Grassland that once supported herds can turn to dust within a generation. Desertification is the process by which fertile land becomes desert. It happens mainly in dry regions that border existing deserts, known as drylands. Poor land management is usually the trigger: overgrazing, overcultivation, and deforestation strip the soil of vegetation that holds it in place. Drought can accelerate the decline, but it rarely causes it alone.

The process feeds on itself. When plants disappear, wind and rain carry away topsoil. Without topsoil, fewer plants can grow. The land becomes lighter in color, reflecting more heat and reducing rainfall. Scientists estimate that desertification affects billions of hectares worldwide, with the Sahel region of Africa among the hardest hit. The Great Green Wall project, launched in 2007, aims to restore degraded land across the continent's dry belt by planting trees and supporting sustainable farming.

Main causes

• Overgrazing by livestock.
• Overcultivation and shortened fallow periods.
• Deforestation for fuel and farmland.
• Poor irrigation that salinizes soil.

Desertification is not inevitable. Terracing, rotational grazing, and drought-resistant crops can slow or reverse it. The fix is rarely about planting trees alone. It is about giving land time to recover.