A quiet, green miracle has been growing in the Sahel.

Farmers in the western Sahel have achieved a remarkable success by deploying a secret weapon often overlooked in wealthier places: trees. Not planting trees. Growing them. Chris Reij, a Dutch environmental specialist at VU University Amsterdam who has worked on agricultural issues in the Sahel for thirty years, and other scientists who have studied the technique say that mixing trees and crops—a practice they have named “farmer-managed natural regeneration,” or FMNR, and that is known generally as agro-forestry—brings a range of benefits. The trees’ shade and bulk offer crops relief from the overwhelming heat and gusting winds. “In the past, farmers sometimes had to sow their fields three, four, or five times because wind-blown sand would cover or destroy seedlings,” said Reij, a silver-haired Dutchman with the zeal of a missionary. “With trees to buffer the wind and anchor the soil, farmers need sow only once.”

Leaves serve other purposes. After they fall to the ground, they act as mulch, boosting soil fertility; they also provide fodder for livestock in a season when little other food is available. In emergencies, people too can eat the leaves to avoid starvation.

The improved planting pits developed by Sawadogo and other simple water-harvesting techniques have enabled more water to infiltrate the soil. Amazingly, underground water tables that plummeted after the droughts of the 1980s had now begun recharging. “In the 1980s, water tables on the Central Plateau of Burkina Faso were falling by an average of one meter a year,” Reij said. “Since FMNR and the water-harvesting techniques began to take hold in the late 1980s, water tables in many villages have risen by at least five meters, despite a growing population.”

Some analysts attributed the rise in water tables to an increase in rainfall that occurred beginning in 1994, Reij added, “but that doesn’t make sense—the water tables began rising well before that.” Studies have documented the same phenomenon in some villages in Niger, where extensive water-harvesting measures helped raise water tables by fifteen meters between the early 1990s and 2005.

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Originally published on the Scientific American website