HOLOCENE CLIMATIC-CHANGE AND THE DISTRIBUTION OF PEATLANDS IN WESTERN INTERIOR CANADA

Dates of basal fen peat at 52 locations across west-central Canada indicate that peat deposition began <6000 yr B.P. in a broad zone north of the present-day grassland. The isopleth of >6000 yr B.P. basal fen peat parallels the foothills of the Rocky Mountains, and extends eastward along 54°30′ north latitude. The absence of >6000 yr B.P. peat within this zone is attributed to a warmdry early to middle Holocene climate that caused severe seasonal droughts and prevented the establishment of peat-forming fen vegetation. Wetlands west (and probably north) of this line experienced lower water tables, but supported fen vegetation. As the climate became cooler and moister, stable water tables allowed the development of fens and rapid peat accumulation ensued, reaching the modern distribution of fens between 2000 and 3500 yr B.P. Projections of climatic parameters indicate that the mean annual growing degree days were 6 to 21% higher during the early and middle Holocene, and that precipitation was reduced through most of the area, resulting in much higher (by 17 to 29%) aridity than at present. © 1990.