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

利用植被、高程、土壤类型、年平均气温和年降水量等数据集对亚洲地区的1°x 1°网格单元进行分类。采用对应分析在三维空间上绘制样本，然后进行聚类分析，将所有样本分为十类。从而绘制出亚洲地区的10种土地类型，掌握了土地类型与植被、高程、土壤、年平均气温、年降水量等自然条件的关系。对应分析结果表明，温度和降水是造成青藏高原为中心、由南向北由热带向亚极转变的同心圆的最主要因素。利用χ 2检验验证了该土地分类与耕作强度和土壤退化分布高度对应。然后，以中国四川省的一个小流域为例，对土地退化进行了进一步的研究，该流域遭受了大规模的森林砍伐和再造林。通过分析近50 a土地覆被变化和生物资源利用现状，对四川省某小流域农业可持续发展进行了评价。这项研究澄清了20世纪50年代大规模的森林砍伐是为了在该地区提供燃料木材。70年代的植树造林使森林资源得到了定量恢复，森林覆盖率达到了全省平均水平的两倍。生物资源利用分析表明，研究区以化肥为主的氮输入显著超过氮输出。

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.