At first, the islands of Cabo Verde housed an extensive savanna and dry forest cover, but mostly it was removed to convert to agricultural land, which, together with the arid climate and rugged terrain, has led to a soil erosion and desertification widespread. However, the archipelago can be divided into four broad ecological zones (arid, semiarid, subhumid and humid), according to altitude and average annual rainfall ranging from 200 mm in the arid areas of the coast to more than 1000 mm in the humid mountain. Mostly rainfall precipitation is due to condensation of the ocean mist. Today much of the forest cover comprises relatively immature agroforestry plantations, in which are used non-native species such as Prosopis juliflora, Leucaena leucocephala and Jatropha curcas. The native laurel forest species are in wet area only in mountainous areas.