Postglacial vegetational history of Tonquin Pass, British Columbia

Abstract

A pollen and macrofossil study of peat sediments in Tonquin Pass, British Columbia provides the oldest dated record of vegetational and climatic changes in the middle Canadian Rockies. Paleoecological interpretation of these events dated by tephrochronology and radiocarbon dating is facilitated by comparisons with other regional pollen profiles.Late Wisconsin ice receded from Tonquin Pass prior to 10 000 years BP. By 9700 years BP a Pinus contorta forest with an understory dominated by ferns had colonized the area. The climate of this period was cool and moist. Following this interval was a brief episode (9000–8040 years BP) of haploxylon pine dominance during which the climate became colder. A long warm period beginning by 8040 years BP was characterized by desiccation of local meadows and fens and invasions of these areas by trees, principally Picea. Dated fossil Picea and Abies logs from alpine bogs within Jasper National Park document that timberlines had advanced beyond present limits by 8770 years BP. These data indicate a considerable lag in the registration of this interval in the Tonquin record.During the last 4300 years the retreat of trees from meadows and increases in the representation of several alpine taxa indicate that generally moist and cool conditions have prevailed. Evidence for Holocene timberline fluctuations in the Jasper area suggests an overall lowering in timberline elevation and further cooling since 1700 years BP.