ORIGINAL ARTICLE: Late-glacial and Holocene palaeovegetation zonal reconstruction for central and north-central North America

• Published in: Journal of biogeography 2005-06, Vol.32 (6), p.1043-1062
• Main Authors: Strong, W L, Hills, LV
• Format: Article
• Language: English
• Subjects: Pinus banksiana
• ISSN: 0305-0270; 1365-2699
• DOI: 10.1111/j.1365-2699.2004.01223.x

Aim: The purpose of this study is to develop palaeovegetation zonation models for central and north-central North America, based on late-Quaternary and Holocene pollen stratigraphic data (n = 246 sites). A secondary purpose was to evaluate an hypothesis () to explain the disjunct distribution of species in western Alberta. Location: Hudson Bay-Lake Michigan to the Rocky Mountains region, north of 36 degree N to the Arctic Ocean (c. 70 degree N). Methods: Pollen profiles spanning 40 years of palaeoecological research in North America were extracted from published and unpublished archival sources. Individual profiles were subdivided into 1000-year increments based on the assumption of a constant sedimentation rate between stratigraphic dates (e.g. surface sediments, radiocarbon super(14)C dates, tephra layers). The pollen composition among profiles was standardized to 54 commonly recognized taxa, with percentage composition within each stratigraphic sample prorated to 100% prior to analysis. Near-surface sediments from these profiles were included as analogues of modern vegetation. Cluster analysis was used as a guide to the classification of 2356 temporal stratigraphic samples, which resulted in the recognition of 16 pollen groups. These groups were summarized in terms of their pollen composition, mapped, and used in combination with terrain information and an ecological knowledge of the study area to construct six physiognomically-based palaeovegetation zonation models at 2000-year intervals from 14,000 to 4000 yr bp (radiocarbon years before present). Results: The 14,000 yr bp model placed Boreal and Cordilleran Forests proximal to the southern glacial front, whereas Arctic tundra dominated the Yukon Territory-Alaska ice-free zone. Pollen and macrofossil evidence suggests that this Boreal Forest zone contained a mixture of coniferous and deciduous tree species. Grassland was postulated immediately south of the forest zone, with its northern extreme near 49 degree N latitude in the Alberta-Montana border area. Separation of the Laurentide and Cordilleran glacial fronts about 12,000 yr bp initiated the northward advance of Boreal Forests into western Canada. By the end of the Hypsithermal at about 6000 yr bp, Boreal Forests occurred near the Arctic Ocean, and Grassland and Aspen Parkland zones may have extended to 54 degree N and 59 degree N latitude in Alberta, respectively. Between 6000 and 4000 yr bp, a 5 degree and 1 degree latitudinal southward shift o