Reconstruction of the forest vegetation around the Kanto plain during the late Glacial and the Holocene

本研究的目的是重建关东平原周围晚冰期和全新世的森林植被，目前的顶峰森林植被被认为是常绿阔叶林。千叶县是关东平原的边缘地区，在日本非常罕见的千叶县出土了一处早期的绳索遗迹，发现即使在绳索时代晚期，森林植被也是由黄柏、欧斯特里亚和猕猴桃等落叶阔叶树的成分组成的。这一发现表明，柔门期的人类活动保留了在全新世扩张的常绿阔叶林中的大陆型落叶阔叶林。为了阐明全新世关东平面周围森林的发育过程，在千叶县的一个小谷头重建了柔门期早期的植被分布。谷底分布着Alnus森林，而山坡和梯田上则分布着锯缘栎林。关东平原晚冰期至全新世植被演化史为：全冰期，常绿阔叶林在关东平面周围占主导地位，主要有鹅绒委陵菜、锯缘栎属、锥栗、宏等。全新世早期，人类活动开始，常绿阔叶林扩展。然而，人类活动阻碍了常绿阔叶林的全面扩张，使大陆类型的落叶阔叶林保留在常绿阔叶林之中。因此，目前关东平原周围的次生落叶阔叶林起源于冰川全盛时期的大陆型落叶阔叶林，这表明这是一个具有重要历史意义的问题，应该仔细保护。

The aim of the present research is to reconstruct the forest vegetation during the late Glacial and the Holocene around the Kanto plain where the present climax forest vegetation is thought to be evergreen broad-leaved forest. The excavation of a early Jomon remain in Chiba Prefecture, a marginal of the Kanto plain, which is very rare in Japan, revealed that even at the late Jomon period the forest vegetation consisted of the elements of the deciduous broad-leaved trees such as Phellodendron, Ostyria and Actinidia.. This finding suggested that the human activity during the Jomon period kept the continental type of the deciduous broad-leaved forests among the evergreen broad-leaved forests which expanded at the Holocene. The vegetation distribution in the early Jomon period was reconstructed in a small valley head at the Chiba prefecture to clarify the development process of the forests around the Kanto plane during the Holocene. On the bottom of the valley distributed the Alnus forests, while on the slopes and the terrace occupied the Quercus serrata forests. The vegetation history of the Kanto plain during the late Glacial and the Holocene was assumed to be as follows : At the full Glacial, the continental type of the deciduous broad-leaved forests prevailed around the Kanto plane consisting of Carpinus, Quercus serrata, Castanea crenata, Acer etc. In the early Holocene, the period human activity started, evergreen broad-leaved forests expanded. However the human activity prevented a full expansion of the evergreen broad-leaved forests, keeping continental type of the deciduous broad-leaved forests among the evergreen broad-leaved forests. Thus the present secondary deciduous broad-leaved forests around the Kanto plain derived from the continental type of the deciduous broad-leaved forests at the full Glacial, suggesting this forest is a historically important issue which should be preserved carefully.