The climate of the Wolof area varies greatly from north to south. The north is nearly desert-like, while the southern region is a tropical rain forest. The crops grown in each area reflect the climate of that zone. Staple crops are sorghum and millet. Tomatoes, peppers, peanuts, and beans are also grown. Fish is very important, and rice is a staple of urban Wolof diets. Until the late 19th century, Wolof rulers played a key part in the slave trade, directing slave raids and selling captured individuals from inland peoples to the Europeans on the coast.