Changes in mixed deciduous forests of boreal Sweden 1866-1999 based on interpretation of historical records

Current knowledge of patterns and abundance of deciduous trees in the pre-industrial landscape of boreal Sweden is limited. This is due to a dramatic transformation of the forest landscape during the last 100 years and the lack of representative forest reserves. We used historical records to study change in five mixed deciduous forests between 1866 and 1999. The results show that large changes occurred due to complex interactions between fire disturbance, fire suppression, logging and silviculture. Before fire suppression, the presence of deciduous trees was mainly determined by earlier fire influence. Later selective logging disturbed natural succession and favoured regeneration of deciduous trees. During the 20(th) century deciduous trees were removed by girdling, thinning and herbicide spraying. Much of the mixed deciduous stands changed to coniferous stands between 1906-15 and 1969-70, and then deciduous trees were totally removed from these stands between late 1960s and 1999. Today mixed deciduous forest occurs mainly in young stands and on other sites than previously. Our results also show that large coniferous trees and multi-aged forest occurred in all sites in the early 1900s. Most sites were dominated by coniferous species and forest dominated by deciduous trees occurred only in smaller areas. These results are not consistent with the current view that deciduous-dominated forest occupied substantial areas in boreal Sweden before fire suppression. Appropriate changes in forest management are discussed, as is the value of historical data in interpreting changes in forest landscapes.