Mauritania has launched a tree-planting program aimed at protecting its capital from the advancing desert and coastal erosion, a project that could eventually extend thousands of kilometers across Africa. President Mohamed Ould Abdel Aziz on Saturday planted the first of some 2 million trees that are meant to form a "green belt" around the capital, Nouakchott, and curb erosion elsewhere in the desert nation that straddles black and Arab Africa.