Editing IPCC:AR6/WGIII/Chapter-7 (section)

=== 7.4.2 Forests and Other Ecosystems ===

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==== 7.4.2.1 Reduce Deforestation and Degradation ====

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'''Activities, co-benefits, risks and implementation opportunities and barriers.''' Reducing deforestation and forest degradation conserves existing carbon pools in forest vegetation and soil by avoiding tree cover loss and disturbance. Protecting forests involves controlling the drivers of deforestation (such as commercial and subsistence agriculture, mining, urban expansion) and forest degradation (such as overharvesting including fuelwood collection, poor harvesting practices, overgrazing, pest outbreaks, and extreme wildfires), as well as by establishing well designed, managed and funded protected areas ( [[#Barber--2014|Barber et al. 2014]] ), improving law enforcement, forest governance and land tenure, supporting community forest management and introducing forest certification (P. [[#Smith--2019|Smith et al. 2019]] a). Reducing deforestation provides numerous and substantial co-benefits, preserving biodiversity and ecosystem services (e.g., air and water filtration, water cycling, nutrient cycling) more effectively and at lower costs than afforestation/reforestation ( [[#Jia--2019|Jia et al. 2019]] ). Potential adverse side effects of these conservation measures include reducing the potential for agriculture land expansion, restricting the rights and access of local people to forest resources, or increasing the dependence of local people to insecure external funding. Barriers to implementation include unclear land tenure, weak environmental governance, insufficient funds, and increasing pressures associated to agriculture conversion, resource exploitation and infrastructure development (Sections 7.3 and 7.6).

'''Conclusions from AR5 and IPCC Special Reports (SR1.5, SROCC''' '''and SRCCL); mitigation potential, costs, and pathways.''' Reducing deforestation and forest degradation represents one of the most effective options for climate change mitigation, with technical potential estimated at 0.4–5.8 GtCO 2 yr –1 by 2050 ( ''high confidence'' ) (SRCCL, Chapters 2 and 4, and Table 6.14). The higher technical estimate represents a complete halting of land-use conversion in forests and peatland forests (i.e., assuming recent rates of carbon loss are saved each year) and includes vegetation and soil carbon pools. Ranges of economic potentials for forestry ranged in AR5 from 0.01–1.45 GtCO 2 yr –1 for USD20 tCO 2 –1 to 0.2–13.8 GtCO 2 yr –1 for USD100 tCO 2 –1 by 2030 with reduced deforestation dominating the forestry mitigation potential LAM and MAF, but very little potential in OECD-1990 and EIT (IPCC AR5).

'''Developments since AR5 and IPCC Special Reports (SR1.5, SROCC and SRCCL).''' Since the SRCCL, several studies have provided updated and convergent estimates of economic mitigation potentials by region ( [[#Busch--2019|Busch et al. 2019]] ; [[#Griscom--2020|Griscom et al. 2020]] ; [[#Austin--2020|Austin et al. 2020]] ; [[#Roe--2021|Roe et al. 2021]] ). Tropical forests and savannas in Latin America provide the largest share of mitigation potential (3.9 GtCO 2 yr –1 technical, 2.5 GtCO 2 yr –1 at USD100 tCO 2 –1 ) followed by South-East Asia (2.2 GtCO 2 yr –1 technical, 1.5 GtCO 2 yr –1 at USD100 tCO 2 –1 ) and Africa (2.2 GtCO 2 yr –1 technical, 1.2 GtCO 2 yr –1 at USD100 tCO 2 –1 ) ( [[#Roe--2021|Roe et al. 2021]] ). Tropical forests continue to account for the highest rates of deforestation and associated GHG emissions. While deforestation shows signs of decreasing in several countries, in others, it continues at a high rate or is increasing ( [[#Turubanova--2018|Turubanova et al. 2018]] ). Between 2010–2020, the rate of net forest loss was 4.7 Mha yr –1 with Africa and South America presenting the largest shares (3.9 Mha and 2.6 Mha, respectively) ( [[#FAO--2020a|FAO 2020a]] ).

A major uncertainty in all studies on avoided deforestation potential is their reliance on future reference levels that vary across studies and approaches. If food demand increases in the future, for example, the area of land deforested will likely increase, suggesting more technical potential for avoiding deforestation. Transboundary leakage due to market adjustments could also increase costs or reduce effectiveness of avoiding deforestation (e.g., [[#Ingalls--2018|Ingalls et al. 2018]] ; [[#Gingrich--2019|Gingrich et al. 2019]] ). Regarding forest regrowth, there are uncertainties about the time for the secondary forest carbon saturation ( [[#Houghton--2017|Houghton and Nassikas 2017]] ; [[#Zhu--2018|Zhu et al. 2018]] ). Permanence of avoided deforestation may also be a concern due to the impacts of climate change and disturbance of other biogeochemical cycles on the world’s forests that can result in future potential changes in terrestrial ecosystem productivity, climate-driven vegetation migration, wildfires, forest regrowth and carbon dynamics ( [[#Ballantyne--2012|Ballantyne et al. 2012]] ; [[#Kim--2017b|Kim et al. 2017b]] ; [[#Lovejoy--2018|Lovejoy and Nobre 2018]] ; [[#Aragão--2018|Aragão et al. 2018]] ).

'''Critical assessment and conclusion.''' Based on studies since AR5, the technical mitigation potential for reducing deforestation and degradation is significant, providing 4.5 (2.3–7) GtCO 2 yr –1 globally by 2050, of which 3.4 (2.3–6.4) GtCO 2 yr –1 is available at below USD100 tCO 2 –1 ( ''medium confidence'' ) (Figure 7.11). Over the last decade, hundreds of subnational initiatives that aim to reduce deforestation related emissions have been implemented across the tropics ( [[#7.6|Section 7.6]] ). Reduced deforestation is a significant piece of the NDCs in the Paris Agreement ( [[#Seddon--2020|Seddon et al. 2020]] ) and keeping the temperature below 1.5°C ( [[#Crusius--2020|Crusius 2020]] ). Conservation of forests provides multiple co-benefits linked to ecosystem services, biodiversity and sustainable development ( [[#7.6|Section 7.6]] .). Still, ensuring good governance, accountability (e.g., enhanced monitoring and verification capacity; [[#Bos--2020|Bos 2020]] ), and the rule of law are crucial for implementing forest-based mitigation options. In many countries with the highest deforestation rates, insecure land rights often are significant barriers for forest-based mitigation options (Gren and Zeleke 2016; [[#Essl--2018|Essl et al. 2018]] ).

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==== 7.4.2.2 Afforestation, Reforestation and Forest Ecosystem Restoration ====

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'''Activities, co-benefits, risks and implementation opportunities and barriers.''' Afforestation and reforestation (A/R) are activities that convert land to forest, where reforestation is on land that has previously contained forests, while afforestation is on land that historically has not been forested (Box 7.2). Forest restoration refers to a form of reforestation that gives more priority to ecological integrity as well, even though it can still be a managed forest. Depending on the location, scale, and choice and management of tree species, A/R activities have a wide variety of co-benefits and trade-offs. Well-planned, sustainable reforestation and forest restoration can enhance climate resilience and biodiversity, and provide a variety of ecosystem services including water regulation, microclimatic regulation, soil erosion protection, as well as renewable resources, income and livelihoods ( [[#Locatelli--2015|Locatelli et al. 2015]] ; [[#Stanturf--2015|Stanturf et al. 2015]] ; [[#Ellison--2017|Ellison et al. 2017]] ; [[#Verkerk--2020|Verkerk et al. 2020]] ). Afforestation, when well planned, can help address land degradation and desertification by reducing runoff and erosion and lead to cloud formation however, when not well planned, there are localised trade-offs such as reduced water yield or biodiversity ( [[#Teuling--2017|Teuling et al. 2017]] ; [[#Ellison--2017|Ellison et al. 2017]] ). The use of non-native species and monocultures may have adverse impacts on ecosystem structure and function, and water availability, particularly in dry regions ( [[#Ellison--2017|Ellison et al. 2017]] ). A/R activities may change the surface albedo and evapotranspiration regimes, producing net cooling in the tropical and subtropical latitudes for local and global climate and net warming at high latitudes ( [[#7.4.2|Section 7.4.2]] ). Very large-scale implementation of A/R may negatively affect food security since an increase in global forest area can increase food prices through land competition ( [[#Kreidenweis--2016|Kreidenweis et al. 2016]] ).

'''Conclusions from AR5 and IPCC Special Reports (SR1.5, SROCC and SRCCL); mitigation potential, costs, and pathways.''' The AR5 did not provide a new specification of A/R potential, but referred to IPCC AR4 mostly for forestry measures ( [[#Nabuurs--2007|Nabuurs et al. 2007]] ). The AR5 did view the feasible A/R potential from a diets change scenario that released land for reforestation and bioenergy crops. The AR5 provided top-down estimates of costs and potentials for forestry mitigation options – including reduced deforestation, forest management, afforestation, and agroforestry, estimated to contribute between 1.27 and 4.23 GtCO 2 yr –1 of economically viable abatement in 2030 at carbon prices up to USD100 tCO 2 -eq –1 (Smith et al. 2014).

The SRCCL remained with a reported wide range of mitigation potential for A/R of 0.5–10.1 GtCO 2 yr –1 by 2050 ( ''medium confidence'' ) ( [[#Kreidenweis--2016|Kreidenweis et al. 2016]] ; [[#Griscom--2017|Griscom et al. 2017]] ; [[#Hawken--2017|Hawken 2017]] ; [[#Fuss--2018|Fuss et al. 2018]] ; [[#Roe--2019|Roe et al. 2019]] ) (SRCCL Chapters 2 and 6). The higher estimate represents a technical potential of reforesting all areas where forests are the native cover type (reforestation), constrained by food security and biodiversity considerations, considering above and below-ground carbon pools and implementation on a rather theoretical maximum of 678 Mha of land ( [[#Griscom--2017|Griscom et al. 2017]] ; [[#Roe--2019|Roe et al. 2019]] ). The lower estimates represent the minimum range from an Earth System Model and a sustainable global CDR potential ( [[#Fuss--2018|Fuss et al. 2018]] ). Climate change will affect the mitigation potential of reforestation due to impacts in forest growth and composition, as well as changes in disturbances including fire. However, none of the mitigation estimates included in the SRCCL account for climate impacts.

'''Developments since AR5 and IPCC Special Reports (SR1.5, SROCC and SRCCL).''' Since SRCCL, additional studies have been published on A/R mitigation potential by [[#Bastin--2019|Bastin et al. (2019)]] , [[#Lewis--2019|Lewis et al. (2019)]] , Doelman et al. (2019), [[#Favero--2020|Favero et al. (2020)]] and [[#Austin--2020|Austin et al. (2020)]] . These studies are within the range reported in the SRCCL stretching the potentials at the higher range. The rising public interest in nature-based solutions, along with high profile initiatives being launched (UN Decade on Restoration announced in 2019, the Bonn challenge on 150 million ha of restored forest in 2020 and the one trillion trees campaign launched by the World Economic Forum in 2020), has prompted intense discussions on the scale, effectiveness, and pitfalls of A/R and tree planting for climate mitigation ( [[#Luyssaert--2018|Luyssaert et al. 2018]] ; [[#Bond--2019|Bond et al. 2019]] ; [[#Anderegg--2020|Anderegg et al. 2020]] ; [[#Heilmayr--2020|Heilmayr et al. 2020]] ; [[#Holl--2020|Holl and Brancalion 2020]] ). The sometimes sole attention on afforestation and reforestation '''–''' suggesting it may solve the climate problem to large extent, in combination with the very high estimates of potentials '''–''' have led to polarisation in the debate, resulting in criticism to these measures or an emphasis on nature restoration only ( [[#Lewis--2019|Lewis et al. 2019]] ). Our assessment based on most recent literature produced regional economic mitigation potential at USD100 tCO 2 –1 estimate of 100–400 MtCO 2 yr –1 in Africa, 210–266 MtCO 2 yr –1 in Asia and Pacific, 291 MtCO 2 -eq yr –1 in Developed Countries (87% in North America), 30 MtCO 2 -eq yr –1 in Eastern Europe and West-Central Asia, and 345–898 MtCO 2 -eq yr –1 in Latin America and Caribbean ( [[#Roe--2021|Roe et al. 2021]] ), which totals to about 1200 MtCO 2 yr –1 , leaning to the lower range of the potentials in earlier IPCC reports. A recent global assessment of the aggregate costs for afforestation and reforestation suggests that at USD100 tCO 2 –1 , 1.6 GtCO 2 yr –1 could be sequestered globally for an annual cost of USD130 billion ( [[#Austin--2020|Austin et al. 2020]] ). Sectoral studies that are able to deal with local circumstances and limits estimate A/R potentials at 20 MtCO 2 yr –1 in Russia (Eastern Europe and West-Central Asia) ( [[#Romanovskaya--2020|Romanovskaya et al. 2020]] ) and 64 MtCO 2 yr –1 in Europe ( [[#Nabuurs--2017|Nabuurs et al. 2017]] ). ( [[#Domke--2020|Domke et al. 2020]] ) estimated for the USA an additional 20% sequestration rate from tree planting to achieve full stocking capacity of all understocked productive forestland, in total reaching 187 MtCO 2 yr –1 sequestration. A new study on costs in the USA estimates 72–91 MtCO 2 yr –1 could be sequestered between now and 2050 for USD100 tCO 2 –1 (Wade et al. 2019). The tropical and subtropical latitudes are the most effective for forest restoration in terms of carbon sequestration because of the rapid growth and lower albedo of the land surface compared with high latitudes ( [[#Lewis--2019|Lewis et al. 2019]] ). Costs may be higher if albedo is considered in North America, Russia, and Africa ( [[#Favero--2017|Favero et al. 2017]] ). In addition, a wide variety of sequestration rates have been collected and published in the IPCC Good Practice Guidance for the AFOLU sector ( [[#IPCC--2006|IPCC 2006]] ).

'''Critical assessment and conclusion.''' There is ''medium confidence'' that the global technical mitigation potential of afforestation and reforestation activities by 2050 is 3.9 (0.5–10.1) GtCO 2 yr –1 , and the economic mitigation potential (&lt;USD100 tCO 2 –1 ) is 1.6 (0.5–3.0) GtCO 2 yr –1 (requiring about 200 Mha). Per hectare a long (about 100 year) sustained effect of 5–10 t CO 2 ha –1 yr –1 is realistic with ranges between 1–20 t(CO 2 ) ha –1 yr –1 . Not all sectoral studies rely on economic models that account for leakage ( [[#Murray--2004|Murray et al. 2004]] ; Sohngen and Brown 2004), suggesting that technical potential may be overestimated.

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==== 7.4.2.3 Improved Forest Management ====

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'''Activities, co-benefits, risks and implementation opportunities and barriers.''' Improved sustainable forest management of already managed forests can lead to higher forest carbon stocks, better quality of produced wood, continuously produced wood, while maintaining and enhancing the forest carbon stock, and can also partially prevent and counteract the impacts of disturbances ( [[#Kurz--2008|Kurz et al. 2008]] ; [[#Marlon--2012|Marlon et al. 2012]] ; [[#Abatzoglou--2016|Abatzoglou and Williams 2016]] ; [[#Seidl--2017|Seidl et al. 2017]] ; [[#Nabuurs--2017|Nabuurs et al. 2017]] ; [[#Tian--2018|Tian et al. 2018]] ; [[#Ekholm--2020|Ekholm 2020]] ). Furthermore, it can provide benefits for climate change adaptation, biodiversity conservation, microclimatic regulation, soil erosion protection and water and flood regulation with reduced lateral carbon fluxes ( [[#Ashton--2012|Ashton et al. 2012]] ; [[#Martínez-Mena--2019|Martínez-Mena et al. 2019]] ; [[#Verkerk--2020|Verkerk et al. 2020]] ). Often, in existing (managed) forests with existing carbon stocks, large changes per hectare cannot be expected, although many forest owners may respond to carbon price incentives ( [[#Favero--2020|Favero et al. 2020]] ; [[#Ekholm--2020|Ekholm 2020]] ). The full mitigation effects can be assessed in conjunction with the overall forest and wood use system i.e., carbon stock changes in standing trees, soil, harvested wood products (HWPs) and its bioenergy component with the avoided emissions through substitution. Forest management strategies aimed at increasing the biomass stock may have adverse side effects, such as decreasing the stand-level structural complexity, large emphasis on pure fast-growing stands, risks for biodiversity and resilience to natural disasters.

Generally, measures can consist of one or combination of longer rotations, less intensive harvests, continuous-cover forestry, mixed stands, more adapted species, selected provenances, high quality wood assortments, and so on. Further, there is a trade-off between management in various parts of the forest product value chain, resulting in a wide range of results on the role of managed forests in mitigation (Agostini et al. 2013; [[#Braun--2016|Braun et al. 2016]] ; [[#Soimakallio--2016|Soimakallio et al. 2016]] ; [[#Gustavsson--2017|Gustavsson et al. 2017]] ; [[#Erb--2017|Erb et al. 2017]] ; [[#Favero--2020|Favero et al. 2020]] ; [[#Hurmekoski--2020|Hurmekoski et al. 2020]] ). Some studies conclude that reduction in forest carbon stocks due to harvest exceeds for decades the joint sequestration of carbon in harvested wood product stocks and emissions avoided through wood use ( [[#Soimakallio--2016|Soimakallio et al. 2016]] ; [[#Seppälä--2019|Seppälä et al. 2019]] ), whereas others emphasise country level examples where investments in forest management have led to higher growing stocks while producing more wood ( [[#Schulze--2020|Schulze et al. 2020]] ; [[#Ouden--2020|Ouden et al. 2020]] ; [[#Cowie--2021|Cowie et al. 2021]] ).

'''Conclusions from AR5 and IPCC Special Reports (SR1.5, SROCC and SRCCL); mitigation potential, costs, and pathways.''' In the SRCCL, forest management activities have the potential to mitigate 0.4–2.1 GtCO 2 -eq yr –1 by 2050 ( ''medium confidence'' ) (SRCCL: [[#Griscom--2017|Griscom et al. 2017]] ; [[#Roe--2019|Roe et al. 2019]] ). The higher estimate stems from assumptions of applications on roughly 1.9 billion ha of already managed forest which can be seen as very optimistic. It combines both natural forest management as well as improved plantations, on average with a small net additional effect per hectare, not including substitution effects in the energy sector nor the buildings sector.

'''Developments since AR5 and IPCC Special Reports (SR1.5, SROCC and SRCCL).''' The area of forest under management plans has increased in all regions since 2000 by 233 Mha ( [[#FAO--2020e|FAO 2020e]] ). The roughly 1 billion ha of secondary and degraded forests would be ideal to invest in and develop a sustainable sector that pays attention to biodiversity, wood provision and climate mitigation at the same time. This all depends on the effort made, the development of expertise, know-how in the field, nurseries with adapted provenances, etc as was also found for Russian climate-smart forestry options ( [[#Leskinen--2020|Leskinen et al. 2020]] ). Regionally, recently updated economic mitigation potential at USD100 tCO 2 –1 have 179–186 MtCO 2 -eq yr –1 in Africa, 193–313 MtCO 2 -eq yr –1 in Asia and Pacific, 215–220 MtCO 2 -eq yr –1 in Developed Countries , 82–152 MtCO 2 -eq yr –1 in Eastern Europe and West-Central Asia, and 62–204 MtCO 2 -eq yr –1 in Latin America and Caribbean ( [[#Roe--2021|Roe et al. 2021]] ).

Regional studies can take into account the local situation better: Russia [[#Romanovskaya--2020|Romanovskaya et al. (2020)]] estimate the potential of forest fires management at 220–420 MtCO 2 yr –1 , gentle logging technology at 15–59, reduction of wood losses at 61–76 MtCO 2 yr –1 . In North America, ( [[#Austin--2020|Austin et al. 2020]] ) estimate that in the next 30 years, forest management could contribute 154 MtCO 2 yr –1 in the USA and Canada with 81 MtCO 2 yr –1 available at less than USD100 tCO 2 –1 . In one production region (British Columbia) a cost-effective portfolio of scenarios was simulated that directed more of the harvested wood to longer-lived wood products, stopped burning of harvest residues and instead produced bioenergy to displace fossil fuel burning, and reduced harvest levels in regions with low disturbance rates. Net GHG emissions were reduced by an average of –9 MtCO 2 -eq yr –1 ( [[#Smyth--2020|Smyth et al. 2020]] ). In Europe, climate-smart forestry could mitigate an additional 0.19 GtCO 2 yr –1 by 2050 ( [[#Nabuurs--2017|Nabuurs et al. 2017]] ), in line with the regional estimates in ( [[#Roe--2021|Roe et al. 2021]] ).

In the tropics, estimates of the pantropical climate mitigation potential of natural forest management (a light intensity management in secondary forests), across three tropical regions (Latin America, Africa, Asia), is around 0.66 GtCO 2 -eq yr –1 with Asia responding for the largest share followed by Africa and Latin America ( [[#Roe--2021|Roe et al. 2021]] ). Selective logging occurs in at least 20% of the world’s tropical forests and causes at least half of the emissions from tropical forest degradation ( [[#Asner--2005|Asner et al. 2005]] ; [[#Blaser--2011|Blaser and Küchli 2011]] ; [[#Pearson--2017|Pearson et al. 2017]] ). Reduced-impact logging for climate (RIL-C; promotion of reduced wood waste, narrower haul roads, and lower impact skidding equipment) has the potential to reduce logging emissions by 44% ( [[#Ellis--2019|Ellis et al. 2019]] ), while also providing timber production.

'''Critical assessment and conclusion.''' There is ''medium confidence'' that the global technical mitigation potential for improved forest management by 2050 is 1.7 (1–2.1) GtCO 2 yr –1 , and the economic mitigation potential (&lt;USD100 tCO 2 –1 ) is 1.1 (0.6–1.9) GtCO 2 yr –1 . Efforts to change forest management do not only require, for example, a carbon price incentive, but especially require knowledge, institutions, skilled labour, good access and so on. These requirements outline that although the potential is of medium size, we estimate a feasible potential towards the lower end. The net effect is also difficult to assess, as management changes impact not only the forest biomass, but also the wood chain and substitution effects. Further, leakage can arise from efforts to change management for carbon sequestration. Efforts, for example to set aside large areas of forest, may be partly counteracted by higher harvesting pressures elsewhere (Kallio et al. 2018). Studies such as ( [[#Austin--2020|Austin et al. 2020]] ) implicitly account for leakage and thus suggest higher costs than other studies. We therefore judge the mitigation potential at medium potential with medium agreement ''.''

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