Reforestation is the restocking of existing forests and woodlands which have been depleted, with native tree stock. The term reforestation can also refer to afforestation, the process of restoring and recreating areas of woodlands or forest that once existed but were deforested or otherwise removed or destroyed at some point in the past. The resulting forest can provide both ecosystem and resource benefits and has the potential to become a major carbon sink.

Afforestation is the process of establishing a forest on land that is not a forest, or has not been a forest for a long time by planting trees or their seeds. The term may also be applied to the legal conversion of land into the status of royal forest. Since the industrial revolution many countries have experienced centuries of deforestation, and governments and Non-governmental organisations (NGO's) directly engage in programs of afforestation to provide the benefits of a forest. The term reforestation generally refers to the reestablishment of the forest shortly after its removal, for example from a timber harvest.

Afforestation in areas of degraded soil In various arid, tropical, or sensitive areas, forests cannot re-establish themselves without assistance due to a variety of environmental factors. One of these factors is that, once forest cover is destroyed in arid zones, the land quickly dries out and becomes inhospitable to new tree growth. Other critical factors include overgrazing by livestock, especially animals such as goats, and over-harvesting of forest resources. Together these may lead to desertification and the loss of topsoil; without soil, forests cannot grow until the very long process of soil creation has been completed - if erosion allows this. In some tropical areas, the removal of forest cover may result in a duricrust or duripan that effectively seal off the soil to water penetration and root growth. In many areas, reforestation is impossible above all because the land is in use by people. In these areas, reforestation requires the planting of tree seedlings, treeplanting. In other areas, mechanical breaking up of duripans or duricrusts is necessary, careful and continued watering may be essential, and special protection, such as fencing, may be required.