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On well-drained sites in northern locations, Podzols have traditionally been observed in association with forest vegetation and the less leached Arctic Brown soils with tundra vegetation. The present study shows that this vegetation-soil association is not a ubiquitous feature in northern Alaska, suggesting that Podzol occurrence beyond the modern tree line is not sufficient evidence to infer past forest expansion. This study was initiated at the boreal forest and alpine tundra transition at Walker Lake, Alaska, to determine whether the lichen-mixed-heath assemblage of the tundra was capable of producing Podzols. Morphologically, soils developed under lichen-heath cover could not be distinguished from those under spruce trees. Standard pedologic parameters, such as pH, CEC, and dithionite (Fed) and pyrophosphate (Fep) extractable iron, also failed to distinguish between these soils. An altitudinal trend unrelated to vegetation cover was apparent in these data. The Fep:Fedratio, as well as Fepand organic carbon in the B2hir, decreases with altitude. Both stable carbon isotopes and lignin oxidation products were used to investigate the plant sources of carbon in the B horizons. Altitudinal increases of both B horizon 13C/12C and present day plant cover 13C/12C indicate that morphologically similar soils may have developed under isotopically and taxonomically different plant communities. The lignin oxidation products from the B2hir of the forest soil are consistent with the prevailing gymnosperm trees growing on the site, and the oxidation products of the B2hir of the tundra soil are consistent with the angiosperm species that predominate at the tundra site. These results and other field evidence suggest that trees have not been more extensive in the past at Walker Lake. Albic horizons in the Arctic are, therefore, not conclusive evidence of a forest environment. Additional evidence, such as relict arboreal material, is needed before inferring tree line fluctuations and associated climatic change.

Pollen analysis of a 14,000-yr-old sediment core from Sithylemenkat Lake provides the first Holocene vegetational history for the Kanuti Flats of north-central Alaska. Basal samples contain a curious and unusual combination of tundra and boreal taxa. Pollen assemblages dating from 13,500 to 9000 yr B.P. are more typical of southern Brooks Range sites and indicate the presence of Betulashrub tundra with increased Populusca. 10,000 to 9000 yr B.P. Picea glaucaappeared ca. 9000 yr B.P. and Alnusca. 8000 yr B.P. P. glaucapopulations declined between 7800 and 5000 yr B.P. with a subsequent reforestation by P. marianaand P. glauca. This pattern is seen at other sites in northeastern Alaska and suggests that the Holocene history of boreal forest is more complex than thought previously.