You planted a forest to fight carbon.
Ten years on — is it a sink, or a source?
Everyone "knows" a forest soaks up carbon. So a young, growing forest must be pulling carbon down hard, right? Commit to an answer before you see the data — that’s the honest way to meet a finding.
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A 10-year-old planted forest in the Pacific Northwest. Trees up to your shoulder, gaps of bare ground still showing between them. Across a whole year, is it a…
Why this is worth a second look. Photosynthesis is only half the ledger. The other half is respiration — the trees burning sugar to live, plus the soil breathing out CO₂ as worms, ants, and microbes break down litter and roots. In a young stand, that respiration can beat photosynthesis for years — until the canopy fills in. As seen on Nova’s “Secrets of the Forest” (PBS) and PBS Terra’s Weathered, with Oregon State’s forest-carbon team.
It bit a famous study, too. In 2019 Tom Crowther’s lab published a global tree-restoration map (Bastin et al., Science) that the world read as “planting trees will fix climate change.” Crowther spent years correcting that: the carbon would take centuries, the potential was overstated, you must not convert grasslands to forest, and none of it replaces cutting emissions or protecting the old forests we already have. Same lesson as the ledger — a tree is a slow, conditional promise, not a receipt.
Scrub the years. Watch it flip.
Green is what photosynthesis pulls down. Orange is what the whole forest breathes out (trees + soil). When orange is on top, the forest is a net source. When green wins, it’s a sink. The flip happens around canopy closure.
Teaching model, not a flux simulator. The curves are tuned to the published shape — young stands run as a net source, crossing to a sink near canopy closure (~20–30 yr in real Pacific-NW conifer stands) — not solved from your plot. Real numbers come from eddy-covariance towers (AmeriFlux). See About & Sources.
Above ground breathes. Underground keeps the books.
That orange "release" line isn’t mostly the trees — a big share is the soil breathing out as decomposers eat dead leaves and roots. But the very same crew also builds the bank: worms and ants mix the soil and lock carbon into stable crumbs (aggregates) that can hold it for decades. Same animals, two opposite jobs — and which one wins depends on one thing.
Pull the thread