Comparisons with the Old World tropics

One striking difference between the agro-forestry systems currently adopted by commercial farmers in Amazonia compared with those in tropical Asia and Africa is the paucity of intercropped annual food crops. Food crops such as maize and rice are occasionally intercropped in Amazonia, but rarely with perennials. Also, farmers are not currently interested in intercropping perennials to ameliorate soil, to supply fuelwood, or to provide fodder for livestock, major criteria for agro-forestry research in India (Nair and Dagar 1991). Trees are interplanted if their fruit, nuts, or timber command a high market value.

Farmers generally do not plant trees just to restore soil, provide fodder, or to establish living fences because they do not bring any immediate remuneration. For example, a farmer in the Tomé-Açu area will no longer interplant Erythrina with cacao to provide nitrogen and shade because the leguminous tree does not provide any tangible products. Similarly, a nearby farmer is discontinuing the practice of using Erythrina sp. as living stakes for black pepper because pepper yields have not increased, and because the labour costs of pruning the Erythrina trees are too high. Although Erythrina enriches the soil with nitrogen, it may compete with crops for other nutrients if planted close by. Labour costs also appear to be the main reason cattle ranchers do not use living fences; perhaps some tree species may be found that require little if any pruning.