Reforestation

 

Reforestation is the natural or intentional restocking of existing forests and woodlands (forestation) that have been depleted, usually through deforestation but also after clearcutting. Two important purposes of reforestation programs are for harvesting of wood or for climate change mitigation purposes.

For example, in the years 2012-2022 China restored more than 70 million hectares (700,000 km2) of forests. China committed to plant and conserve 70 billion trees by the year 2030 as part of the Trillion Tree Campaign.

At the same time there are calls for a more selective approach to identifying reforestation areas, taking into account the possible displacement of customary land uses.

Definition

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

According to FAO terminology any type of reforestation activity does not contribute to an increase in forest area.

Whereas, the term afforestation means establishing new forest on lands that were not forest before (for example, abandoned agriculture).

A forest, six years after reforestation efforts

Purposes

Reforestation is not only used for recovery of accidentally destroyed forests. In some countries, such as Finland, many of the forests are managed by the wood products and pulp and paper industry. In such an arrangement, like other crops, trees are planted to replace those that have been cut. The Finnish Forest Act from 1996 obliges the forest to be replanted after felling. In such circumstances, the industry can cut the trees in a way to allow easier reforestation. The wood products industry systematically replaces many of the trees it cuts, employing large numbers of summer workers for tree planting work. For example, in 2010, Weyerhaeuser reported planting 50 million seedlings. However replanting an old-growth forest with a plantation is not replacing the old with the same characteristics in the new.

In just 20 years, a teak plantation in Costa Rica can produce up to about 400 m³ of wood per hectare. As the natural teak forests of Asia become more scarce or difficult to obtain, the prices commanded by plantation-grown teak grows higher every year. Other species, such as mahogany, grow more slowly than teak in Tropical America but are also extremely valuable. Faster growers include pine, eucalyptus, and Gmelina.

Reforestation, if several indigenous species are used, can provide other benefits in addition to financial returns, including restoration of the soil, rejuvenation of local flora and fauna, and the capturing and sequestering of 38 tons of carbon dioxide per hectare per year.

The reestablishment of forests is not just simple tree planting. Forests are made up of a community of species and they build dead organic matter into soils over time. A major tree-planting program could enhance the local climate and reduce the demands of burning large amounts of fossil fuels for cooling in the summer.

For climate change mitigation

Forests are an important part of the global carbon cycle because trees and plants absorb carbon dioxide through photosynthesis. Therefore, they play an important role in climate change mitigation.  By removing the greenhouse gas carbon dioxide from the air, forests function as terrestrial carbon sinks, meaning they store large amounts of carbon. At any time, forests account for as much as double the amount of carbon in the atmosphere.  Forests remove around three billion tons of carbon every year. This amounts to about 30% of all anthropogenic carbon dioxide emissions. Therefore, an increase in the overall forest cover around the world would mitigate global warming.

At the beginning of the 21st century, interest in reforestation grew over its potential to mitigate climate change. Even without displacing agriculture and cities, earth can sustain almost one billion hectares of new forests. This would remove 25% of carbon dioxide from the atmosphere and reduce its concentration to levels that existed in the early 20th century. A temperature rise of 1.5 degrees would reduce the area suitable for forests by 20% by the year 2050, because some tropical areas will become too hot.[16] The countries that have the most forest-ready land are: Russia, Canada, Brazil, Australia, the United States and China.

The four major strategies are:

• Increase the amount of forested land through reforestation
• Increase density of existing forests at a stand and landscape scale
• Expand the use of forest products that sustainably replace fossil-fuel emissions
• Reduce carbon emissions caused by deforestation and degradation. 

The second strategy has to do with selecting species for tree-planting. In theory, planting any kind of tree to produce more forest cover would absorb more carbon dioxide from the atmosphere. However, a genetically modified variant might grow much faster than unmodified specimens.  Some of these cultivars are under development. Such fast-growing trees would be planted for harvest and can absorb carbon dioxide faster than slower-growing trees.  A meta-analysis found that mixed species plantations would increase carbon storage alongside other benefits of diversifying planted forests.

Impacts on temperature are affected by the location of the forest. For example, reforestation in boreal or subarctic regions has less impact on climate. This is because it substitutes a high-albedo, snow-dominated region with a lower-albedo forest canopy. By contrast, tropical reforestation projects lead to a positive change such as the formation of clouds. These clouds then reflect the sunlight, lowering temperatures.

Planting trees in tropical climates with wet seasons has another advantage. In such a setting, trees grow more quickly (fixing more carbon) because they can grow year-round. Trees in tropical climates have, on average, larger, brighter, and more abundant leaves than non-tropical climates. A study of the girth of 70,000 trees across Africa has shown that tropical forests fix more carbon dioxide pollution than previously realized. The research suggested almost one fifth of fossil fuel emissions are absorbed by forests across Africa, Amazonia and Asia. Simon Lewis stated, "Tropical forest trees are absorbing about 18% of the carbon dioxide added to the atmosphere each year from burning fossil fuels, substantially buffering the rate of change."

As of 2008 1.3 billion hectares of tropical regions were deforested every year. Reducing this would reduce the amount of planting needed to achieve a given degree of mitigation.

Comparison to forest protection

Researchers have found that, in terms of environmental services, it is better to avoid deforestation than to allow for deforestation to subsequently reforest, as the former leads to irreversible effects in terms of biodiversity loss and soil degradation. Furthermore, the probability that legacy carbon will be released from soil is higher in younger boreal forest. Global greenhouse gas emissions caused by damage to tropical rainforests may have been substantially underestimated until around 2019. Additionally, the effects of af- or reforestation will be farther in the future than keeping existing forests intact. It takes much longer − several decades − for the benefits for global warming to manifest to the same carbon sequestration benefits from mature trees in tropical forests and hence from limiting deforestation. Therefore, scientists consider "the protection and recovery of carbon-rich and long-lived ecosystems, especially natural forests" to be "the major climate solution".

Methods

A study finds that almost 300 million people live on tropical forest restoration opportunity land in the Global South, constituting a large share of low-income countries' populations, and argues for prioritized inclusion of "local communities" in forest restoration projects.

Over 90% of the world's forests regenerate organically, and more than half are covered by forest management plans or equivalents.

Using existing trees and roots

Planting new trees often leads to up to 90% of seedlings failing. However, even in deforested areas, existing root systems often exist. Growth can be accelerated by pruning and coppicing where a few branches of new shoots are cut and often used for charcoal, itself a major driver of deforestation. Since new seeds are not planted, it is cheaper. Additionally, they are much more likely to survive as their root systems already exist and can tap into groundwater during harsher seasons with no rain. While this method has existed for centuries, it is now sometimes referred to as farmer-managed natural regeneration or assisted natural regeneration.

Forest plantations

Globally, planted forests increased from 4.1% to 7.0% of the total forest area between 1990 and 2015. Plantation forests made up 280 million ha (hectare) in 2015, an increase of about 40 million ha in the last ten years. Globally, planted forests consist of about 18% exotic or introduced species while the rest are species native to the country where they are planted.

The highest share of plantation forest is in South America, where this forest type represents 99 percent of the total planted-forest area and 2 percent of the total forest area. The lowest share of plantation forest is in Europe, where it represents 6 percent of the planted forest estate and 0.4 percent of the total forest area. Globally, 44 percent of plantation forests are composed mainly of introduced species. There are large differences between regions: for example, plantation forests in North and Central America mostly comprise native species and those in South America consist almost entirely of introduced species.

In South America, Oceania, and East and Southern Africa, planted forests are dominated by introduced species: 88%, 75% and 65%, respectively. In North America, West and Central Asia, and Europe the proportions of introduced species in plantations are much lower at 1%, 3% and 8% of the total area planted, respectively.

Plantation forests are intensively managed, composed of one or two species, even-aged, planted with regular spacing, and established mainly for productive purposes. Other planted forests, which comprise 55 percent of all planted forests, are not intensively managed, and they may resemble natural forests at stand maturity. The purposes of other planted forests may include ecosystem restoration and the protection of soil and water values.

Financial incentives

Policy that promote reforestation for incentives in return have shown promising results of being an effective and motivative concept to re-plant globally on a mass scale. Some incentives for reforestation can be as simple as a financial compensation. Streck and Scholz (2006) explain how a group of scientists from various institutions have developed a compensated reduction of deforestation approach which would reward developing countries that disrupt any further act of deforestation. Countries that participate and take the option to reduce their emissions from deforestation during a committed period of time would receive financial compensation for the carbon dioxide emissions that they avoided.  To raise the payments, the host country would issue government bonds or negotiate some kind of loan with a financial institution that would want to take part in the compensation promised to the other country. The funds received by the country could be invested to help find alternatives to the extensive cutdown of forests. This whole process of cutting emissions would be voluntary, but once the country has agreed to lower their emissions they would be obligated to reduce their emissions. However, if a country was not able to meet their obligation, their target would get added to their next commitment period. The authors of these proposals see this as a solely government-to-government agreement; private entities would not participate in the compensation trades.

Another emerging revenue source to fund reforestation projects deals with the sale of carbon sequestration credits, which can be sold to companies and individuals looking to compensate their carbon footprint. This approach allows for private landowners and farmers to gain a revenue from the reforestation of their lands, while simultaneously benefiting from improved soil health and increased productivity.

Alongside past financial incentive strategies, reforestation tax benefits have been another way the government has encouraged companies to promote reforestation tactics through the promises of a tax break.

As many landholders seek to earn carbon credits through sequestration, their participation also encourages biodiversity and provides ecosystem services for crops and livestock.

Related concepts

A similar concept, afforestation, refers to the process of restoring and recreating areas of woodlands or forests that may have existed long ago but were deforested or otherwise removed at some point in the past or lacked it naturally (for example, natural grasslands). Sometimes the term "re-afforestation" is used to distinguish between the original forest cover and the later re-growth of forest to an area. Special tools, for example, tree planting bars, are used to make planting of trees easier and faster.

Another alternative strategy, proforestation, is similar as it can be used to counteract the negative environmental and ecological effects of deforestation through growing an existing forest intact to its full ecological potential.

Limitations and challenges

There is often insufficient integration between the different purposes of reforestation, namely economic utilisation, enhancement of biodiversity and carbon sequestration. This can lead to a range of different challenges :

Competition with other land uses and displacement risk

Reforestation can compete with other land uses, such as food production, livestock grazing, and living space, for further economic growth. Reforestation can also divert large amounts of water from other activities. A map created by the World Resources Institute in collaboration with the IUCN identifies 2 billion hectares for potential forest restoration and is criticised for including 900 million hectares of grasslands. An assessment of the pledges of governments for reforestation found that the sum of global pledges translates to a required land area of 1.2bn hectares, until 2060, which is equal to a tenth of the global land area und thus deemed unrealistic without a significant encroachment on non-forest areas. Experts are calling for a better integration of social data, such as the dependence of livelihoods on specific land uses, into restoration efforts. Possible solutions include the integration of other land uses into forests through agroforestry, such as growing coffee plants under trees, reducing the delineation between forests and other land uses.

Effects on biodiversity

Reforestation can also reduce biodiversity leading to severe soil erosion, which if done improperly will lead to loss of water resources.

Reforesting sometimes results in extensive canopy creation that prevents growth of diverse vegetation in the shadowed areas and generating soil conditions that hamper other types of vegetation. Trees used in some reforesting efforts (for example, Eucalyptus globulus) tend to extract large amounts of moisture from the soil, preventing the growth of other plants. The European Commission found that, in terms of environmental services, it is better to avoid deforestation than to allow for deforestation to subsequently reforest, as the former leads to irreversible effects in terms of biodiversity loss and soil degradation.

The effects reforestation has on biodiversity is not limited to just other forms of vegetation, it can affect all forms of living organisms all contained in the present ecosystem. Due to the major role trees have on ecosystems it is important to better understand components like the ecosystem, waterways, and species present in areas that are being re-planted. Prior research helps limit the depletion of biodiversity which can hinder medicinal discoveries, and alter gene flow in organisms.

A debated issue in managed reforestation is whether the succeeding forest will have the same biodiversity as the original forest. If the forest is replaced with only one species of tree and all other vegetation is prevented from growing back, a monoculture forest similar to agricultural crops would be the result. However, most reforestation involves the planting of different selections of seedlings taken from the area, often of multiple species.

Reforestation often has the tendency to create large fuel loads, resulting in significantly hotter combustion than fires involving low brush or grasses.[8] Reduced harvesting rates and fire suppression have caused an increase in the forest biomass in the western United States over the past century. This causes an increase of about a factor of four in the frequency of fires due to longer and hotter dry seasons.

Permanance of carbon stocks

There is also the risk that, through a forest fire or insect outbreak, much of the stored carbon in a reforested area could make its way back to the atmosphere. Furthermore, the probability that legacy carbon will be released from soil is higher in younger boreal forest. An example of this can be seen in the peatlands in Central Africa, which house an abundance of carbon in the mud called peat. Much like the forest fire or insect outbreak which can harm tropical rainforests, money can also be seen an incentive to harm forests and be paid off to protect it. The global greenhouse gas emissions caused by damage to tropical rainforests may be underestimated by a factor of six.

Also the possible harvesting and utilisation of wood from reforested areas, limits the permanence of carb sequestered through reforestation. For example, it was found that nearly half of the pledgs under the Bonn Challenge were areas earmarked for commercial wood use.

Additionally the effects of afforestation and reforestation will be farther in the future than those of proforestation (the conservation of intact forests). It takes much longer − several decades − for the benefits for global warming to manifest to the same carbon sequestration benefits from mature trees in tropical forests and hence from limiting deforestation.

Some researchers note that instead of planting entirely new areas, reconnecting forested areas and restoring the edges of forest, to protect their mature core and make them more resilient and longer-lasting, should be prioritized.

Implementation challenges

Seed shortage: the Seed to Forest Alliance was founded in 2022 in response to a global seed shortage. It will promote the establishment of national seed banks, while focusing on the tropics and biodiversity hotspots.

Seedling survival rate: a common challenge for reforestation is the low survival rate of seedlings. Planted trees often do not mature, for example due to difficult climatic conditions or insufficient care after planting.