Late Wisconsin and Holocene vegetational history of the Upper Koyukuk region, Brooks Range, AK

Abstract

Three pollen diagrams provide information on late Wisconsin and Holocene vegetation history at high elevation and midelevations (1000 and 600 m) in the east-central Brooks Range. After the retreat of glacial ice and until about 12 000 years before present, the vegetation was a tundra, dominated by Salix, Cyperaceae, Gramineae, Artemisia, and other herbaceous taxa. However, because the early pollen spectra do not have close modern analogs, the detailed composition and ecology of this tundra cannot be inferred. Between ca. 12 000 and ca. 8 000 years before present, Betula nana–glandulosa was the dominant pollen producer at both elevations; a significant ericaceous component was present in the vegetation of the alpine sites, but not at the lower elevation site. During the period 10 500 – 8 500 years before present, Populus balsamifera and Juniperus were probably abundant at the lower site and may also have been present at the higher sites, where they are now absent. Picea glauca, Alnus spp., Picea mariana, and Betula papyrifera became established at the lower site between ca. 8500 and 6000 years before present. None of these species currently grows at the high sites, but their arrival at lower elevations is represented in the regional pollen rain at these sites. The arrival times of Picea glauca and Picea mariana in the study area are consistent with the hypothesis that P. glauca preceded P. mariana into the central Brooks Range.