The reestablishment of forest cover either naturally or artificially. Given enough time, natural regeneration will usually occur in areas where temperatures and rainfall are adequate and when grazing and wildfires are not too frequent.
Reforestation occurs on land where trees have been recently removed due to harvesting or to natural disasters such as a fire, landslide, flooding, or volcanic eruption. When abandoned cropland, pastureland, or grasslands are converted to tree cover, the practice is termed afforestation (where no forest has existed in recent memory). Afforestation is common in countries such as Australia, South Africa, Brazil, India, and New Zealand. Although natural regeneration can occur on abandoned cropland, planting trees will decrease the length of time required until the first harvest of wood. Planting also has an advantage in that both tree spacing and tree species can be prescribed. The selection of tree species can be very important since it affects both wood quality and growth rates. Direct seeding is also used for both afforestation and reforestation, although it often is less successful and requires more seed than tree planting. Unprotected seed are often eaten by birds and rodents, and weeds can suppress growth of newly germinated seed. For these reasons, direct seeding accounts for only about 5% and 1% of artificial reforestation in Canada and the United States, respectively.