Understanding the human impact on Akita-sugi cedar (Cryptomeria japonica) forest in the late Holocene through pollen analysis of annually laminated sediments from Ichi-no-Megata, Akita, Japan

摘要

Akita-sugi (Cryptomeria japonica, Japanese cedar that is grown in Akita) forests are among the most important for commercially valuable timber in Japan. Historically, these forests have been severely exploited, although now some parts of them are conserved. It is important to know the detailed history of the forests in order to utilize them sustainably in the future. This study analyzes the pollen in an annually laminated lake sediment core from Ichi-no-Megata on the Oga peninsula, Akita, Japan, to understand the history of Akita-sugi cedar forests. An age-depth model was developed based on the results of an accelerator mass spectrometer dating of 13 plant macrofossils from the surface to 422 cm in depth, the Towada-a tephra and other well-known event layers. The dominant pollen taxa were Cryptomeria and Fagus crenata by ad 1000. The first increase of Cryptomeria was detected around 1700 bc. By the 1st century ad, Cryptomeria forest was established. At that time, Cryptomeria was mixed with deciduous trees, mainly F. crenata. The pollen analysis found evidence that the main loss of woodland occurred during the 11th century ad, when forest lands were cleared for agriculture. Substantial natural forests nevertheless remained until the 16th century, after which forest resources were exhausted. Conservation and plantation activities took place later, but human activity in response to severe famines prevented the recovery of the forests. After the famine periods, the remaining forests recovered to their previous condition, but after World War II, the natural forests shrank further and plantation forests without deciduous trees were established over large areas.