Alley farming was developed as a means of maintaining soil fertility in fields under permanent cultivation in Africa, as population pressure makes the traditional practice of slash-and-burn combined with fallowing unsustainable. It is an agroforestry system under which food crops are grown in alleys formed by hedgerows of leguminous trees and shrubs. Studies have shown that it works, but farmers are only taking it up very slowly. Recent work suggests that land tenure might be a factor in the spread of alley cropping.