Postglacial spread of hemlock (Tsuga) and vegetation history in Mount Revelstoke National Park, British Columbia, Canada

Abstract

To investigate postglacial environmental changes in southeastern British Columbia, subfossil pollen was analyzed from Eagle Lake, Mount Revelstoke National Park. Palynological evidence suggests that during the early Holocene, Eagle Lake was surrounded by an open forest. The pollen assemblage indicates that climatic conditions were warmer and drier than at present with high alder pollen values. Spruce and fir were common in local forests throughout the Holocene. Western hemlock pollen first occurs at approximately 3500 14C years BP. The migration path of western hemlock into this region is currently unclear. Data from palynological records appear insufficient to resolve the migration pattern, although several routes are possible. The available data support northward migration into southeastern British Columbia. The arrival of this conifer may be in response to the late Holocene increase in precipitation, as inferred from many lower elevation and coastal sites. Mountain hemlock pollen does not appear until about 2100 14C years BP. Mountain hemlock's migration route into southeastern British Columbia is also unresolved. In the late Holocene, the presence of mountain hemlock, and increases of Ericales and Valeriana sitchensis pollen, suggest a shift to the more open, cool, and moist conditions characteristic of the modern-day subalpine parkland. These climatic inferences correspond closely to those derived from other palynological and geological evidence throughout southern British Columbia.Key words: pollen, vegetation, Tsuga, hemlock, British Columbia, Holocene, climate.