A mid-Holocene record of vegetative change in central Alberta

Sediments from three lakes in central Alberta, Smallboy Lake (53°35′N, 114°8′W), E.I. Pond (53°38′N, 112°51′W), and Hastings Lake (53°25′N, 112°53′W), have been analyzed for their pollen content, charcoal remains, and (in two lakes) pyrite spherule concentration. The earliest record (radiometrically dated at 7400 years BP) indicates the existence of mixed-wood parkland vegetation. By 5000 years BP the regional vegetation had a considerably more open structure than now and was subject to frequent fires, presumably a response to the warm, dry Hypsithermal climate of this time. The termination of the Hypsithermal Interval (4000 years bp) is recorded in all three lakes by a marked increase in precipitation. The onset of a cooler, moister climatic regime stimulated forest closure and reduced regional fire activity, although the local vegetation of each of the three study sites responded in a unique way to the changing climate. By 3000 years BP the vegetation resembled the modern vegetation. Little change is recorded in the sediments from 3000 years BP to the present.