Information on the Wisconsin environment of interior Alaska has been obtained from study of pollen as well as the plant and animal macrofossils contained in sediments of a 27 m core at Isabella Creek, near Fairbanks, Alaska. The pollen assemblages indicate three major zones.Zone A (35 000 to 32 000 BP) represents a mid-Wisconsin interstadial during which spruce treeline was lower in elevation than at present though not nearly as low as during early and late Wisconsin time. Zone B represents a late Wisconsin interval of severe arctic climate. Forests disappeared from interior Alaska or were greatly diminished and much of the region was characterized by steppe-tundra vegetation. Steppe conditions may have been favored by rapid deposition of primary and reworked loess. Zone C shows that spruce forests and some of the associated boreal biota had returned to interior Alaska by 8500 years BP. A fluctuation of alder percentages within Zone C may result from mid-Holocene warming.Plant macrofossils from the Isabella sequence show that some species now having a boreal or taiga distribution survived the late Wisconsin of interior Alaska in a steppe-tundra environment. Other plants that were growing at Isabella during mid-Wisconsin time apparently became extinct in Alaska during the late Wisconsin.

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