Analysis of Environment and Ecosystem of Yakushima using Geographic Information Systems

主要研究成果如下。(1)利用FT和U-Pb测年方法估算了八岛岩体的冷却和抬升速率。通过基本填图和磁化率各向异性研究了八岛岩体及其围岩构造格架的发育。我们提出了构造诱导构造与发育于吸积棱柱中的重力驱动构造的区分标准。(2)利用50m格网DEM进行地貌分析，揭示了南北向收缩的地形特征。我们开发了利用数字化等高线对坡度、坡向、坡形进行分类的计算机程序，并以1：25,000的比例尺应用于整个屋久岛。(3)在Nakama、Koseda、Shiratani-Unsuikyo、Yodogawa Hut和山顶进行了土壤剖面调查。宫原，揭示了他们的特点。(4)测定了不同植被类型森林土壤CO_2和CH_4通量的季节变化。结果表明，森林具有CO_2汇的功能。森林土壤每年分解甲烷9.5公斤/公顷。(5)采集不同海拔和植被的土壤样品，对土壤中的细菌进行DGGE分析。在细菌类群中，季节和植被变化很小。(6)利用卫星遥感数据，分析了1994-2002年的植被变化。岛屿西北部植被指数增加，中部和东南部植被指数下降。随后的地理信息系统分析表明，酸雨可能会产生影响。(7)通过地球化学分析，研究了酸雨对土壤-植被生态系统的影响。(8)在社会经济层面，通过对长田村复兴的山神崇拜的研究，分析了长田村居民对环境的认同度。此外，还对屋久岛最重要的产业之一--安久木的木材手工艺进行了调查。

The main results of research are as follows. (1) Cooling and uplift rate of the Yakushima pluton was estimated using FT and U-Pb dating method. Development of structural frameworks of the Yakushima pluton and its host rocks was studied through basic mappings and using anisotropy of magnetic susceptibility. We suggested criteria for separation of tectonic-induced structures from gravity-driven structures developed in accretionary prism. (2) Landform analysis was done by using 50-m grid DEM, thereby revealing north-south contract in characteristics of topography. We developed computer program with which to classify slope gradient, aspect, forms using digitized contours, which was applied to whole Yakushima at a scale of 1:25,000. (3) We investigated soils profiles at Nakama, Koseda, Shiratani-unnsuikyo, Yodogawa Hut and the top of Mt. Miyanoura, revealing their characteristics. (4) We measured the seasonal variation in soil CO_2 and CH_4 fluxes in forests with different vegetations. The results imply that the forest is functioning as CO_2 sink. Forest soil decomposes CH_4 9.5kg/ha annually. (5) Soils were sampled from different altitudes and vegetations, and bacteria in soils were subjected to the DGGE analysis. Among the groups of bacteria, little seasonal and vegetation variations were found out. (6) Using satellite remote sensing data, we analyzed vegetation changes 1994-2002. The vegetation index increased in the NW part of the island, whereas it decreased in the central and SE parts. The subsequent GIS analyzes suggest the possible influence of acid rain. (7) By geochemical analysis the influence of acid rain on the soil-vegetation ecosystem was investigated. (8) As to socio-economic aspect, environmental recognition of the inhabitants was analyzed through studying the revived Mountain worship of Nagata village. Wood handcraft of Yakusugi (ceder), one of the most important industry of Yakushima, was also investigated.