Identifying Dendroecological Growth Releases in Old-growth Cryptomeria japonica Forest on Yakushima Island, Japan

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Old-growth Cryptomeria japonica forests on Yakushima Island, Japan have been affected by logging activities. The most ancient record related to logging of Cr. japonica on Yakushima Island dates back to 1563. Systematic large scale logging activities of Cr. japonica occurred over a 300 year period starting in 1642. Forests on the island currently consist of 200-300 year-old regenerated Cr. japonica, although 400 to over 1000 year-old trees have survived logging activities. The objective of the present study was to identify the points in time and the scale of past disturbances and to verify of ancient records of logging activities using dendroecological approaches. Tree-ring analysis using samples obtained from eight Cr. japonica individuals was employed to develop an understanding of and pinpoint the time of past disturbances. Percent growth change (%GC) was calculated to detect release events caused by gaps created by human or natural disturbances and basal area increments (BAI) were calculated to detect growth rates. One older sample tree showed evidence of release events from the middle of 1700s to about 1800 and at the end of the 1900s, and another old-aged sample tree showed similar evidence from 1600 to the middle of 1900s. The BAI value showed an increase for one old-aged sample tree from the middle of 1700s to the beginning of 1900s and the other old-aged sample tree from 1800 to the end of 1900s; thus both trees showed high BAI values for 150 years after releases. Germination year of six regenerated trees subsequent to the inaugural year of logging was estimated within the relatively narrow range between 1791 and 1835. This regeneration timing was consistent with release events followed by high BAI values of old-aged trees. Evidence showing all regenerated samples germinated on stumps and logs indicates the detected releases might have been caused by large scale of logging activities. This study clarified that large scale of logging activity encouraged the growth rate of approximately 500 to 600 years old trees, and also large scale of disturbance was important for regeneration of Cr. japonica.

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