Afforestation plants trees where forests did not recently exist. It differs from reforestation, which restores forests that were cut down. A grassland, a degraded pasture, or a bare hillside converted to woodland is afforestation. The goal is usually carbon capture, soil protection, or timber production.

China's Three-North Shelterbelt Program, often called the Great Green Wall, is the largest afforestation effort in history. It has planted billions of trees across northern China to slow desert expansion. Other countries, including Ethiopia, India, and Pakistan, have launched mass planting campaigns. Some succeed. Others plant the wrong species in the wrong place and watch them die.

Afforestation has critics. Planting trees on naturally treeless ecosystems, like savannas or peatlands, can harm biodiversity and even release carbon. Water use is another concern. Trees drink a lot. In dry regions, a new forest can drain aquifers and reduce streamflow. The science is clear: where you plant matters as much as how many.

Common goals

• Carbon sequestration
• Soil erosion control
• Desertification prevention
• Timber and fuelwood
• Watershed protection