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

===== 2.4.4.4.2 Observed stocks in high-carbon terrestrial ecosystems =====

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The ecosystem that attains the highest above-ground carbon density in the world is the coast redwood ( ''Sequoia sempervirens'' ) forest in California, USA, with 2600 ± 100 tonnes ha -1 carbon ( [[#Van%20Pelt--2016|Van Pelt et al., 2016]] ). The ecosystem with the second highest documented carbon density in the world is the mountain ash ( ''Eucalyptus regnans'' ) forest in Victoria, Australia, with ~1900 tonnes ha -1 ( [[#Keith--2009|Keith et al., 2009]] ). In the Tropics, tropical evergreen broadleaf forests (rainforests) in the Amazon, the Congo and Indonesia attain the highest carbon densities, reaching a maximum of 230 tonnes ha -1 in the Amazon ( [[#Mitchard--2014|Mitchard et al., 2014]] ) and the Congo ( [[#Xu--2017|Xu et al., 2017]] ). Temperature increases reduce the tropical rainforest above-ground carbon density 9.1 tonnes ha -1 per degree Celsius, through reduced growth and increased tree mortality ( [[#Sullivan--2020|Sullivan et al., 2020]] ).

Tropical forests contain the largest vegetation carbon stocks in the world, with 180–250 GtC above and below ground ( [[#Saatchi--2011|Saatchi et al., 2011]] ; [[#Baccini--2012|Baccini et al., 2012]] ; [[#Avitabile--2016|Avitabile et al., 2016]] ). The Amazon contains a stock of 45–60 GtC ( [[#Baccini--2012|Baccini et al., 2012]] ; [[#Mitchard--2014|Mitchard et al., 2014]] ; [[#Englund--2017|Englund et al., 2017]] ).

Ecosystems with high soil carbon densities include the peat bogs in Ireland with up to 3000 tonnes ha -1 ( [[#Tomlinson--2005|Tomlinson, 2005]] ), the Cuvette Centrale swamp forest peatlands in Congo with an average of ~2200 tonnes ha -1 ( [[#Dargie--2017|Dargie et al., 2017]] ), the Arctic tundra with an average of ~900 tonnes ha -1 ( [[#Tarnocai--2009|Tarnocai et al., 2009]] ) and the mangrove peatlands in Kalimantan, Indonesia, with an average of 850 ± 320 tonnes ha -1 ( [[#Murdiyarso--2015|Murdiyarso et al., 2015]] ). Arctic permafrost contains 1400 ± 200 GtC to a depth of 3 m, the largest soil carbon stock in the world ( [[#Hugelius--2014|Hugelius et al., 2014]] ). Globally, peatlands contain 470–620 GtC ( [[#Page--2011|Page et al., 2011]] ; [[#Hodgkins--2018|Hodgkins et al., 2018]] ), of which boreal and temperate peatlands contain 415 ± 150 GtC ( [[#Hugelius--2020|Hugelius et al., 2020]] ) and tropical peatlands contain 80–350 GtC ( [[#Page--2011|Page et al., 2011]] ; [[#Dargie--2017|Dargie et al., 2017]] ; [[#Gumbricht--2017|Gumbricht et al., 2017]] ; [[#Ribeiro--2021|Ribeiro et al., 2021]] ). Other analyses increase the upper estimates for boreal and temperate peatlands to 800–1200 GtC ( [[#Nichols--2019|Nichols and Peteet, 2019]] ; [[#Mishra--2021b|Mishra et al., 2021b]] ).

Tropical forests and Arctic permafrost contain the highest ecosystem carbon stocks in above-ground vegetation and soil, respectively, in the world ( ''robust evidence'' , ''high agreement'' ). These ecosystems form natural sinks that prevent the emission to the atmosphere of 1400–1800 GtC that would otherwise increase the magnitude of climate change ( ''high confidence'' ).

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