Retrospective land cover/land use change trajectories as drivers behind the local distribution and abundance patterns of oaks in south-western Finland

Abstract

Valuable cultural landscapes are challenging to sustain. They are usually rare and reflect unique histories of nature–human interactions. We have studied the influence of environmental factors on the present distribution, age and abundance of oaks in a unique forest site in south-western Finland. The Landscape Change Trajectory Analysis (LCTA) approach was tested to improve management strategies at a local level. We used geospatial analysis in GIS on existing data from a recent forest inventory, a multi-temporal land cover/land use analysis, and a digital elevation model. The results show that mature Pendunculate oaks ( Quercus robur) are restricted to the eastern parts of Ruissalo island and their present abundance patterns can be linked with change trajectories as opposed to physical conditions. While the prevailing strategy of strict protection seems to lead to an increasing amount of dead wood, the lack of management hampers the regeneration of oaks. We suggest four principles for future management of these sites that could be applied throughout the hemiboreal region of Europe with similar historical development: (1) management regimes should be spatially explicit in terms of land cover history instead of treating valuable oak biotopes as one homogenous unit; (2) management units should be determined by biotope dynamics and development rather than present status and distribution; (3) management should allow strict protection of sites with long duration of protection and high abundance of decaying oak wood to support biodiversity; (4) alternative management regimes should be introduced in sites with high potential for re-establishment of light-abundant favourable conditions.