Does the Relationship between Quadratic Mean Diameter and Stem Density in Old Thinned and Unthinned Cryptomeria japonica Forests Deviate from a Power Function?

Abstract

In approximately 100-year-old forest stands, we investigated whether the relationship between quadratic mean diameter (D_q) and stem density in thinned and unthinned stands (N_t and N_u) deviates from a power function. We also examined the effects of changes in stand leaf mass during stand development on the form of these two relationships. To answer these questions, we used data from 29 long-term experimental monitoring plots established in Japanese cedar (Cryptomeria japonica D. Don) plantations in northeastern Japan. In old thinned stands, the D_q-N_t relationship deviated from the power function, whereas the D_q-N_u relationship in unthinned stands did not deviate from this function during the self-thinning period. These results were strongly affected by changes in total leaf mass with stand development. Comparison of stand development in unthinned and thinned forests indicated that thinning delayed forests from entering the self-thinning period, leading to an apparent rejuvenation effect.