West African rainforest soil was poor despite heavy rainfall and lush growth.

Evidence

The second most striking feature of West Africa was the rain forest (200 miles at its widest point). Here, in spite of two rainy seasons a year and the luxuriant foliage, the soil was poorer; ensuring a livelihood was thus more difficult. The main crops in the rain forest were rice, yams, and maize. — Alice L. Conklin, A Mission to Civilize_ The Republican…, 95