Montane climate and vegetation dynamics in easternmost Beringia during the Late Quaternary

Abstract

New and published palynological data are used to investigate the Quaternary vegetation history of high-elevation sites in the Mackenzie Mountains of easternmost Beringia (Northwest Territories, Canada). During some previous interglacials, sites that are presently treeless supported spruce forest, indicating conditions were warmer than present and possibly warmer than at any time in the Holocene. No information is available on vegetation in unglaciated portions of the Mountains during the Last Glacial Maximum, but in the Lateglacial (ca 12,000–10,000 14C yr BP), a shrub- and herb-dominated vegetation, characterized in the pollen record by Artemisia, Betula, Salix, gramnoids and herbs, grew at all elevations, and extended in a continuous corridor southwards to Alberta. Populus balsamifera probably grew up to and above present treeline between about 11,000 and 9000 yr BP. The late Pleistocene vegetation of the Mackenzie Mountains contrasts with the rest of eastern and central Beringia, which supported a Betula-dominated shrub tundra by 12,000 yr BP. Betula shrub tundra expanded at all elevations in the mountains by 10,000 yr BP, followed by the expansion of Picea glauca and Picea mariana forest at ca 8000 yr BP. There is evidence for limited elevational shifts in treeline during the Holocene. Picea population densities in the forest–tundra were probably greater than at present in the early and mid-Holocene. Vegetation changes in the Mackenzie Mountains during this time are consistent with increased summer insolation and temperatures during the early to mid-Holocene. Higher resolution analysis (decadal to century scale) of small lake basins at treeline in this region also provide evidence for a late Holocene increase in forest–tundra density and/or a treeline rise centered on 3000 yr BP. Slight warming at this time has been noted at sites in the southern Rocky Mountains, and provides evidence for century-scale climatic fluctuations superimposed on the longer-term changes resulting from variations in insolation.