Editing Test:SRCCL/Chapter-1 (section)

== CCB2 Implications of large-scale conversion from non-forest to forest land ==

<div id="section-1-3-1-targeted-decarbonisation-relying-on-large-land-area-need-block-1"></div>

{| class="wikitable"
|-
|
|-

Baldur Janz (Germany), Almut Arneth (Germany), Francesco Cherubini (Norway/Italy), Edouard Davin (Switzerland/France), Aziz Elbehri (Morocco), Kaoru Kitajima (Japan), Werner Kurz (Canada).

Efforts to increase forest area

While deforestation continues in many world regions, especially in the tropics, large expansion of mostly managed forest area has taken place in some countries. In the IPCC context, reforestation (conversion to forest of land that previously contained forests but has been converted to some other use) is distinguished from afforestation (conversion to forest of land that historically has not contained forests; see Glossary). Past expansion of managed forest area occurred in many world-regions for a variety of reasons, from meeting needs for wood fuel or timber (Vadell et al. 2016 <sup>[[#fn:r591|591]]</sup> ; Joshi et al. 2011 <sup>[[#fn:r592|592]]</sup> ; Zaloumis and Bond 2015 <sup>[[#fn:r593|593]]</sup> ; Payn et al. 2015 <sup>[[#fn:r594|594]]</sup> ; Shoyama 2008 <sup>[[#fn:r595|595]]</sup> ; Miyamoto et al. 2011 <sup>[[#fn:r596|596]]</sup> ) to restoration-driven efforts, with the aim of enhancing ecological function (Filoso et al. 2017 <sup>[[#fn:r597|597]]</sup> ; Salvati and Carlucci 2014 <sup>[[#fn:r598|598]]</sup> ; Ogle et al. 2018 <sup>[[#fn:r599|599]]</sup> ; Crouzeilles et al. 2016 <sup>[[#fn:r600|600]]</sup> ; FAO 2016 <sup>[[#fn:r601|601]]</sup> ) (Sections 3.7 and 4.9).

In many regions, net forest area increase includes deforestation (often of native forests) alongside increasing forest area (often managed forest, but also more natural forest restoration efforts) (Heilmayr et al. 2016 <sup>[[#fn:r602|602]]</sup> ; Scheidel and Work 2018 <sup>[[#fn:r603|603]]</sup> ; Hua et al. 2018 <sup>[[#fn:r604|604]]</sup> ; Crouzeilles et al. 2016 <sup>[[#fn:r605|605]]</sup> ; Chazdon et al. 2016b <sup>[[#fn:r606|606]]</sup> ). China and India have seen the largest net forest area increase, aiming to alleviate soil erosion, desertification and overgrazing (Ahrends et al. 2017 <sup>[[#fn:r607|607]]</sup> ; Cao et al. 2016 <sup>[[#fn:r608|608]]</sup> ; Deng et al. 2015 <sup>[[#fn:r609|609]]</sup> ; Chen et al. 2019 <sup>[[#fn:r610|610]]</sup> ) (Sections 3.7 and 4.9) but uncertainties in exact forest area changes remain large, mostly due to differences in methodology and forest classification (FAO 2015a <sup>[[#fn:r611|611]]</sup> ; Song et al. 2018 <sup>[[#fn:r612|612]]</sup> ; Hansen et al. 2013 <sup>[[#fn:r613|613]]</sup> ; MacDicken et al. 2015 <sup>[[#fn:r614|614]]</sup> ).

'''What are the implications for ecosystems?'''

''1. Implications for biogeochemical and biophysical processes''

There is robust evidence and medium agreement that whilst forest area expansion increases ecosystem carbon storage, the magnitude of the increased stock depends on the type and length of former land use, forest type planted, and climatic regions (Bárcena et al. 2014 <sup>[[#fn:r615|615]]</sup> ; Poeplau et al. 2011 <sup>[[#fn:r616|616]]</sup> ; Shi et al. 2013 <sup>[[#fn:r617|617]]</sup> ; Li et al. 2012 <sup>[[#fn:r618|618]]</sup> ) (Section 4.3). While reforestation of former croplands increases net ecosystem carbon storage (Bernal et al. 2018 <sup>[[#fn:r619|619]]</sup> ; Lamb 2018 <sup>[[#fn:r620|620]]</sup> ), afforestation on native grassland results in reduction of soil carbon stocks, which can reduce or negate the net carbon benefits which are dominated by increases in biomass, dead wood and litter carbon pools (Veldman et al. 2015, 2017 <sup>[[#fn:r621|621]]</sup> ).

Forest vs non-forest lands differ in land surface reflectiveness of shortwave radiation and evapotranspiration (Anderson et al. 2011 <sup>[[#fn:r622|622]]</sup> ; Perugini et al. 2017 <sup>[[#fn:r623|623]]</sup> ) (Section 2.4). Evapotranspiration from forests during the growing season regionally cools the land surface and enhances cloud cover that reduces shortwave radiation reaching the land, an impact that is especially pronounced in the tropics. However, dark evergreen conifer-dominated forests have low surface reflectance, and tend to cause warming of the near-surface atmosphere compared to non-forest land, especially when snow cover is present such as in boreal regions (Duveiller et al. 2018 <sup>[[#fn:r624|624]]</sup> ; Alkama and Cescatti 2016 <sup>[[#fn:r625|625]]</sup> ; Perugini et al. 2017 <sup>[[#fn:r626|626]]</sup> ) (medium evidence, high agreement).

''2. Implications for water balance''

Evapotranspiration by forests reduces surface runoff and erosion of soil and nutrients (Salvati et al. 2014 <sup>[[#fn:r627|627]]</sup> ). Planting of fast-growing species in semi-arid regions or replacing natural grasslands with forest plantations can divert soil water resources to evapotranspiration from groundwater recharge (Silveira et al. 2016 <sup>[[#fn:r628|628]]</sup> ; Zheng et al. 2016 <sup>[[#fn:r629|629]]</sup> ; Cao et al. 2016 <sup>[[#fn:r630|630]]</sup> ). Multiple cases are reported from China where afforestation programs, some with irrigation, without having been tailored to local precipitation conditions, resulted in water shortages and tree mortality (Cao et al. 2016; Yang et al. 2014 <sup>[[#fn:r631|631]]</sup> ; Li et al. 2014 <sup>[[#fn:r632|632]]</sup> ; Feng et al. 2016 <sup>[[#fn:r633|633]]</sup> ). Water shortages may create long-term water conflicts (Zheng et al. 2016 <sup>[[#fn:r634|634]]</sup> ). However, reforestation (in particular for restoration) is also associated with improved water filtration, groundwater recharge (Ellison et al. 2017 <sup>[[#fn:r635|635]]</sup> ) and can reduce risk of soil erosion, flooding, and associated disasters (Lee et al. 2018 <sup>[[#fn:r636|636]]</sup> ) (Section 4.9).

''3. Implications for biodiversity''

Impacts of forest area expansion on biodiversity depend mostly on the vegetation cover that is replaced: afforestation on natural non-tree-dominated ecosystems can have negative impacts on biodiversity (Abreu et al. 2017 <sup>[[#fn:r637|637]]</sup> ; Griffith et al. 2017 <sup>[[#fn:r638|638]]</sup> ; Veldman et al. 2015 <sup>[[#fn:r639|639]]</sup> ; Parr et al. 2014 <sup>[[#fn:r640|640]]</sup> ; Wilson et al. 2017 <sup>[[#fn:r641|641]]</sup> ; Hua et al. 2016 <sup>[[#fn:r642|642]]</sup> ; see also IPCC 1.5° report (2018)). Reforestation with monocultures of fast-growing, non-native trees has little benefit to biodiversity (Shimamoto et al. 2018 <sup>[[#fn:r643|643]]</sup> ; Hua et al. 2016). There are also concerns regarding some commonly used plantation species (e.g., Acacia and Pinus species) to become invasive (Padmanaba and Corlett 2014 <sup>[[#fn:r644|644]]</sup> ; Cunningham et al. 2015b <sup>[[#fn:r645|645]]</sup> ).

|}

Reforestation with mixes of native species, especially in areas that retain fragments of native forest, can support ecosystem services and biodiversity recovery, with positive social and environmental co-benefits (Cunningham et al. 2015a <sup>[[#fn:r646|646]]</sup> ; Dendy et al. 2015 <sup>[[#fn:r647|647]]</sup> ; Chaudhary and Kastner 2016 <sup>[[#fn:r648|648]]</sup> ; Huang et al. 2018 <sup>[[#fn:r649|649]]</sup> ; Locatelli et al. 2015b <sup>[[#fn:r650|650]]</sup> ) (Section 4.5). Even though species diversity in re-growing forests is typically lower than in primary forests, planting native or mixed species can have positive effects on biodiversity (Brockerhoff et al. 2013 <sup>[[#fn:r651|651]]</sup> ; Pawson et al. 2013 <sup>[[#fn:r652|652]]</sup> ; Thompson et al. 2014 <sup>[[#fn:r653|653]]</sup> ). Reforestation has been shown to improve links among existing remnant forest patches, increasing species movement, and fostering gene flow between otherwise isolated populations (Gilbert-Norton et al. 2010 <sup>[[#fn:r654|654]]</sup> ; Barlow et al. 2007 <sup>[[#fn:r655|655]]</sup> ; Lindenmayer and Hobbs 2004 <sup>[[#fn:r656|656]]</sup> ).

''4. Implications for other ecosystem services and societies''

Forest area expansion could benefit recreation and health, preservation of cultural heritage and local values and knowledge, livelihood support (via reduced resource conflicts, restoration of local resources). These social benefits could be most successfully achieved if local communities’ concerns are considered (Le et al. 2012 <sup>[[#fn:r657|657]]</sup> ). However, these co-benefits have rarely been assessed due to a lack of suitable frameworks and evaluation tools (Baral et al. 2016 <sup>[[#fn:r658|658]]</sup> ).

Industrial forest management can be in conflict with the needs of forest-dependent people and community-based forest management over access to natural resources (Gerber 2011 <sup>[[#fn:r659|659]]</sup> ; Baral et al. 2016 <sup>[[#fn:r660|660]]</sup> ) and/or loss of customary rights over land use (Malkamäki et al. 2018 <sup>[[#fn:r661|661]]</sup> ; Cotula et al. 2014 <sup>[[#fn:r662|662]]</sup> ). A common result is out-migration from rural areas and diminishing local uses of ecosystems (Gerber 2011 <sup>[[#fn:r663|663]]</sup> ). Policies promoting large-scale tree plantations gain traction if these are reappraised in view of potential co-benefits with several ecosystem services and local societies (Bull et al. 2006 <sup>[[#fn:r664|664]]</sup> ; Le et al. 2012 <sup>[[#fn:r665|665]]</sup> ).

'''Scenarios of forest area expansion for land-based climate change mitigation'''

Conversion of non-forest to forest land has been discussed as a relatively cost-effective climate change mitigation option when compared to options in the energy and transport sectors (medium evidence, medium agreement) (de Coninck et al. 2018 <sup>[[#fn:r666|666]]</sup> ; Griscom et al. 2017 <sup>[[#fn:r667|667]]</sup> ; Fuss et al. 2018 <sup>[[#fn:r668|668]]</sup> ), and can have co-benefits with adaptation.

Sequestration of CO <sub>2</sub> from the atmosphere through forest area expansion has become a fundamental part of stringent climate change mitigation scenarios (Rogelj et al. 2018a <sup>[[#fn:r669|669]]</sup> ; Fuss et al. 2018 <sup>[[#fn:r670|670]]</sup> ) (e.g., Sections 2.5, 4.5 and 6.2). The estimated mitigation potential ranges from about 0.5 to 10 GtCO <sub>2</sub> yr–1 (robust evidence, medium agreement), and depends on assumptions regarding available land and forest carbon uptake potential (Houghton 2013 <sup>[[#fn:r671|671]]</sup> ; Houghton and Nassikas 2017 <sup>[[#fn:r672|672]]</sup> ; Griscom et al. 2017 <sup>[[#fn:r673|673]]</sup> ; Lenton 2014 <sup>[[#fn:r674|674]]</sup> ; Fuss et al. 2018 <sup>[[#fn:r675|675]]</sup> ; Smith 2016 <sup>[[#fn:r676|676]]</sup> ) (Section 2.5.1). In climate change mitigation scenarios, typically, no differentiation is made between reforestation and afforestation despite different overall environmental impacts between these two measures. Likewise, biodiversity conservation, impacts on water balances, other ecosystem services, or land-ownership – as constraints when simulating forest area expansion (Cross-Chapter Box 1 in Chapter 1) – tend not to be included as constraints when simulating forest area expansion.

Projected forest area increases, relative to today’s forest area, range from approximately 25% in 2050 and increase to nearly 50% by 2100 (Rogelj et al. 2018a <sup>[[#fn:r677|677]]</sup> ; Kreidenweis et al. 2016 <sup>[[#fn:r678|678]]</sup> ; Humpenoder et al. 2014 <sup>[[#fn:r679|679]]</sup> ). Potential adverse side-effects of such large-scale measures, especially for low-income countries, could be increasing food prices from the increased competition for land (Kreidenweis et al. 2016 <sup>[[#fn:r680|680]]</sup> ; Hasegawa et al. 2015 <sup>[[#fn:r681|681]]</sup> , 2018 <sup>[[#fn:r682|682]]</sup> ; Boysen et al. 2017 <sup>[[#fn:r683|683]]</sup> ) (Section 5.5). Forests also emit large amounts of biogenic volatile compounds that under some conditions contribute to the formation of atmospherically short-lived climate forcing compounds, which are also detrimental to health (Ashworth et al. 2013 <sup>[[#fn:r684|684]]</sup> ; Harrison et al. 2013 <sup>[[#fn:r685|685]]</sup> ). Recent analyses argued for an upper limit of about 5 million km2 of land globally available for climate change mitigation through reforestation, mostly in the tropics (Houghton 2013 <sup>[[#fn:r686|686]]</sup> ) – with potential regional co-benefits.

Since forest growth competes for land with bioenergy crops (Harper et al. 2018 <sup>[[#fn:r687|687]]</sup> ) (Cross-Chapter Box 7 in Chapter 6), global area estimates need to be assessed in light of alternative mitigation measures at a given location. In all forest-based mitigation efforts, the sequestration potential will eventually saturate unless the area keeps expanding, or harvested wood is either used for long-term storage products or for carbon capture and storage (Fuss et al. 2018 <sup>[[#fn:r688|688]]</sup> ; Houghton et al. 2015 <sup>[[#fn:r689|689]]</sup> ) (Section 2.5.1). Considerable uncertainty in forest carbon uptake estimates is further introduced by potential forest losses from fire or pest outbreaks (Allen et al. 2010 <sup>[[#fn:r690|690]]</sup> ; Anderegg et al. 2015 <sup>[[#fn:r691|691]]</sup> ) (Cross-Chapter Box 3 in Chapter 2). And like all land-based mitigation measures, benefits may be diminshed by land-use displacement, and through trade of land-based products, especially in poor countries that experience forest loss (e.g., Africa) (Bhojvaid et al. 2016 <sup>[[#fn:r692|692]]</sup> ; Jadin et al. 2016 <sup>[[#fn:r693|693]]</sup> ).

'''Conclusion'''

Reforestation is a mitigation measure with potential co-benefits for conservation and adaptation, including biodiversity habitat, air and water filtration, flood control, enhanced soil fertility and reversal of land degradation. Potential adverse side-effects of forest area expansion depend largely on the state of the land it displaces as well as tree species selections. Active governance and planning contribute to maximising co-benefits while minimising adverse side-effects (Laestadius et al. 2011 <sup>[[#fn:r694|694]]</sup> ; Dinerstein et al. 2015 <sup>[[#fn:r695|695]]</sup> ; Veldman et al. 2017 <sup>[[#fn:r696|696]]</sup> ) (Section 4.8 and Chapter 7). At large spatial scales, forest expansion is expected to lead to increased competition for land, with potentially undesirable impacts on food prices, biodiversity, non-forest ecosystems and water availability (Bryan and Crossman 2013 <sup>[[#fn:r697|697]]</sup> ; Boysen et al. 2017 <sup>[[#fn:r698|698]]</sup> ; Kreidenweis et al. 2016 <sup>[[#fn:r699|699]]</sup> ; Egginton et al. 2014 <sup>[[#fn:r700|700]]</sup> ; Cao et al. 2016 <sup>[[#fn:r701|701]]</sup> ; Locatelli et al. 2015a <sup>[[#fn:r702|702]]</sup> ; Smith et al. 2013 <sup>[[#fn:r703|703]]</sup> ).

<span id="land-management"></span>