Agroforestry is a term that covers an enormous range of land uses at all scales of tenure and investment, ranging from subsistence to plantation farming, and from dozens of species to only two or three.
The careful integration of trees with other agricultural activities is thought to enhance the long-term sustainability and productivity of many agroecosystems. This is generally attributed to the role these trees play in controlling erosion, maintaining soil organic matter, improving nutrient cycling efficiency, and ameliorating microclimates.
The traditional shifting cultivation system in the lowlands of Papua New Guinea consists of mixed food crop gardens in which yams ([Dioscorea] spp.), bananas, taro [Colocasia esculenta] and sugar cane predominate. The cropping cycle is usually for 18 months, followed by a fallow cycle of up to 30 years. During the cropping cycle, two species of fruit trees, [Pometia pinnata] and [Artocarpus altilis] are also planted, the leaves of the former also being used as a mulch and green manure in yam cultivation. Fallow succession follows rather systematic patterns about which farmers have a thorough understanding. Robusta coffee, a cash-crop component, has been added to the system in some areas since the late 1950s. It is usually grown in permanent blocks, but is interplanted with [Leucaena] as shade. Food crops are planted in the establishment stage, bananas and [Xantohosoma] being retained even in mature coffee gardens. The system seems to be a potentially promising one. But very little quantitative information is available on the production and performance of the system and practically no systematic research has been undertaken. Since the Papua New Guinea fallow gardeners are willing to accept innovations, it will be appropriate and timely to undertake serious studies so that the system can be improved.
Traditional agroforestry systems in the communal areas of Zimbabwe centres on main fields, on home gardens, on homesites and on grazing areas. In the main fields, the major tree-related management practice is the conservation of preferred indigenous fruit trees. Fruit trees are also the focus of forestry activities around the gardens and the homesite; but here it is the planting of exotic species. In a localized area of Zimbabwe, [Acacia albida] is important in fields. There is almost no use of tree fallows in Zimbabwe. Trees in grazing areas have numerous roles, but at present there is little knowledge about traditional management practices in these areas.
Traditional agroforestry in Ifugao, Philippines, uses an indigenous shade tree with coffee for enhanced production. Coffee, introduced during Spanish occupation, is grown under raintree [Samanea caman] along with rattan vines [Calamus merrillii] which is in demand locally for the cottage industry. There is little to no exogenous technological influence in this system (except the introduction of coffee) because there is no pruning, fertilization or improved plant varieties of coffee. The system is probably sustainable based on nutrient and water cycling advantages of raintree (a nitrogen fixer) and particularly soil nutrient additions of litter fall.
Tongan agriculture is based on the intercropping of a number of annual and perennial crops. A lower stratum which is characterized by mixed and staggered planting is tightly integrated with a dense stand of trees, bananas and coconuts. Ecological stability and the production of a wide variety of outputs are both secured by such an agroforestry system. However, mechanization, cash cropping and the beginning of a land shortage have started to change traditional land-use patterns in negative ways. A growing number of farmers see their tree crops as obstacles to intensive cash cropping. Regard for ecologically sound farming practices, which were followed by custom rather than by understanding, is falling away. A combination of modern and traditional farming practices could lead to higher returns with sustainable environmental stability. The natural, organizational and educational infrastructures for the evolution of such farming systems in Tonga are considered to be excellent.
Generally in the Pacific Islands, agroforestry has evolved into sustainable, diverse and productive land use systems in many areas. However, at the same time as the scientific world is trying to catch up with the traditional knowledge, Pacific Islands farmers are abandoning their agroforestry systems in great numbers. It is mainly intensified agriculture for cash crop production that follows. Soil erosion and soil fertility deficiencies are close companions of this intensification.
In the Krui area, (South Sumatra, Indonesia), the damar agroforest ([Shorea javanica]) is one farming element of several cropping systems, including irrigated and rainfed rice cultivation and coffee plantation. Rainfed rice is cultivated in forest clearings, in order to meet rice requirements which cannot be met with irrigated rice crop only. In the forest clearings, coffee stands are established in rice crop, and later, damar are planted among coffee plants. As a result of this cropping system, the damar agroforest spreads while the forest dwindles. In one village, no more forest land is available for peasants' clearings. The resulting high land pressure causes cropping systems and farming systems to change or to be exported to neighbouring areas where forest land is still available.