Everyone talks about trees when they talk about forest carbon. But the real story is underground.

A new study published in Science by researchers at Lund University and Stanford finds that old-growth forests in Sweden store 72% more carbon per acre than managed forests — even when you give managed forests credit for the carbon locked in harvested wood products like lumber and furniture. Without that generous credit? The gap widens to 83%.

And here’s the kicker: the difference is 2.7 to 8 times larger than official Swedish estimates suggested.

It’s the Soil, Not the Trees

The most important finding isn’t about trees at all. The bulk of the carbon storage difference is in the soil. As Stanford’s Rob Jackson put it: “There is far more carbon in soil than in trees in old-growth boreal forests.”

This makes intuitive sense if you think about it. Old-growth forest soils have had centuries to accumulate organic matter — layers of decomposing leaves, roots, fungi, and microbial biomass building up over hundreds of years. When you log a forest, you don’t just remove the trees. You disturb the soil through road-building, heavy equipment, and the furrow-cutting that prepares land for replanting. That soil disturbance releases carbon that took centuries to accumulate.

Jackson’s assessment is blunt: “Carbon storage capacity lost once furrow-cut and logged can’t easily be recovered.”

The BECCS Problem

This is where it gets uncomfortable for carbon removal. Several CDR pathways — particularly bioenergy with carbon capture and storage (BECCS) — assume that you can harvest biomass from managed forests, burn it for energy, capture the CO₂, and store it underground. The math works because models assume the forests regrow and reabsorb the carbon.

But if managed forests hold dramatically less carbon than the old-growth forests they replaced — especially in the soil — those models may be systematically overestimating the climate benefits of forest-based bioenergy. You can’t just count the carbon in the new trees. You have to count the carbon that isn’t in the soil anymore.

The researchers estimate that restoring Sweden’s managed forests to old-growth conditions could keep approximately 8 billion tonnes of CO₂ out of the atmosphere. For context, that’s roughly 15 years of Sweden’s total emissions.

What This Means for CDR

The implication isn’t “stop doing BECCS.” It’s more nuanced than that:

  1. Protect existing carbon sinks before building new ones. The cheapest tonne of CO₂ avoided is the one you don’t release.
  2. Soil carbon accounting in forestry-based CDR needs an overhaul. If official estimates are off by 3-8x, our models are working with bad inputs.
  3. Boreal forests are not interchangeable. Old-growth and managed forests are fundamentally different carbon systems, and treating them as equivalent in climate models produces misleading results.

The research team’s next step is studying what drives this extraordinary soil carbon storage — which could eventually help design management practices that preserve it. But right now, the data is clear: when it comes to carbon, the most valuable forests are the ones we haven’t touched.

Sometimes the best carbon removal technology is leaving things alone.

Sources: Lund University & Stanford University study, Science (2026); Carbon Herald; Rob Jackson quotes via Stanford University.