Assessment of humus retention capacity on the decomposition of soil organic matter supposed to increase with global warming

屋久岛（岛）属于亚热带气候带，但在宫原峰（峰，1935米）的顶部可以看到凉爽的温带气候带和植被。关于屋久岛的性质有很多研究（Hayashi, 1952; Tagawa and Hotta, 1996）。Kimura et al.,1996)，还有一些关于土壤的研究（Yagi et al., 1979; Yambe,1979）。然而，屋久岛的成土作用研究得并不好。因此，为了研究土壤的形成和分布，我们对土壤形态进行了调查。在本报告中，我们报告了土壤的形态特征。土壤剖面的描述依据《土壤调查手册》（日本土壤学会，1997年），土壤分类依据《统一分类》（1986年）和《森林土壤分类》（1976年）。“中间”号的地平线为B，呈红棕色，表明粘土堆积。因此，《统一分类》以森林土壤划分为红壤，将中山县划分为典型红黄壤。由于B层的颜色，安波加瓦地和屋谷地被统一分类为“典型黄褐色土壤”，被森林土壤分类为“黄褐色森林土壤”。根据“统一分类法”将花山hodo和Yodogo-koya划分为酸性棕色森林土壤，或根据B层的颜色将森林土壤划分为棕色森林土壤。由于miyanoura - ake具有在草地下的剖面特征，a层较厚，呈棕褐色至深褐色，因此按统一分类将其归类为腐殖质棕色森林土，或按森林土分类将其归类为黑土。结果表明，屋久岛土壤具有垂直地带性，即红/黄棕壤-棕森林土-黑土。

Yakushima (shima=island) belongs to the semitropical climate zone, but we can see the cool temperate climatic zone and vegetation at the top of Miyanoura-dake (dake=peak,1935 m).There are many studies about the nature of Yakushima (Hayashi, 1952 ; Tagawa and Hotta, 1996. Kimura et al.,1996), and there are several studies about soils (Yagi et al., 1979 ; Yambe,1979).In Yakushima, however, pedogenesis was not studied well. Therefore, in order to investigate soil formation and distribution, we have surveyed soil morphology. In this report, we report morphological characteristics of soils.Soil profiles are described according to the Handbook of Soil Survey (Japanese Society of Pedology,1997), and the soil classification follows those by the Unified Classification (1986), and the Forest Soil Division (1976).The Nakama had the B horizon, with reddish brown color indicating accumulation of clay. Therefore, the Unified Classification, as Red soil by the Forest Soil Division, classified Nakama as Typic Red-Yellow soil. The Anbo-gawa and the Yakusugi Land were classified as Typic Yellow-Brown soil by the Unified Classification, or as Yellowish Brown Forest soil by the Forest Soil Division, because of color of the B horizon. The Hanayama-hodo and the Yodogo-koya were classified as Acid Brown Forest soil by the Unified Classification, or as Brown Forest soil by the Forest Soil Division because of color of the B horizon. Since the Miyanoura-dake had the characteristic of a profile under the grassland, with thick A horizon showing brownish brown to dark brown, it was classified as Humic Brown Forest soil by the Unified Classification, or Black soil by the Forest Soil Division. These results suggest that soils indicate the vertical zonality, that is, Red/Yellow Brown soil Brown Forest soil Black soil, in Yakushima.