Fossil pollen data, as illustrated by isopoll and isochrone maps, document the complex late Quaternary history of tundra and boreal forest development in northcentral Alaska. Major plant taxa behaved independently over time, resulting in substantial differences in the vegetation history of eastern and western regions. Major vegetation changes are in general agreement with GCM simulations and confirm the importance of the continental ice sheet and insolation variations in determining late Quaternary climatic trends. Herb-dominated tundra characterized the vegetation between 18 and 14 ka BP, with mesic graminoid tundra in lower elevations of western areas and more xeric, sparse tundra communities in the east and at higher elevations. Moist Betula tussock tundra rapidly replaced the western herb tundra ca. 14 ka BP. However, Betula shrubs expanded more slowly in the east, establishing relatively dry shrub tundra as the predominant regional vegetation by ca. 12 ka BP. River valleys and south-facing slopes supported Populus woodlands between 11 and 9 ka BP, but shrub tundra continued to dominate most upland sites. Alnus shrubs first expanded in the southwestern Brooks Range between 10 and 9 ka BP, spreading rapidly throughout the entire region between 8 and 7 ka BP. Picea glauca populations also expanded between 10 and 9 ka BP, but from source areas in northwestern Canada. The P. glauca forests were most abundant in riparian settings, but isolated stands probably also established in the shrub tundra. P. glauca reached the central Brooks Range by ca. 8 ka BP, followed by an apparent population decline between 8 and 7 ka BP. P. mariana became the dominant tree species ca. 6 ka BP, when it invaded non-riparian P. glauca forests in eastern and central areas and moist shrub tussock tundra in the west. The modern distribution of communities in northcentral Alaska was achieved between 6 and 4 ka BP.