No, Old Trees Don't Stop Locking Away Carbon — They Actually Store More Than Young Ones
“Carbon absorbed by trees after growth stops tends to flow toward shorter-lived uses such as foliage and internal metabolic processes rather than being locked into wood for decades or centuries”
The argument in brief
The claim says that once trees stop growing tall, absorbed carbon shifts toward short-lived uses like leaves and metabolism rather than being stored in wood for centuries. This is mostly false. Research by Stephenson et al. in Nature found that large, old trees add more wood mass per year than younger trees of the same species — meaning they lock away more carbon, not less.
Data: Stephenson et al., Nature 2014
Why it spread
The claim feels logical because we naturally map tree growth onto a human lifecycle — young and vigorous, then slowing down with age. It also has clear ideological utility: the forestry and timber industries have used versions of this argument to justify logging old-growth forests, giving it a well-funded platform and repeated exposure in policy circles.
The claim argues that mature trees become carbon-storage dead ends: once height growth slows, carbon supposedly flows into leaves and metabolic upkeep rather than being locked into wood for decades or centuries. It sounds plausible, but the evidence says otherwise.
The most direct rebuttal comes from Stephenson et al. (2014) in Nature, who measured trees across the globe and found that the biggest, oldest trees gain the most wood carbon per year — sometimes by a wide margin. A very large tropical tree stores roughly 100 kg of carbon in new wood annually, compared to just over 1 kg for a small tree. The idea that old trees quietly stop banking carbon in wood simply does not hold up.
Luyssaert et al. (2008), also in Nature, confirmed that old-growth forests — trees well past their rapid height-growth phase — remain net carbon sinks, pulling in more carbon than they release and storing it in wood and soil. The IPCC's Sixth Assessment Report echoes this, recognizing mature forests as long-term carbon stores.
There is a kernel of truth here worth acknowledging. Ryan et al. (1997) and Gower et al. (1996) both show that maintenance respiration does rise in older trees, and net primary productivity can dip in aging stands. Körner (2003) notes that carbon allocation in mature trees is genuinely complex. So yes, a slightly larger share of photosynthesis goes to keeping the tree running. But this does not mean carbon stops going into wood — it just means the tree is doing more with what it takes in.
This misinformation matters because it has been used in policy debates to argue that old forests should be logged and replaced with fast-growing young trees. That argument gets the science backwards. Cutting an old forest releases centuries of stored carbon immediately, while a young plantation takes decades to recapture even a fraction of it.
Watch for claims that use lifecycle analogies — 'old trees are like old people, slowing down' — to make this argument feel intuitive. The analogy is catchy but misleading. When it comes to carbon storage, bigger and older usually means better.
Sources
- Körner (2003) - Carbon limitation in trees, Nature
Mature trees continue to allocate substantial carbon to wood increment even after height growth slows; carbon allocation to wood is not simply redirected to short-lived pools when height growth ceases.
- Stephenson et al. (2014) - Rate of tree carbon accumulation increases continuously with tree size, Nature
Large, old trees actually accumulate more carbon in wood per year than younger trees of the same species, directly contradicting the claim that carbon shifts away from wood as trees mature.
- Luyssaert et al. (2008) - Old-growth forests as global carbon sinks, Nature
Old-growth forests (trees well past rapid height growth) remain net carbon sinks, sequestering carbon in wood and soil, refuting the idea that mature trees stop locking carbon into long-lived pools.
- Ryan et al. (1997) - Hydraulic limits to tree height and tree growth, BioScience
While respiration costs do increase in older trees and some carbon is diverted to maintenance, wood production continues and remains a dominant carbon sink in mature trees.
- IPCC AR6 Working Group I (2021) - Carbon cycle chapter
Forests, including mature stands, are recognized as long-term carbon stores; the IPCC does not support the characterization that mature tree carbon flows predominantly to short-lived metabolic pools.
- Gower et al. (1996) - Aboveground net primary production decline with stand age, Trends in Ecology & Evolution
Net primary productivity does decline in older stands partly due to increased respiration, lending partial support to the claim, but wood carbon storage continues and does not simply redirect to foliage or metabolism.