Pollen-vegetation calibration for tundra communities in the Arctic Foothills, northern Alaska
W. Wyatt Oswald, Harvard Forest, Harvard University, PO Box 68, Petersham, MA 01366, USA (tel. +1 978 724 3302; fax +1 978 724 3595; e-mail email@example.com).
- 1Palynology has been portrayed as a ‘blunt’ tool for reconstructing variations in arctic tundra vegetation. We tested this characterization in the Arctic Foothills of northern Alaska by analysing 56 modern pollen assemblages from lakes on contrasting glaciated surfaces. The two surfaces, which date to the Sagavanirktok (> 125 000 years BP) and Itkillik II (c. 11 500 years BP) ice advances from the Brooks Range, have considerably different geomorphology, soil characteristics and plant communities. Sagavanirktok surfaces are dominated by dwarf-shrub tundra (DST), and Itkillik II surfaces by prostrate-shrub tundra (PST).
- 2We used two multivariate approaches, dissimilarity metrics (squared chord distance and Canberra metric distance) and discriminant analysis, to assess the ability of the pollen data to distinguish between the Sagavanirktok and Itkillik II landscapes, and to identify the taxa most strongly associated with one surface or the other. Receiver operating characteristic (ROC) analysis was used to evaluate the performance of the dissimilarity metrics and to determine their ‘critical values’ for distinguishing between assemblages from like and unlike plant communities.
- 3According to the discriminant analysis, taxa indicative of the Sagavanirktok surface include Rubus chamaemorus, Sphagnum and Ericales, whereas Equisetum, Thalictrum and Polypodiaceae were faithful to the Itkillik II surface. These differences between the pollen assemblages make it possible to differentiate between the two landscapes using Canberra metric distance comparisons. The ROC analysis demonstrated that the Canberra metric distance is more effective than squared chord distance for distinguishing between the two surfaces. This study illustrates that palynology can be used to explore questions regarding the landscape-scale heterogeneity of past tundra vegetation.