Montane climate and vegetation dynamics in easternmost Beringia during theLate Quaternary

New and published palynological data are used to investigate the Quaternary vegetation history of high-elevation sites in the Mackenzie Mountains of e asternmost Beringia (Northwest Territories, Canada). During some previous i nterglacials, sites that are presently treeless supported spruce forest, in dicating conditions were warmer than present and possibly warmer than at an y time in the Holocene. No information is available on vegetation in unglac iated portions of the Mountains during the Last Glacial Maximum, but in the Lateglacial (ca 12,000-10,000 C-14 yr BP), a shrub- and herb-dominated veg etation, characterized in the pollen record by Artemisia, Betula, Salix, gr amnoids and herbs, grew at all elevations: and extended in a continuous cor ridor southwards to Alberta. Populus balsamifera probably grew up to and ab ove present treeline between about 11,000 and 9000 yr BP. The late Pleistoc ene vegetation of the Mackenzie Mountains contrasts with the rest of easter n and central Beringia, which supported a Betula-dominated shrub tundra by 12,000 yr BP. Betula shrub tundra expanded at all elevations in the mountai ns by 10,000 yr BP, followed by the expansion of Picea glauca and Picea mar iana forest at ca 8000 yr BP. There is evidence for limited elevational shi fts in treeline during the Holocene. Picea population densities in the fore st-tundra were probably greater than at present in the early and mid-Holoce ne. Vegetation changes in the Mackenzie Mountains during this time are cons istent with increased summer insolation and temperatures during the early t o mid-Holocene. Higher resolution analysis (decadal to century scale) of sm all 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 variati ons in insolation. (C) 2000 Elsevier Science Ltd. All rights reserved.