Time-series changes of stand structures and species composition of old natural evergreen broad-leaved forest in southern Kyushu, Japan

In the WWF red-data book published for the plant communities it was pointed out that conservation counter-measures should be made on to Distylium racemosum and Quercus salicina. In this study, as the first step for bringing forth the conservation guideline for the proper management of the natural ever-green forests, including these above mentioned 2 species, examinations were carried out on the time-series changes of stand-structures and the species compositions, making use of the data obtained by the three times repeated making repeated measurements executed at the five plots (total 0.3675 ha) established at the Takakuma Experimental Forest, Kagoshima University, Japan. The field measurements were carried out in 1987, 1992 and 1997 successively, and 28 species were observed at the plots and were classified into ten species-groups of Distylium, 4 Quercus species, Castanopsis (Castanopsis sieboldii Hats.), Lithocarpus (Lithocarpus edulis Rehd.), P. thunbergii (Persea thunbergii Kostermans), arborescence group and shrubby group. Analyses were made on the following items: the time-series changes of appearance frequency, mean DBH, mean tree height, basal area, density and SDR from monitoring data. Consequently, it was ascertained that, in accordance with the decreasing in the tree-frequency of the Quercus species, shrubby group was on the way of increasing. From 1987 to 1992, there was a dense decreasing in the basal area of Q. acuta, Q. salicina and Castanopsis. As to the diameter distribution, unimodal distribution was shown by the Distylium, Q. acuta and Q. salicina and L-shaped distribution by the shrubby group. In the Q. acuta, Q. salicina and Castanopsis, a large number of mortality-trees were observed through 10-year monitoring. As to the species-group compositions, Distylium was dominant constantly and shrubby-group was on the way of increasing for 10 years. As to the Q. acuta, Q. salicina and Castanopsis, however, decreasing was fixed in the percentage of species compositions. Lastly, there was no regeneration-trees of Distylium and Quercus species that these species were not supposed to regenerate continuously. From the results obtained, it was assumed that this stand might naturally be dominated by Distylium in the upper story and be occupied by small size shrubbies in lower story