Editing IPCC:AR6/WGII/Cross-Chapter-Paper-3 (section)

==== CCP3.2.1.5 Tree Death and Woody Cover Decline ====

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Field measurements have also detected tree mortality and loss of mesic tree species at some Sahel sites during drought periods ( [[#Gonzalez--2012|Gonzalez et al., 2012]] ; [[#Kusserow--2017|Kusserow, 2017]] ; [[#Brandt--2018|Brandt et al., 2018]] ; [[#Ibrahim--2018|Ibrahim et al., 2018]] ; [[#Trichon--2018|Trichon et al., 2018]] ; [[#Zwarts--2018|Zwarts et al., 2018]] ; [[#Bernardino--2020|Bernardino et al., 2020]] ; [[#Zida--2020|Zida et al., 2020]] ) and a reduction of mesic species in favour of drought-tolerant species ( ''high confidence'' ) ( [[#Hänke--2016|Hänke et al., 2016]] ; [[#Kusserow--2017|Kusserow, 2017]] ; [[#Ibrahim--2018|Ibrahim et al., 2018]] ; [[#Trichon--2018|Trichon et al., 2018]] ; [[#Dendoncker--2020|Dendoncker et al., 2020]] ; [[#Zida--2020|Zida et al., 2020]] b), with attribution to climate change ( [[#Gonzalez--2012|Gonzalez et al., 2012]] ). Furthermore, vegetation productivity per unit of rainfall showed a net decline of 4% in the period 2000–2015 across drylands globally, with the greatest net declines in Africa (16%) and Asia (33%) ( [[#Abel--2021|Abel et al., 2021]] ), but with location-specific increases in vegetation-rainfall sensitivity, for example, in southern and eastern Africa and parts of the Sahel. Furthermore, NDVI declines were reported across the Sahel from 1999 to 2015 ( [[#Yuan--2019|Yuan et al., 2019]] ; [[#Zida--2020a|Zida et al., 2020a]] ). However, field site monitoring showed a strong regeneration of the decimated woody populations except on shallow soil where the runoff system had evolved towards a web of gullies ( [[#Hiernaux--2009a|Hiernaux et al., 2009a]] ; [[#Trichon--2018|Trichon et al., 2018]] ; [[#Wendling--2019|Wendling et al., 2019]] ) .

Other site-specific impacts include tree mortality in southwestern Morocco ( [[#Le%20Polain%20de%20Waroux--2012|Le Polain de Waroux and Lambin, 2012]] ), mortality of ''Austrocedrus'' and ''Nothofagus'' forests in the dry Patagonia forest-steppe ( [[#Rodríguez-Catón--2019|Rodríguez-Catón et al., 2019]] ) and a tree range contraction of ''Aloidendron dichotmum'' in southern Africa ( [[#Foden--2007b|Foden et al., 2007b]] ). In Morocco, tree mortality was most highly correlated to an increase in aridity, measured by the Palmer Drought Severity Index (PDSI), which showed a statistically significant increase since 1900 due to climate change ( [[#Dai--2004|Dai et al., 2004]] ; [[#Esper--2007|Esper et al., 2007]] ; [[#Dai--2011|Dai, 2011]] ).

In deserts of the southwestern USA, a drought since 2000, mainly due to climate change ( [[#Williams--2020|Williams et al., 2020]] ), together with land use change, invasive plant species and wildfire ( [[#Syphard--2017|Syphard et al., 2017]] ), has led to reductions in native desert plant species ( [[#Defalco--2010|Defalco et al., 2010]] ; [[#Conver--2017|Conver et al., 2017]] ) and perennial vegetation cover ( [[#Munson--2016a|Munson et al., 2016a]] ; 2016b). An increase in invasive exotic grasses has increased wildfires in these desert ecosystems in which fire had been rare ( [[#Brooks--2006|Brooks and Matchett, 2006]] ; [[#Abatzoglou--2011|Abatzoglou and Kolden, 2011]] ; [[#Hegeman--2014|Hegeman et al., 2014]] ; Horn and St. Clair, 2017). In the Mojave Desert in the USA, a loss of bird biodiversity has also been detected and attributed to increased aridity caused by climate change ( [[#Iknayan--2018|Iknayan and Beissinger, 2018]] ; [[#Riddell--2019|Riddell et al., 2019]] ).

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