The AR5 found increased tree mortality, wildfire and plant phenology changes in boreal and temperate forests . 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 ; range shifts of plants ; earlier blooming and leafing of plants ; poleward shifts in tree-feeding insects ; increases in insect pest outbreaks ; increases in the area burned by wildfire in western North America ; increased drought-induced tree mortality in western North America ; and thawing of the permafrost that underlies extensive areas of boreal forest ). Atmospheric CO2 from anthropogenic sources has also increased net primary productivity  . 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,
IPCC
Climate Change 2022: Impacts, Adaptation and Vulnerability
IPCC Report