Editing IPCC:AR6/WGII/Chapter-2 (section)

==== 2.5.2.3 Risk to Arid Regions ====

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Shifts in arid system structure and functioning that have been observed to date ( [[#2.4.3.3|Section 2.4.3.3]] ) are projected to continue ''(medium confidence)'' . These include widespread woody plant encroachment, notably in savanna systems in Africa, Australia and South America, and are attributed to interactions of LULCC, climate change and CO 2 fertilisation effects ( [[#Fensholt--2012|Fensholt et al., 2012]] ; [[#Fang--2017|Fang et al., 2017]] ; [[#Stevens--2017|Stevens et al., 2017]] ). Arid Mongolian steppe grassland did not respond to experimentally elevated CO 2 ( [[#Song--2019|Song et al., 2019]] ). Woody encroachment is projected to continue or not reverse in North American drylands ( [[#Caracciolo--2016|Caracciolo et al., 2016]] ) and southern African arid ecosystems ( [[#Moncrieff--2014b|Moncrieff et al., 2014b]] ). Dryland woody encroachment may increase carbon stocks, depending on emissions scenario ( [[#Martens--2021|Martens et al., 2021]] ), but reduce soil water and biodiversity of grassland-dependent species diversity ( [[#Archer--2017|Archer et al., 2017]] ). Warm season (C4) grass expansion into arid shrublands risks sudden ecosystem transformation due to introduced wildfire ( [[#Bradley--2016|Bradley et al., 2016]] ), a risk anticipated for grass-invaded desert ecosystems of Australia and the southwestern USA (Horn and St. Clair, 2017). Novel fire regimes in grassy shrublands have enhanced grass cover locally in the southern African Nama-Karoo ( [[#du%20Toit--2015|du Toit et al., 2015]] ).

Range retractions are projected for endemic plants in southern Africa ( [[#Young--2016|Young et al., 2016]] ) and dry woodlands in Morocco ( [[#Alba-Sánchez--2015|Alba-Sánchez et al., 2015]] ). Increasing thermal stress is projected to increase woody plant mortality in the Sonoran Desert ecosystems ( [[#Munson--2016|Munson et al., 2016]] ) and facilitate perennial grass replacement by xeric shrubs in the southwestern USA ( [[#Bestelmeyer--2018|Bestelmeyer et al., 2018]] ). Ecological effects may occur rapidly when extreme events compound long-term trends ( [[#Hoover--2015|Hoover et al., 2015]] ), but evolve more slowly as opportunity costs accumulate due to warming (Cross-Chapter Paper 3) ( [[#Cunningham--2021|Cunningham et al., 2021]] ).

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