The Finnish classification of forestry land is based on the annual forest increment. On productive forest land the annual increment per hectare is over one cubic metre. On poorly productive forest land the increment is 0.1–1 cubic metres, and on unproductive land less than 0.1 cubic metres per hectare per year. In addition to this, forestry land is taken to include protected forests logging roads, intermediate timber storage areas by the roadside and other similar areas.
Source: Natural Resources Institute Finland (stat.luke.fi) and National Forest Inventory. Graph updated 7.6.2019.