The area with increased vegetation growth equals around 1.5 million km2 in Senegal, Mauritania, Mali, Burkina Faso and Niger. The area with increased Rain Use Efficiency, however, is only 1/3 of this (0.5 million km2), and concentrated in a rather narrow band at 15-16 deg N and coinciding with the present 300 mm isohyet. 300 mm of annual rainfall is a pproximately what is needed for rainfed dryland agriculture, and this might hence explain the increase in RUE in this region. In general, however, it must be concluded that other factors have hampered the vegetation from fully utilizing the increase in rainfall over the Sahel. Other authors have pointed at changes in land use, fuel wood consumption, or irreversible land degradation following the droughts in the 1970's and 1980's as possible causes. Some fringing areas with less rainfall increase, including southern Mali and Burkina Faso, and the Senegal River Valley, have experienced increases in vegetation growth unrelated to increases in rainfall. This points at improved agricultural methods, including irrigation.