Abstract: Pollen records from Long Last Lake and Two Horsemen Pond, near the centre of the arid region of southwest Yukon Territory, do not support the hypotheses that (i) black spruce was a dominant species in the region and (ii) the southwest Yukon supported widespread grasslands during most of the past 10 000 years. Black spruce became established between 8500 and 8000 BP, shortly after the arrival of white spruce, but its low pollen percentages (< 5%) indicate that it was a minor component of forests. Between 6000 and 5000 BP, white spruce populations decreased as black spruce and green alder increased, but black spruce remained a minor constituent of the forest, never becoming a dominant species as at Kettlehole Pond near the southeast margin of the arid southwest Yukon. The initial vegetation was a poplar woodland, dating from 9200 to 8500 BP at Long Last Lake. At both Long Last Lake and Two Horsemen Pond, the high percentages of herb pollen indicate that the forest was open, but the low values of grass pollen suggest that grasslands were not extensive. Coincident with the establishment of spruce woodland at 8500 BP, pollen of herbs declines and remains comparatively low until 1300 BP when herbs, including grasses, increase to maximum values for the period of record, indicating the grassland communities were probably never more abundant during the Holocene than they are now. Key words: southwest Yukon, black spruce, pollen analysis, paleoecology, climate change.

Authors: Keenan, T.J. and Cwynar, L.C.

Citation: Keenan, T.J. and Cwynar, L.C., 1990. Late Quaternary history of black spruce and grasslands in southwest Yukon Territory. Canadian Journal of Botany, Vol. 70, p. 1336-1345

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