The present study focuses on agriculture-forestry-based livelihood systems of Northwestern Lao people through village studies, including semi-structured group interviews, questionnaire survey, participatory observation and wealth ranking in Luang Namtha province. The study also examined the use of natural biological resources and identified their roles in household economy. The study revealed that lowland, hillside and mountain villages have different sets of farming practices including lowland paddy and shifting cultivations and natural biological resources use under the given agro-ecological setting, and natural biological resources play a crucial role in household food security in terms of providing an important source of cash income, particularly for poor people. Multiple functions of forest resources including bio-diversity conservation, fallow for coming cultivation and production of non-timber forest products should be further examined in order to guide development toward environmental conservation, food security and poverty alleviation.

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Contemporary land-use change during the past century in Northeast Thailand was analyzed at four socio-ecological scales: region, community, landscape and field plot. The main objectives were to elucidate factors influencing the change and identify effects of the change on the present land conditions. At all scales the land was transformed from forest to cultivated fields by pioneering farmers but such land transformation did not lead to rapid forest loss in the earlier subsistence economy period. Rapid forest loss only occurred after the economy became more commercialized with the expansion of cash crop cultivation in the early 1950s. Land transformation began in the lowland (prime areas for paddy fields) and expanded upward to the uplands. Population growth was the major factor for land-use change in the earlier stage while subsequently the growing commercialization of agriculture was the main factor. Changes in land use have resulted in degradation of land in the upland fields but not in the paddy fields. The upland fields have higher soil erosion and lower soil organic matter pools than the natural forest. The paddy fields, however, do not show indications of being degraded, probably because of their inherent soil properties and their location in the low-lying areas where they receive continuing in-flows of nutrients eroded from higher parts of the landscape. A number of measures to counter the land degradation are suggested including adopting of a more polycultural form of agriculture by integrating trees into agroecosystems at all scales. Such polycultural systems mimic the natural forest ecosystem which is more sustainable ecologically than monocultural systems. In addition, farmers in the Northeast should readopt some degree of subsistence-orientation which would increase the economic and social sustainability of Northeastern agriculture.

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Large areas of undulating terrain in Northeast Thailand are dominated by farming systems based on rainfed upland crops and lowland rice. Evidence of a substantial decline in land productivity from current land uses and management points out the need for a more detailed assessment on land-use sustainability of the region. The present study evaluated nutrient balances of different types of sugarcane fields as an indicator of land-use sustainability. The crop is currently the most widely grown field crop in the region, and its production practices involve high fertilizer inputs and considerable soil disturbances. Kham Muang village in Khon Kaen province was selected as a study site. Four types of sugarcane subsystems were recognized based on their differences in nutrient input and output parameters. These included combinations of two rates (high and low) of fertilizers and two practices of field burning prior to harvesting (burned and not burned). Sources of nutrient inputs and outputs were identified for the individual subsystems. Amounts of major nutrients (N, P and K) were determined for the individual sources, based primarily on actual field measurements in farmers' fields in Kham Muang and adjacent villages and in a mini-watershed in Kham Muang village. Nutrient balances were then calculated for the full three-year cycle of the individual subsystems and at three yield levels (high, moderate and low). The results showed that N balances were mostly positive but P and K balances were negative for all subsystems. Positive balances of N were high at the high fertilizer rate and low yield level, declined at the low fertilizer rate and higher yield levels, and became negative when the field was burned. Negative P and K balances increased as yield level increased and when the low rate of fertilizer was applied. Field burning caused significant losses for all three nutrients, making negative balances even higher for P and K in burned field; the amounts were quite substantial in all subsystems. Excess N is likely to be lost through water flow, but continuation of current practices can cause P and K depletion in the long run. Measures to adjust the balances of these two nutrients are needed to improve land-use sustainability of sugarcane production in the region.

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This paper reports some results of the first three years of an on-going research project on nutrient balances in a composite swidden agroecosystem. In a composite swiddening system, households simultaneously cultivate both swidden fields on hill slopes and paddy fields in the valleys. The study is being carried out in Ban Tat, a small settlement of Da Bac Tay ethnic minority people in Hoa Binh Province in Vietnam's Northern Mountain Region. Nutrient inputs and outputs for a swidden field on a hill slope and a wet rice field in the valley below it were recorded and nutrient balances for each subsystem calculated. The swidden had large negative balances for N, P, and K in all years of the experiment whereas in the paddy field only K was in serious deficit. Nutrients lost from the swidden field constituted a major source of inputs into the paddy field. This suggests that the sustainability of wet rice agriculture in the valleys is heavily dependent on interactions with the hill slopes.
 At the level of the composite swidden system as a whole, nutrient inputs and outputs were not in balance. Outputs of N exceeded inputs by 159 kg/ha and outputs of K exceeded inputs by 867 kg/ha. Only P showed a positive balance with inputs exceeding outputs by 220 kg/ha. Comparison of the nutrient balances for the swidden and the wet rice field revealed that the negative imbalance of nutrient inputs to outputs was much greater in the swidden field than in the paddy field. Thus, if the farmers at Ban Tat relied exclusively on swiddens to meet their food requirements, their agricultural system would be much less sustainable than it is now. This confirms the main hypothesis of this research that it is the fact that most households simultaneously cultivate both wet rice fields and swiddens that explains the relatively high sustainability of the land use system in Ban Tat.

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In the mountainous region of Northern Vietnam, there are various systems for agricultural land use. This paper describes the impact of agricultural practices on the original properties of slope land soils with special reference to changes in soil fertility and weathering in relation topsoil erosion. Soil fertility was not extremely low in the higher commune, where the cooler climate would be more dominant factor controlling productivity. Therefore, the people made well-managed terraces to maintain their fields. On the other hand, in the lower commune, shifting cultivation is a dominant way of agriculture supported by the warmer climatic condition. Weathering status of soils was not greatly different among the three communes, but the current climatic conditions would affect the reactivity of soils. The clay dispersion ratio of all the sites studied was very low. In addition, the clay dispersion ratio and clay content were not different among different land uses. This means that soil erosion would not have a strong impact under current farming systems in the three communes. However, activity ratios of Aland Fe (Alo/Ald and Feo/Fed) became lower after cultivation, and therefore, in the long term, slight but continuous erosion might have occurred to reduce the activity of soils.

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The physico-chemical properties of the soil in shifting cultivation fields in Xiang Ngeun district, Luang Phabang province were investigated in order to provide a basis for developing an agricultural system that will be sustainable under higher population pressure on the land and increased demand to engage in intensive farming. The soils in the study area have reasonably high contents of soil nutrients despite being on erosion-prone sloping land. Soil fertility status may not be fully restored even when the length of fallow is 10 years. The nutrients accumulated in the soil during fallow period are small compared with the nutrients supplied from the ash input when the biomass is burned so that soil nutrients were found not to be exhausted after a single year of cultivation. However, the density of weeds increases as the fallow period is shortened. Therefore, fallow plays an important role in weed control during the cropping period. These findings suggest that an agroforestry system that combines crop cultivation with paper mulberry production could be a sustainable farming system for short-fallow shifting cultivation. To be acceptable to the farmers, this agroforestry system must be effective both in controlling weeds and in generating income for the shifting cultivators.

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The present study describes a complex multiple cropping system of six crops which has evolved in a Lisu village in Chiang Mai during the last 17 years. The system involves relay planting of three viny legumes [cowpea (Vigna unguiculata), rice bean (Vigna umbellata) and lablab bean (Lablab purpureus)] after inter-cropping of maize and wax gourd (Benincasa hispida) or pumpkin (Cucurbita moschata). The relay-cropping of the three viny legumes could be considered as a locally evolved type of accelerated seasonal fallow management aimed at soil fertility replenishment and income generation in an intensified shifting cultivation system. The Lisu farmers adopted this system because of their prior experiences on market economy and their knowledge of multiple cropping technology through previous maize-opium based farming, as well as because of the availability of a large area of fertile land to sustain intensive cultivation without external inputs. The ability of the multiple cropping system to generate acceptable income and the availability of transportation for the products were also positive factors favoring its adoption. On the other hand, its lower profitability than competitive cropping systems, such as vegetable seed production, and its requirement for good transportation, large farm size and fertile soils constrained its expansion. The present study also revealed that external factors of economy and technology development are crucial in determining if environmentally beneficial cropping systems will continue in use in the long-term or be replaced with less environmentally friendly agricultural practices.

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Most of the people who live in the mountainous region depend on agriculture for their livelihood. They are facing increasing difficulties in meeting their daily subsistence needs, let alone raising their living standards to levels enjoyed by the lowland populations. At the same time, the agro-resources on which the economic welfare of the mountain people depends have been suffering severe degradation with consequent reductions in productivity. Finding ways to intensify agricultural production in a sustainable manner is a critical problem facing both the farmers who inhabit the mountainous region and for the national governments of Laos, Thailand, and Vietnam. In this paper, drawing on the detailed case studies of specific local areas that are presented in the papers in this special issue, we describe some key problems facing agricultural populations in the mountains, examine the driving forces for change, look at the adaptive responses of the farmers to the changing resource situation in the mountains, assess some potential solutions, and set-out some research priorities.

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