Planting a tree is one of the most concrete actions we can take for the climate.
But how much CO₂ does a tree actually absorb? Where does that CO₂ go once it’s “captured”? And what happens when the tree dies or is cut down?
In this article, we’ll explore how photosynthesis works, how CO₂ is stored in trees, what the numbers say (and why they vary so much), and take a critical look at why planting a tree — especially with Treedom — should always be a conscious choice.
We’ll look together at:
How CO₂ absorption works
Where and how CO₂ is stored in a tree: wood, roots, soil
The estimates of absorption — from “a few dozen kilograms” to “several dozen per year” — and why the variability is so high
What factors influence absorption capacity: species, age, climate, soil, maintenance
What happens when a tree dies, is cut, or burns
What this means for mitigation, and what questions remain open
To understand how much a tree can absorb, we need to start with the chemistry and biology behind it. We already have a great article on photosynthesis on our blog — highly recommended!
In breve:
In short:
Through its leaves, the tree absorbs carbon dioxide (CO₂) from the atmosphere and water from the soil.
With sunlight energy, and thanks to chlorophyll pigments, CO₂ is transformed into sugars (carbohydrates) and oxygen (O₂) is released.
Some of these sugars are used by the tree to grow — to build leaves, branches, trunk, and roots — increasing its biomass.
In this process, the carbon (C) from CO₂ becomes “fixed” in the tree’s biomass (wood, roots, leaves) and partly in the soil (roots, organic matter, humus).
Wood is largely made of lignin, cellulose, and other carbon-rich compounds — in other words, trees store carbon as they grow.
However, the net absorption (how much remains stored in the tree or soil) also depends on respiration (the tree’s own CO₂ emissions), decomposition of leaves and branches, and events like death, fire, or logging.
This means a tree isn’t a simple “sponge” that endlessly soaks up CO₂ — it’s a living organism with cycles of growth, decay, and renewal. And its environment — light, water, nutrients, temperature — strongly affects the efficiency of this process.
Once the carbon is fixed, where does it go?
Vegetative biomass: trunk (wood), branches, leaves, living roots. Most carbon is stored in the wood — the largest and most durable part.
Dead roots and soil: dead roots and plant residues (leaves, branches) become part of the soil as humus or organic matter, which can retain carbon for decades or even centuries.
Soil and litter: organic matter enriches the soil, which is a critical carbon reservoir — meaning trees and forests function as an integrated “vegetation + soil” system.
Wood products: if the wood is used (for furniture or construction), carbon remains stored. But if it’s burned or decomposes quickly, the carbon returns to the atmosphere.
To truly contribute to net CO₂ removal, a tree’s biomass must remain stored as long as possible, avoiding rapid carbon release.
Here’s where things get interesting — and confusing — because numbers vary widely.
Arbor Day Foundation (via USDA): a mature tree can absorb “more than 48 pounds (≈ 22 kg) of CO₂ per year.”
EcoTree: average range between 10 and 40 kg of CO₂ per year, depending on species, age, and soil.
The Tree App: examples include an oak tree (~25 kg/year) or a mangrove (~12.3 kg/year).
A recent study also suggests that globally, trees may absorb about 31% more CO₂ than previously estimated — and many African trees aren’t even included in conventional forest maps, meaning global storage is likely underestimated.
Tree species: fast-growing or slow-growing? Dense or light wood? Broadleaf or conifer? Tropical or temperate? Species is the first and most critical variable.
Age and growth stage: young trees grow rapidly and absorb more relative to their size; mature trees grow slower but store significant amounts; older trees absorb less and risk releasing CO₂.
Initial biomass and growth potential: larger trees have higher absorption and storage potential.
Environmental conditions: soil quality, water availability, sunlight, local climate, temperature, stress (pests, drought, fire) — all affect growth. Tropical trees generally absorb more CO₂ thanks to continuous growth and photosynthesis year-round.
Forest density: in dense forests, competition can slow growth; in managed systems, trees may grow more efficiently.
Management and permanence: maintenance, survival, and protection are crucial — a dead or burned tree releases its stored carbon.
Storage duration: not only how much a tree absorbs, but how long the carbon stays stored.
Land use and opportunity cost: land could otherwise be used for farming, grazing, or construction — as the MIT “forest removal supply curve” study points out.
A reasonable average estimate for a healthy tree: 20–25 kg of CO₂ per year, within the 10–40 kg range cited by multiple sources.
Over a 100-year lifetime, that would mean about 2.5 tonnes of CO₂ fixed — assuming the tree survives and remains intact.
This part is often overlooked but critical. When a tree dies — whether naturally, from disease, fire, or cutting — its biomass decomposes or burns, releasing much of its stored carbon back into the atmosphere.
MIT researchers note that models often assume trees “last forever,” which is clearly not true. A forest can even become a net emitter of CO₂ if biomass loss exceeds accumulation (due to deforestation, fires, or pests).
In reforestation or compensation projects, planting isn’t enough: survival, growth, and permanence are key. Wood used in durable products can keep carbon stored longer.
Fires, on the other hand, release massive amounts of CO₂ in very short timeframes — a major immediate and long-term environmental concern.
A tree is good for the planet: it absorbs CO₂, builds biomass, enriches the soil, supports biodiversity, and provides social and environmental benefits.
But we must avoid simplistic slogans like “X trees = zero emissions.” That’s misleading and a form of greenwashing. Trees can help reduce or offset emissions, but only if planted and maintained thoughtfully — the right tree, in the right place, for the right purpose.
Reforestation, afforestation, and agroforestry are powerful tools, but they must be integrated with soil health, management, and longevity. These are all priorities for Treedom in designing sustainable and regenerative agroforestry systems.
The key metric isn’t just annual absorption, but net long-term storage.
And we always emphasize that CO₂ and social impact must go hand in hand. Planting trees that make sense for local communities ensures care, survival, and long life — while enhancing biodiversity and strengthening ecosystems.
A tree is more than wood and leaves: it’s a vital link in the great cycle of life.
When you gift a tree, you’re gifting oxygen, investing in a greener and fairer future — and committing to care, patience, and trust.
Because those CO₂ molecules stored in wood and soil today can stay there tomorrow only if the tree lives, grows, and stays protected.
And then there’s the beauty of quiet growth — a branch, a leaf, an organism that breathes, stores sunlight and sap, and connects with the soil through its roots.
A single tree won’t cancel our emissions, but it takes part in the great breath of the planet.
Gift it. Protect it. Remember it.