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

==== 7.2.2.5 Vegetation degradation ====

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There are clear links between climate change and vegetation cover changes, tree mortality, forest diseases, insect outbreaks, forest fires, forest productivity and net ecosystem biome production (Allen et al. 2010 <sup>[[#fn:r115|115]]</sup> ; Bentz et al. 2010 <sup>[[#fn:r116|116]]</sup> ; Anderegg et al. 2013 <sup>[[#fn:r117|117]]</sup> ; Hember et al. 2017 <sup>[[#fn:r118|118]]</sup> ; Song et al. 2018 <sup>[[#fn:r119|119]]</sup> ; Sturrock et al. 2011 <sup>[[#fn:r120|120]]</sup> ). Forest dieback, often a result of drought and temperature changes, not only produces risks to forest ecosystems but also to people with livelihoods dependent on forests. A 50-year study of temperate forest, dominated by beech ( ''Fagus sylvatica'' L.), documented a 33% decline in basal area and a 70% decline in juvenile tree species, possibly as a result of interacting pressures of drought, overgrazing and pathogens (Martin et al. 2015 <sup>[[#fn:r121|121]]</sup> ). There is ''high confidence'' that such dieback impacts ecosystem properties and services including soil microbial community structure (Gazol et al. 2018 <sup>[[#fn:r122|122]]</sup> ). Forest managers and users have reported negative emotional impacts from forest dieback such as pessimism about losses, hopelessness and fear (Oakes et al. 2016 <sup>[[#fn:r123|123]]</sup> ). Practices and policies such as forest classification systems, projection of growth, yield and models for timber supply are already being affected by climate change (Sturrock et al. 2011 <sup>[[#fn:r124|124]]</sup> ).

While risks to ecosystems and livelihoods from vegetation degradation are already detectable at current levels of GMT increase, risks are expected to reach ''high'' levels between 1.6°C and 2.6°C ( ''medium confidence'' ). Significant uncertainty exists due to countervailing factors: CO <sub>2</sub> fertilisation encourages forest expansion but increased drought, insect outbreaks, and fires result in dieback (Bonan 2008 <sup>[[#fn:r125|125]]</sup> ; Lindner et al. 2010 <sup>[[#fn:r126|126]]</sup> ). The combined effects of temperature and precipitation change, with CO <sub>2</sub> fertilisation, make future risks to forests very location specific. It is challenging therefore to make global estimates. However, even locally specific studies make clear that ''very high'' risks occur between 2.6°C and 4°C ( ''medium confidence'' ). Australian tropical rainforests experience significant loss of biodiversity with 3.5°C increase. At this level of increase there are no areas with greater than 30 species, and all endemics disappear from low- and mid-elevation regions (Williams et al. 2003 <sup>[[#fn:r127|127]]</sup> ). Mountain ecosystems are particularly vulnerable (Loarie et al. 2009 <sup>[[#fn:r128|128]]</sup> ).

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