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

==== 2.4.3.7 Observed Changes in Boreal and Temperate Forests ====

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The AR5 found increased tree mortality, wildfire and plant phenology changes in boreal and temperate forests ( [[#Settele--2014|Settele et al., 2014]] ). Expanding on these conclusions, this assessment, using analyses of causal factors, attributes the following observed changes in boreal and temperate forests in the 20th and 21st centuries to anthropogenic climate change: upslope and poleward biome shifts at sites in Asia, Europe and North America ( [[#2.4.3.2.1|Section 2.4.3.2.1]] ); range shifts of plants ( [[#2.4.2.1|Section 2.4.2.1]] ); earlier blooming and leafing of plants ( [[#2.4.2.4|Section 2.4.2.4]] ); poleward shifts in tree-feeding insects ( [[#2.4.2.1|Section 2.4.2.1]] ); increases in insect pest outbreaks ( [[#2.4.4.3.3|Section 2.4.4.3.3]] ); increases in the area burned by wildfire in western North America ( [[#2.4.4.2.1|Section 2.4.4.2.1]] ); increased drought-induced tree mortality in western North America ( [[#2.4.4.3.1|Section 2.4.4.3.1]] ); and thawing of the permafrost that underlies extensive areas of boreal forest ( [[#2.4.3.9|Section 2.4.3.9]] )( [[#2.3|Section 2.3.2.5]] in ( [[#Gulev--2021|Gulev et al., 2021]] )). Atmospheric CO 2 from anthropogenic sources has also increased net primary productivity (NPP) ( [[#2.4.4.5.1|Section 2.4.4.5.1]] ). In summary, anthropogenic climate change has caused substantial changes in temperate and boreal forest ecosystems, including biome shifts and increases in wildfire, insect pest outbreaks and tree mortality, at a global mean surface temperature (GMST) increase of 0.9°C above the pre-industrial period ( ''robust evidence'' , ''high agreement'' ).

Other changes detected in boreal forests and consistent with, but not formally attributed to, climate change, include increased wildfire in Siberia ( [[#2.4.4.2.3|Section 2.4.4.2.3]] ), long-lasting smouldering below-ground fires in Canada and the USA ( [[#Scholten--2021|Scholten et al., 2021]] ), tree mortality in Europe ( [[#2.4.4.3.3|Section 2.4.4.3.3]] ) and post-fire shifts of boreal conifer to deciduous broadleaf tree species in Alaska ( [[#Mack--2021|Mack et al., 2021]] ). From 1930 to 1960, boreal forest growth became limited more by precipitation than temperature in the Northern Hemisphere ( [[#Babst--2019|Babst et al., 2019]] ).

For some vegetation, changes in land use and management have exerted more influence than climate change. These include upslope and poleward forest shifts in Europe following the abandonment of timber harvesting or livestock grazing ( [[#2.4.3.2.2|Section 2.4.3.2.2]] ), changes in wildfire in Europe affected by fire suppression, fire prevention and agricultural abandonment ( [[#2.4.4.2.3|Section 2.4.4.2.3]] ), and forest species composition changes in Scotland due to nitrogen deposition from air pollution ( [[#Hester--2019|Hester et al., 2019]] ). Remote sensing suggests that the area of temperate and boreal forests increased in Asia and Europe between 1982 and 2016 ( [[#Song--2018|Song et al., 2018]] ) and in Canada between 1984 and 2015 ( [[#Guindon--2018|Guindon et al., 2018]] ), but forest plantations and regrowth are probable drivers ( [[#Song--2018|Song et al., 2018]] ).

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