地球環境問題とランドスケープ 湿潤熱帯における持続可能な地域生態系の再構築

Abstract

Traditional recycling societies of the rural humid tropics have been changing due to the influence of rapid population growth and urbanization. This study examined the feasibility of recycling-oriented society based on local bio-resource utilization at watershed-scale, following the results of surveys at hamlet-scale representing that rural ecosystem in the study area had already become an open system in terms of material flow. Estimation of amount of potential bio-resource supply and consumption, based on the data of land use, population, number of livestock, suggested that local bio-resources could support the consumption of food and fodder in the study watershed area except consumption of fodder in poultry farms. Potential supply of organic fertilizers from livestock dung accounted for 18% of current total nitrogen input to the agricultural lands in the watershed area. Taking account of nitrogen supply from compost of garbage and human excrement, nitrogen supply via organic fertilizer could reach 46% of current total nitrogen input. Estimation of nitrogen input to the upland fields and tea plantation in the upper stream area suggested that the input had the high potential for causing nitrogen loading in the lower stream area. Land use planning taking account of nitrogen removal function of paddy fields and catenary sequence of landform and land use can be one of the options to solve the nitrogen loading problem.