Thursday, August 9, 2007 - 2:30 PM

OOS 42-8: Climate-induced dieback of forest species and a shift of vegetation zones across West Africa

Patrick Gonzalez, The Nature Conservancy, Compton J. Tucker, National Aeronautics and Space Administration, and Hamady Sy, Réseau du Système d’Alerte Précoce contre la Famine.

Global climate change, acting through warmer sea surface temperatures, and desertification, acting through a reduction in vegetation cover, have reduced rainfall over the West African Sahel by up to 30% in the 20th Century. In addition, mean annual temperature in the Sahel increased up to 1ºC in the 20th Century. During the 1968-1973 drought, rainfall fell more than one standard deviation below the long-term mean for up to five consecutive years. The drought reduced agricultural yields so significantly that it contributed to the death of up to a quarter of a million people. The drought also caused forest dieback across West Africa. Field inventories of 135 1-ha plots across 7600 km2 in Senegal and at 14 sites in Burkina Faso, Chad, Mali, Mauritania, and Niger showed decreases in species richness of up to 57% in the period 1945-2000. Analyses of 1954 and 1989 aerial photos in Senegal showed a statistically significant (p < 0.001) decline in tree density of 23 ± 5%. Field inventories of 12 1-ha plots and analyses of 1954 aerial photographs and 2002 1-meter resolution IKONOS satellite images of three 200 km2 areas in Senegal and Mauritania also show forest dieback. Species from Mimosaceae and other xeric families expanded in the north, tracking a concomitant retraction of species from Anacardiaceae, Meliaceae, and other mesic families to the south. Climate change has shifted the Sahel, Sudan, and Guinea ecological zones south 25-30 km towards areas of higher rainfall. The vegetation shift has altered ecosystems, reduced the provision of ecosystem services, and rendered local people more vulnerable to climate change and desertification.