The purpose of natural fallow in bush-fallow cultivation systems is to improve soil fertility following a phase of cultivation and to provide useful forest products, including livestock feed. When natural fallow fails to serve these purposes, it can be supplemented or replaced by planted trees.
A study of an Acacia fallow system in the Soli tribal land of central Zambia found that of 31 woody species, dominated by Acacia polyacantha, 39% were leguminous and nitrogen-fixing while 42% were fodder plants. These species make this Acacia fallow suitable for regeneration of soil fertility and production of fodder. Acacia fallow has the advantage of regenerating from seed and root-stocks but is poor in edible wild fruits and durable construction wood. The scarcity of fruits had been compensated by widespread planting of exotic fruit trees; 90% of households have fruit trees. (In spite of the scarcity of good construction wood in the Soli tribal land, no local initiative has developed to plant timber trees.)