Afforestation

Afforestation is the establishment of a forest or stand of trees in an area where there was no recent tree cover. There are three types of afforestation: natural regeneration, agroforestry and tree plantations. In the context of climate change, afforestation can be helpful for climate change mitigation through the route of carbon sequestration. Afforestation can also improve the local climate through increased rainfall and by being a barrier against high winds. The additional trees can also prevent or reduce topsoil erosion (from water and wind), floods and landslides. Finally, additional trees can be a habitat for wildlife, and provide employment and wood products.

In comparison, reforestation means re-establishing forest that have either been cut down or lost due to natural causes, such as fire, storm, etc. Nowadays, the boundaries between afforestation and reforestation projects can be blurred as it may not be so clear what was there before at what point in time.

An essential aspect of successful afforestation efforts lies in the careful selection of tree species that are well-suited to the local climate and soil conditions. By choosing appropriate species, afforested areas can better withstand the impacts of climate change.

Earth offers enough room to plant an additional 0.9 billion ha of tree canopy cover. Planting and protecting them would sequester 205 billion tons of carbon which is about 20 years of current global carbon emissions. This level of sequestration would represent about 25% of the atmosphere's current carbon pool. However, there has been debate about whether afforestation is beneficial for the sustainable use of natural resources, with some researchers pointing out that tree planting is not the only way to enhance climate mitigation and CO₂ capture. Non-forest areas, such as grasslands and savannas, also benefit the biosphere and humanity, and they need a different management strategy - they are not supposed to be forests.

Afforestation critics argue that ecosystems without trees are not necessarily degraded, and many of them can store carbon as they are; for example, savannas and tundra store carbon underground. Carbon sequestration estimates in these areas often do not include the total amount of carbon reductions in soils and slowing tree growth over time. Afforestation can also negatively affect biodiversity by increasing fragmentation and edge effects on the habitat outside the planted area.

Australia, Canada, China, India, Israel, United States and Europe have afforestation programs to increase carbon dioxide removal in forests and in some cases to reduce desertification.

The term afforestation means establishing new forest on lands that were not forest before (e.g. abandoned agriculture). The same definition in other words states that afforestation is "conversion to forest of land that historically has not contained forests".

In comparison, reforestation means the "conversion to forest of land that has previously contained forests but that has been converted to some other use".