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Should some of below be put in Land use, land-use change, and forestry?

from carbon sequestration

Forestry
Trees absorb carbon dioxide from the atmosphere through the process of photosynthesis. Throughout this biochemical process, chlorophyll in the tree's leaves harnesses sunlight to convert and water into glucose and oxygen. While glucose serves as a source of energy for the tree, oxygen is released into the atmosphere as a byproduct. Trees store carbon in the form of biomass, encompassing roots, stems, branches, and leaves. Throughout their lifespan, trees continue to sequester carbon, acting as long-term storage units for atmospheric CO 2. Sustainable forest management, afforestration, reforestation and proforestation are therefore important contributions to climate change mitigation. Afforestation is the establishment of a forest in an area where there was no previous tree cover. Proforestation is the practice of growing an existing forest intact toward its full ecological potential. An important consideration in such efforts is that the carbon sink potential of forests will saturate and forests can turn from sinks to carbon sources. The Intergovernmental Panel on Climate Change (IPCC) concluded that a combination of measures aimed at increasing forest carbon stocks, and sustainable timber offtake will generate the largest carbon sequestration benefit.

In terms of carbon retention on forest land, it is better to avoid deforestation than to remove trees and subsequently reforest, as deforestation leads to irreversible effects e.g. biodiversity loss and soil degradation. Additionally, the effects of af- or reforestation will be farther in the future compared to keeping existing forests intact. It takes much longer − several decades − for reforested areas to return to the same carbon sequestration levels found in mature tropical forests.

There are four primary ways in which reforestation and reducing deforestation can increase carbon sequestration. First, by increasing the volume of existing forest. Second, by increasing the carbon density of existing forests at a stand and landscape scale. Third, by expanding the use of forest products that will sustainably replace fossil-fuel emissions. Fourth, by reducing carbon emissions that are caused from deforestation and degradation.

The planting of trees on marginal crop and pasture lands helps to incorporate carbon from atmospheric into biomass. For this carbon sequestration process to succeed the carbon must not return to the atmosphere from biomass burning or rotting when the trees die. To this end, land allotted to the trees must not be converted to other uses and management of the frequency of disturbances might be necessary in order to avoid extreme events. Alternatively, the wood from them must itself be sequestered, e.g., via biochar, bioenergy with carbon capture and storage, landfill or stored by use in construction.

Reforestation with long-lived trees (>100 years) will sequester carbon for substantial periods and be released gradually, minimizing carbon's climate impact during the 21st century. Earth offers enough room to plant an additional 1.2 trillion trees. Planting and protecting them would offset some 10 years of CO2 emissions and sequester 205 billion tons of carbon. This approach is supported by the Trillion Tree Campaign. Restoring all degraded forests world-wide would capture about 205 billion tons of carbon in total, which is about two-thirds of all carbon emissions.

Although a bamboo forest stores less total carbon than a mature forest of trees, a bamboo plantation sequesters carbon at a much faster rate than a mature forest or a tree plantation. Therefore, the farming of bamboo timber may have significant carbon sequestration potential.

During a 30-year period to 2050 if all new construction globally utilized 90% wood products, largely via adoption of mass timber in low rise construction, this could sequester 700 million net tons of carbon per year, thus negating approximately 2% of annual carbon emissions as of 2019. This is in addition to the elimination of carbon emissions from the displaced construction material such as steel or concrete, which are carbon-intense to produce.

As enforcement of forest protection may not sufficiently address the drivers behind deforestation – the largest of which being the production of beef in the case of the Amazon rainforest – it may also need policies. These could effectively ban and/or progressively discourage deforestation-associated trade via e.g. product information requirements, satellite monitoring like the Global Forest Watch, related eco-tariffs, and product certifications.

from carbon sink

Favourable factors and carbon sink saturation in forests
Forests are generally carbon dioxide sinks when they are high in diversity, density or area. However, they can also be carbon sources if diversity, density or area decreases due to deforestation, selective logging, climate change, wildfires or diseases. In 2019 forests took up a third less carbon than they did in the 1990s, due to higher temperatures, droughts and deforestation. The typical tropical forest may become a carbon source by the 2060s.

An assessment of European forests found early signs of carbon sink saturation, after decades of increasing strength. The Intergovernmental Panel on Climate Change (IPCC) concluded that a combination of measures aimed at increasing forest carbon stocks, and sustainable timber offtake will generate the largest carbon sequestration benefit.

Life expectancy of forests varies throughout the world, influenced by tree species, site conditions and natural disturbance patterns. In some forests, carbon may be stored for centuries, while in other forests, carbon is released with frequent stand replacing fires. Forests that are harvested prior to stand replacing events allow for the retention of carbon in manufactured forest products such as lumber. However, only a portion of the carbon removed from logged forests ends up as durable goods and buildings. The remainder ends up as sawmill by-products such as pulp, paper and pallets, which often end with incineration (resulting in carbon release into the atmosphere) at the end of their lifecycle. For instance, of the 1,692 megatonnes of carbon harvested from forests in Oregon and Washington from 1900 to 1992, only 23% is in long-term storage in forest products.

The Food and Agriculure Organization (FAO) reported that: "The total carbon stock in forests decreased from 668 gigatonnes in 1990 to 662 gigatonnes in 2020". However, another study finds that the leaf area index has increased globally since 1981, which was responsible for 12.4% of the accumulated terrestrial carbon sink from 1981 to 2016. The CO2 fertilization effect, on the other hand, was responsible for 47% of the sink, while climate change reduced the sink by 28.6%. In Canada's boreal forests as much as 80% of the total carbon is stored in the soils as dead organic matter.

Carbon offset programs are planting millions of fast-growing trees per year to reforest tropical lands, for as little as $0.10 per tree. Over their typical 40-year lifetime, one million of these trees can sequester up to one million tons of carbon dioxide.

Changes in albedo effect
August 2023 research, drawing from 176 flux stations globally, reveals a climate trade-off: increased carbon uptake from afforestation results in reduced albedo. Initially, this reduction may lead to moderate global warming over a span of approximately 20 years, but it is expected to transition into significant cooling thereafter.

from albedo

Trees
Forests generally have a low albedo because the majority of the ultraviolet and visible spectrum is absorbed through photosynthesis. For this reason, the greater heat absorption by trees could offset some of the carbon benefits of afforestation (or offset the negative climate impacts of deforestation). In other words: The climate change mitigation effect of carbon sequestration by forests is partially counterbalanced in that reforestation can decrease the reflection of sunlight (albedo).

In the case of evergreen forests with seasonal snow cover, albedo reduction may be significant enough for deforestation to cause a net cooling effect. Trees also impact climate in extremely complicated ways through evapotranspiration. The water vapor causes cooling on the land surface, causes heating where it condenses, acts as strong greenhouse gas, and can increase albedo when it condenses into clouds. Scientists generally treat evapotranspiration as a net cooling impact, and the net climate impact of albedo and evapotranspiration changes from deforestation depends greatly on local climate.

Mid-to-high-latitude forests have a much lower albedo during snow seasons than flat ground, thus contributing to warming. Modeling that compares the effects of albedo differences between forests and grasslands suggests that expanding the land area of forests in temperate zones offers only a temporary mitigation benefit.

In seasonally snow-covered zones, winter albedos of treeless areas are 10% to 50% higher than nearby forested areas because snow does not cover the trees as readily. Deciduous trees have an albedo value of about 0.15 to 0.18 whereas coniferous trees have a value of about 0.09 to 0.15. Variation in summer albedo across both forest types is associated with maximum rates of photosynthesis because plants with high growth capacity display a greater fraction of their foliage for direct interception of incoming radiation in the upper canopy. The result is that wavelengths of light not used in photosynthesis are more likely to be reflected back to space rather than being absorbed by other surfaces lower in the canopy.

Studies by the Hadley Centre have investigated the relative (generally warming) effect of albedo change and (cooling) effect of carbon sequestration on planting forests. They found that new forests in tropical and midlatitude areas tended to cool; new forests in high latitudes (e.g., Siberia) were neutral or perhaps warming.

from reforestation

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. 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.

A 2019 study of the global potential for tree restoration showed that there is space for at least 9 million km2 of new forests worldwide, which is a 25% increase from current conditions. This forested area could store up to 205 gigatons of carbon or 25% of the atmosphere's current carbon pool by reducing in the atmosphere.

Financial incentives
Policies 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.

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".

from tree planting

Role in climate change mitigation
The development of markets for tradeable pollution permits in recent years have opened up a new source of funding for tree planting projects: carbon offsets. The creation of carbon offsets from tree planting projects hinges on the notion that trees help to mitigate climate change by sequestering carbon dioxide as they grow. However, the science linking trees and climate change is largely unsettled, and trees remain a controversial source of offsets.

Climate impacts
The United Nations, World Bank and other leading nongovernmental organizations are encouraging tree planting to mitigate the effects of climate change.

Trees sequester carbon through photosynthesis, converting carbon dioxide and water molecules into molecular dioxygen (O2) and plant organic matter, such as carbohydrates (e.g., cellulose). Hence, forests that grow in area or density and thus increase in organic biomass will reduce atmospheric levels. (Carbon is released as if a tree or its lumber burns or decays, but as long as the forest is able to grow back at the same rate as its biomass is lost due to oxidation of organic carbon, the net result is carbon neutral.) In their 2001 assessment, the IPCC estimated the potential of biological mitigation options (mainly tree planting) is on the order of 100 Gigatonnes of carbon (cumulative) by 2050, equivalent to about 10% to 20% of projected fossil fuel emissions during that period.

However, the global cooling effect of forests from carbon sequestration is not the only factor to be considered. For example, the planting of new forests may initially release some of the area's existing carbon stores into the atmosphere. For example, if one included emissions from the conversion of peat bogs into oil palm plantations in national GHG totals, this would move Indonesia from 21st to third place as the world's largest producer of greenhouse gases.

Compared to less vegetated lands, forests affect climate in three main ways:


 * Cooling the Earth by functioning as carbon sinks, and adding water vapor to the atmosphere and thereby increasing cloudiness.
 * Warming the Earth by absorbing a high percentage of sunlight due to the low reflectivity of a forest's dark surfaces. This warming effect, or reduced albedo, is large where evergreen forests, which have very low reflectivity, shade snow cover, which is highly reflective.

To date, most tree planting offsets strategies have taken only the first effect into account. A study published in December 2005 combined all these effects and found that tropical forestation has a large net cooling effect, because of increased cloudiness and because of high tropical growth and carbon sequestration rates.

Trees grow three times faster in the tropics than in temperate zones; each tree in the rainy tropics removes about 22 kilograms (50 pounds) of carbon dioxide from the atmosphere each year. However, this study found little to no net global cooling from tree planting in temperate climates, where warming due to sunlight absorption by trees counteracts the global cooling effect of carbon sequestration. Furthermore, this study confirmed earlier findings that reforestation of colder regions—where long periods of snow cover, evergreen trees, and slow sequestration rates prevail—probably results in global warming. According to Ken Caldeira, a study co-author from the Carnegie Institution for Science, "To plant forests outside of the tropics to mitigate climate change is a waste of time.".

His premise that grassland reflects more sun, keeping temperatures lower, is, however, applicable only in arid regions. A well-watered lawn, for example, is as green as a tree, but absorbs far less. Deciduous trees also have the advantage of providing shade in the summer and sunlight in the winter; so these trees, when planted close to houses, can be utilized to help increase energy efficiency of these houses.

This study remains controversial and criticized for assuming dark colored trees might replace the frozen, white tundra in the upper northern hemisphere. Regular tree planting projects typically take place on lands that are only slightly different in color. The warming impact was also measured over hundreds of years, rather than a 30- to 70-year time horizon most climate experts believe we have to fix climate change.

Furthermore, the described warming effect (of temperate and boreal latitude forest) is only apparent once the trees have grown to create a dense 'close canopy', and it is at precisely this point that trees grown for offset purposes should be harvested and their absorbed carbon fixed for the long-term as timber.

Costs
While the benefits of tree planting are subject to debate, the costs are low compared to many other mitigation options. The IPCC has concluded that "The mitigation costs through forestry can be quite modest (US$0.1–US$20 / metric ton carbon dioxide) in some tropical developing countries ... The costs of biological mitigation, therefore, are low compared to those of many other alternative measures". The cost-effectiveness of tropical reforestation is due not only to growth rate, but also to farmers from tropical developing countries who voluntarily plant and nurture tree species which can improve the productivity of their lands. As little as US$90 will plant 900 trees, enough to annually remove as much carbon dioxide as is annually generated by the fossil-fuel usage of an average United States resident.

from sustainable energy

Bioenergy
Biomass is renewable organic material that comes from plants and animals. It can either be burned to produce heat and electricity or be converted into biofuels such as biodiesel and ethanol, which can be used to power vehicles.

The climate impact of bioenergy varies considerably depending on where biomass feedstocks come from and how they are grown. For example, burning wood for energy releases carbon dioxide; those emissions can be significantly offset if the trees that were harvested are replaced by new trees in a well-managed forest, as the new trees will absorb carbon dioxide from the air as they grow. However, the establishment and cultivation of bioenergy crops can displace natural ecosystems, degrade soils, and consume water resources and synthetic fertilisers. Approximately one-third of all wood used for traditional heating and cooking in tropical areas is harvested unsustainably. Bioenergy feedstocks typically require significant amounts of energy to harvest, dry, and transport; the energy usage for these processes may emit greenhouse gases. In some cases, the impacts of land-use change, cultivation, and processing can result in higher overall carbon emissions for bioenergy compared to using fossil fuels.

Use of farmland for growing biomass can result in less land being available for growing food. In the United States, around 10% of motor gasoline has been replaced by corn-based ethanol, which requires a significant proportion of the harvest. In Malaysia and Indonesia, clearing forests to produce palm oil for biodiesel has led to serious social and environmental effects, as these forests are critical carbon sinks and habitats for diverse species. Since photosynthesis captures only a small fraction of the energy in sunlight, producing a given amount of bioenergy requires a large amount of land compared to other renewable energy sources.

Second-generation biofuels which are produced from non-food plants or waste reduce competition with food production, but may have other negative effects including trade-offs with conservation areas and local air pollution. Relatively sustainable sources of biomass include algae, waste, and crops grown on soil unsuitable for food production.

Carbon capture and storage technology can be used to capture emissions from bioenergy power plants. This process is known as bioenergy with carbon capture and storage (BECCS) and can result in net carbon dioxide removal from the atmosphere. However, BECCS can also result in net positive emissions depending on how the biomass material is grown, harvested, and transported. Deployment of BECCS at scales described in some climate change mitigation pathways would require converting large amounts of cropland.

from carbon dioxide removal

Afforestation, reforestation, and forestry management
Trees use photosynthesis to absorb carbon dioxide and store the carbon in wood and soils. Afforestation is the establishment of a forest in an area where there was previously no forest. Reforestation is the re-establishment of a forest that has been previously cleared. Forests are vital for human society, animals and plant species. This is because trees keep air clean, regulate the local climate and provide a habitat for numerous species.

As trees grow they absorb from the atmosphere and store it in living biomass, dead organic matter and soils. Afforestation and reforestation – sometimes referred to collectively as 'forestation' – facilitate this process of carbon removal by establishing or re-establishing forest areas. It takes forests approximately 10 years to ramp- up to the maximum sequestration rate.

Depending on the species, the trees will reach maturity after around 20 to 100 years, after which they store carbon but do not actively remove it from the atmosphere. Carbon can be stored in forests indefinitely, but the storage can also be much more short-lived as trees are vulnerable to being cut, burned, or killed by disease or drought. Once mature, forest products can be harvested and the biomass stored in long-lived wood products, or used for bioenergy or biochar. Consequent forest regrowth then allows continuing removal.

Risks to deployment of new forest include the availability of land, competition with other land uses, and the comparatively long time from planting to maturity.

from carbon farming

Reforestation
Forestry and agriculture are both land-based human activities that add up to contribute approximately a third of the world's greenhouse gas emissions. There is a large interest in reforestation, but in regards to carbon farming most of that reforestation opportunity will be in small patches with trees being planted by individual land owners in exchange for benefits provided by carbon farming programs. Forestry in carbon farming can be both reforestation, which is restoring forests to areas that were deforested, and afforestation which would be planting forests in areas that were not historically forested. Not all forests will sequester the same amount of carbon. Carbon sequestration is dependent on several factors which can include forest age, forest type, amount of biodiversity, the management practices the forest is experiences and climate. Biodiversity is often thought to be a side benefit of carbon farming, but in forest ecosystems increased biodiversity can increase the rate of carbon sequestration and can be a tool in carbon farming and not just a side benefit.

Bamboo farming
A bamboo forest will store less total carbon than most types of mature forest. However, it can store a similar total amount of carbon as rubber plantations and tree orchards, and can surpass the total carbon stored in agroforests, palm oil plantations, grasslands and shrublands. A bamboo plantation sequesters carbon at a faster rate than a mature forest or a tree plantation. However it has been found that only new plantations or plantations with active management will be sequestering carbon at a faster rate than mature forests. Compared with other fast-growing tree species, bamboo is only superior in its ability to sequester carbon if selectively harvested. Bamboo forests are especially high in potential for carbon sequestration if the cultivated plant material is turned into durable products that keep the carbon in the plant material for a long period because bamboo is both fast growing and regrows strongly following an annual harvest.

While bamboo has the ability to store carbon as biomass in cultivated material, more than half of the carbon sequestration from bamboo will be stored as carbon in the soil. Carbon that is sequestered into the soil by bamboo is stored by the rhizomes and roots which is biomass that will remain in the soil after plant material above the soil is harvested and stored long-term. Bamboo can be planted in sub-optimal land unsuitable for cultivating other crops and the benefits would include not only carbon sequestration but improving the quality of the land for future crops and reducing the amount of land subject to deforestation. The use of carbon emission trading is also available to farmers who use bamboo to gain carbon credit in otherwise uncultivated land. Therefore, the farming of bamboo timber may have significant carbon sequestration potential.

from agroforestry

Agroforestry can significantly contribute to climate change mitigation along with adaptation benefits. A case study in Kenya found that the adoption of agroforestry drove carbon storage and increased livelihoods simultaneously among small-scale farmers. In this case, maintaining the diversity of tree species, especially land use and farm size are important factors.

from deforestation and climate change

Reforestation, afforestation and agroforestry
Possible methods of reforestation include large-scale industrial plantations, the introduction of trees into existing agricultural systems, small-scale plantations by landowners, the establishment of woodlots on communal lands, and the rehabilitation of degraded areas through tree planting or assisted natural regeneration. Afforestation is the planting of trees where there was no previous tree coverage. There are three different types of afforestation that could have varying effects on the amount of carbon dioxide that is taken from the atmosphere. The three kinds of afforestation are natural regeneration, commercial plantations, and agroforestry. Although afforestation can help reduce the carbon emissions given off as a result of climate change, natural regeneration tends to be the most effective out of the three. Natural regeneration typically concerns a wide variety of vegetation, making natural forest levels so plants can receive sunlight to undergo photosynthesis. Commercial plantations typically result in mass amounts of lumber, which if used for fuel, will release the stored back into the atmosphere. Agroforestry stores energy based on the size and type of plant, meaning that the effect will vary depending on what is planted.

Wood harvesting and supply have reached around 550 million m3 per year, while the total increasing stock of European forests has more than quadrupled during the previous six decades. It now accounts for around 35 billion m3 of forest biomass. Since the beginning of the 1990s, the amounts of wood and carbon stored in European forests have increased by 50% due to greater forest area and biomass stocks. Every year, European woods adsorb and store around 155 million tonnes equivalent. This is comparable to 10% of all other sectors' emissions in Europe.

The forestry industry tries to mitigate climate change by boosting carbon storage in growing trees and soils and improving the sustainable supply of renewable raw materials via sustainable forest management.