Fire has been a major source of instability in the postglacial forests surrounding Everitt Lake in southwest Nova Scotia. Time series analyses of preserved pollen and charcoal reveal the processes involved. Correlograms and pollen sequence splits confirm that prior to 6000 years BP repeated widespread fires maintained the forest in constant disequilibrium. Each fire triggered rapid major forest composition changes, especially the proliferation of invading tree species that had previously been excluded by competition. The absence of such widespread fires is shown to have left most tree populations in near-equilibrium for much of the last 6000 years. Power spectra for different pollen sections suggest the changing ecological strategies and affinities of tree taxa through time and imply that much forest change occurred by piecewise replacement of individual stands in the forest mosaic. ©1982 Blackwell Scientific. Abstract reproduced by permission.