Shifting cultivation, under its diverse forms of slash and burn systems, is a traditional method of cultivating tropical upland soils, mostly for subsistence purposes. Swidden agricultural systems occur in various forms in South America, Southeast Asia and Africa. Native forest is cut and burned, or just burned. The wood ash gives an initial nutrient burst to the soil, which is then planted with various crops. Crop rotations can be complicated and extend the cropping life of the land, but inevitably it is exhausted and the cycle repeated in a new or rested area. During the rest or fallow periods intervening between crops, the natural fertility of the soil is restored for renewed utilization in a subsequent period of crop growth. This traditional system of cultivation is in ecological balance with the environment and does not irreversibly degrade the soil resource, provided a sufficient length of fallow is allowed for soil restoration.
Swidden, a word created by Harold C. Conklin, is defined as a systematic study of shifting cultivation. A survey on swidden cultivation agreed on two principle themes, 'a manmade ecosystem', and the way it relates to population and patterns of settlement. Swidden has made a great contribution to the process of understanding ecology and evolution.
The Bora Agroforestry Project carried out research on swidden fallow management in the Bora Indian Village of Brillo Nuevo in the northeast Peruvian Amazon. Young fallow fields (up to ten years old) and old fallow fields (from 10-35 years old) were examined in terms of composition, structure, and utility. The objective was to demonstrate how fields are gradually abandoned. This contrasts with most studies of shifting cultivation which focus on why fields are abandoned and which present a sharp distinction between the field (swidden) and the abandoned field (fallow). For the Bora, there is no clear transition between swidden and fallow, but rather a continuum from a swidden dominated by cultivated plants to an old fallow composed entirely of natural vegetation. Thirty-five years or more may be required before the latter condition prevails. Abandonment is not a moment in time but rather a process over time.
The Machiguenga are Native American inhabitants of the tropical rainforest of the Upper Amazon, Peru, As is typical of the montana region, Machiguenga settlements vary from single families to small hamlets of related families located on a stream that provides clean water for household needs, near a river suitable for fishing, and with abundant forest for hunting and from which gardens are cleared. Population density is 0.3 persons/km2. The Machiguenga spend nearly as much time procuring wild foods as they do cultivating their gardens, but it is from their gardens that the vast bulk of their food derives, including a great overproduction of starchy tubers for food security under isolated and vulnerable living conditions.
A study has been made of the ecological aspects of rainforest shifting cultivation, as practised by Andoke and Witoto Indians in the Caqueta basin of the Colombian Amazonia. In general, the indigenous cultivation system (mainly of manioc-dominated swiddens) functions in a stable manner. At the individual field level, this is achieved through a relatively specialized response to adverse environmental conditions. Weed competition, rather than progressive loss of soil fertility, is reported to be the primary cause of abandoning manioc cultivation after 2-3 years. Field/forest relationships, that juxtapose crop production with extended periods of forest regeneration, are equally critical to the stability of the system. Lengthy forest fallowing between cultivations reflects the dispersed nature of indigenous settlements. In all, this system contrasts with the more damaging impact of equally small-scale, but more concentrated, colonist agriculture in adjacent areas.
It has been suggested that indigenous tropical forest agriculture, in contrast with other agricultural systems, is characterized by a high degree of polyculture, and, being similar in diversity to the forest itself, has little disturbing effect on the generalized ecosystem that surrounds native gardens. The comparative study of four Central Brazilian Indian groups shows, however, that while each of these groups practices polyculture to some extent, the crop mix found in their swidden plots is highly patterned, and includes single crop stands at certain stages of garden life. Different crops are planted in the same swidden plot from year to year, in accordance with variation in soil fertility within the swidden cycle. None of the swiddens observed compared in complexity to the surrounding forest. The suggestion is that polyculture, rather than being regarded as the distinguishing characteristic of swidden cultivation, should be considered as a varying dimension -- along with other variables such as use of wild plants, soil fertility and exhaustion, tillage practices, the introduction of novel crops, and production for the market -- within the overall subsistence strategy of a group.
In the Upper Orinoco area of Venezuela are found 'conucos' - plots in active cultivation and 'rastrojos' -- fallow plots in the early stages of forest regeneration'. In conucos, bananas and manioc are planted and flourish. The rastrojo is harder to define because of the time and the regeneration process of the forest. However, there is a change in soil nutrients: organic carbon, phosphorus, exchangeable calcium and magnesium all increased; potassium and sodium decreased, as well as a change in pH.
About 25% of Laos' four million people practise shifting cultivation (mainly of rice) on a third of the country's cropped area. Official policy is to eliminate shifting cultivation by the year 2000. Diagnostic surveys of shifting cultivation have been conducted in Luang Prabang and Oudomsay Provinces in northern Laos to understand the practice from a farmer's perspective, to observe fields, and to identify and give priority to problems and research to address problems. Weeds, low and possibly declining soil fertility, intensification of the cropping cycle, rats (plus birds, wild pigs), and insects lowered rice yields or reduced system sustainability. The forest ecosystem has been degraded by logging, burning, and rice monocropping; and potentials for environmental rehabilitation through natural succession are minimal. Farmers cannot adopt high labour and cash cost innovations; and improved fallow is needed as an intermediate step prior to crop diversification, adoption of agroforestry technologies, and sedentary agriculture.
The Kaingin peoples of the Philippines practice swidden agriculture by burning pine forest in the mountains. The outcome is a floral succession from primary montane to secondary pine forests. On southeastern Mindanoa Island the Yagaw Hanunoo also practice a sophisticated swidden agriculture that combines complex labour intense fields, use of secondary forest, controlled burning, multi-cropping, and highly efficient yield to labor outputs. These systems deny easy labels that swidden agriculture is a wasteful, gluttonous, simple/uncomplicated, and destructive endeavour.
The Karen people, the largest highland minority group in Thailand, have traditionally used a conservative short cultivation-long fallow swidden system. Land resources are loosely held by the community, which depends heavily on reciprocal exchange labour to cultivate family farms, and volunteer labour for the communal tasks necessary to protect village lands from fire and other hazards. The swidden system resembles agro-forestry in that the farmers encourage forest regeneration by allowing regrowth from stumps and coppiced trees in cultivated fields, and by controlling fire in fallow swiddens. Trees are used for construction and domestic fuel, and to bring nutrients where they can be used (as ash) to fertilize rice and a wide variety of non-tree crops. Swiddens are cultivated with minimal disturbance to the soil. With low population density the system sustained a subsistence economy for hundreds of years without major environmental deterioration. In recent years the system has been destabilized. Most development projects have not been integrated into existing land-use systems. Agro-forestry techniques have not generally been applied to increase swidden productivity. Extensive reforestation projects in swidden land areas have reduced the amount of land available to Karens at the same time as population has grown due to decline in mortality and migration into the hills. Commercialization of the subsistence economy has led to a decline in the availability of reciprocal exchange labour. Increased demand for forest resources has led to decrease in security of tenure of swiddens and other communally held land. Karens are now placing greater emphasis on irrigated fields, while the swidden system has tended to deteriorate, with more frequent cultivation and shorter fallow, and less adequate control of fire.
The tribal Kantu' of West Kalimantan, Indonesia have traditionally made a distinction between primary and secondary forest, based on the differing inputs, outputs and chronologies of swiddens that are cut from them. Historically this distinction was important to the Kantu' because farming of primary forest bore decisive economic and military advantages within the then context of chronic intertribal warfare. This distinction has maintained its importance into the postwar, contemporary era, although for different reasons. Today the average Kantu' household farms both primary and secondary forest, in part because the former has jural advantages whereas the latter has economic advantages, but largely so as to exploit the differences between the two. This is a major element in a strategy, designed first to minimize risk and stabilize the return on labour, and second, to intensify utilization of this labour.
Agriculture and fishing are the principle sources of Turkuna economy (Kenya). The slash and burn farming is usually done by a communal work party of men. The four crops of major importance are bitter manioc, sweet manioc, maize, and yam. Fishing is the principal occupation of the men, who are taught to fish at an early age. Most boys can provide the household with the fish required at age 9 or 10.