QUATERNARY MIGRATION PATTERN OF SELAGINELLA-SELAGINOIDES IN THE NORTHPACIFIC

Late-glacial-postglacial migration of Selaginella selaginoides from fu ll-glacial refugia in the North Pacific is reconstructed utilizing fos sil microspores contained in radiocarbon-dated deposits. Refugia are a ssociated with 16 late Pleistocene localities of S. selaginoides, whic h in America are found in western Washington State and on the Queen Ch arlotte Islands of British Columbia and in Japan on the islands of Hon shu and Hokkaido. Holocene data are derived from 10 mires selected fro m some 30 sites distributed across the North Pacific arc. Data based o n first occurrences of the microspores in the dated deposits show that migration in the Eastern Pacific proceeded rapidly at first, the spec ies reaching southeastern and south-central Alaska between 9000 and 80 00 yr BP, whereas later the range did not extend farther westward to t he Aleutians until after 4000 yr BP. In the Western Pacific, migration from refugia in Japan, by contrast, is not readily evident, aside fro m altitudinally higher movement in the mountains of Honshu and Hokkaid o. Failure to migrate in the Western Pacific can be explained by the i solation of populations, distantly removed from habitats at higher lat itudes, and by past and present climatic conditions, physical barriers , and volcanic activity.