| Abstract: | Abstract. Computer simulations were used to elaborate hypotheses about controls on forest structure and composition in a 0.7 km ≤ area of boreal forest in Central Sweden. DBH and species of all adult trees and stand conditions were recorded for 57–10 m radius plots. Ordination of these data suggested that nutrient-availability and time-since-disturbance were the main controls of forest composition and structure within the area. The simulation model couples equations representing the effect of tree canopy structure and biomass on light and soil conditions with equations representing the effect of these conditions on reproduction, growth and mortality in height cohorts of trees on a 0.1 ha patch. Nitrogen-availability levels for each modeled plot were simulated by species-specific growth multipliers. The model was run for 400 simulated yr at six levels of N availability. Age and N status of each study plot were inferred by matching with the most similar model output. Inferred ages agreed with what is known of the disturbance history, and site factors related to soil fertility were correctly correlated with the inferred N status. The consequences of size-selective disturbance were explored by model experiments. Biomass was removed from large or small size classes at 100 - 200 yr and the simulations were run for an additional 300 yr. Disturbed stands of high N status often became similar to undisturbed stands of different N status. Size-selective disturbances produced stands that were different from any in the undisturbed succession, but these differences disappeared within 50 - 100 yr, implying successional convergence in stand structure and composition. Plots of simulated basal area against time and nitrogen-availability for the four species illustrate the time dependence of species performance along a fertility gradient. |
