Postglacial vegetation and climatic change in the upper Peace River district, Alberta

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Abstract
Pollen analysis and radiometric dating of sediment cores from two lakes in the Saddle Hills, Peace River district, Alberta, were used to investigate postglacial vegetation and climatic change. A poplar – willow – sage – grass – sedge zone began about 11 700 ± 260 years BP. A distinct pine and spruce rise indicates the local presence of conifers. Peace River spruce could have served as a source for spruce in the Yukon, transported by glacial meltwater conceivably as early as about 11 100 years BP. A paper birch rise and spruce decline between about 8700 and 8200 years BP is likely due to fires during a period of enhanced seasonality. It is suggested that subsequent weakening of the anticyclone associated with the Laurentide ice lengthened the growing season, permitting pine to be the major fire successor to spruce. During the pine peak ca. 7400 years BP there was no grassland over the Saddle Hills, so the Peace River grasslands cannot be explained as Hypsithermal relict vegetation. Conditions similar to the present were apparently reached by about 5000 years BP.