Farmers in Niger are nurturing gao trees to drive Africa’s biggest environmental change Rain had come to nearby villages, but not yet to Droum in south-east Niger. The sand under its stately trees looked completely barren, but Souley Cheibou, a farmer in his 60s, was not worried. He crooked a finger, fished in the sand, and brought out a millet seed. In a week or two, this seed would germinate and sprout, and soon the whole field would be green.