The continental scale migrations of Fagus sylvatica L. and Picea abies (L.) Karst. are under a broad climatic control, but disturbance and local factors influence the immigration of these species into individual forest stands. Palaeoecological analysis of a small forest hollow in the boreo-nemoral zone of southern Sweden has shown that a forest stand with largely unbroken forest continuity resisted immigration of Fagus for almost 1000 years. Two fires about 950 and 330 years ago were the disturbing factors that facilitated eventual Fagus immigration. Picea immigrated and achieved co-dominance in a single generation, without resistance from the existing forest. Thus migrational lag is demonstrable for Fagus but not Picea. The immigration of these two dominating species coupled with a severe reduction in tree species diversity has resulted in a total change in forest competition during the last few centuries despite the maintenance of a structural forest continuity. Some of these changes are attributable to changes in the grazing regime, but the forest stand is as close to «natural» conditions as can be found in S. Sweden.