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

=== 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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'''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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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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