Quaternary Migration Pattern of Selaginella selaginoides in the North Pacific

Abstract

Late-glacial-postglacial migration of Selaginella selaginoides from full-glacial refugia in the North Pacific is reconstructed utilizing fossil microspores contained in radiocarbon-dated deposits. Refugia are associated with 16 late Pleistocene localities of S. selaginoides, which in America are found in western Washington State and on the Queen Charlotte Islands of British Columbia and in Japan on the islands of Honshu and Hokkaido. Holocene data are derived from 10 mires selected from some 30 sites distributed across the North Pacific arc. Data based on first occurrences of the microspores in the dated deposits show that migration in the Eastern Pacific proceeded rapidly at first, the species reaching southeastern and south-central Alaska between 9000 and 8000 yr BP, whereas later the range did not extend farther westward to the Aleutians until after 4000 yr BP. In the Western Pacific, migration from refugia in Japan, by contrast, is not readily evident, aside from altitudinally higher movement in the mountains of Honshu and Hokkaido. Failure to migrate in the Western Pacific can be explained by the isolation of populations, distantly removed from habitats at higher latitudes, and by past and present climatic conditions, physical barriers, and volcanic activity.