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Land use change and its impacts on watershed function and food security in Huaynamphung Subwatershed, Thailand
Dissertation Abstract:
The study was conducted in the 66,073.59 ha Huaynamphung Subwatershed in Thailand covering four districts having different topographies (i.e., mountainous on the western side and relatively flat on the eastern side. The study assessed the land use change from 1989 to 2008, determined the factors affecting the farmers’ decision-making, predicted the impact of land use change on watershed function and food sufficiency, and prepared recommendations for land use management in the subwatershed. Satellite imageries of the area were interpreted to create land use maps for 1989–2008. Factors affecting land use change were determined through interviews of farmer-respondents who were chosen purposively based on the dominant crops planted in the area. Data were analyzed using descriptive statistics and linear regression analysis to find out the factors affecting farmer respondents’ decision to change crops to plant and the relationship among these factors. Fallow model was used to predict the impacts of land use changes after 25, 50, 75, and 100 years on soil physical quality, sediment loss, water yield, base flow, and food sufficiency. The simulations were run in five scenarios: Scenario 1 (original land use), Scenario 2 (teak plantation and agricultural crops), Scenario 3 (tamarind and rubber and agricultural crops), Scenario 4 (agroforestry system with agricultural crops), and Scenario 5 (only agricultural crops).
Results showed that the areas of natural forest and field crop changed the most among all land uses. However, the land area for natural forest decreased, while that of field crop increased. Similarly, the land areas for orchards and tree plantations, settlements, and water increased. As to factors affecting land use changes, nearly half (101) of the 204 respondents changed crops due to both biophysical and socioeconomic factors. Price of produce, management, government advocacy, and diseases, insects, and pests were the most important factors cited for the farmers’ decision to shift to other crops.
Simulated land use change using the original land use map in 2008 showed the shifts to higher stages of tree plantation. The most obvious change happened when the plantation area became an agroforestry system after 25 years of simulation.
Among scenarios, Scenario 3 (tamarind and rubber plantation) sowed the highest increase in simulated soil physical quality, and the highest decrease in water yield and sediment loss. Other scenarios displayed similar results in simulated water yield, base flow, and sediments loss. Scenario 4 (tamarind-based agroforestry system) showed better soil physical quality than Scenario 1 (original land use), 2 (teak plantation), and 5 (only agricultural crops). Food sufficiency was pronounced in Scenario 1 (original and use) and 4 (agroforestry system), while the remaining scenarios exhibited food deficiency only after 13 years.
Recommended land use management in the Sub-watershed was specific for the mountainous, lowland, and upland areas to support the government in encouraging the farmers to plant crops that would help improve socioeconomic status and conserve the environment in the Subwatershed. In the mountainous areas, it is recommended that farmer’s area encourage planting rotation of vegetables suited to low temperature to break cycles of pests and diseases as well as applied organic fertilizer. Tamarind and rubber based-agroforestry system should be promoted in the upland and lowland area of the Subwatershed as it helps conserve the environment, maintain watershed functions, and provide food security to smallholder farmers in the Subwatershed.