Size-class structure of the forests of Finland during 1921–2013: a recovery from centuries of exploitation, guided by forest policies

• Published in: European journal of forest research 2020-04, Vol.139 (2), p.279-293
• Main Authors: Henttonen, Helena M., Nöjd, Pekka, Suvanto, Susanne, Heikkinen, Juha, Mäkinen, Harri
• Format: Article
• Language: English
• Subjects: Agricultural management; Agriculture; Biomedical and Life Sciences; Conifers; Economic conditions; Financial management; Forest management; Forestry; Forests; Land use; Legislation; Life Sciences; National forests; Original Paper; Plant Ecology; Plant Sciences; Population density; Shifting cultivation; Silviculture; Slash and burn; Trees
• ISSN: 1612-4669; 1612-4677
• DOI: 10.1007/s10342-019-01241-y

Frequency distributions of tree diameters are a powerful tool for analyzing changes of tree populations in large areas. We analyzed the densities and mean volume estimates of trees in different size classes for the Finnish forests over the time-span of the National Forest Inventories (1921–2013). The results display a general increase in trees in all size classes, species group and geographical area, mainly after the 1970s. The densities of medium- and large-sized conifers showed large increases in the southern boreal subzone, spruces even more than pines. Small- to medium-sized pines have increased in the middle and northern boreal subzones. The shifts in growing stock are related to changing land use, resulting from the development of the society. The low quantities of both growing stock and large trees during the 1920s reflect a poor initial state of forests. Several land use forms of the former agriculture-based society were detrimental to forests, including slash and burn agriculture, cattle grazing and tar production. The pressure from alternative land use forms was stronger in southern Finland, where the population density (people per km 2 ) is much higher. Between 1971 and 2013, the changes in size-class structure can be attributed mainly to intensified silviculture boosted by actions of the Finnish governments, including both legislation and financial support for management activities. Not only the development of growing stock has exceeded expectations, but the increase has also concentrated in the economically valuable trees in the large size classes.