北海道における最終氷期の植生変遷

Abstract

The vegetational changes which occurred during the Last Glacial Age in Hokkaido were clarified by studies of plant macrofossils and pollen and spore assemblages. Five major pollen zones, one of which contained 2 subzones, were distinguished.(1) Picea-Abies-Betula ZoneBefore ca., 40, 000y.B.P., mixed forests dominated by spruce, fir and birch trees were continuously developed under cooler climatic conditions than those of the present.(2) Picea-Abies-Larix ZoneDuring ca., 40, 000-26, 000y.B.P., Picea glehnii and/or Picea jezoensis and Abies sachalinensis were dominant and coexisted with Larix gmelini and Betula around moor lands under colder and moister conditions than those of the present. However, two short-lived warm spells, Betula-Tsuga-Quercus subzone and Betula-Abies-Ulmus subzone, were newly recognized from samples of pollen and spore assemblages and molluscan faunas which are believed to have existed ca., 34, 000y.B.P. and ca., 31, 000y.B.P. respectively.(3) Abies-Picea-Ulmus ZoneAnother comparatively small scale warm spell was identified by the increase of Abies and Ulmus during ca., 26, 000-25, 000y.B.P..(4) Picea- Larix ZoneLarix gmelini became dominant in most parts of Hokkaido during ca., 25, 000-12, 000 y.B.P. and formed boreal forests together with Picea glehnii and/or Picea jezoensis. However, in the eastern and the northern parts of Hokkaido, forest tundra may have existed at the same time under colder and drier climatic condition than those of the present.(5) Abies-Juglans ZoneIn the Ishikari Plain, another comparatively warm climatic period which was characterized by a sudden increase of Juglans, Ulmus and Quercus appeared to have occurred during ca., 12, 000-11, 000y.B.P..