Editing IPCC:AR6/SRCCL/Chapter-4 (section)

== 4.1 Introduction ==

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=== 4.1.1 Scope of the chapter ===

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This chapter examines the scientific understanding of how climate change impacts land degradation, and vice versa, with a focus on non-drylands. Land degradation of drylands is covered in Chapter 3. After providing definitions and the context (Section 4.1) we proceed with a theoretical explanation of the different processes of land degradation and how they are related to climate and to climate change, where possible (Section 4.2). Two sections are devoted to a systematic assessment of the scientific literature on status and trend of land degradation (Section 4.3) and projections of land degradation (Section 4.4). Then follows a section where we assess the impacts of climate change mitigation options, bioenergy and land-based technologies for carbon dioxide removal (CDR), on land degradation (Section 4.5). The ways in which land degradation can impact on climate and climate change are assessed in Section 4.6. The impacts of climate-related land degradation on human and natural systems are assessed in Section 4.7. The remainder of the chapter assesses land degradation mitigation options based on the concept of sustainable land management: avoid, reduce and reverse land degradation (Section 4.8), followed by a presentation of eight illustrative case studies of land degradation and remedies (Section 4.9). The chapter ends with a discussion of the most critical knowledge gaps and areas for further research (Section 4.10).

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=== 4.1.2 Perspectives of land degradation ===

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Land degradation has accompanied humanity at least since the widespread adoption of agriculture during Neolithic time, some 10,000 to 7,500 years ago (Dotterweich 2013 <sup>[[#fn:r2|2]]</sup> ; Butzer 2005 <sup>[[#fn:r3|3]]</sup> ; Dotterweich 2008 <sup>[[#fn:r4|4]]</sup> ) and the associated population increase (Bocquet-Appel 2011 <sup>[[#fn:r5|5]]</sup> ). There are indications that the levels of greenhouse gases (GHGs) – particularly carbon dioxide (CO <sub>2</sub> ) and methane (CH <sub>4</sub> ) – in the atmosphere already started to increase more than 3,000 years ago as a result of expanding agriculture, clearing of forests, and domestication of wild animals (Fuller et al. 2011 <sup>[[#fn:r6|6]]</sup> ; Kaplan et al. 2011 <sup>[[#fn:r7|7]]</sup> ; Vavrus et al. 2018 <sup>[[#fn:r8|8]]</sup> ; Ellis et al. 2013 <sup>[[#fn:r9|9]]</sup> ). While the development of agriculture (cropping and animal husbandry) underpinned the development of civilisations, political institutions and prosperity, farming practices led to conversion of forests and grasslands to farmland, and the heavy reliance on domesticated annual grasses for our food production meant that soils started to deteriorate through seasonal mechanical disturbances (Turner et al. 1990 <sup>[[#fn:r10|10]]</sup> ; Steffen et al. 2005 <sup>[[#fn:r11|11]]</sup> ; Ojima et al. 1994 <sup>[[#fn:r12|12]]</sup> ; Ellis et al. 2013 <sup>[[#fn:r13|13]]</sup> ). More recently, urbanisation has significantly altered ecosystems (Cross-Chapter Box 4 in Chapter 2). Since around 1850, about 35% of human-caused CO <sub>2</sub> emissions to the atmosphere has come from land as a combined effect of land degradation and land-use change (Foley et al. 2005 <sup>[[#fn:r14|14]]</sup> ) and about 38% of the Earth’s land area has been converted to agriculture (Foley et al. 2011 <sup>[[#fn:r15|15]]</sup> ). See Chapter 2 for more details.

Not all human impacts on land result in degradation according to the definition of land degradation used in this report (Section 4.1.3). There are many examples of long-term sustainably managed land around

the world (such as terraced agricultural systems and sustainably managed forests) although degradation and its management are the focus of this chapter. We also acknowledge that human use of land and ecosystems provides essential goods and services for society (Foley et al. 2005 <sup>[[#fn:r16|16]]</sup> ; Millennium Ecosystem Assessment 2005 <sup>[[#fn:r17|17]]</sup> ).

Land degradation was long subject to a polarised scientific debate between disciplines and perspectives in which social scientists often proposed that natural scientists exaggerated land degradation as a global problem (Blaikie and Brookfield 1987 <sup>[[#fn:r18|18]]</sup> ; Forsyth 1996 <sup>[[#fn:r19|19]]</sup> ; Lukas 2014 <sup>[[#fn:r20|20]]</sup> ; Zimmerer 1993 <sup>[[#fn:r21|21]]</sup> ). The elusiveness of the concept in combination with the difficulties of measuring and monitoring land degradation at global and regional scales by extrapolation and aggregation of empirical studies at local scales, such as the Global Assessment of Soil Degradation database (GLASOD) (Sonneveld and Dent 2009 <sup>[[#fn:r22|22]]</sup> ) contributed to conflicting views. The conflicting views were not confined to science only, but also caused tension between the scientific understanding of land degradation and policy (Andersson et al. 2011 <sup>[[#fn:r23|23]]</sup> ; Behnke and Mortimore 2016 <sup>[[#fn:r24|24]]</sup> ; Grainger 2009 <sup>[[#fn:r25|25]]</sup> ; Toulmin and Brock 2016 <sup>[[#fn:r26|26]]</sup> ). Another weakness of many land degradation studies is the exclusion of the views and experiences of the land users, whether farmers or forest-dependent communities (Blaikie and Brookfield 1987 <sup>[[#fn:r27|27]]</sup> ; Fairhead and Scoones 2005 <sup>[[#fn:r28|28]]</sup> ; Warren 2002 <sup>[[#fn:r29|29]]</sup> ; Andersson et al. 2011 <sup>[[#fn:r30|30]]</sup> ). More recently, the polarised views described above have been reconciled under the umbrella of Land Change Science, which has emerged as an interdisciplinary field aimed at examining the dynamics of land cover and land-use as a coupled human-environment system (Turner et al. 2007 <sup>[[#fn:r31|31]]</sup> ). A comprehensive discussion about concepts and different perspectives of land degradation was presented in Chapter 2 of the recent report from the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) on land degradation (Montanarella et al. 2018 <sup>[[#fn:r32|32]]</sup> ).

In summary, agriculture and clearing of land for food and wood products have been the main drivers of land degradation for millennia ( ''high confidence'' ). This does not mean, however, that agriculture and forestry always cause land degradation ( ''high confidence'' ); sustainable management is possible but not always practised ( ''high confidence'' ). Reasons for this are primarily economic, political and social.

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=== 4.1.3 Definition of land degradation ===

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To clarify the scope of this chapter, it is important to start by defining land itself. The Special Report on Climate Change and Land (SRCCL) defines land as ‘the terrestrial portion of the biosphere that comprises the natural resources (soil, near surface air, vegetation and other biota, and water), the ecological processes, topography, and human settlements and infrastructure that operate within that system’ (Henry et al. 2018 <sup>[[#fn:r33|33]]</sup> , adapted from FAO 2007 <sup>[[#fn:r34|34]]</sup> ; UNCCD 1994 <sup>[[#fn:r35|35]]</sup> ).

Land degradation is defined in many different ways within the literature, with differing emphases on biodiversity, ecosystem functions and ecosystem services (e.g., Montanarella et al. 2018 <sup>[[#fn:r36|36]]</sup> ). In this report, land degradation is defined as a ''negative trend in land condition, caused by direct or indirect human-induced processes including anthropogenic climate change, expressed as long-term reduction or loss of at least one of the following: biological productivity, ecological integrity or value to humans.'' This definition applies to forest and non-forest land: forest degradation is land degradation that occurs in forest land. Soil degradation refers to a subset of land degradation processes that directly affect soil.

The SRCCL definition is derived from the IPCC AR5 definition of desertification, which is in turn taken from the United Nations Convention to Combat Desertification (UNCCD): ’Land degradation in arid, semi-arid, and dry sub-humid areas resulting from various factors, including climatic variations and human activities. Land degradation in arid, semi-arid, and dry sub-humid areas is a reduction or loss of the biological or economic productivity and integrity of rainfed cropland, irrigated cropland, or range, pasture, forest, and woodlands resulting from land uses or from a process or combination of processes, including processes arising from human activities and habitation patterns, such as (i) soil erosion caused by wind and/ or water; (ii) deterioration of the physical, chemical, biological, or economic properties of soil; and (iii) long-term loss of natural vegetation’ (UNCCD 1994 <sup>[[#fn:r37|37]]</sup> , Article 1).

For this report, the SRCCL definition is intended to complement the more detailed UNCCD definition above, expanding the scope to all regions, not just drylands, providing an operational definition that emphasises the relationship between land degradation and climate. Through its attention to the three aspects – biological productivity, ecological integrity and value to humans – the SRCCL definition is consistent with the Land Degradation Neutrality (LDN) concept, which aims to maintain or enhance the land-based natural capital, and the ecosystem services that flow from it (Cowie et al. 2018 <sup>[[#fn:r38|38]]</sup> ).

In the SRCCL definition of land degradation, changes in land condition resulting solely from natural processes (such as volcanic eruptions and tsunamis) are not considered land degradation, as these are not direct or indirect human-induced processes. Climate variability exacerbated by human-induced climate change can contribute to land degradation. Value to humans can be expressed in terms of ecosystem services or Nature’s Contributions to People.

The definition recognises the reality presented in the literature that land-use and land management decisions often result in trade-offs between time, space, ecosystem services, and stakeholder groups (e.g., Dallimer and Stringer 2018 <sup>[[#fn:r39|39]]</sup> ). The interpretation of a negative trend in land condition is somewhat subjective, especially where there is a trade-off between ecological integrity and value to humans. The definition also does not consider the magnitude of the negative trend or the possibility that a negative trend in one criterion may be an acceptable trade-off for a positive trend in another criterion. For example, reducing timber yields to safeguard biodiversity by leaving on site more wood that can provide habitat, or vice versa, is a trade-off that needs to be evaluated based on context (i.e. the broader landscape) and society’s priorities. Reduction of biological productivity or ecological integrity or value to humans can constitute degradation, but any one of these changes need not necessarily be considered degradation. Thus, a land-use change that reduces ecological integrity and enhances sustainable food production at a specific location is not necessarily degradation. Different stakeholder groups with different world views value ecosystem services differently. As Warren (2002) <sup>[[#fn:r40|40]]</sup> explained: land degradation is contextual. Further, a decline in biomass carbon stock does not always signify degradation, such as when caused by periodic forest harvest. Even a decline in productivity may not equate to land degradation, such as when a high-intensity agricultural system is converted to a lower-input, more sustainable production system.

In the SRCCL definition, degradation is indicated by a negative trend in land condition during the period of interest, thus the baseline is the land condition at the start of this period. The concept of baseline is theoretically important but often practically difficult to implement for conceptual and methodological reasons (Herrick et al. 2019 <sup>[[#fn:r41|41]]</sup> ; Prince et al. 2018 <sup>[[#fn:r42|42]]</sup> ; also Sections 4.3.1 and 4.4.1). Especially in biomes characterised by seasonal and interannual variability, the baseline values of the indicators to be assessed should be determined by averaging data over a number of years prior to the commencement of the assessment period (Orr et al. 2017 <sup>[[#fn:r43|43]]</sup> ) (Section 4.2.4).

Forest degradation is land degradation in forest remaining forest. In contrast, deforestation refers to the conversion of forest to non-forest that involves a loss of tree cover and a change in land use. Internationally accepted definitions of forest (FAO 2015 <sup>[[#fn:r44|44]]</sup> ; UNFCCC 2006 <sup>[[#fn:r45|45]]</sup> ) include lands where tree cover has been lost temporarily, due to disturbance or harvest, with an expectation of forest regrowth. Such temporary loss of forest cover, therefore, is not deforestation.

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=== 4.1.4 Land degradation in previous IPCC reports ===

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Several previous IPCC assessment reports include brief discussions of land degradation. In AR5 WGIII land degradation is one factor contributing to uncertainties of the mitigation potential of land-based ecosystems, particularly in terms of fluxes of soil carbon (Smith et al. 2014, p. 817). In AR5 WGI, soil carbon was discussed comprehensively but not in the context of land degradation, except forest degradation (Ciais et al. 2013 <sup>[[#fn:r46|46]]</sup> ) and permafrost degradation (Vaughan et al. 2013 <sup>[[#fn:r47|47]]</sup> ). Climate change impacts were discussed comprehensively in AR5 WGII, but land degradation was not prominent. Land-use and land-cover changes were treated comprehensively in terms of effects on the terrestrial carbon stocks and flows (Settele et al. 2015 <sup>[[#fn:r48|48]]</sup> ) but links to land degradation were, to a large extent, missing. Land degradation was discussed in relation to human security as one factor which, in combination with extreme weather events, has been proposed to contribute to human migration (Adger et al. 2014 <sup>[[#fn:r49|49]]</sup> ), an issue discussed more comprehensively in this chapter (Section 4.7.3). Drivers and processes of degradation by which land-based carbon is released to the atmosphere and/or the long-term reduction in the capacity of the land to remove atmospheric carbon and to store this in biomass and soil carbon, have been discussed in the methodological reports of IPCC (IPCC 2006 <sup>[[#fn:r50|50]]</sup> , 2014a <sup>[[#fn:r51|51]]</sup> ) but less so in the assessment reports.

The Special Report on Land Use, Land-Use Change and Forestry (SR-LULUCF) (Watson et al. 2000 <sup>[[#fn:r52|52]]</sup> ) focused on the role of the biosphere in the global cycles of GHG. Land degradation was not addressed in a comprehensive way. Soil erosion was discussed as a process by which soil carbon is lost and the productivity of the land is reduced. Deposition of eroded soil carbon in marine sediments was also mentioned as a possible mechanism for permanent sequestration of terrestrial carbon (Watson et al. 2000, p. 194). The possible impacts of climate change on land productivity and degradation were not discussed comprehensively. Much of the report was about how to account for sources and sinks of terrestrial carbon under the Kyoto Protocol.

The IPCC Special Report on Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation (SREX) (IPCC 2012 <sup>[[#fn:r53|53]]</sup> ) did not provide a definition of land degradation. Nevertheless, it addressed different aspects related to some types of land degradation in the context of weather and climate extreme events. From this perspective, it provided key information on both observed and projected changes in weather and climate (extremes) events that are relevant to extreme impacts on socio-economic systems and on the physical components of the environment, notably on permafrost in mountainous areas and coastal zones for different geographic regions, but few explicit links to land degradation. The report also presented the concept of sustainable land management as an effective risk-reduction tool.

Land degradation has been treated in several previous IPCC reports, but mainly as an aggregated concept associated with GHG emissions, or as an issue that can be addressed through adaptation and mitigation.

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=== 4.1.5 Sustainable land management (SLM) and sustainable forest management (SFM) ===

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Sustainable land management (SLM) is defined as ‘the stewardship and use of land resources, including soils, water, animals and plants, to meet changing human needs, while simultaneously ensuring the long-term productive potential of these resources and the maintenance of their environmental functions’ – adapted from World Overview of Conservation Approaches and Technologies (WOCAT n.d.). Achieving the objective of ensuring that productive potential is maintained in the long term will require implementation of adaptive management and ‘triple loop learning’, that seeks to monitor outcomes, learn from experience and emerging new knowledge, modifying management accordingly (Rist et al. 2013 <sup>[[#fn:r54|54]]</sup> ).

Sustainable Forest Management (SFM) is defined as ‘the stewardship and use of forests and forest lands in a way, and at a rate, that maintains their biodiversity, productivity, regeneration capacity, vitality and their potential to fulfill, now and in the future, relevant ecological, economic and social functions, at local, national, and global levels, and that does not cause damage to other ecosystems’ (Forest Europe 1993 <sup>[[#fn:r55|55]]</sup> ; Mackey et al. 2015 <sup>[[#fn:r56|56]]</sup> ). This SFM definition was developed by the Ministerial Conference on the Protection of Forests in Europe and has since been adopted by the Food and Agriculture Organization. Forest management that fails to meet these sustainability criteria can contribute to land degradation.

Land degradation can be reversed through restoration and rehabilitation. These terms are defined in the Glossary, along with other terms that are used but not explicitly defined in this section of

the report. While the definitions of SLM and SFM are very similar and could be merged, both are included to maintain the subtle differences in the existing definitions. SFM can be considered a subset of SLM – that is, SLM applied to forest land.

Climate change impacts interact with land management to determine sustainable or degraded outcome (Figure 4.1). Climate change can exacerbate many degradation processes (Table 4.1) and introduce novel ones (e.g., permafrost thawing or biome shifts). To avoid, reduce or reverse degradation, land management activities can be selected to mitigate the impact of, and adapt to, climate change. In some cases, climate change impacts may result in increased productivity and carbon stocks, at least in the short term. For example, longer growing seasons due to climate warming can lead to higher forest productivity (Henttonen et al. 2017 <sup>[[#fn:r57|57]]</sup> ; Kauppi et al. 2014 <sup>[[#fn:r58|58]]</sup> ; Dragoni et al. 2011 <sup>[[#fn:r59|59]]</sup> ), but warming alone may not increase productivity where other factors such a water supply are limiting (Hember et al. 2017 <sup>[[#fn:r60|60]]</sup> ).

The types and intensity of human land-use and climate change impacts on lands affect their carbon stocks and their ability to operate as carbon sinks. In managed agricultural lands, degradation can result in reductions of soil organic carbon stocks, which also adversely affects land productivity and carbon sinks (Figure 4.1).

The transition from natural to managed forest landscapes usually results in an initial reduction of landscape-level carbon stocks. The magnitude of this reduction is a function of the differential in frequency of stand-replacing natural disturbances (e.g., wildfires) and harvest disturbances, as well as the age-dependence of these disturbances (Harmon et al. 1990 <sup>[[#fn:r61|61]]</sup> ; Kurz et al. 1998 <sup>[[#fn:r62|62]]</sup> ; Trofymow et al. 2008 <sup>[[#fn:r63|63]]</sup> ).

SFM applied at the landscape scale to existing unmanaged forests can first reduce average forest carbon stocks and subsequently increase the rate at which CO <sub>2</sub> is removed from the atmosphere, because net ecosystem production of forest stands is highest in intermediate stand ages (Kurz et al. 2013 <sup>[[#fn:r64|64]]</sup> ; Volkova et al. 2018 <sup>[[#fn:r65|65]]</sup> ; Tang et al. 2014 <sup>[[#fn:r66|66]]</sup> ). The net impact on the atmosphere depends on the magnitude of the reduction in carbon stocks, the fate of the harvested biomass (i.e. use in short – or long-lived products and for bioenergy, and therefore displacement of emissions associated with GHG-intensive building materials and fossil fuels), and the rate of regrowth. Thus, the impacts of SFM on one indicator (e.g., past reduction in carbon stocks in the forested landscape) can be negative, while those on another indicator (e.g., current forest productivity and rate of CO <sub>2</sub> removal from the atmosphere, avoided fossil fuel emissions) can be positive. Sustainably managed forest landscapes can have a lower biomass carbon density than unmanaged forest, but the younger forests can have a higher growth rate, and therefore contribute stronger carbon sinks than older forests (Trofymow et al. 2008 <sup>[[#fn:r67|67]]</sup> ; Volkova et al. 2018 <sup>[[#fn:r68|68]]</sup> ; Poorter et al. 2016 <sup>[[#fn:r69|69]]</sup> ).

Selective logging and thinning can maintain and enhance forest productivity and achieve co-benefits when conducted with due care for the residual stand and at intensity and frequency that does not exceed the rate of regrowth (Romero and Putz 2018 <sup>[[#fn:r70|70]]</sup> ). In contrast, unsustainable logging practices can lead to stand-level degradation. For example, degradation occurs when selective logging (high-grading) removes valuable large-diameter trees, leaving behind damaged, diseased, non-commercial or otherwise less productive trees, reducing carbon stocks and also adversely affecting subsequent forest recovery (Belair and Ducey 2018 <sup>[[#fn:r71|71]]</sup> ; Nyland 1992 <sup>[[#fn:r72|72]]</sup> ).

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'''Figure 4.1'''

<span id="conceptual-figure-illustrating-that-climate-change-impacts-interact-with-land-management-to-determine-sustainable-or-degraded-outcome.-climate-change-can-exacerbate-many-degradation-processes-table-4.1-and-introduce-novel-ones-e.g.-permafrost-thawing-or-biome-shifts-hence-management-needs-to-respond-to-climate-impacts-in-order-to-avoid-reduce-or-reverse-degradation.-the-types-and"></span>
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'''Conceptual figure illustrating that climate change impacts interact with land management to determine sustainable or degraded outcome. Climate change can exacerbate many degradation processes (Table 4.1) and introduce novel ones (e.g., permafrost thawing or biome shifts), hence management needs to respond to climate impacts in order to avoid, reduce or reverse degradation. The types and […]'''
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[[File:0ad40379a33040f4e40832134c834e4b Figure-4.1-1024x699.jpg]]

Conceptual figure illustrating that climate change impacts interact with land management to determine sustainable or degraded outcome. Climate change can exacerbate many degradation processes (Table 4.1) and introduce novel ones (e.g., permafrost thawing or biome shifts), hence management needs to respond to climate impacts in order to avoid, reduce or reverse degradation. The types and intensity of human land-use and climate change impacts on lands affect their carbon stocks and their ability to operate as carbon sinks. In managed agricultural lands, degradation typically results in reductions of soil organic carbon stocks, which also adversely affects land productivity and carbon sinks. In forest land, reduction in biomass carbon stocks alone is not necessarily an indication of a reduction in carbon sinks. Sustainably managed forest landscapes can have a lower biomass carbon density but the younger forests can have a higher growth rate, and therefore contribute stronger carbon sinks, than older forests. Ranges of carbon sinks in forest and agricultural lands are overlapping. In some cases, climate change impacts may result in increased productivity and carbon stocks, at least in the short term.

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SFM is defined using several criteria (see above) and its implementation will typically involve trade-offs among these criteria. The conversion of primary forests to sustainably managed forest ecosystems increases relevant economic, social and other functions but often with adverse impacts on biodiversity (Barlow et al. 2007 <sup>[[#fn:r73|73]]</sup> ). In regions with infrequent or no stand-replacing natural disturbances, the timber yield per hectare harvested in managed secondary forests is typically lower than the yield per hectare from the first harvest in the primary forest (Romero and Putz 2018 <sup>[[#fn:r74|74]]</sup> ).

The sustainability of timber yield has been achieved in temperate and boreal forests where intensification of management has resulted in increased growing stocks and increased harvest rates in countries where forests had previously been overexploited (Henttonen et al. 2017 <sup>[[#fn:r75|75]]</sup> ; Kauppi et al. 2018 <sup>[[#fn:r76|76]]</sup> ). However, intensification of management to increase forest productivity can be associated with reductions in biodiversity. For example, when increased productivity is achieved by periodic thinning and removal of trees that would otherwise die due to competition, thinning reduces the amount of dead organic matter of snags and coarse woody debris that can provide habitat, and this loss reduces biodiversity (Spence 2001 <sup>[[#fn:r77|77]]</sup> ; Ehnström 2001 <sup>[[#fn:r78|78]]</sup> ) and forest carbon stocks (Russell et al. 2015 <sup>[[#fn:r79|79]]</sup> ; Kurz et al. 2013 <sup>[[#fn:r80|80]]</sup> ). Recognition of adverse biodiversity impacts of high-yield forestry is leading to modified management aimed at increasing habitat availability through, for example, variable retention logging and continuous cover management (Roberts et al. 2016 <sup>[[#fn:r81|81]]</sup> ) and through the re-introduction of fire disturbances in landscapes where fires have been suppressed (Allen et al. 2002 <sup>[[#fn:r82|82]]</sup> ). Biodiversity losses are also observed during the transition from primary to managed forests in tropical regions (Barlow et al. 2007 <sup>[[#fn:r83|83]]</sup> ) where tree species diversity can be very high – for example, in the Amazon region, about 16,000 tree species are estimated to exist (ter Steege et al. 2013 <sup>[[#fn:r84|84]]</sup> ).

Forest certification schemes have been used to document SFM outcomes (Rametsteiner and Simula 2003 <sup>[[#fn:r85|85]]</sup> ) by assessing a set of criteria and indicators (e.g., Lindenmayer et al. 2000 <sup>[[#fn:r86|86]]</sup> ). While many of the certified forests are found in temperate and boreal countries (Rametsteiner and Simula 2003 <sup>[[#fn:r87|87]]</sup> ; MacDicken et al. 2015 <sup>[[#fn:r88|88]]</sup> ), examples from the tropics also show that SFM can improve outcomes. For example, selective logging emits 6% of the tropical GHG annually and improved logging practices can reduce emissions by 44% while maintaining timber production (Ellis et al. 2019 <sup>[[#fn:r89|89]]</sup> ). In the Congo Basin, implementing reduced impact logging (RIL-C) practices can cut emissions in half without reducing the timber yield (Umunay et al. 2019 <sup>[[#fn:r90|90]]</sup> ). SFM adoption depends on the socio-economic and political context, and its improvement depends mainly on better reporting and verification (Siry et al. 2005 <sup>[[#fn:r91|91]]</sup> ).

The successful implementation of SFM requires well-established and functional governance, monitoring, and enforcement mechanisms to eliminate deforestation, illegal logging, arson, and other activities that are inconsistent with SFM principles (Nasi et al. 2011 <sup>[[#fn:r92|92]]</sup> ). Moreover, following human and natural disturbances, forest regrowth must be ensured through reforestation, site rehabilitation activities or natural regeneration. Failure of forests to regrow following disturbances will lead to unsustainable outcomes and long-term reductions in forest area, forest cover, carbon density, forest productivity and land-based carbon sinks (Nasi et al. 2011 <sup>[[#fn:r93|93]]</sup> ).

Achieving all of the criteria of the definitions of SLM and SFM is an aspirational goal that will be made more challenging where climate change impacts, such as biome shifts and increased disturbances, are predicted to adversely affect future biodiversity and contribute to forest degradation (Warren et al. 2018 <sup>[[#fn:r94|94]]</sup> ). Land management to enhance land sinks will involve trade-offs that need to be assessed within their spatial, temporal and societal context.

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=== 4.1.6 The human dimension of land degradation and forest degradation ===

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Studies of land and forest degradation are often biased towards biophysical aspects, both in terms of its processes, such as erosion or nutrient depletion, and its observed physical manifestations, such as gullying or low primary productivity. Land users’ own perceptions and knowledge about land conditions and degradation have often been neglected or ignored by both policymakers and scientists (Reed et al. 2007 <sup>[[#fn:r95|95]]</sup> ; Forsyth 1996 <sup>[[#fn:r96|96]]</sup> ; Andersson et al. 2011 <sup>[[#fn:r97|97]]</sup> ). A growing body of work is nevertheless beginning to focus on land degradation through the lens of local land users (Kessler and Stroosnijder 2006 <sup>[[#fn:r98|98]]</sup> ; Fairhead and Scoones 2005 <sup>[[#fn:r99|99]]</sup> ; Zimmerer 1993 <sup>[[#fn:r100|100]]</sup> ; Stocking et al. 2001 <sup>[[#fn:r101|101]]</sup> ) and the importance of local and indigenous knowledge within land management is starting to be appreciated (Montanarella et al. 2018 <sup>[[#fn:r102|102]]</sup> ). Climate change impacts directly and indirectly on the social reality, the land users, and the ecosystem, and vice versa. Land degradation can also have an impact on climate change (Section 4.6).

The use and management of land is highly gendered and is expected to remain so for the foreseeable future (Kristjanson et al. 2017 <sup>[[#fn:r103|103]]</sup> ). Women often have less formal access to land than men and less influence over decisions about land, even if they carry out many of the land management tasks (Jerneck 2018a <sup>[[#fn:r104|104]]</sup> ; Elmhirst 2011 <sup>[[#fn:r105|105]]</sup> ; Toulmin 2009 <sup>[[#fn:r106|106]]</sup> ; Peters 2004 <sup>[[#fn:r107|107]]</sup> ; Agarwal 1997 <sup>[[#fn:r108|108]]</sup> ; Jerneck 2018b <sup>[[#fn:r109|109]]</sup> ). Many oft-cited general statements about women’s subordination in agriculture are difficult to substantiate, yet it is clear that gender inequality persists (Doss et al. 2015 <sup>[[#fn:r110|110]]</sup> ). Even if women’s access to land is changing formally (Kumar and Quisumbing 2015 <sup>[[#fn:r111|111]]</sup> ), the practical outcome is often limited due to several other factors related to both formal and informal institutional arrangements and values (Lavers 2017 <sup>[[#fn:r112|112]]</sup> ; Kristjanson et al. 2017 <sup>[[#fn:r113|113]]</sup> ; Djurfeldt et al. 2018 <sup>[[#fn:r114|114]]</sup> ). Women are also affected differently than men when it comes to climate change, having lower adaptive capacities due to factors such as prevailing land tenure frameworks, less access to other capital assets and dominant cultural practices (Vincent et al. 2014 <sup>[[#fn:r115|115]]</sup> ; Antwi-Agyei et al. 2015 <sup>[[#fn:r116|116]]</sup> ; Gabrielsson et al. 2013 <sup>[[#fn:r117|117]]</sup> ). This affects the options available to women to respond to both land degradation and climate change. Indeed, access to land and other assets (e.g., education and training) is key in shaping land-use and land management strategies (Liu et al. 2018b <sup>[[#fn:r118|118]]</sup> ; Lambin et al. 2001 <sup>[[#fn:r119|119]]</sup> ). Young people are also often disadvantaged in terms of access to resources and decision-making power, even though they carry out much of the day-to-day work (Wilson et al. 2017 <sup>[[#fn:r120|120]]</sup> ; Kosec et al. 2018 <sup>[[#fn:r121|121]]</sup> ; Naamwintome and Bagson 2013 <sup>[[#fn:r122|122]]</sup> ).

Land rights differ between places and are dependent on the political-economic and legal context (Montanarella et al. 2018 <sup>[[#fn:r123|123]]</sup> ). This means that there is no universally applicable best arrangement. Agriculture in highly erosion-prone regions requires site-specific and long-lasting soil and water conservation measures, such as terraces (Section 4.8.1), which may benefit from secure private land rights (Tarfasa et al. 2018 <sup>[[#fn:r124|124]]</sup> ; Soule et al. 2000 <sup>[[#fn:r125|125]]</sup> ). Pastoral modes of production and community-based forest management systems are often dominated by, and benefit from, communal land tenure arrangements, which may conflict with agricultural/forestry modernisation policies implying private property rights (Antwi-Agyei et al. 2015 <sup>[[#fn:r126|126]]</sup> ; Benjaminsen and Lund 2003 <sup>[[#fn:r127|127]]</sup> ; Itkonen 2016 <sup>[[#fn:r128|128]]</sup> ; Owour et al. 2011 <sup>[[#fn:r129|129]]</sup> ; Gebara 2018 <sup>[[#fn:r130|130]]</sup> ).

Cultural ecosystem services, defined as the non-material benefits people obtain from ecosystems through spiritual enrichment, cognitive development, reflection, recreation and aesthetic experiences (Millennium Ecosystem Assessment 2005 <sup>[[#fn:r131|131]]</sup> ) are closely linked to land and ecosystems, although often under-represented in the literature on ecosystem services (Tengberg et al. 2012 <sup>[[#fn:r132|132]]</sup> ; Hernández-Morcillo et al. 2013 <sup>[[#fn:r133|133]]</sup> ). Climate change interacting with land conditions can impact on cultural aspects, such as sense of place and sense of belonging (Olsson et al. 2014 <sup>[[#fn:r134|134]]</sup> ).

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