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, 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.

Definition

The term afforestation means establishing new forest on lands that were not forest before. 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".

Types

There are three types of afforestation:

Natural regeneration.
Agroforestry.
Tree plantations.

However, the term afforestation can also "imply the intentional conversion of native non-forest ecosystems to exotic tree cover and violate biodiversity safeguards".

Procedure

The process of afforestation begins with site selection. Several environmental factors of the site must be analyzed, including climate, soil, vegetation, and human activity. These factors will determine the quality of the site, what species of trees should be planted, and what planting method should be used.
After the forest site has been assessed, the area must be prepared for planting. Preparation can involve a variety of mechanical or chemical methods, such as chopping, mounding, bedding, herbicides, and prescribed burning. Once the site is prepared, planting can take place. One method for planting is direct seeding, which involves sowing seeds directly into the forest floor. Another is seedling planting, which is similar to direct seeding except that seedlings already have an established root system. Afforestation by cutting is an option for tree species that can reproduce asexually, where a piece of a tree stem, branch, root, or leaves can be planted onto the forest floor and sprout successfully. Sometimes special tools, such as a tree planting bar, are used to make planting of trees easier and faster.
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.

Benefits

There are several benefits from afforestation such as carbon sequestration, increasing rainfall, prevention of topsoil erosion, flood and landslide mitigation, barriers against high winds, shelter for wildlife, employment and alternative sources of wood products.
Afforestation projects create employment opportunities, particularly in rural areas, thus promoting sustainable livelihoods. They can create many jobs in various forest-related activities.

Climate change mitigation

Environmental benefits

Afforestation provides other environmental benefits, including increasing the soil quality and its organic carbon levels, reducing the risk of erosion and desertification. The planting of trees in urban areas is also able to reduce air pollution via the trees' absorption and filtration of pollutants, including carbon monoxide, sulfur dioxide, and ozone, in addition to.
Afforestation protects the biodiversity of plants and animals which allows the sustenance of ecosystems that provide clean air, soil fertilization, etc. Forests support biodiversity conservation, providing habitats for about 80% of the world's biodiversity and contributing to ecosystem restoration and resilience. Water management can be improved afforestation, as trees regulate hydrological cycles, reduce soil erosion, and prevent water runoff. Their capacity to capture and store water helps in mitigating floods and droughts.
Forests act as natural air filters, absorbing pollutants and improving air quality. Urban forestation projects have been successful in reducing respiratory illnesses and enhancing overall air quality in cities. Trees provide shade and cooling effects. By shading and evaporation, forests can lower local temperatures, offering a more comfortable environment in urban areas and reducing the impact of extreme heat.

Criticism

Afforestation in grasslands and savanna

Tree-planting campaigns are criticised for sometimes targeting areas where forests would not naturally occur, such as grassland and savanna biomes. Carbon sequestration forecasts of afforestation programmes often insufficiently consider possible carbon reductions in soils as well as slowing tree growth over time.

Impact on biodiversity

Afforestation can negatively affect biodiversity through increasing fragmentation and edge effects for the habitat remaining outside the planted area. New forest plantations can introduce generalist predators that would otherwise not be found in open habitat into the covered area, which could detrimentally increase predation rates on the native species of the area. A study by scientists at the British Trust for Ornithology into the decline of British populations of Eurasian curlew found that afforestation had impacted curlew populations through fragmentation of their naturally open grassland habitats and increases in generalist predators.

Surface albedo

Questions have also been raised in the scientific community regarding how global afforestation could affect the surface albedo of Earth. The canopy cover of mature trees could make the surface albedo darker, which causes more heat to be absorbed, potentially raising the temperature of the planet. This is particularly relevant in parts of the world with high levels of snow cover, due to the significant difference in albedo between highly reflective white snow and darker forest cover which absorbs more solar radiation.

Monoculture

One significant criticism of reforestation or afforestation efforts that rely on monocultures of - usually conifer - trees is that, while they may increase tree cover, they fail to provide the diverse and complex habitat needed by most woodland creatures. Monocultures, often planted for commercial purposes or ease of management, lack the biodiversity of natural forests. These single-species forests provide limited food sources, shelter, and nesting sites for a wide range of wildlife, and in purely coniferous forests low levels of light may reach the forest floor reducing habitat and variety of plant life. Many woodland creatures, such as birds, mammals, and insects, rely on a variety of tree species and plant life for survival, and the uniformity of monocultures does not support these varied ecological needs. As a result, such reforestation or afforestation efforts may unintentionally create environments that are unsuitable for the very species they aim to protect, thus undermining broader conservation goals.

Examples

Africa

is a ~5,000 mile forest being planted across the continent to stop the spread of the Sahara Desert to the south.

Australia

In Adelaide, South Australia, Premier Mike Rann launched an urban forest initiative in 2003 to plant 3 million native trees and shrubs by 2014 on 300 project sites across the metro area. Thousands of Adelaide citizens participated in community planting days on sites including parks, reserves, transport corridors, schools, water courses and coastline. Only native trees were planted to ensure genetic integrity. Rann said the project aimed to beautify and cool the city and make it more livable, improve air and water quality, and reduce Adelaide's greenhouse gas emissions by 600,000 tonnes of a year.