Final answer:
The Mediterranean zone in Africa is the area that produces a surplus of crops due to its mild climate and sufficient rainfall for agriculture.
Step-by-step explanation:
The African zone that produces a surplus of crops is the Mediterranean zone. This zone is known for its mild climate with sufficient rainfall, wet winters, and dry summers. The arable land in the Mediterranean zone of Africa is suitable for growing grains like wheat and barley. By contrast, the Sahara Desert is arid and does not support extensive agriculture. Tropical rainforests have dense vegetation but aren't typically used for agricultural overproduction. The savannas do have rich grasslands, however, they are not as fertile as the Mediterranean zone. The savannas are characterized by tall grasses, sparse trees, and are a transitional biome between the rainforest and drier regions such as the Sahara, supporting a mix of agriculture and herding practices.
Africa's savanna, with its more temperate and wet condition, provides an environment conducive to human settlement and agriculture. The plains of the savanna have historically supported larger human populations due to their hospitable environment and have been the site of intensive agriculture along the banks of the Niger River, which was critical to the development of medieval West African kingdoms.