Absolute pollen frequencies and carbon-14 age of a section of Holocene Lake sediment from the Riding Mountain area of Manitoba

A section of Holocene lake sediment in the Southern Boreal Forest of Manitoba was re-sampled, and the sedimentation rate (0.039 cm per annum) calculated from eight carbon-14 age determinations. Pollen accumulation rates were computed, and an absolute pollen frequency diagram constructed. It suggests modifications of an earlier reconstruction of vegetation, based on relative pollen frequencies. A spruce-dominated assemblage occurred from about 11 500 to 10 000 B.P., when there was a change to a treeless vegetation of a grassland type. This persisted until about 2500 B.P., with the possible interpolation of an aspen parkland phase from 6500 to 2500 B.P. The boreal forest in its present form (dominated by spruce, birch, and aspen, with local occurrences of pine, fir, larch, and oak) returned at 2500 B.P., presumably in response to a deterioration in climate (cooler and (or) wetter).