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Claim check

Do old trees stop absorbing carbon?

Not supported

No good evidence supports this, or the evidence points the other way.

The opposite, at the level of the tree. Repeat measurements of 673,046 trees across 403 species found that for most species, the bigger a tree gets the more mass it adds each year — some of the largest add as much in a year as a mid-sized tree contains.

The claim as it circulates

“Old trees stop taking up carbon, so cutting them down and planting young fast-growing ones is better for the climate.”

Where you may have met it: Forestry and land-management debate; Comment sections and opinion columns about felling mature trees; Carbon offset marketing materials

Taking it apart

What was claimed
That carbon uptake declines to zero as a tree ages, making an old tree a static store at best, and that replacing it with fast-growing young trees increases carbon capture.
What was actually observed
Individually tagged trees in long-term forest plots worldwide were re-measured over years, their mass estimated from diameter, and annual mass gain plotted against size separately for each of 403 species.
What the evidence supports
That absolute carbon accumulation increases continuously with tree size for the large majority of species. Separately, that old forest stands are on average still net carbon sinks, more slowly than young ones, while holding accumulated stocks built over centuries.
What it does not support
That every species accelerates — a minority do slow — and that the individual-tree result settles the stand-level question, which involves mortality and decay as well as growth. It also does not support the reverse claim that young plantations are worthless; they grow fast, and that matters too.

The confusion is between relative and absolute growth, and both statements underneath it are true. A sapling doubles in size in a season and a giant does not come close — that is relative growth, and it does decline. But a large tree adding a thin layer to an enormous circumference is laying down far more wood than a sapling doubling itself, and carbon accounting cares about the quantity, not the proportion. Only one of the two facts is about carbon.

The second half of the popular claim fails for a different reason: it counts the flow and ignores the stock. A mature tree holds carbon accumulated over its entire life, and felling it releases that on a schedule set by what happens to the timber — quickly if it burns or rots, slowly if it becomes a building. A replacement takes decades to centuries to rebuild the same store, and emissions are a problem now.

The whole carbon account

  • Trees and carbon

    Where a tree’s carbon comes from, where it goes, and how long it stays

  • Forests

    Why an old forest and an old plantation are not the same thing

The claims underneath

Each one carries its own evidence, scope and caveats. Expand any of them to reach the studies.

Big old trees do not stop absorbing carbon. Most of them speed up.

Well supported

Good evidence backs this, though some details remain open.

In repeat measurements of 673,046 individually tagged trees across 403 species, absolute above-ground mass increment increased continuously with tree size for the large majority of species, even though relative growth rate declined.

Who this applies to
Individual trees across tropical and temperate forests; a statement about trees, not about stands.
Studied in
Tracheophyta

You may have heard

“Old trees stop absorbing carbon, so it is better to cut them and plant new ones.”

The first half is wrong at the level of the tree and the second half ignores the stock. A large tree adds carbon faster than a small one, and felling it releases centuries of accumulated carbon that a replacement takes centuries to rebuild.

Why we rate it this way, and what the caveats are
Well supportedHigh confidence

A very large, global, repeat-measurement dataset with a clear result analysed within species. The main uncertainty is in the allometric conversion from diameter to mass, which is weakest for the very largest trees.

How far it can be extended

The pattern was tested within each of 403 species separately across both tropical and temperate plots, so it is not an artefact of comparing species.

Caveats

  • Relative growth does slow: a large tree adds a smaller fraction of itself each year. The absolute quantity is what matters for carbon.
  • An individual result does not scale automatically to a forest, where mortality and decay run against growth.
  • A minority of species do slow in absolute terms.

Still unanswered

  • How far the acceleration continues in the very largest trees, where the mass equations are least well tested.

Last reviewed 2026-08-30

The evidence (2 studies)

Old forests are still absorbing carbon, and they are holding centuries of it already.

Well supported

Good evidence backs this, though some details remain open.

Compiled flux measurements from boreal and temperate stands over about 150 years old found net carbon uptake continuing rather than reaching balance, alongside very large accumulated stocks in wood and soil that are released if the stand is disturbed.

Who this applies to
Old boreal and temperate forest stands; tropical old growth is under-represented in the data.
Studied in
Tracheophyta

You may have heard

“An old forest is carbon-neutral, so there is no carbon reason to protect it.”

Even where uptake has slowed, the stock is what matters. An old forest holds centuries of accumulated carbon in wood and soil, and disturbing it returns that carbon on a timescale of years rather than centuries.

Why we rate it this way, and what the caveats are
Well supportedModerate confidence

A substantial compilation with a clear average result, but flux measurements at a limited number of sites are extrapolated widely, and the variation between stands is large.

How far it can be extended

The measurements are concentrated in the northern hemisphere, and stands that are net sources exist within the same dataset.

Caveats

  • The stock is the larger number, and the more consequential one: it took centuries to build and can be released in a season.
  • Averages conceal stands that are net sources, particularly after disturbance.

Still unanswered

  • How tropical old-growth forests behave, where flux measurements remain sparse.

Last reviewed 2026-08-30

The evidence (2 studies)

Go deeper

Trees and carbon

Almost every gram of a tree came out of the air. What the soil supplied is roughly one per cent of it.

Related things people ask

Last reviewed 2026-08-30