A palynological study on postglacial vegetation changes in the Choshi area, Central Japan

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  • 銚子地域における後氷期の植生変遷
  • チョウシ チイキ ニ オケル コウヒョウキ ノ ショクセイ ヘンセン

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Abstract

This study aimed to clarify the vegetation changes in the postglacial period of the Choshi area with a particular focus on Castanopsis pollen under SEM. The murus differences between Castanopsis and Castanea pollen are useful for the pollen identification. This study examined these criteria and classified into five types as A〜E, based on the murus width and shape. As the result, the following four forests stages in the vegetation change were recognized: 1) Deciduous broad-leaved pioneer forest: DBL (P) with Castanopsis, 2) Conifer and deciduous broad-leaved mixed forest: CDBM, 3) Mid temperate forest with Laurel (evergreen broad-leaved trees): ML and 4) Pine secondary forest: Ps. The continuous vegetation changes were considered the result of soil disturbance on riverside and coastline transgression and regression associated with the climatic change. The Zelkova - Ulmus dominated DBL (P), which occupied the disturbed area in the postglacial early period, and Castanopsis already distributed c. 8,000 Cal BP with Castanea. Also, Araliaceae emerged sporadically, at the exposed coastal land due to transgression in the early period between c. 10,000 Cal BP and c. 8,000 Cal BP. Continuously, coniferous trees increased in DBL (P) and changed to CDBM, after which Cyclobalanopsis appeared in the CDBM and ML developed around the upland area from c. 7,000 Cal BP. Upon investigation however, the comparatively high coniferous pollen rate appears to be an overestimation in pollen sedimentation by the Neves effect; coniferous trees did not dominate the vegetation of the period. On the other hand, evergreen broad-leaved forests consist of Cyclobalanopsis developed along the coastal area during a period of coastal regression c. 4,000 Cal BP. And the deforestation resulted in the increased Pinus pollen c. 2,000 Cal BP. Further study would be needed to obtain more sufficient data, especially in the periods from c. 2,000 Cal BP to c. 3,000 Cal BP and c. 5,000 Cal BP when this study did not examine.

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