Pollen dispersal and representation on an offshore island



The effects of spatial isolation on pollen representation were examined in a study of seven small kettle ponds on Block Island, a small, unforested island 19 km off the New England Coast (USA). Modern pollen assemblages from the ponds were compared with modern assemblages from similar ponds on the adjacent, partly forested mainland and in extensively forested northern New York. Representation of pollen from local and extralocal sources was amplified on the island owing to spatial isolation. However, variation among pollen assemblages on the island was not clearly related to spatial variation in vegetation composition. Significant transport of pollen from the mainland to the island was observed. There appeared to be little or no decrease in representation of large, poorly dispersed mainland pollen types between the mainland and island. This latter result may indicate differences between the mainland and island in the predominant modes of pollen transport, or alternatively, effects of local pollen source strength on representation of pollen from distant sources. Based on our results, we propose a theory of pollen representation on islands that can be tested and applied on offshore islands and patchy landscapes.