Each year, the world loses more grasslands, croplands and even forests to encroaching deserts. Desertification threatens one-third of the earth's land area, and a billion people in the world's poorer, arid regions. Patrick Gonzalez had a first- hand look at desertification during a five year stay in West Africa. Currently he works for the U.S. Agency for International Development (US AID). Mr. Gonzalez was the first researcher to document a large-scale decline in species richness and tree densities in the West African Sahel in Senegal. To conduct his research he spent a year hiking more than 1,200 miles through west Africa. Steve Curwood talks with Patrick Gonzalez about his long walk.