A mid-Holocene record of vegetative change in central Alberta

Abstract

Sediments from 3 lakes in central Alberta, Smallboy Lake (53.degree.35''N [north], 114.degree.8''W [west]), E.I. [Elk Island] Pond (53.degree.38''N, 112.degree.51''W), and Hastings Lake (53.degree.25''N, 112.degree.53''W), were analyzed for their pollen content, charcoal remains and (in 2 lakes) pyrite spherule concentration. The earliest record (radiometrically dated at 7400 yr BP) indicates the existence of mixed-wood parkland vegetation. By 5000 yr 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 yr BP) is recorded in all 3 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 3 study sites responded in a unique way to the changing climate. By 3000 yr BP, the vegetation resembled the modern vegetation. Little change is recorded in the sediments from 3000 yr BP to the present.