with maize and bananas or plantains. The components of home gardens and many other traditional systems are selected for high productivity and minimum effort. Weeding and pest control efforts are reduced by using a combination of shade, domesticated animals, and plant species. These household plots also serve as sites for conducting small-scale crop experimentation and for cultivating seedlings before transplanting them to agricultural plots.

Typical cultivation and management practices include integrating the placement and planting times of tree species so that different products can be collected and harvested throughout the year. The heterogeneity of mixed tree systems provides a protective upper canopy that protects lower canopy and ground species from seasonal torrential rains and direct tropical sunlight. In harsh tropical environments, this practice allows the production of delicate economic species, such as cacao. In addition, the upper canopy helps maintain relatively constant moisture and temperature levels and contributes to soil regeneration (Niñez, 1985; Soemarwoto et al., 1985).

Types of mixed tree systems range from intensive systems such as home gardens, where the trees are planted along with other useful species directly adjacent to a dwelling, to more extensive systems of natural forest management, such as the artificial forests described by Alcorn (1990). Orchards sometimes integrate pastureland with trees (including timber species) for livestock production combined with annual and perennial crops (Altieri and Merrick, 1987; Fernandes et al., 1983; Russell, 1968). Mixed tree systems can also be found in the fallow fields of shifting cultivators, where useful tree species are spared or planted in the cleared agricultural plot and the subsequent forest regeneration is managed to encourage forest patches that provide desired products (Caballero, 1988; Soemarwoto and Soemarwoto, 1984). Many farmers also conserve a strip of mature vegetation between or surrounding their agricultural plots (Pinton, 1985). Research and historical accounts throughout the tropics indicate that mature forests are often composed of patches dominated by species that have been encouraged, spared, or planted by past and present human inhabitants (Gómez-Pompa and Kaus, 1990).

Indigenous groups of small-scale farmers are predominately responsible for maintaining and cultivating mixed tree areas in tropical regions, without subsidies or international expertise. In contrast, single species tree plantations, such as for coffee, cacao, rubber, or oil palm production, have been encouraged and managed for large-scale production through foreign or agribusiness investments (see below). Smaller scale production in single species plantations has typically been supported by bank credits, government-funded agricultural extension