The timing and nature of Late Quaternary vegetation changes in the northern Great Plains, USA and Canada: A re-assessment of the spruce phase
Catherine H. Yansa
This paper revises the chronology for the northward migration
of Picea glauca (white spruce) across the northern Great Plains, following the
recession of the Laurentide Ice Sheet, and reinterprets the species composition
and structure of the late-glacial vegetation on the basis of pollen and
plant-macrofossil analysis. The timing of spruce migration is based on 26 14C
ages obtained from Picea macrofossils. The date for the appearance of white
spruce in southern South Dakota, USA, remains unchanged, 12,600 14C yr BP (c.
15,000 cal yr BP), but its arrival in southern Saskatchewan, Canada, by 10,300
14C yr BP (c. 12,100 cal yr BP) is about 1500 years later than previously
estimated based on an organic sediment date. Picea glauca thus migrated
northwards at an average rate of 0.38 km/14C year (0.30 km/calendar year),
significantly slower than the previously published rate of 2 km/14C year. White
spruce probably inhabited lake shorelines, whereas prairie, parkland, and boreal
plants occupied both lowlands and uplands, forming an open white spruce
parkland. This interpretation differs from a previous reconstruction of a
boreal-type spruce forest and thus offers another paleoclimatic interpretation.
Precipitation was probably low and summer temperatures relatively mild,
averaging about 19C.