The Late Holocene history of beech Fagus sylvatica and Norway spruce Picea abies at stand-scale in southern Sweden

University dissertation from Quaternary Sciences

Abstract: High resolution pollen analysis was carried out on five peat profiles from small forest hollows at four sites in southern Sweden. The general aim was to investigate the establishment of Fagus sylvatica and Picea abies at stand-scale. The sites used for this study were all located within the area where the present distribution limits of Fagus and Picea overlap each other. The results from the different sites are presented in more detail in separate papers (Appendices I-IV). Viewed on a continental scale the migration pattern of Fagus can be correlated with climate and its change over the millennia, but at finer scales such a correlation is weaker. At stand-scale there are factors other than climate that are crucial for the establishment of Fagus (e.g., disturbance, seed dispersal, human activities). The establishment of Fagus does not show a regional coherence in southern Sweden, and this may imply that climate was not the limiting factor for its establishment. The present day distribution of Fagus in southern Sweden suggests a migration with a discontinuous front with outlying populations, and this model probably applies to its past distribution. This type of migration means that the landscape becomes infilled by dispersal from outpost stands. The timing of stand-scale establishment is then largely influenced by site-specific factors and chance. Fagus may still be migrating northwards in Sweden. It grows well in its outpost area, and it seems that present day land-use, not climate, is the limiting factor for local Fagus expansion. Fagus seeds are highly dependent on ground disturbance for successful establishment, and an undisturbed forest then consequently would be able to resist Fagus invasion for some time. A semi-open cultural landscape may be optimal for Fagus establishment, as cultural activities may create conditions particularly suitable for its regeneration. Picea invaded southern Sweden from the north during a period when the cultural landscape had already been evolving for some time. Picea is a dominant tree with an effective seed dispersal, and the relatively open and probably grazed forests in the area were not particular resistant to Picea invasion. An intensive grazing regime may not affect Picea, as grazing animals normally avoid Picea. The timing of local Picea establishment seems to be mostly controlled by its migration, i.e., it became established when its front reached the studied sites.

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