Forest landscape change in boreal Sweden 1850-2000

In the project described in this thesis, structural changes that have occurred in the boreal Swedish forest during the last 150 years were studied through analysis of historical records. Historical perspectives on forest landscapes provide a better understanding of natural disturbance dynamics as well as anthropogenic changes and a frame of reference for assessing current ecological patterns and processes. The studies were performed at various spatial scales, and were conducted in two different forest regions in boreal Sweden. In the district of Lycksele, Västerbotten county, changes were studied from stand to regional scale within the same geographic context. In the county of Dalarna changes in the age distribution of large diameter trees were studied at county and landscape scales. Different types of spatially explicit historical data were used, including delineation and forest surveys, early timber counts and data from the first Swedish National Forest Inventory. Quantitative data on changes in logging and forest management were also included, and Geographic Information Systems (GIS) were used to integrate various types of historical records and to perform spatial analysis at different scales. During the last 100 years a sharp reduction in complexity of the forest structure has occurred at all spatial levels. A multi-aged forest matrix has been replaced by a patchwork of forest stands of various ages. Most stands are younger than 100 years and dominated by even-aged forest. The current landscape structure created by forest management differs radically from the earlier landscape structure created by fire disturbance. At the end of the 19th century, deciduous patches were large and occurred at recently burned areas at higher altitudes. Today deciduous stands are distributed more evenly in the landscape and are connected to logging disturbance. Deciduous trees have been systematically removed during the 20 m century and today most deciduous trees occur in young stands. Both mean tree age and age variation of large diameter trees has decreased and nowadays large trees older than 400 years are rare in the boreal forest. Historical records provide unique spatially explicit information on forest structure at various spatial levels that could not be gathered in any other way. Forest surveys are useful for describing historical landscape structure and structural changes from larger stand (>100 hectares) up to regional levels. At smaller spatial scales the resolution of the forest survey maps are too coarse and analysis should be complemented with other types of historical records or other historical methods. A systematic approach to increase our knowledge of previous landscape patterns and regional variation in disturbance dynamics is presented. "Retrospective gap analysis" involves local analysis of historical records and integration of historical data in ecological landscape planning. In intensively managed landscapes the method can provide a framework for multi-objective forest management and restoration efforts at regional level. The method can also be used to develop regional goals for strategic conservation planning, or to refine goal-setting in forest certification