中海・宍道湖周辺地域における過去2000年間の花粉分帯と植生変化  [in Japanese] Pollen zones and vegetational change around Lake s Nakaumi and Shinji, during the last 2,000 years  [in Japanese]

中海・宍道湖周辺地域の過去約2400年の最上部完新統はイネ科花粉帯に属する。この花粉帯は次の4亜帯に細分される。スギ亜帯:約2400年前〜西暦約700年。この亜帯は高率のスギ属とイネ科で特徴づけられ, 湖周辺の低地にはスギ林がひろがっていた, 水田の開発はこの亜帯の初めに始まった。カシ・シイ亜帯:西暦約700年〜約1500年。この亜帯の初めにスギ属花粉は低率となる。イネ科とカシ類・ナラ類などの広葉樹の花粉は高率である。開発は更に進み, 水田は低地の大部分を被ったが, 丘陵地では照葉樹林が繁茂していた。マツ亜帯:西暦約1500年〜約1930年。この亜帯は二葉マツ類著しい高率で特徴づけられる。人為的な影響により, 照葉樹林は急速にアカマツの二次林に変わっていった。マツ・スギ亜帯:西暦約1930年以後。この亜帯はスギ属の増加で特徴づけられる。いたるところでスギが植林された。

In and around lakes Nakaumi and Shinji, the uppermost Holocene deposits which are younger than about 2,400 years B.P. belong to Gramineae Pollen Zone. This pollen zone is subdivided into the following four subzones in ascending order. Cryptomeria subzone: about 2,400 y.B.P. to about A.D. 700. This subzone is characterized by high percentages of Cryptomeria and Gramineae. So that, Cryptomeria forest may be expanded on lowland around lakes. The reclaimation of paddy field starts at the beginning of this subzone. Cyclobalanopsis-Quercus subzone: about A.D. 7000 to about A.D. 1500. The beginning of this subzone, Cryptomeria pollen fall to low percentages. Pollen grains of Gramineae and broard leved tree, such as Cyclobalanopsis, Quercus etc. are still high. The reclaimation is advanced still more, and paddy field may cover almost all parts of lowland. Laurer forests are continuously flourished on hilly land. Pinus (Diploxylon) subzone: about A.D. 1500 to about A.D. 1930. This subzone is marked by extremely high percentages of Pinus (Diploxylon). According to artificial effects, laurer forests are rapidly replaced by secondary forests of Pinus densiflora. Pinus (Diploxyloy)-Cryptomeria subzone: about A.D. 1930 to present. This subzone is marked by increase of Cryptomeria. Cryptomeria may be affforested at many places.