Trees as Carbon Sinks: What Forests Really Store
At the global scale, oceans and terrestrial ecosystems absorb a substantial share of the CO₂ released into the atmosphere. Forests play a major role in this balance: trees take up CO₂ through photosynthesis, while carbon is stored in biomass, dead wood, litter and forest soils.
In this article:
Natural carbon sinks and photosynthesis
A carbon sink is a system that absorbs more carbon than it releases over a given period. Carbon can then remain stored for varying lengths of time in different reservoirs. There are several major natural carbon sinks: oceans on the one hand, and terrestrial ecosystems on the other, where vegetation and soils hold large amounts of carbon. Forests, peatlands and grasslands are particularly important terrestrial stores.
Trees and other plants take up atmospheric carbon dioxide (CO₂) through photosynthesis. In simplified terms, roots absorb water and minerals, while leaves capture light and CO₂. Using solar energy, the plant converts water and carbon dioxide into organic matter such as sugars, releasing oxygen as a by-product.
On land, forest ecosystems — including living trees, dead wood, litter and soils — form one of the major natural carbon sinks, alongside ecosystems such as peatlands and grasslands.
Are some tree species more effective than others?
By absorbing part of the carbon dioxide associated with human activities, forests play an important climatic role. But tree species, stands and ecosystems differ greatly in growth and carbon storage. In particular, there is no universal figure for how much CO₂ “one tree” absorbs each year: uptake varies greatly with species, age, size, climate, soil and growing conditions. This makes simple rankings of “super-absorbing” species misleading.
Native to parts of East and Southeast Asia, the genus Paulownia includes several fast-growing species and is often promoted for its rapid biomass production. Some publications report higher carbon uptake than certain comparison species under favourable conditions, but there is no universal tenfold advantage. Performance depends strongly on site conditions, and rapid growth alone does not make it a universal climate solution. A 2024 study published in Frontiers discusses growing interest in Paulownia for some carbon-sequestration projects and reports performance that may reach roughly twice that of certain comparison species under favourable conditions. Such results still need to be balanced against local adaptation, biodiversity and the ecological implications of planting introduced species rather than focusing only on rapid carbon uptake.
Pines can also store substantial amounts of carbon, but again there is no universal champion: performance depends on climate, soil, stand age, density and management. The ponderosa pine (Pinus ponderosa), for example, forms extensive forests in western North America, but it should not be treated as inherently superior to every other species.
Why forest management matters: the case of France
Recent French National Forest Inventory data show that forest area is still expanding while the carbon sink has weakened significantly. In 2026, forests cover about 17.7 million hectares across mainland France and Corsica. For 2016–2024, the national forest carbon balance is estimated at around 39 million tonnes of CO₂ sequestered per year, compared with about 63 million tonnes per year in 2005–2013. Rising tree mortality, droughts, heatwaves and forest-health crises are among the main reasons for this decline.
This change is a reminder that a forest is not automatically or permanently a carbon sink. As France’s national geographic and forest information institute (IGN) explains in its analyses of the forest carbon balance, some forest areas can even show a negative carbon balance when mortality and removals exceed growth. Forests cannot be infinite carbon sinks. Carbon stocks cannot increase without limit: forest area and biomass per hectare do not expand indefinitely, and climate stress can reverse previous gains.
As France’s National Forest Office (ONF) explains on its website, one priority is to make forests less vulnerable to climate change. This can involve anticipating dieback, favouring suitable and diverse species, and adapting management to changing conditions. Harvested wood products can also continue to store part of the carbon originally captured by trees for a highly variable period — from a few years to several decades depending on the product, its use, recycling and end of life.
Conclusion
Forests play a major role in carbon storage and sequestration, but they are neither infinite sinks nor a substitute for cutting greenhouse-gas emissions. Their ability to remain carbon sinks depends on forest health, resilience, soil conservation, biodiversity and management choices. Planting trees can help, but simply seeking the fastest-growing species is too simplistic: the right tree is first of all one suited to its environment and capable of becoming part of a resilient living ecosystem.
Would you like to discover another side of trees? Experience a guided forest therapy walk in the Pays d’Ancenis, between Nantes and Angers, or join me for a three-hour walk or a five-day forest therapy training programme at the Ranch in Mouzeil. You can also offer a gift card.
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