The Nok people probably used an agroforestry system, combining cultivated crops with useful trees on the same plot of land. These plots are ecologically sustainable and inter-cropping of trees and several cultivated plant species were common from the savannas to the rain forest, with the origins of the practice going back to the first millennium BC, right at the time of the Nok culture. Most West African trees are not domesticated but are part of the wild vegetation which is left after farmers clear their fields of their crops. Because they are left to grow they multiply naturally without needing to be planted. Trees can produce food, medicine and animal feed.