sentences:  In the Sahelian sector, where the rainfall is only of the order of , the vegetation is mostly of shrubs and wooded grassland or steppe.The sub-Sahelian sector represents the transition zone, receives an average annual rainfall of and represents the transition between the Sahelian and Sudanian bioclimatic zones.The vegetation in this sector has moist Sudan savanna vegetation in the river valleys, while the western half is largely inhabited by humans; most of the large trees in the northern half of the sector are reported to have vanished due to climate change.