この論文は国立情報学研究所の学術雑誌公開支援事業により電子化されました。In Northeast Thailand, upland is a place of conflict between upland field expansion and forest conservation, and between land suitability and external market demand. This paper highlights the dynamic process of upland utilization and forest land management during the last several decades through a case study of upland in an area dominated by paddy fields in Yasothon province, and discusses the impacts of commercial cultivation on land resources management. Upland utilization showed dynamic changes according to individual villagers' demands for upland crop cultivation, and forest land management was also affected by this demand. Nevertheless, upland utilization was, as a whole, well balanced between upland field expansion and forest conservation. Diversification of villagers' income sources is found to be a key issue in flexible and proper land resources management.