Comparing 30-year diameter censuses and tree-ring chronologies in natural old-growth Cryptomeria japonica forest on Yakushima Island, Japan

Abstract

The quality of diameter measurements for natural old-growth forest was evaluated by comparing repeated field measurements in a diameter census and treering chronologies. The diameter census was repeated three times from 1973 at 10-to 19-year intervals in old-growth Cryptomeria japonica forests on Yakushima Island, Japan. The diameter growth in the three intervals between (1) first and second measurement (15-19 years), (2) second and third measurement (10-13 years), and (3) first and third measurement (28-30 years) were calculated. The diameter growth of each interval was also measured using tree-ring chronologies as a control. There were significant differences in paired t tests for diameter growth calculated from the diameter census data and from the tree-ring chronologies when the interval was \20 years. Conversely, no significant differences were observed when the measurement interval was [27 years. The average percentage differences (APDs) were relatively high for every interval and for all diameter classes, but the APDs for the 28-to 30-year intervals were better than the 10-to 19-year intervals. The APDs followed a rising trend with increasing diameter at breast height for every interval. In conclusion, data from an interval of [27 years is required for accurate estimation of diameter growth. Furthermore, extra care should be taken when measuring large diameter trees. The results from this study demonstrated the difficulty of using a diameter census in natural old-growth forest.