The postglacial vegetation history of Anticosti Island in the Gulf of St. Lawrence, Québec, was reconstructed from pollen analysis of three sites, providing the first paleoecological data for the island. The earliest plant communities (8550–7770 14 C yr B.P.; 9500–8500 cal yr B.P.) were characterized by a high representation of green alder (Alnus crispa), indicating an open environment with sparse spruce (Picea). Between 7770 and 3700 14 C yr B.P. (8500–4000 cal yr B.P.), the island was colonized by mixed deciduous and coniferous forests dominated by paper birch (Betula papyrifera) and spruce. A major increase in the abundance of balsam fir (Abies balsamea) occurred ca. 3700 14 C yr B.P. (4000 cal yr B.P.), indicating development of the closed fir–spruce forests as they exist today. The island's remoteness from continental seed plant sources influenced plant colonization, afforestation, and ecological succession. The Gulf of St. Lawrence slowed plant migration, and tree species had to spread from the Gaspé Peninsula. Repeated drops in fir pollen percentages during the last 4,000 years may reflect the activity of defoliating insects.