<P> Considerable controversy exists over the proper definition of the term "desertification" for which Helmut Geist (2005) has identified more than 100 formal definitions . The most widely accepted of these is that of the Princeton University Dictionary which defines it as "the process of fertile land transforming into desert typically as a result of deforestation, drought or improper / inappropriate agriculture". Desertification has been neatly defined in the text of the United Nations Convention to Combat Desertification (UNCCD) as "land degradation in arid, semi-arid and dry sub-humid regions resulting from various factors, including climatic variations and human activities ." </P> <P> Another major contribution to the controversy comes from the sub-grouping of types of desertification . Spanning from the very vague yet shortsighted view as the "man - made - desert" to the more broad yet less focused type as the "Non-pattern - Desert" </P> <P> The earliest known discussion of the topic arose soon after the French colonization of West Africa, when the Comité d'Etudes commissioned a study on desséchement progressif to explore the prehistoric expansion of the Sahara Desert . </P> <P> The world's most noted deserts have been formed by natural processes interacting over long intervals of time . During most of these times, deserts have grown and shrunk independent of human activities . Paleodeserts are large sand seas now inactive because they are stabilized by vegetation, some extending beyond the present margins of core deserts, such as the Sahara, the largest hot desert . </P>

What is a major cause of desertification in north africa