Afforestation is when people create forests in areas that did not have trees recently. There are three types of afforestation: natural regeneration, agroforestry, and tree plantations. In the context of climate change, afforestation can help reduce the amount of carbon dioxide in the atmosphere by absorbing it. It can also increase rainfall in local areas and act as a barrier against strong winds. Trees can prevent or reduce the loss of topsoil from water and wind, as well as help stop floods and landslides. Trees also provide homes for animals and can create jobs and supply wood products.

Reforestation means restoring forests that were lost due to human activity, such as cutting down trees, or natural events, such as fires or storms. Sometimes, it can be hard to tell the difference between afforestation and reforestation projects because it may not be clear what the area looked like in the past.

A key part of successful afforestation is choosing tree species that grow well in the local climate and soil. Trees that are well-suited to the environment are more likely to survive and thrive.

The Earth has enough space to add 0.9 billion hectares of tree cover. Planting and protecting these trees could absorb 205 billion tons of carbon, which is about 20 years of the world’s current carbon emissions. This amount of carbon absorption would be about 25% of the carbon currently in the atmosphere. However, some scientists argue that planting trees is not the only way to reduce carbon emissions. Grasslands and savannas, which are not forests, also help the environment and need different management methods.

Some people who criticize afforestation say that areas without trees are not always damaged and can store carbon naturally. For example, savannas and tundra store carbon in the ground. Studies about carbon absorption often do not include all the carbon stored in soil or the effects of slower tree growth over time. Afforestation can also harm wildlife by breaking up habitats and creating edges between forests and other areas.

Countries such as Australia, Canada, China, India, Israel, the United States, and Europe have afforestation programs to help forests absorb more carbon dioxide and, in some cases, reduce desertification.

Definition

Afforestation is the process of planting trees on land that was not a forest before, such as land that was used for farming but is no longer used for farming. This can also be described as changing land that never had forests into forests.

Reforestation refers to planting trees on land that once had forests but was changed to another use, such as for farming or construction.

Types of afforestation

There are three types of afforestation:

• Natural regeneration (when native tree seeds are planted; this helps create new ecosystems and allows trees to absorb carbon dioxide from the air).
• Agroforestry (a farming method that grows crops like fruits and nuts alongside trees).
• Tree plantations (trees are planted to produce wood and paper products; this is sometimes used instead of cutting down natural forests).

However, the term afforestation can also mean "intentionally changing non-forest areas, such as grasslands or wetlands, into forests with non-native tree species. This process may harm the variety of plants and animals that live in those areas."

Procedure

The process of planting trees in an area that does not have a forest begins with choosing a suitable location. To select the best site, several environmental factors must be studied, including the local climate, type of soil, existing plants, and human activities in the area. These factors help determine how good the site is for planting, which tree species should be used, and what method should be chosen for planting.

After the site is evaluated, the area must be prepared for planting. Preparation can include using different mechanical or chemical methods, such as cutting plants, creating small hills, making flat areas for planting, using chemicals to remove unwanted plants, or using controlled fires. Once the site is ready, planting can begin. One planting method is direct seeding, which means placing seeds directly into the soil. Another method is seedling planting, which is similar to direct seeding but uses young trees that already have roots. For certain tree species that can grow new trees from parts of existing trees, planting pieces of stems, branches, roots, or leaves into the soil can help them grow. Sometimes, special tools like a tree planting bar are used to make planting easier and faster.

A key part of successful tree planting efforts is choosing tree species that are well-suited to the local climate and soil. Selecting the right species helps ensure that the planted trees can survive and grow even as weather patterns change over time.

Benefits

Afforestation has many benefits, including storing carbon, increasing rainfall, preventing soil erosion from water and wind, reducing floods and landslides, blocking strong winds, providing shelter for animals, creating jobs, and offering wood products.

Afforestation projects often create jobs in rural areas, helping people earn a living in a sustainable way. These projects can provide work in activities related to forests, such as planting and managing trees.

Forests are important in the global carbon cycle because trees and plants take in carbon dioxide during photosynthesis. This helps reduce the effects of climate change. Forests act as carbon sinks, storing large amounts of carbon in their roots, stems, branches, and leaves. Every year, forests store about 25% of human carbon emissions, which helps control Earth’s climate. Over their lifetime, trees continue to store carbon, keeping it out of the atmosphere for a long time. Managing forests wisely, planting new trees, and replanting forests are important ways to reduce climate change.

A key point to consider is that forests can change from storing carbon to releasing it. In 2019, forests absorbed about one-third less carbon than they did in the 1990s because of higher temperatures, droughts, and deforestation. Data from 1999 to 2020 shows some forests are nearing a point where they no longer store carbon but instead release it. Some tropical forests may become carbon sources by the 2060s.

Studies show that avoiding deforestation is better than allowing it and then replanting later. This is because deforestation can cause long-term harm, such as loss of wildlife and poor soil quality. Younger boreal forests are more likely to release carbon from the soil, especially because of a root disease called Armillaria, which weakens trees. Damage to tropical rainforests may have caused more greenhouse gas emissions than previously thought. Protecting existing forests is more effective for reducing climate change than planting new ones, as it takes decades for new trees to store as much carbon as older, mature trees. Scientists say protecting and restoring natural forests is a major solution to climate change.

Planting trees on unused farmland helps store carbon in tree biomass. For this to work, the carbon must stay in the trees and not return to the air when the trees die. Some Ficus species, like Ficus wakefieldii, store carbon as calcium oxalate with the help of bacteria and fungi. This process also makes the soil more alkaline. These trees are being studied for use in agroforestry. The Iroko tree can store up to one ton of calcium carbonate in the soil over its lifetime. Cacti, like the Saguaro, also store carbon by forming calcium carbonate in the soil.

The Earth has enough space to plant an additional 0.9 billion hectares of forest. However, some experts say the actual area that cools the climate when considering factors like how much sunlight is reflected is 20-80% smaller. If these trees survive to grow fully, they could store 205 billion tons of carbon, which is about 20 years of global carbon emissions as of 2019. This would store about 25% of the atmosphere’s carbon in 2019.

The lifespan of forests varies worldwide, depending on tree types, soil conditions, and natural events like fires. In some forests, carbon is stored for centuries, while in others, frequent fires release it quickly. When forests are harvested before fires occur, some carbon remains in products like wood and buildings. However, much of the carbon from logged forests becomes waste products like paper and pulp. If 90% of new construction used wood instead of materials like concrete and steel, it could store 700 million tons of carbon each year. This would also reduce emissions from producing other materials.

A study found that planting forests with a mix of tree species increases carbon storage and other benefits.

Although bamboo forests store less total carbon than mature forests, they absorb carbon faster. This makes bamboo a promising option for storing carbon.

The Food and Agriculture Organization (FAO) reported that the total carbon stored in forests decreased from 668 gigatonnes in 1990 to 662 gigatonnes in 2020. In Canada’s boreal forests, up to 80% of carbon is stored in the soil as dead organic matter.

The IPCC Sixth Assessment Report states that regrowing forests and restoring damaged ecosystems can store large amounts of carbon and help protect biodiversity.

The climate impact of forests depends on where they are planted. For example, planting trees in boreal or subarctic areas has a smaller effect on climate because these areas reflect more sunlight than forests do. In contrast, planting trees in tropical regions can create clouds that reflect sunlight, lowering temperatures.

Planting trees in tropical areas with wet seasons has an added benefit. Trees in these regions grow faster and store more carbon because they can grow year-round. Tropical trees typically have larger, brighter leaves than trees in other climates. A study of 70,000 trees across Africa showed that tropical forests absorb more carbon dioxide than previously thought. Research suggests that forests in Africa, the Amazon, and Asia absorb nearly one-fifth of fossil fuel emissions. Simon Lewis said, “Tropical forest trees absorb about 18% of the carbon dioxide added to the atmosphere each year from burning fossil fuels, which helps slow climate change.”

Afforestation also improves soil quality and increases organic carbon in the soil. Planting trees in cities helps reduce air pollution by absorbing and filtering harmful gases like carbon monoxide.

Criticism

Tree-planting efforts are sometimes criticized for focusing on areas where forests would not naturally grow, such as grasslands and savannas. Plans to plant trees for carbon storage often do not fully consider how planting trees might change soil carbon levels or how tree growth might slow over time.

Planting trees in new areas can harm wildlife by breaking up habitats and increasing the edges of remaining open spaces. New forests may bring in predators that are not usually found in open areas, which can harm native animals. A study by scientists found that planting trees in Britain reduced the numbers of Eurasian curlews, a type of bird, because their natural grassland homes were split into smaller areas and more predators moved in.

Scientists also question how planting trees worldwide might change how much sunlight Earth reflects back into space. Mature tree canopies can darken the Earth's surface, absorbing more heat and possibly raising global temperatures. This is especially important in snowy regions, where white snow reflects more sunlight than darker forests.

A major concern about reforestation projects that use only one type of tree, often conifers, is that while they increase tree cover, they do not create the varied and complex homes needed by many forest animals. These single-species forests, usually planted for money or ease of care, lack the variety of plants and animals found in natural forests. They offer fewer food sources, shelter, and nesting spots for wildlife. In forests with only conifers, little sunlight reaches the ground, limiting plant life. Many animals, such as birds, mammals, and insects, depend on a mix of tree types and plants for survival. The lack of variety in these forests can make them unsuitable for the species they aim to help, which may harm conservation efforts.

Examples

The Great Green Wall of Africa is a forest about 5,000 miles long being grown across the continent to stop the Sahara Desert from spreading southward.

In Adelaide, South Australia (a city with 1.3 million people as of June 2016), Premier Mike Rann (2002 to 2011) started an urban forest project in 2003. The goal was to plant 3 million native trees and shrubs by 2014 across 300 locations in the city area. Thousands of Adelaide residents helped plant trees in parks, reserves, transportation areas, schools, waterways, and coastal regions. Only native trees were planted to protect the natural traits of local plants. Rann said the project aimed to make the city more beautiful, cooler, and livable, improve air and water quality, and reduce greenhouse gas emissions by 600,000 tonnes of CO2 each year.

In 2003, the Canadian government began a four-year project called the Forest 2020 Plantation Development and Assessment Initiative. This project involved planting 6,000 hectares of fast-growing forests on non-forested land across the country. These forests were studied to learn how planting trees can help store more carbon and reduce greenhouse gas emissions. The project also looked at whether planting forests could be a good investment. Results showed that while Canada does not have enough land to completely balance its greenhouse gas emissions, planting forests can still help reduce emissions, especially until better long-term carbon storage methods are available.

On December 14, 2020, Canada’s Minister of Natural Resources, Seamus O’Regan, announced a $3.16 billion investment to plant 2 billion trees over the next 10 years. This plan aims to reduce greenhouse gas emissions by about 12 million tonnes by 2050.

Between 1980 and 2021, the amount of forest coverage in the world doubled.

China had the highest rate of afforestation in the world, planting 4.77 million hectares (47,000 square kilometers) of new forests in 2008. According to the 2021 government work report, China plans to increase forest coverage to 24% by the end of the 14th Five-Year Plan period.

A law in China from 1981 requires every student over the age of 11 to plant at least one tree each year.

From 2011 to 2016, the city of Dongying in Shandong Province planted trees on 13,800 hectares of salty soil through the Shandong Ecological Afforestation Project, supported by the World Bank. In 2017, the Saihanba Afforestation Community won the UN Champions of the Earth Award for transforming poor land into a lush forest.

The successful afforestation of the Loess Plateau involved teamwork between international and local experts and villagers. This effort helped millions of people in four of China’s poorest provinces improve farming, increase income, and reduce poverty. Careful tree selection helped create a healthy, self-sustaining ecosystem between trees and soil, which stored carbon. However, the project cost nearly $500 million.

In more recent efforts, China planted mostly red pine trees in large areas to make the process cheaper and faster. However, this approach ignored environmental needs, leading to more soil erosion, desertification, and short-lived trees. This has lowered China’s environmental sustainability index to one of the lowest in the world.

Afforestation helps store carbon, but the benefits increase only after trees are more than 5 years old. Monoculture plantings that fail to