Epsilon Open Archive

Abstract

Temperate broadleaves used to be abundant in the primeval forests in southern Sweden, yet today they cover only fractions of the forest land. Considering the present small area of the forest type, the habitat is of considerable interest for biodiversity, and knowledge about the history of temperate broadleaves is crucial for forest conservation and management. The main method used for studying past forest composition is pollen analysis, yet differences in pollen production and dispersal among taxa have hampered the estimation of historical cover of temperate broadleaves. By applying the Landscape Reconstruction Algorithm (LRA), a new model for translating pollen data into quantitative cover estimates, significantly improved understanding of the vegetation cover can be gained.

The applications of the LRA to local and regional pollen data from southern Sweden carried out in this thesis show that in many areas, large cover of temperate broadleaves prevailed locally until rather recently, which is likely to be an important cause for the survival of the many threatened species associated with these tree taxa today, although in small and vulnerable populations. Many of our study sites showed no tendencies of local decline of temperate broadleaves until during the most recent 500 years, which is considerably later than in the region as a whole, as well as what has often been emphasized in other studies. For Tilia, the cover of which has confounded researchers since the introduction of pollen analysis, the decline in the southernmost parts of the country was not as early as commonly thought, but in general almost as recent as for many other temperate broadleaves.

In this thesis it is also shown that in many presently protected biodiversity hotspots the forest composition changed radically during the last 500 years, and hence not even these hotspots can be claimed to have unbroken continuity back to ancient forests, or to be a reflection of "natural" forest in southern Sweden. Land use changes, such as forest clearance for agricultural purposes, as well as grazing and browsing by domestic animals are likely to have been important causes for this vegetation change.