What Is Afforestation? Definition, Examples, Pros, and Cons

Afforestation involves planting trees in areas that haven't recently had any tree cover, in order to create a forest. The type of land planted could include areas that have turned into desert (through desertification), places that have long been used for grazing, disused agricultural fields, or industrial areas.

The main goals of afforestation are to serve as a method to reduce atmospheric CO2, to increase soil quality, and to either avoid or reverse desertification. The forests created through afforestation also provide a habitat to local wildlife, create wind breaks, support soil health, and may also help improve water quality. Afforestation is considered to be one of the most "natural" and technologically simple ways to reduce carbon dioxide emissions.

Afforestation Definition

Afforestation usually involves tree planting in agricultural or other lands that have been abandoned due to poor soil quality or overgrazing. Over time, the soil was depleted, so now not much will grow there. Abandoned urban areas, such as land formerly cleared for buildings that no longer stand, can also be good candidates for smaller afforestation projects.

Afforestation can occur on land where there may or may not have been forests at one point in history. Deforestation may have occurred on lands hundreds of years ago, or there may not be a record of a forest existing in the place targeted for afforestation.

During the last 50 years, afforestation of abandoned lands, usually completely empty, has become more common—especially in the United States and the United Kingdom. Currently, grasslands and pastures throughout Europe are being turned back into forests. China, India, and countries in North and Central Africa, the Middle East, and Australia are all working on afforestation projects.

Afforestation Goals

Carbon capture is usually cited as the primary reason to spend the time and money to commit to afforestation. As a tree grows, it naturally sequesters CO2 into itself and the soil it grows in.

The ultimate goal of drawing down CO2 from the atmosphere is, of course, to help mitigate climate change. Estimates of the amount of CO2 removed from the atmosphere for various afforestation projects vary, but a study that looked at large-scale afforestation potential found that it could remove more than 191 gigatons of carbon by 2100 (current annual emissions of carbon are about 36 gigatons per year).

But afforestation has many other benefits, which is why communities and governments choose to invest in it. Soils are a key component for two reasons. The first is that soils are able to hold about three times as much carbon as the atmosphere, so they are a critical part of the climate change mitigation puzzle. Healthy soils are also important as a natural water filtration system and as a source of nutrition for plants, the animals that eat them, and insects. Soil planted with trees is less likely to erode during floods and cause catastrophic damage to nearby communities.

Forests can, over time, improve topsoil. Nitrogen is fixed at higher rates in afforested areas, which have also been shown to neutralize soil pH (reducing acidity in acid soils and alkalinity in alkaline soils). According to a study published in the journal Nature Communications, more neutral soil may "improve soil fertility and promote ecosystem productivity."

A shelterbelt is the name for an afforestation project in an arid or semiarid environment that aims to shelter farmland or crops from wind, which can also reduce soil erosion. In China, for example, an afforestation project was specifically planted to reduce dust storms. Part of a shelterbelt also might be used as a source of wood for fuel or income for the local community. In Kyrgyzstan, walnut and fruit trees were planted as part of an afforestation project with the goal of providing both food and income to the local population.

In addition, research has shown that forests can improve water quality (primarily through reducing runoff into streams), so cleaner water may be a strong motivation for afforestation in some areas. However, other studies have revealed that afforestation can disturb the local water circulation systems, at least in the short term, highlighting the importance of analyzing local hydrologic cycles to determine if a new forest will use too much water.

Trees can also have social benefits, like providing shade areas for people or livestock. And of course, forests can provide habitat for wildlife, especially birds and insects, some of which may be a food source for human beings or contribute to the biodiversity of a place.

Types of Afforestation

Not every country's goals are noble and climate-focused when it comes to afforestation. There are roughly three categories. Natural regeneration is defined as "the planting of native trees in an attempt to restore an area to what resembles a natural forest," but other forms of afforestation include commercial plantations and agroforestry. The former is planting a crop for harvest, such as timber or pulp for paper production; the latter is planting trees for crop production, such as mangoes, avocados, or cashews, or including trees in agricultural settings.

These all store varying amounts of carbon, with natural regeneration tending to be more carbon-rich. It holds "anywhere from three to 600 tonnes of carbon per hectare—you're never going to get that level of storage within timber plantations," according to Dr. Charlotte Wheeler, a forestry scientist from the University of Edinburgh.

The Process of Creating a Forest

Afforestation isn't as simple as just planting trees. Depending on the quality of the soil and especially the topsoil, some site preparation is usually necessary. If a duripan (a hard, near-impenetrable surface to the soil) has formed, that needs to be broken up and the soil aerated. In other places, weed control might be important before planting. Invasive plants should be removed.

The trees planted need to be carefully chosen to suit the local environment. For example, in arid and semi-arid regions, where afforestation might be needed in areas of desertification, drought-resistant trees are important. In more tropical regions, those trees that will grow best in hot and humid conditions are planted.

Spacing of the trees depends on the ultimate goal of the afforestation project. If it's a shelterbelt, trees may be planted more closely together. The number of trees also depends on the goals of the project.

Other considerations include prevailing winds (if looking to create a wind block) and the direction of sunlight in different seasons. For example, if an afforestation project is planted near active agricultural fields, it's important to plan so that sunlight will be able to reach the crops when the trees are grown.

Over time, an afforestation project may need to be maintained depending on its use and aims.

In urban areas, small afforestation projects (such as a vacant lot on the edge of town) can be created following similar steps, but on a different scale. There are even specific plans and organizations that enable fast-growing forests in unused spaces in cities.

Afforestation Around the World

Afforestation projects are happening all over the planet as countries start to understand the benefits of prioritizing tree-planting. Our World in Data reports that in richer countries, forest cover is generally increasing, whereas in middle- to low-income countries, it's decreasing.

China

China's central and local governments have made significant investments in tree planting since the 1970s, planting more than 60 billion trees since then, an effort that has been ramped up in recent years. Currently it has replanted more hectares than any other nation in the world, followed by Vietnam, Turkey, Morocco, Uzbekistan, Venezuela, Argentina, and Sweden (in no particular order).

However, its achievement diminishes somewhat when the amount is compared to its geographic size. Ranked by proportion of total land area covered in planted forest, China is overtaken by Czech Republic, Sweden, Poland, Japan, Marshall Islands, Cape Verde, and others.

Many of these new forests are in a part of China called the Loess plateau, an area the size of France. Afforestation efforts doubled the forest cover in the area over the course of 15 years from 2001-2016.

China plans to continue increasing forest coverage to 25% by 2035 and 42% by 2050. This effort includes participation of private companies as well; Alibaba and Alipay plan to invest $28 million in tree-planting projects.

North Africa

African countries that border the Sahara Desert are working together on the Great Green Wall project to fight desertification in the Sahel region. This is especially important as the population in the area is expected to double over the next 30 years.

The aim is to plant 100 million hectares (almost 250 million acres) of land across the width of Africa by 2030. Countries participating include Algeria, Burkina Faso, Benin, Chad, Cape Verde, Djibouti, Egypt, Ethiopia, Libya, Mali, Mauritania, Niger, Nigeria, Senegal, Somalia, Sudan, The Gambia, and Tunisia.

The effort is supported by over 20 different NGOs, including various United Nations agencies, the Pan African Farmers Organization, the Arab Mahgreb Union, the Sahara and Sahel Observatory, the World Bank, and others. The project is about 15% complete so far, with 12 million drought-resistant trees planted on degraded land in Senegal; 15 million hectares (37 million acres) of degraded land restored in Ethiopia; and 5 million hectares restored in Nigeria.

India

According to a 2019 study, India and China lead the planet in greening efforts (although China leads with forests and India's is more croplands). Still, India has increased forest cover by 30 million hectares (74 million acres) since the 1950s, and now the country is about 24% forest-covered.

While many of the country's old-growth forests—which support biodiversity at greater rates than newer forests—have been destroyed, there have been renewed efforts in recent years to protect forests and add to them.

In 2019, Prime Minister Narendra Modi allocated $6.6 billion to various Indian states for different projects, including afforestation, and the goal is to eventually extend forest cover to one third of the country. In Uttar Pradesh, the most populous Indian state, 1 million people gathered to plant 220 million trees in one day. (That record was broken by Ethiopia, when it planted 350 million trees in a single day.)

Much of this work is being done to help India meet its Paris climate change agreements, and increase carbon sink to achieve India's goal of drawing down 2.5 to 3 billion tons of CO2 by 2030, which is its Intended Nationally Determined Contribution (INDC).

Is It Working?

Afforestation programs are working and some goals have already been achieved. One of the first large-scale plans is the 2011 Bonn Challenge (supported by the International Union for Conservation of Nature), which aims for 350 million hectares (865 million acres) of degraded land to be restored by 2030. The 2020 goal of 150 million hectares (370 million acres) was exceeded early, according to the IUCN.

Bonn Challenge promoters believe that part of the reason for its success is that, while the forests draw down carbon and provide other environmental benefits, there are also significant economic benefits: for every $1 spent on forest restoration, at least $9 of economic benefits are realized. If the majority of degraded land were restored, nearly $76 trillion could be made, so there are compelling economic as well as environmental reasons for the dozens of countries that have committed to do the work of afforestation.

Criticisms

There aren't too many downsides to afforestation projects; however, the most significant risk is the use of non-local tree species. These trees may be fast-growers that will draw down carbon, but may use more water than the area has available, or they may outcompete local forests.

This issue has come up in China, where black locust tree afforestation projects have been found to negatively affect the local hydrological cycle. "Black locust plantations—which make up the bulk of the China afforestation—are much more thirsty than natural grassland. They use 92% of annual rainfall (700mm in a wet year) for biomass growth, leaving only 8% of annual rainfall for human uses. As a result, not enough water remains to recharge groundwater or flow into rivers and lakes," explained United Nations University researcher Lulu Zhang.

As this example illustrates, choosing locally appropriate trees and considering water needs, especially in semi-arid areas, is incredibly important for successful afforestation.