Abstract
Field data and simulations were used to investigate possible edaphic causes of patchy dominance by conifers and temperate deciduous trees in the boreonemoral transition zone of east- central Sweden. Tree species, basal area and soil conditions were recorded for 39 plots of 10 m radius on a ca 30-ha uninhabited island in Lake Malaren. Canonical correspondence analysis produced a single dominant axis of variation in species composition related to soil depth, pH, organic mailer and texture. The forests on the island included most types found in the surrounding region. The simulation model links patch-scale tree demography to the effects of trees on the light environment, with tree growth rates further influenced by climatic variables, soil moisture and nitrogen availability. Soil water holding capacity and nitrogen availability were varied systematically in a model experiment. The simulated response surfaces of tree species accord with reality. When each field site was matched to the most similar model treatment. the observed soil conditions of the field sites were strongly correlated with the modelled nitrogen-availability gradient. These results are consistent with a systems approach to vegetation dynamics that incorporates interactions between species composition and nitrogen-availability with climate, soil conditions and landscape position as external constraints.
