Changes in stand structure during a 12-year period in a natural fir-hemlock forest in mountain regions of Kyushu.

摘要

A permanent plot (0.25 ha) was established in a fir-hemlock (Abies firma/Tsuga sieboldii) forest in the mountainous regions in Kyushu, SW west Japan, to investigate the dynamics of the forest. Changes in stand structure were analysed based on species composition, size distribution (diameter and height), stratification and behaviour of trees over a 12-yr period (observation were made in 1983 and 1995). The number of tree species and the species diversity evaluated by H' both decreased during this period. Two trends were found in tree size distribution - fir trees in the upper layer were recruited into larger classes and the number of broadleaved shrubs in smaller size classes decreased. In addition to these trends, hemlock and broadleaved trees were recruited into the higher classes of height distribution. The stratification of the stand in both survey years was composed of 4 layers, indicated in an H-h diagram that was drawn using mean tree height and individual tree height. In all layers, numberof individuals and number of tree species decreased, and the survival rate was lower in the understorey. It is considered that the light environment under the 4th layer was not suitable for survival or growth of regenerated trees, and that attack by wild deer influenced disappearance of trees. Behaviour of trees was different among layers, for example, more than half number of trees in second layer were exchanged with trees from other layers. Analysing the behaviour of individuals based on stratification was an effective method of investigating temporal changes in stand structure.