Editing IPCC:AR6/SRCCL/Chapter-6 (section)

==== 6.3.4.1 Integrated response options based on land management ====

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In this section, the impacts on land degradation of integrated response options based on land management are assessed.

''Integrated response options based on land management in agriculture''

Burney et al. (2010) <sup>[[#fn:r545|545]]</sup> estimated that an additional global cropland area of 11.11–15.14 Mkm <sup>2</sup> would have been needed if productivity had not increased between 1961 and 2000. As for desertification, given that agricultural expansion is a main driver of land degradation (FAO and ITPS 2015 <sup>[[#fn:r546|546]]</sup> ), increased food productivity has prevented up to 11.11–15.14 Mkm <sup>2</sup> from exploitation and land degradation (Table 6.37).

Land degradation can be addressed by the implementation of improved cropland, livestock and grazing land management practices, such as those outlined in the recently published Voluntary Guidelines for Sustainable Soil Management (FAO 2017b <sup>[[#fn:r547|547]]</sup> ). Each one could potentially affect extensive surfaces, not less than 10 Mkm <sup>2</sup> .

The guidelines include a list of practices aimed at minimising soil erosion, enhancing soil organic matter content, fostering soil nutrient balance and cycles, preventing, minimising and mitigating soil salinisation and alkalinisation, soil contamination, soil acidification, soil sealing, soil compaction, and improving soil water management. Land cover and land cover change are key factors and indicators of land degradation. In many drylands, land cover is threatened by overgrazing, so management of stocking rate and grazing can help to prevent the advance of land degradation (Smith et al. 2016a <sup>[[#fn:r548|548]]</sup> ).

Agroforestry can help stabilise soils to prevent land degradation; so, given that there is around 10 Mkm <sup>2</sup> of land with more than 10% tree cover (Garrity 2012 <sup>[[#fn:r549|549]]</sup> ), agroforestry could benefit up to 10 Mkm <sup>2</sup> of land.

Agricultural diversification usually aims at increasing climate and food security resilience, such as under ‘climate smart agriculture’ approaches (Lipper et al. 2014 <sup>[[#fn:r550|550]]</sup> ). Both objectives are closely related to land degradation prevention, potentially affecting 1–5 Mkm <sup>2</sup> .

Shifting from grassland to tilled crops increases erosion and soil loss, so there are significant benefits for addressing land degradation, by stabilising degraded soils (Chapter 3). Since cropland expansion during 1985 to 2005 was 17,400 km <sup>2</sup> yr <sup>–1</sup> (Foley et al. 2011 <sup>[[#fn:r551|551]]</sup> ) – and not all of this expansion will be from grasslands or degraded land – the maximum contribution of prevention of conversion of grasslands to croplands is 17,400 km2 yr-1 , a small global benefit for control of land degradation (Table 6.37).

Most land degradation processes that are sensitive to climate change pressures (e.g., erosion, decline in soil organic matter, salinisation, waterlogging, drying of wet ecosystems) can benefit from integrated water management. Integrated water management options include management to reduce aquifer and surface water depletion, and to prevent over-extraction, and provide direct co-benefits for prevention of land degradation. Land management practices implemented for climate change mitigation may also affect water resources. Globally, water erosion is estimated to result in the loss of 23–42 MtN and 14.6–26.4 MtP annually (Pierzynski et al. 2017 <sup>[[#fn:r552|552]]</sup> ). Forests influence the storage and flow of water in watersheds (Eisenbies et al. 2007 <sup>[[#fn:r553|553]]</sup> ) and are therefore important for regulating how climate change will impact on landscapes.

Table 6.37 summarises the impact on land degradation of options in agriculture, with confidence estimates based on the thresholds outlined in Table 6.53 in Section 6.3.6, and indicative (not exhaustive) references upon which the evidence in based.

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'''Table 6.37'''

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'''Effects on land degradation of response options in agriculture.'''
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''Integrated response options based on land management in forestry''

Based on the extent of forest exposed to degradation (Gibbs and Salmon 2015 <sup>[[#fn:r554|554]]</sup> ), the estimated global potential effect for reducing land degradation, for example, through reduced soil erosion (Borrelli et al. 2017 <sup>[[#fn:r555|555]]</sup> ), is large for both forest management and for reduced deforestation and forest degradation when cumulated for at least 20 years (Table 6.38). The uncertainty of these global estimates is high. More robust qualitative, and some quantitative, estimates are available at regional level. For example, in Indonesia, Santika et al. (2017) <sup>[[#fn:r556|556]]</sup> demonstrated that reduced deforestation (Sumatra and Kalimantan islands) contributed to significantly reduced land degradation.

Forest restoration is a key option to achieve the overarching frameworks to reduce land degradation at global scale, such as, for example, Zero Net Land Degradation (ZNLD; UNCCD 2012 <sup>[[#fn:r557|557]]</sup> ) and Land Degradation Neutrality (LDN), not only in drylands (Safriel 2017 <sup>[[#fn:r558|558]]</sup> ). Indeed, it has been estimated that more than 20 Mkm <sup>2</sup> are suitable for forest and landscape restoration, of which 15 Mkm <sup>2</sup> may be devoted to mixed plant mosaic restoration (UNCCD 2012 <sup>[[#fn:r559|559]]</sup> ). Moreover, the Bonn Challenge <sup>[[#fn:6|6]]</sup> aims to restore 1.5 Mkm <sup>2</sup> of deforested and degraded land by 2020, and 3.5 Mkm <sup>2</sup> by 2030. Under a restoration and protection scenario (implementing restoration targets), Wolff et al. (2018) <sup>[[#fn:r560|560]]</sup> simulated that there will be a global increase in net tree cover of about 4 Mkm <sup>2</sup> by 2050 (Table 6.38). At local level, Brazil’s Atlantic Restoration Pact aims to restore 0.15 Mkm <sup>2</sup> of forest areas in 40 years (Melo et al. 2013 <sup>[[#fn:r561|561]]</sup> ). The Y Ikatu Xingu campaign (launched in 2004) aims to contain deforestation and forest degradation processes by reversing the liability of 3000 km2 in the Xingu Basin, Brazil (Durigan et al. 2013 <sup>[[#fn:r562|562]]</sup> ).

Afforestation and reforestation are land management options frequently used to address land degradation (see Section 6.3.3.1 for details, and Table 6.38).

Table 6.38 summarises the impact on land degradation of options in forestry, with confidence estimates based on the thresholds outlined in Table 6.53 in Section 6.3.6, and indicative (not exhaustive) references upon which the evidence in based.

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'''Table 6.38'''

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''Integrated response options based on land management of soils''

Increasing soil organic matter content is a measure to address land

degradation. With around 120,000 km2 lost to degradation every year, and over 3.2 billion people negatively impacted on by land degradation globally (IPBES 2018 <sup>[[#fn:r563|563]]</sup> ), practices designed to increase soil organic carbon have a large potential to address land degradation, estimated to affect more than 11 Mkm2 globally (Lal 2004 <sup>[[#fn:r564|564]]</sup> ) (Table 6.39).

Control of soil erosion could have large benefits for addressing land degradation. Soil erosion control could benefit up to 1.50 Mkm2 of land to 2050 (IPBES 2018 <sup>[[#fn:r565|565]]</sup> ). Lal (2004) <sup>[[#fn:r1271|1271]]</sup> suggested that interventions to prevent wind and water erosion (two of the four main interventions proposed to address land degradation), could restore 11 Mkm2 of degraded and desertified soils globally (Table 6.39).

Oldeman et al. (1991) <sup>[[#fn:r566|566]]</sup> estimated that the global extent soil affected by salinisation is 0.77 Mkm2 yr-1, which sets the upper limit on the area that could benefit from measures to address soil salinisation (Table 6.39). The global extent of chemical soil degradation (salinisation, pollution and acidification) is about 1.03 Mkm2 (Oldeman et al. 1991) giving the maximum extent of land that could benefit from the management of pollution and acidification.

Biochar could provide moderate benefits for the prevention or reversal of land degradation, by improving water-holding capacity and nutrient- use efficiency, managing heavy metal pollution, and other co-benefits (Sohi 2012 <sup>[[#fn:r567|567]]</sup> ), though the global effects are not quantified.

Table 6.39 summarises the impact on land degradation of soil-based options, with confidence estimates based on the thresholds outlined in Table 6.53 in Section 6.3.6, and indicative (not exhaustive) references upon which the evidence in based.

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'''Table 6.39'''

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'''Effects on land degradation of soil-based response options.'''
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''Integrated response options based on land management across all/other ecosystems''

For fire management, details of estimates of the impact of wildfires (and thereby the potential impact of their suppression) are given in Section 6.3.3.1 (Table 6.40).

Management of landslides and natural hazards aims at controlling a severe land degradation process affecting sloped and hilly areas, many of them with poor rural inhabitants (FAO and ITPS 2015 <sup>[[#fn:r568|568]]</sup> ; Gariano and Guzzetti 2016 <sup>[[#fn:r569|569]]</sup> ), but the global potential has not been quantified.

There are no global data on the impacts of management of invasive species/encroachment on land degradation, though the impact is presumed to be positive.

Since large areas of coastal wetlands are degraded, restoration could potentially deliver moderate benefits for addressing land degradation, with 0.29 Mkm2 globally considered feasible for restoration (Griscom et al. 2017 <sup>[[#fn:r1272|1272]]</sup> ) (Table 6.40).

Table 6.39 summarises the impact on land degradation of soil-based options, with confidence estimates based on the thresholds outlined in Table 6.53 in Section 6.3.6, and indicative (not exhaustive) references upon which the evidence in based.

Considering that large areas (0.46 Mkm2) of global peatlands are degraded and considered suitable for restoration (Griscom et al. 2017 <sup>[[#fn:r570|570]]</sup> ), peatland restoration could deliver moderate benefits for addressing land degradation (Table 6.40).

There are no global estimates of the effects of biodiversity conservation on reducing degraded lands. However, at local scale, biodiversity conservation programmes have been demonstrated to stimulate gain of forest cover across large areas over the last three decades (e.g., in China; Zhang et al. 2013 <sup>[[#fn:r571|571]]</sup> ). Management of wild animals can influence land degradation processes by grazing, trampling and compacting soil surfaces, thereby altering surface temperatures and chemical reactions affecting sediment and carbon retention (Cromsigt et al. 2018 <sup>[[#fn:r572|572]]</sup> ).

Table 6.40 summarises the impact on land degradation of options in all/other ecosystems, with confidence estimates based on the thresholds outlined in Table 6.53 in Section 6.3.6, and indicative (not exhaustive) references upon which the evidence in based.

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'''Table 6.40'''

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'''Effects on land degradation of response options in all/other ecosystems.'''
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''Integrated response options based on land management specifically for carbon dioxide removal (CDR)''

While spreading of crushed minerals onto land as part of enhanced weathering can provide soil/plant nutrients in nutrient-depleted soils, increase soil organic carbon stocks and help to replenish eroded soil (Beerling et al. 2018 <sup>[[#fn:r573|573]]</sup> ), there is no literature on the global potential for addressing land degradation.

Large-scale production of bioenergy can require significant amounts of land (Smith et al. 2016a <sup>[[#fn:r574|574]]</sup> ; Clarke et al. 2014 <sup>[[#fn:r575|575]]</sup> ; Popp et al. 2017 <sup>[[#fn:r576|576]]</sup> ) – as much as 15 Mkm2 in 2°C scenarios (Popp et al. 2017 <sup>[[#fn:r577|577]]</sup> ) – therefore increasing pressures for land conversion and land degradation (Table 6.13). However, bioenergy production can either increase (Robertson et al. 2017b <sup>[[#fn:r578|578]]</sup> ; Mello et al. 2014 <sup>[[#fn:r579|579]]</sup> ) or decrease (FAO 2011b <sup>[[#fn:r580|580]]</sup> ; Lal 2014 <sup>[[#fn:r581|581]]</sup> ) soil organic matter, depending on where it is produced and how it is managed. These effects are not included in the quantification in Table 6.41.

Table 6.41 summarises the impact on land degradation of options thresholds outlined in Table 6.53 in Section 6.3.6, and indicative specifically for CDR, with confidence estimates based on the (not exhaustive) references upon which the evidence in based.

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'''Table 6.41'''

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'''Effects on land degradation of response options specifically for CDR.'''
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