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

==== 7.4.3.3 Agroforestry ====

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'''Activities, co-benefits, risks and implementation opportunities and barriers.''' Agroforestry is a set of diverse land management systems that integrate trees and shrubs with crops and/or livestock in space and/or time. Agroforestry accumulates carbon in woody vegetation and soil ( [[#Ramachandran%20Nair--2010|Ramachandran Nair et al. 2010]] ) and offers multiple co-benefits such as increased land productivity, diversified livelihoods, reduced soil erosion, improved water quality, and more hospitable regional climates ( [[#Ellison--2017|Ellison et al. 2017]] ; [[#Kuyah--2019|Kuyah et al. 2019]] ; [[#Mbow--2020|Mbow et al. 2020]] ; [[#Zhu--2020|Zhu et al. 2020]] ). Incorporation of trees and shrubs in agricultural systems, however, can affect food production, biodiversity, local hydrology and contribute to social inequality ( [[#Amadu--2020|Amadu et al. 2020]] ; [[#Fleischman--2020|Fleischman et al. 2020]] ; [[#Holl--2020|Holl and Brancalion 2020]] ). To minimise risks and maximise co-benefits, agroforestry should be implemented as part of support systems that deliver tools, and information to increase farmers’ agency. This may include reforming policies, strengthening extension systems and creating market opportunities that enable adoption ( [[#Jamnadass--2020|Jamnadass et al. 2020]] ; [[#Sendzimir--2011|Sendzimir et al. 2011]] ; P. [[#Smith--2019|Smith et al. 2019]] a). Consideration of carbon sequestration in the context of food and fuel production, as well as environmental co-benefits at the farm, local, and regional scales can further help support decisions to plant, regenerate and maintain agroforestry systems ( [[#Kumar--2011|Kumar and Nair 2011]] ; [[#Miller--2020|Miller et al. 2020]] ). In spite of the advantages, biophysical and socio-economic factors can limit the adoption ( [[#Pattanayak--2003|Pattanayak et al. 2003]] ). Contextual factors may include, but are not limited to; water availability, soil fertility, seed and germplasm access, land policies and tenure systems affecting farmer agency, access to credit, and to information regarding the optimum species for a given location.

'''Conclusions from AR5 and IPCC Special Reports (SR1.5, SROCC and SRCCL); mitigation potential, costs, and pathways.''' The SRCCL estimated the global technical mitigation potential of agroforestry, with medium confidence, to be between 0.08 and 5.6 GtCO 2 -eq yr –1 by 2050 ( [[#Griscom--2017|Griscom et al. 2017]] ; [[#Dickie--2014a|Dickie et al. 2014a]] ; [[#Zomer--2016|Zomer et al. 2016]] ; [[#Hawken--2017|Hawken 2017]] ). Estimates are derived from syntheses of potential area available for various agroforestry systems, for example, windbreaks, farmer managed natural regeneration, and alley cropping and average annual rates of carbon accumulation. The cost-effective economic potential, also with medium confidence, is more limited at 0.3–2.4 GtCO 2 -eq yr –1 ( [[#Zomer--2016|Zomer et al. 2016]] ; [[#Griscom--2017|Griscom et al. 2017]] ; [[#Roe--2019|Roe et al. 2019]] ). Despite this potential, agroforestry is currently not considered in integrated assessment models used for mitigation pathways ( [[#7.5|Section 7.5]] ).

'''Developments since AR5 and IPCC Special Reports (SR1.5, SROCC and SRCCL).''' Updated estimates of agroforestry’s technical mitigation potential and synthesised estimates of carbon sequestration across agroforestry systems have since been published. The most recent global analysis estimates technical potential of 9.4 GtCO 2 -eq yr –1 ( [[#Chapman--2020|Chapman et al. 2020]] ) of agroforestry on 1.87 and 1.89 billion ha of crop and pasture lands below median carbon content, respectively. This estimate is at least 68% greater than the largest estimate reported in the SRCCL ( [[#Hawken--2017|Hawken 2017]] ) and represents a new conservative upper bound as [[#Chapman--2020|Chapman et al. (2020)]] only accounted for above-ground carbon. Considering both above- and below-ground carbon of windbreaks, alley cropping and silvopastoral systems at a more limited areal extent ( [[#Griscom--2020|Griscom et al. 2020]] ), the economic potential of agroforestry was estimated to be only about 0.8 GtCO 2 -eq yr –1 . Variation in estimates primarily result from assumptions on the agroforestry systems including, extent of implementation and estimated carbon sequestration potential when converting to agroforestry.

Regional estimates of mitigation potential are scant with agroforestry options differing significantly by geography ( [[#Feliciano--2018|Feliciano et al. 2018]] ). For example, multi-strata shaded coffee and cacao are successful in the humid tropics ( [[#Somarriba--2013|Somarriba et al. 2013]] ; [[#Blaser--2018|Blaser et al. 2018]] ), silvopastoral systems are prevalent in Latin American ( [[#Peters--2013|Peters et al. 2013]] ; [[#Landholm--2019|Landholm et al. 2019]] ) while agrosilvopastoral systems, shelterbelts, hedgerows, and windbreaks are common in Europe ( [[#Joffre--1988|Joffre et al. 1988]] ; Rigueiro-Rodriguez 2009). At the field scale, agroforestry accumulates between 0.59 and 6.24 t ha –1 yr –1 of carbon above-ground. Below-ground carbon often constitutes 25% or more of the potential carbon gains in agroforestry systems (De Stefano and Jacobson 2018; [[#Cardinael--2018|Cardinael et al. 2018]] ). [[#Roe--2021|Roe et al. (2021)]] estimate greatest regional economic (up to USD100 tCO 2 –1 ) mitigation potential for the period 2020–2050 to be in Asia and the Pacific (368.4 MtCO 2 -eq yr –1 ) and Developed Countries (264.7 MtCO 2 -eq yr –1 ).

Recent research has also highlighted co-benefits and more precisely identified implementation barriers. In addition to aforementioned co-benefits, evidence now shows that agroforestry can improve soil health, regarding infiltration and structural stability ( [[#Muchane--2020|Muchane et al. 2020]] ); reduces ambient temperatures and crop heat stress ( [[#Arenas-Corraliza--2018|Arenas-Corraliza et al. 2018]] ; [[#Sida--2018|Sida et al. 2018]] ); increases groundwater recharge in drylands when managed at moderate density ( [[#Ilstedt--2016|Ilstedt et al. 2016]] ; Bargués-Tobella et al. 2020); positively influences human health ( [[#Rosenstock--2019|Rosenstock et al. 2019]] ); and can improve dietary diversity ( [[#McMullin--2019|McMullin et al. 2019]] ). Along with previously mentioned barriers, low social capital, assets, and labour availability have been identified as pertinent to adoption. Practically all barriers are interdependent and subject to the context of implementation.

'''Critical assessment and conclusion.''' There is medium confidence that agroforestry has a technical potential of 4.1 (0.3–9.4) GtCO 2 -eq yr –1 for the period 2020–2050, of which 0.8 (0.4–1.1) GtCO 2 -eq yr –1 is available at USD100 tCO 2 –1 . Despite uncertainty around global estimates due to regional preferences for management systems, suitable land availability, and growing conditions, there is high confidence in agroforestry’s mitigation potential at the field scale. With countless options for farmers and land managers to implement agroforestry, there is medium confidence in the feasibility of achieving estimated regional mitigation potential. Appropriately matching agroforestry options, to local biophysical and social contexts is important in maximising mitigation and co-benefits, while avoiding risks ( [[#Sinclair--2019|Sinclair and Coe 2019]] ).

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