ABSTRACT: Late Quaternary vegetation and climate change in the Canadian Rocky Mountain region: evidence from the Diana Lake pollen record, British Columbia.

CGRG Bibliography of Canadian Geomorphology
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Abstract

A pollen record recovered from bottom sediments of Diana Lake, British Columbia, provides the first detailed record of late Pleistocene and Holocene vegetation change on the western slope of the Canadian Rocky Mountains. Diana Lake (2160m) is located very close to modern timberline, providing a climatically sensitive record. Two sediment cores recovered from Diana Lake show similar stratigraphic records with massive inorganic glacial diamict overlain by clay and massive gyttja. Pollen was examined down the length of one core (DL3) and provides a detailed paleoenvironmental record divided into four assemblage zones (DL3-1,2,3,4), representing four main phases of vegetation change. Zone DL3-1 (> ca. 11,900 cal. yr BP) is dominated by Pinus, while Artemisia and other various non-arboreal taxa are well represented. An increase, relative to DL3-1, in arboreal taxa such as Pinus, Picea, and Abies, and a decrease in non-arboreal taxa such as Artemisia characterize DL3-2 (ca. 11,900 - 9700 cal. yr BP). Assemblage zone DL3-3 (ca. 9700 - 2080 cal. yr BP) is characterized by increases in Picea, Abies, and Alnus. Beginning ca. 2080 cal. yr BP, DL3-4 is characterized by decreasing amounts of Picea and Abies, whereas Tsuga Heterophylla and Larix/Pseudotsuga increase rapidly. The influx of Pinus pollen is low relative to non-arboreal pollen, suggesting the period prior to ca. 11,900 cal. yr BP was probably an alpine tundra ecozone. Increasing percentages of Pinus, Picea, Alnus, and Abies at the transition between zones DL3-1 and DL3-2 portray the development of modern, sub-alpine vegetation. By ca. 7500 cal. yr BP, subalpine forests grew near and above Diana Lake, as indicated by greater influxes of arboreal pollen and timberline reconstruction. A comparison to modern pollen transects suggests that, beginning ca. 2080 cal. yr BP, timberline moved downslope in response to 'Little Ice Age' cooling.

Bibliography of Canadian Geomorphology