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

==== 2.5.2.7 Risks to Boreal and Temperate Forests ====

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As in the Arctic, warming substantially exceeding the global average has already been observed in the northern parts of the temperate and boreal forest zone ( [[#Gauthier--2015|Gauthier et al., 2015]] ), and is projected to continue (see [https://www.ipcc.ch/chapter/cross-chapter-paper-6 Cross-Chapter Paper 6] and ( [[#Lee--2021|Lee et al., 2021]] )). As a consequence, boreal tree species are expected to move northwards (or in mountainous regions, upwards) into regions dominated by tundra, unless constrained by edaphic features, and temperate species are projected to grow in regions currently occupied by southern boreal forest ( ''high confidence'' ). In both biomes, deciduous trees are simulated to grow increasingly in regions currently dominated by conifers ( [[#Wårlind--2014|Wårlind et al., 2014]] ; [[#Boulanger--2017|Boulanger et al., 2017]] ). These simulation results have been supported by observational examples. In eastern Siberia, fire disturbance of larch-dominated forest was followed by recovery to birch-dominated forest ( [[#Stuenzi--2020|Stuenzi and Schaepman-Strub, 2020]] ). In Alberta, lodgepole pine ( ''Pinus contorta'' ) lost its dominant status after attacks by mountain pine beetles ( ''Dendroctonus ponderosae'' ) caused the canopy to switch to non-pine conifers and broadleaf trees ( [[#Axelson--2018|Axelson et al., 2018]] ). In contrast to the examples above, some boreal forests have proven resilient to disturbances including recent unprecedented insect outbreaks ( [[#Campbell--2019a|Campbell et al., 2019a]] ; [[#Prendin--2020|Prendin et al., 2020]] ).

Reforestation, either natural or anthropogenic, leads to summer cooling and winter warming of the ground, while forest thinning or removal by fire has reverse effects, deepening the upper layer that is free of permafrost ( [[#Stuenzi--2021a|Stuenzi et al., 2021a]] ). Interactions between permafrost and vegetation are important. For example, trees in the east Siberian taiga obtained water mostly from rain in wet summers and permafrost melt water in dry summers ( [[#Sugimoto--2002|Sugimoto et al., 2002]] ), suggesting that these forests will be particularly vulnerable to the combination of drought with the retraction of permafrost further underground due to climate warming.

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