>> Background information

Development

The age structure of Finnish forests has changed considerably during the past 90 years. From the point of view of biodiversity, the most remarkable change was the decline of old forests in northern Finland by more than half between the 1920s and present. In the 1920s almost 45% of all forests in northern Finland were above 141 years of age, but by 1990 the share of old forests had declined to 19%. During the past twenty years the share of 141+ forests has declined by a further 12% although between the two latest National Forests Inventories there was no change.

The age structure of forests in Southern Finland was already heavily altered by human activities in the 1920s. Mostly due to widespread slash-and-burn cultivation the share of 141+ forests was as low as 0.7%. Since then the share of the oldest age group has increased more than two-fold. On the whole, however, their share remains small (1.6%) and has not increased since 1990.

Simultaneously with the marked decrease of old forests in Northern Finland and slight increase in Southern Finland, the share of very young stands (1-20 years) has increased threefold in both parts of the country. On the other hand, the area of treeless areas has remained at approximately one percent of the total forest area.

Impact on biodiversity

The age structure of a natural forest is normally much more heterogenous than that of a managed forest. Commercial regeneration fellings create even-aged stands with small retention tree groups. Natural forests are composed of different aged and sized trees that normally include some very old individuals. Due to natural loss, these forests contain large quantities of dead and decaying wood (see FO6). Disturbances which occur at random intervals in the crown of a spruce forest, for example, enable also deciduous trees to thrive. This increases the heterogeneity of a forest stand even further.