow on the verge of a forest road. Nutrients flowing down to the foot of a small steep slope provide growing conditions for a group of small-leaved limes.
The group of alders by the shore contains trees of many ages, some already decaying. A gust of wind makes the glossy-shelled alder leaf beetles feeding on the alder leaves glimmer in the sunlight. The milkcaps rising from the ground are a reminder of the seamless cooperation between root fungi and their host trees below ground. Alder trunks are adorned with a diverse range of polypore species, like a tree-species-specific display table. The most distinctive are alder bracket fungi. On fallen wood, the flower-like alder leather fungi, with their broad caps, stand out proudly. On standing trunks, alder polypores grow in dense groups. On top of old alder polypores, a yellow southern bright spot of the polypore world can be seen: the butter polypore. It requires alder polypore and the wood decayed by it as its substrate. There is often a fascinating sense of endlessness in the interdependencies between successive species.
In summer 2022, Metsä Group limited its wood purchasing and its industrial use of pulpwood, sawlogs and energy wood to pine, spruce, birch and aspen with a diameter of less than 40 centimetres. Grey alder, black alder, large aspens, goat willow and other tree-like willows, rowan, bird cherry, maple, oak, juniper, small-leaved lime, elms, ash and a few sparse south-western tree species are left in forests. The list of tree species to be retained in forests is long, and the list of associated species dependent on these trees is even longer. Even so, rare broadleaved trees account for only three per cent of the total volume of Finland’s growing stock.
We can now estimate that, in addition to the reserve of retention trees from the dominant growing stock, millions of rare broadleaved trees have been left in forests over the past four years to grow, develop into old trees and eventually become deadwood. All insect-pollinated tree species are among the trees to be retained, which, from the perspective of forest pollination services, supports the observed positive development in the coverage of lingonberry and bilberry together with lighter soil preparation.
Forestry in the 20th century simplified the tree species composition. Hostility towards aspen and the removal of so-called “worthless trees” weakened the position of rare broadleaved tree species in forest nature. Deadwood, too, was not desired, and both its diversity and total amount declined. Since then, the direction has changed. The aim of regenerative forestry is to increase the proportion of deciduous trees on suitable sites, increase the number of rare broadleaved trees, and increase the number of old tree individuals and large-diameter decaying trunks for all tree species that occur naturally in Finland. This also helps forests remain healthier, as single-species stands are more vulnerable to damage.
Forest owners have welcomed Metsä Group’s tree species policy as a positive initiative. Forest-related discussions are now increasingly focusing on different tree species. Forest owners are interested not only in the site requirements and associated species of different tree species, but also in the potential of different tree species to help forests adapt to our rapidly changing climate. Finland indeed needs a tree species vision and roadmap that strengthens the climate resilience of forests and increases the number of forest species in commercial forests. The range of tree species used industrially should be diversified, which would also promote the favourable development of forest nature.
Both forestry and forest biodiversity are based on an overall system defined by tree species composition, the site factors of forests and their stages of development. Both wood production and the safeguarding of forest biodiversity can be developed from these same basic starting points. Today, this is no longer done separately, but simultaneously as a mutually supportive whole.
The forest of tomorrow grows from the quiet power of biodiversity. With every planted seedling and every tree retained in the forest, we are writing the future of our forests. When we give the forest options, we give them to ourselves as well.