Agro-forestry may be practiced either within or outside forest reserves. Within forest reserves, the object is to establish plantations of selected species to replace the natural understorey. The emphasis here is on the production of tree crops while satisfying the demand of farmers for fertile land, i.e., the taungya system. It offers a solution to the problem of shifting cultivation and reconciles the often conflicting interests of the tropical foresters and farmers. When agro-forestry is practiced in agricultural lands outside forest reserves, the principal object is food crop production.
Tree crops play only a secondary, though important, role.
If the trees used are legumes or other species able to fix nitrogen, there is an increase in soil fertility. Forest crops may be raised with both food crops and farm animals. Trees are planted for fodder, shade, or as live fences. At the beginning of this century, the high forest in Nigeria was very extensive and rich in large trees. With the increase in human population, the area of the high forest started to diminish as a result of demand on forest land for farming and other forms of land use.