School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemAgroforestry strategies for catchments in the humid tropics( 1995)Catchments in the humid tropics play an important role in the ecosystems and the economies of countries they are in. They are slowly deteriorating because of inappropriate land-use systems being practised by people in them. Agroforestry is seen as a potential land-use system which could help rehabilitate degraded catchments and prevent others from deteriorating. However, selection of appropriate agroforestry strategies to be used for a particular catchment is a problem. The aim of this study was to develop a method that would be able to determine the best combination of agroforestry strategies for a catchment in the humid tropics, that is the one that would yield the maximum net social benefit subject to the constraints of maintaining agricultural yield and net income, keeping erosion within acceptable limits, enhancing soil nutrition, and providing a source of firewood for the catchment users. To achieve this aim, Mt. Masaraga catchment in the Philippines was selected as a case study from which some implications could be drawn that would relate to other similar catchments. Potential agroforestry strategies were presented to the upland farmers in the catchment for acceptability. The selected agroforestry strategies were then evaluated for their capability to prevent soil erosion, to supply firewood, and to provide organic fertiliser for three slope classes. A fuel study was also conducted to determine the fuel consumption of the catchment users. Financial and economic analyses of each selected agroforestry strategy for the three slope classes were then conducted. Linear programming models for the catchment were constructed using average value of the rainfall erosivity index value for the computation of soil erosion. A chance-constrained model which takes into account the probability of rainfall erosivity index value exceeding the average was also constructed. Four agroforestry strategies were found to be acceptable to the upland farmers: contour hedgerow; hedgerow with contour canal; live fences; and combination of contour hedgerow and hedgerow with contour canal. Two models were formulated, a model which assumed that the whole catchment would be converted to agroforestry immediately, and one that incorporated the time of adoption of the agroforestry technologies as a further constraint. It was established that in the Mt. Masaraga catchment, it would be profitable to farmers to adopt agroforestry strategies, but the benefit to society was far greater than to the farmers. The cumulative NPV of the incremental net benefits for the optimum combination of agroforestry strategies for the Mt. Masaraga was P72.4 million greater than if the catchment remained under conventional farming. The chance-constrained model indicated that savings would be even higher if the rainfall erosivity index value in individual years exceeded the average rainfall erosivity index value used in the deterministic model. It was established that the land with steepest slopes should be converted to agroforestry first, because of its ability to reduce the high level of erosion expected on these slopes with conventional farming. More rapid adoption of the strategies resulted in greater savings, indicating that it would be worth spending money on education programs to speed up the rate of adoption. Although these results were specific to the Mt. Masaraga catchment, there is nothing to prevent construction of similar models for similar catchments in the humid tropics, and similar results could be expected.