Thesis Abstract of AGS Students

Pisut Salakij (1997)

The degradation of watershed ecosystem in Northern Thailand has been a great concern of the Thai government. The cabinet resolution on the watershed classification was issued to manage land utilization in the highland. To implement this policy effiectively, meaningful information regarding land quality and suitability is needed. Land evaluation served as a tool for land use planning and supporting system for managing the watershed. Land evaluation procedure should be based on relevant land mapping unit and their qualities. The application of GIS and multicriteria decision making were examined in this study in order to delineate terrain mapping unit (TMU)and to evaluate the suitability of each TMU found in the study area for various land utilization types. The study area was located in Muang Na sub-district, Chiang Dao district, Chiang Mai province with an elevation of 960 m to 1,100 m above mean sea level.

Terrain mapping unit delineation was achieved by overlaying the slope class map and drainage density. This was implemented in IDRISI, a raster GIS. Twenty seven TMU were identified from this process.

The soil properties in each TMU were described and analyzed from the soil survey and saved as attributes of TMU to represent land characteristic for evaluation process. Land utilization type (LUT) was identified from the result of informal interviewing which involved extension workers, researchers and farmers and covered socioeconomic aspects as well as farm practice and management. Land use requirement of each LUT were obtained from the published tables of DLD and FAO and used for matching with LC in each TMU.

Multicriteria evaluation was used to rate each TMU for its suitability and produced the suitability index ranging from 0 to 1.0. These were classified into 4 classes according to FAO by using their statistical distribution. The suitability map of particular LUT was used to compare and analyze with present land use and watershed classification maps.

The results of overlay analysis between the land use in 1994 and the watershed classification map indicated that 74% of the arable land in the study area occupied class III watershed which was restricted for pasture and fruit trees with proper conservative measures.

This study also revealed that 55% of the upland rice and field crops cultivated in 1994 were grown on the S₂ (moderately suitable) land. These areas should be allowed to continue the production to support the livelihood of the people in the community Most of marginal suitability (S₃) for field crop area could be safely used for growing fruit trees. Planting of local fast-growing trees species was suggested in the S₃ land in the study area to sustain the need for ecological balance and fuelwood of the community.

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