サハリン南西部に分布する後期完新世埋没土層からのッガ属花粉の産出

摘要

サハリン南西部のアルカンザスに分布する後期完新世の黒色埋没腐植土から，高率のッガ属(Tsuga)花粉が産出した.ッガ属は現在サハリンと北海道には分布しない常緑針葉樹である.しかし，これまでに両島の完新統から花粉の産出は報告されていた.サハリン南東部トウナイチャからのッガ属花粉の母樹は,現在の分布北限地とトウナイチャの気象条件の類似からコメッガ(Tsuga diversifolia)の可能性が高いとされたが，花粉包含層が陸成層でないことから,二次堆積した可能性も考えられた.これに対し，今回報告するアルカンザスの化石包含層は陸成層である.ッガ属花粉は風により遠距離飛散しないため，母樹が調査地周辺に分布した可能性が高い.さらに今回，化石の花粉形態を検討した結果も，コメッガの特徴を持つことが明らかになった.1,700〜630 ~(14)Cyrs BPのアルカンザスにコメッガが分布したことは，北海道とサハリンにおけるコメッガの変遷史を解明するうえで重要である.%Pollen Tsuga from the late Holocene (1,700-630 yrs BP) were found in buried soil distributed at Arkanzas, southwest Sakhalin. Two kinds of Tsuga trees, Tsuga sieboldii and Tsuga diversifolia, are distributed in Japan. However, Tsuga trees do not grow naturally in Sakhalin or Hokkaido at present. On the other hand, fossil Tsuga pollen were reported from Holocene sediments in both islands. The analyzed soils from Arkanzas are terrestrial sediments which do not include pollen transported by water. The pollen Tsuga are also not transported long distances by wind. Accordingly, Tsuga pollen could be added to the sediment from mother trees which grow near the study site. The grain morphology of pollen Tsuga from the study samples are within the range of T. diversifolia. The reconstructed vegetation in the mountains behind the study site was an evergreen conifer forest with T. diversifolia, and the grassland was developed on the terrace between 1,700 and 630 ~(14)C yrs BP. Afterward T. diversifolia and grassland disappeared from the study site. The pollen data from Arkanzas shows that T. diversifolia had been distributed until several centuries ago in southern Sakhalin. This fact is important for the reconstruction of the history of T. diversifolia in Sakhalin.