Structure and growth in an old-growth sugi (cryptomeria japonica) forest in akita prefecture, Northeastern Japan

Abstract

Periodic annual net increment of stand volume and stand structure dynamics were analyzed by using data collected in long-term monitoring during a 77-year period in a sugi (Cryptomeria japonica) natural forest located in Akita Prefecture, Northeastern Japan. Forest age was estimated at the end of the monitoring period to be 244 years. The research forest was thinned twice during the monitoring period, first at 168 years old and again at 190 years old. The periodic annual net increment of stand volume peaked at about 10 years after each of the thinning operations. The increase in volume growth of individual trees following each thinning operation may be seen as a cause of the peaks in periodic annual net increment of stand volume. After each of the two peaks mentioned, the periodic annual net increment markedly decreased from 32.2 to 6.1 m3ha-1yr-1 just before the second thinning operation, and decreased from 14.9 to 3.7 m3ha-1 yr -1 at the end of the monitoring period. Both thinning operations had a strong impact on the distributions of DBH and tree height; the research forest transformed from a multi-storied forest to a single-storied forest. The tree height growth declined earlier than basal area growth. Therefore, the stem volume growth of old-growth trees is produced by basal area growth rather than height growth.