Traditionally, most of the people in the Sahel have been semi-nomads, farming and raising livestock in a system of transhumance, which is probably the most sustainable way of utilizing the Sahel. The difference between the dry North with higher levels of soil nutrients and the wetter South with more vegetation, is utilized by having the herds graze on high-quality feed in the North during the wet season, and trek several hundred kilometers to the South to graze on more abundant, but less nutritious feed during the dry period.[citation needed]