Holocene fossil pollen data of fine temporal and spatial resolution were obtained from two small, closed lake basins in southern Ontario, Canada. Forest development is recorded in the pollen sequences, which document the invasion and expansion of tree populations during the early Holocene. Subsequent forest dynamics are discussed in terms of the main factors driving vegetation change, including climate, soil development, migration, disturbance regime (abiotic and biotic), and competition, which operate on a species pool with a variety of biological and ecological characteristics. The relative importance of these factors, influencing forest dynamics during the Holocene, appears to have varied over time. © 1997 NRC Canada.