Limiting Factors in Paleoenvironmental Reconstruction

Abstract

It is a basic tenet of paleoecologists that the data set, consisting principally of pollen, spores, diatoms, or other microfossils and the enclosing sediment, is better than anything yet done with it. Distributional problems include differential pollen production, dispersal, sedimentation, and preservation. Changes in dominant air mass patterns, whether seasonal or in response to climatic trends, alter source pollen frequency independently of vegetational sources near depositional sites. Approximately 50% of the pollen at the center of a small (ca 1 km diam.) pond comes from within 7 km of the site, and from less than 300m of the source in a bog. With more than 300 published pollen sequences and nearly 500 contemporary pollen records available in North America since the 1230s, the sampling interval, even if uniformly spaced, is ca 10 km per sample site. At this spacing, approximately 11 stations at 110 km intervals would be available to describe the vegetational diversity of Ohio.

External influences upon the data set include site-specific variables such as topography, exposure, soil type and geology, and trophic status of the depositional site. Increasing attention to sampling and quantitative preparation techniques, inclusing close interval stratigraphic control by radiocarbon dates, is improving the precision of reconstruction of the stratigraphic record. Proliferation of large computers and sophisticated statistical procedures promise isolation and identification of quantitative changes in important climatic variables.

Despite the necessity for increased sample coverage, a growing responsibility to fully utilize existing records and preserve existing and potential sites for future more sophisticated investigations must be recognized.