Silviculture guidelines for developing mixed forests in old coniferous plantations under long-rotation stand density control

摘要

This study presents guidelines for developing mixed broadleaf-conifer forests in old coniferous plantations under a long-j-otation silviculture system. We established nine square sample plots in Chamaecyparis obtusa (hinoki) plantation forests of various stand ages (22-116 years) and densities (250-1650 trees ha~(-1)). Tree height and diameter at breast height were recorded for all standing trees taller than 1.3 m. This step revealed the varying diameters of coniferous plantation trees and natural broadleaf trees and showed that the density of large trees increased with stand age. The older the plantation forest, the smaller its canopy openness. The standard deviation of canopy openness ranged from 20-30%, with the largest values observed in the middle-aged forests. We estimated the stand density index under which understory vegetation may be established; the maximum stand density index (1028) in the forest studied was considered to be the critical upper limit of stand density control for introducing understory vegetation. Finally, we reviewed previous studies to confirm the validity of our recommendations of long rotation and low stand density control for the development of mixed old plantation forests.