Late Quaternary vegetation of the Aleutian Islands, southwestern Alaska

Abstract

Late Quaternary vegetational history of the Aleutian Islands is interpreted from fossil pollen and spore stratigraphy and radiocarbon chronology of sections of mires on the islands of Attu, Adak, Atka, and Umnak. Mires postdate the withdrawal of ice-age glaciers between approximately 12000 and 10000 years ago with the exception of the mire on Attu Island, where deglaciation apparently began as late as 7000 years ago. No uniform pattern of change in Pacific coastal tundra communities is evident in the fossil assemblages. Pollen assemblages, consisting variably of Gramineae, Cyperaceae, Empetrum, Umbelliferae, Salix, Ranunculaceae, Compositae, Polypodiaceae, and Lycopodium, reflect conditions in effect in different sectors of the Aleutian chain. Climate, soil, topography, volcanism, and sesmic activity are noteworthy parameters influencing vegetation composition and distribution. Volcanism has been of major importance, as shown by thickness, distribution, and frequency of tephra layers that number 5 on Attu, 24 on Adak, 17 on Atka, and 5 on Umnak. A repeated condition of patch dynamics, created in the main by recurrent volcanic eruptions with widespread accompanying ashfalls, has apparently overprinted the effects of climatic change.