A 12000 YEAR RECORD OF VEGETATION CHANGE AND SOIL DEVELOPMENT FROM WIEN LAKE, CENTRAL ALASKA

Pollen, plant-macrofossil, macroscopic-charcoal, and geochemical analy ses of a sediment core from Wien Lake provide new information on the l ate Quaternary environmental history of central Alaska. Shrub tundra d ominated by Betula glandulosa occupied the area 12 000 - 10 500 BP. Lo w plant cover and intensive soil erosion of the tundra landscape are i ndicated by low pollen-accumulation rates, high sediment inorganic con tent, and high allogenic elemental concentrations. Around 10 500 BP, P opulus and Salix invaded the shrub tundra and open ground to form dens e stands within the lake catchment. The marked increases in sediment o rganic content and authigenic concentrations of Fe, Mn, and Al during the period of Populus - Salix dominance suggest humic buildup and stab ilization of the catchment soils. These soil changes in turn may have contributed to the demise of Populus-Salix communities 9500 BP. Fossil seeds indicate that Betula papyrifera arrived 9500 BP, rather than in the middle to late Holocene as suggested by previous palynological st udies. Picea glauca codominated open woodlands with B. papyrifera 9500 -7500 BP. The decline of Picea glauca 7500 BP was probably due to an e pisode of climatic cooling rather than autogenic processes resulting i n waterlogged soils. Alnus arrived in the region 7500 BP. After 6500 B P, modern boreal forest dynamics are indicated by the dominance of Pic ea mariana, fluctuations of Picea glauca, and frequent occurrence of l ocal fires.