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 Zone
Before 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 Zone
During 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 Zone
Another 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 Zone
Larix 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 Zone
In 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..
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