Fig. 1. Cities, regional boundaries, and vegetation zones of Niger, West Africa. The green outline shows an estimate of the area regreened in Maradi and Zinder regions of south–central Niger (source: USGS), and the hatched lines show the southward shift of the 100-mm and 500-mm rainfall isohyets during the drying trend from 1970 to the late 1980s (Koechlin 1997:17). The boundaries between vegetation zones are more gradual shifts in species distributions than sharp, distinct borders.