Pollen analysis of three sections from the Grizzly Creek basin, Yukon Territory was undertaken in order to reconstruct the paleoecology of the region over the last two millennia.Diagrams for two sites show three well defined pollen zones, whose boundaries are based on fluctuation of pollen spectra. The oldest zone corresponds to vegetation comparable to that of the present and a climate similar to or a little colder than the present climate. In zone 2, the strong decline of Picea is interpreted as a break in pollen production caused by a decrease in precipitation and a warming of the climate. The forest survived for several centuries in a state of degeneration, which favoured the development of a stratum of shrubs and herbaceous plants. Zone 3 reflects a return to vegetation and to climatic conditions similar to those of zone 1.The positions of two layers of volcanic ash, dated at approximately 1230 and 1890 years BP and corresponding to two lobes of White River Ash, indicate the rhythm of sedimentation. The presence of loess in the sediments helps explain the great accumulation of sediment before 1250 years BP and supports an increase in aridity during this period. The pollen record also suggests that the deposition of volcanic ash had an influence on the geomorphological evolution of the area.

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