LONG‐DISTANCE POLLEN IN LATE WISCONSIN QUANTITATIVE ANALYSIS*

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Abstract
SUMMARY: In Late Wisconsin sediments of Minnesota there occur fossil pollen and spores of certain taxa that are unlikely on ecological or phytogeographical grounds to have grown in Minnesota at that time. Long‐distance dispersal is believed to be the cause. The occurrences of 21 such types in three sites in Minnesota are analyzed statistically. Contingency‐table analysis suggests that some types occur together more commonly or more rarely than would be expected by chance. Principal co‐ordinates analysis similarly reveals groups of taxa whose pollen commonly occur together in time.The patterns within the series of occurrences, when viewed as point processes, are characterized by the techniques of statistical analysis of series of events. These analyses show that the series of occurrences ofAcer saccharum, Carya, Celtis occidentalis, Juglans cinerea, Platanus occidentalis, and probablyA. saccharinum‐typeandTilia americanapollen all have statistically significant trend and that their rates of occurrence are higher between 8300 and 10200 B.P.Athyrium filix‐feminaspores show a higher rate of occurrence between 20500 and 12000 B.P. The series of occurrences of all the other pollen types accord with a trend‐free renewal process. The series ofAcer negundo, Iva ciliata‐type, I. xatithifolia‐type, Morus rubra, andSarcobatus vermiculatuspollen are long enough to permit more detailed analysis. All these series appear to reflect a homogeneous Poisson process with random occurrences in time.Hypotheses to explain these patterns are discussed in terms of migration and population expansion to the south and east of Minnesota and of changing atmospheric circulation patterns during the Late Wisconsin. The need for more detailed series of occurrences is emphasized.