Reforestation is the replanting of trees on land that was previously forested. This differs from afforestation, which refers to the planting of trees on land that never had many trees or has not had trees for a very long time.
The benefits of reforestation can include rebuilding natural habitats and ecosystems, mitigating climate change via sequestration of atmospheric carbon dioxide, improving the quality of human life by absorbing pollution and dust from the air, and increasing the supply of timber and other resources.
Reforestation can be accomplished by planting seeds or seedlings. Forests can also regenerate naturally to varying extents, depending on the size and location of the treeless area, the type of forest, etc., by making use of existing root systems, from seeds remaining in the ground from before deforestation, and by the dispersal of seeds by the wind and by birds and other animals.
An important consideration in reforestation is whether or not the resulting forest will have the same biota as the original forest. Planting a selection of seeds similar to that of the original forest will tend to result in a similar biota, whereas replacement with only a single species could result a monoculture forest similar to agricultural crops with minimal biodiversity.