Clarification of land degradation phenomena and establishment of sustainable land use system in East Asia

利用植被、海拔、土壤类型、年平均气温和年降水量等资料，对亚洲地区1°×1°网格单元进行了分类。通过对应分析将样本绘制在三维空间上，然后进行聚类分析，将所有样本分为十大类。从而可以绘制出亚洲这10种土地类型的地图，并掌握这些土地类型与植被、海拔、土壤、年平均气温和年降水量等自然条件的关系。对应分析的结果表明，温度和降水是造成明显空间结构的最重要因素，即以西藏高地和南至北为中心的同心圆由热带向亚极转变。利用χ平方检验验证了该土地分类与耕作强度和土壤退化分布的高度一致性。然后，以四川省某小流域遭受大规模毁林还林的中国为例，对土地退化进行了进一步的研究。分析了四川南部小流域中国地区近50年来的土地覆被变化和生物资源利用现状，评价了该地区农业的可持续性。这项研究澄清了1950年代的大规模砍伐森林是为了给该地区提供薪材。上世纪70年代的造林绿化使森林资源得到了定量的恢复，森林覆盖率达到了四川省平均水平的两倍。生物资源利用分析表明，研究区以化肥为主的氮素输入显著大于氮素输出。

1° x 1° grid cells in the Asia region were classified using the datasets of vegetation, elevation, soil type, mean annual temperature and annual precipitation. Correspondence analysis was used for plotting the samples on three-dimensional space, followed by the cluster analysis for classifying all samples into ten categories. As a result, those ten land types in Asia could be mapped and the relationship between the land types and natural conditions such as vegetation, elevation, soil, mean annual temperature and annual precipitation were grasped. The result of correspondence analysis indicates that temperature and precipitation are the most important factors causing remarkable spatial structures, that is, the concentric circle centering Tibetian Highlands and South to North change from tropics to subpolar. This land classification is verified by using χ Square test to highly correspond to cultivation intensity and distribution of soil degradation.Then taking a small catchment in Sichuan Province, China that had been exposed to massive deforestation and reafforestation as a case study of land degradation, further study was made. Land cover changes during the past 50 years and actual status of bio-resources utilization were analyzed to evaluate the agricultural sustainability in a small catchment area in Sichuan Province, Southern China. This study clarified massive deforestation in the 1950's was for fuel wood supply in this area. Afforestaion in the 1970's restored the forest resources quantitatively, which means the forest cover ratio became twice as large as the average in Sichuan Province. The analysis of bio-resources utilization suggested that the nitrogen input mainly consisting of chemical fertilizer remarkably exceeds the nitrogen output in the study area.