Strukturella förändringar i Östergötlands skogar : En jämförelse mellan år 1927 och 1983–2017

Sammanfattning: Humans have affected the Swedish forests for a long time, mainly through agriculture and forestry. Since the beginning of the 20th century, a lot of changes have taken place in forest policy, which have affected the structures of our forests, such as tree age, size and species distributions. By using information from different types of historical data, we can increase our understanding of the earlier structures of forests and how to manage them in the future. This study investigated changes in annual growth and changes in age, diameter, height and tree species distribution in the forests of Östergötland from year 1927 to the period 1983-2017, using data from the Swedish National Forest Inventory. Six tree species where used, Picea spp, Pinus spp, Quercus robur, Betula spp, Alnus spp and Populus tremula. There was an increase in the proportion of Picea spp, and a decrease in the proportion of Pinus spp since 1927. The proportion of deciduous trees also increased but not as much. Interestingly, the proportion of Betula spp had fallen since 1927, but the now larger proportion of young trees indicate that the proportion of Betula spp is increasing again. Q. robur, P. tremula, Picea spp and Pinus spp also had a larger proportion of younger trees in the more recent period. There was a significantly higher proportion of tall trees during the latter period for all tree species. For growth rate in width, the results varied among tree species. For Betula spp it had decreased and for Q. robur it had increased. For the coniferous trees there was hardly any difference between the periods. Overall, the results show that Östergötland's forests have been influenced by forestry and increased ungulate populations since the first inventory 1927 and that there have been changes in the composition of the forests.