Studies on the stand composition and growth of the natural young Luchu pine (Pinus luchuensis Mayr) forest in the northern district of Okinawa Island (Preliminary report).

摘要

The research was made on a young forest of naturally grown. Luchu pines (Pinus luchuensis Mayr) in Yona Forest of University of the Ryukyus which is located in the north of Okinawa Island. According to the density of trees, the forest was divided into seven (7) plots, and the trees in each plot were classified into four (4) hight classes in accordance with the height of the trees・・・・classes : 0-3 m, 3-4 m, 4-5 m, and 5 m up. As the result of measurements of the amount of leaves, volumes of stems and branches, and stem anylysis of every tree, the following were found : 1. The ages of the trees are between 7 and 12 years. The plots are narrow areas where the land conditions are similar. The number of trees per ha in each plot is between 8,426 and 20,899. The number of trees in each plot is vanous. 2. The average height of trees in the plots are between 3.88 and 4.31 m. The average height of trees of the tallest height class (over 5 m) which are not suppressed are between 5.18 and 5.66 m. The calculated average age of trees in each plot is between 7.75 and 8.75. 3. In each plot, the trees which belong to the height classes of 4-5 m (average trees) and 5 m up (dominant trees) are more numerous. One plot has 48 % of those classes of trees; another, 53 %; and the rest of the plots, between 60 and 75 %. 4. Since the Ryukyuan pine is light demander, the difference in height due to age and the growth rate while small is closely related to the differences in the growths of diameter, the volume of stem, the amount of leaves, the volume of branches, etc. 5. The growth in the first one and two years is relatively small, and the difference in height is small; but in the second to third year, the growth rate of trees is generally increased, and the difference among the trees becomes greater. From the fourth to fifth year on, the difference of the growth rate of the trees becomes much more greater, -there are some which show very great growth rate, and some which show smaller growth rate than when they were in the second and third years. 6. The diameters at the land level of 7 year old trees are between 1.63 and 6.30 cm, and those at the height of breast are between 0.98 and 8.08. There are great differences of diameters among the height classes. The trees of the Class 5 m up have especially greater diameters and those of Class 4 to 5 m have relatively large diameters, but those of the smaller height classes have much smaller diameters. 7. The stem volume of each tree of 7 years old is between 0.0002025 and 0.0049450 m^3 That of Class 5 m up is the largest, that of Class 4-5 m is relatively large, but those of the smaller height classes have much smaller volumes. The tree of Class 0-3 m has especially small volume.