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1. We investigated the potential drivers of Holocene vegetation changes recorded at four Scandinavian pollen sites, two in Sweden and two in Finland, at a time when they were largely free of anthropogenic influence. 2. We used the generalized dynamic vegetation model LPJ-GUESS forced with climate anomaly output from an atmospheric general circulation model to simulate tree species dynamics from 10 000 years ago to the present. The model results were compared to high-resolution pollen accumulation rates gathered at the sites. 3. Our results indicate that both the observed northern distributional limits of temperate trees, and the limits of Pinus sylvestris and Alnus incana at the tree line, are a result of millennial variations in summer and winter temperatures. The simulation of several distinct trends in species occurrence observed in the pollen record indicates that a time lag due to the slow spreading of species need not be invoked for most species. 4. Sensitivity studies indicate that competition, natural disturbance and the magnitude of interannual variability play key roles in determining the biomass, establishment and even the presence of species near their bioclimatic limits. However, neither disturbance due to fire nor limits on establishment due to drought were likely to have been major determinants of the observed trends on the timescales considered. 5. We were unable to limit the modelled occurrence of Picea abies at the study sites to the periods at which it was observed in the pollen records, indicating that we have still not completely understood the driving or limiting factors for Holocene changes in Picea abies abundance. 6. Synthesis. This study shows that by combining quantitative vegetation reconstructions with a modern, process-based dynamic vegetation model, we may gain new insights into the potential biotic and abiotic drivers of Holocene vegetation dynamics, and their relative importance. This knowledge will be crucial in enabling us to assess more confidently the response of northern European vegetation to future climate change. [ABSTRACT FROM AUTHOR]

Abstract 1 We assess the robustness of a 1500-year palaeoclimate data base and forest gap model in simulating northern Scandinavian boreal forest succession since ad 500. We also evaluate trends in species abundance in a nemoral woodland in southern Scandinavia by comparing modelling results to palaeoecological data. 2 Simulated biomass trends for Picea, Pinus and Betula growing at Penningholmen (northern Sweden) are strikingly similar to those observed in the local pollen record, particularly in the replication of the early Little Ice Age (LIA) decline in Betula and the late-LIA dieback of Picea and Pinus. 3 LIA decreases in Betula may therefore be partly due to the effects of climate on its competitive interactions with Pinus, as well as the previously proposed effects of insect herbivory. 4 Simulations of Draved Forest (western Denmark), suggest that Tilia is under-represented in modern-day Scandinavian nemoral woodlands, and consequently that the present dominance of Fagus probably reflects strong human–plant interactions from as early as the beginning of the 17th century. 5 This study highlights the importance, despite general limitations associated with vegetation models, of model-data comparisons for understanding mechanisms and processes underlying past forest succession, and emphasizes the usefulness of forest models for reconstructing climate influences on past vegetation. [ABSTRACT FROM AUTHOR]

Discusses the modelling of the potential distribution and community dynamics of lodgepole pine Pinus contorta in Scandinavia. Subspecies of the lodgepole pine whose distribution in native North America is described; Prediction of Scandinavian forest dynamics through the climatic parameters derived from a bioclimatic model STASH; Possibility of invasion of the species into sites outside the plantation areas.