Forestation refers to the establishment of a forest by planting trees. A distinction is made between afforestation - the planting in areas that lacked forests for a longer period of time - and reforestation - forestation in areas that recently had forest.
Carbon Dioxide Removal with Trees
Trees, like all plants, naturally sequester carbon (C) out of carbon dioxide (CO₂) to convert into what they are made of - biomass. They do that through the process called photosynthesis in which CO₂, water (H₂O) and light energy is converted into sugar (C₆H₁₂O₆) and oxygen (O₂). While the O₂ is released into the atmosphere the sugar is used as an energy source, plant energy storage and as plant building material 1. Plants convert CO₂ as they grow over time - the bigger the tree, the more C was sequestered by that tree. This is why forestation is a carbon dioxide removal method. If the tree is burned or dies and decomposes, all the biomass is converted back into CO₂, which is released back into the atmosphere. Therefore for carbon sequestration through trees, it is important that those trees survive and are not burned.
Global Tree Restoration Potential
Earth has the potential of a total area of 4.4 billion hectares of tree canopy cover (figure 1, A). Extracting the current tree cover - currently there are about 3.04 trillion trees on Earth, but the number is decreasing 2 - and the agricultural and urban areas, this leaves an area of 0.9 billion ha of canopy cover to be planted (figure 1, B and C). This area has space for about 1.2 trillion trees to be planted 3.