Sweden's Old-Growth Forests Hold 83% More Carbon Than Managed Timber Stands

Lund University / Science

The soil beneath an old-growth boreal forest in Sweden holds a secret that took a decade to measure properly. It stores roughly as much carbon as an entire managed forest, trees, dead wood, and soil combined. That single finding upends the arithmetic behind Sweden's climate strategy and raises hard questions about the true cost of industrial forestry across the northern hemisphere.

Ten years of digging, literally

No national map of Sweden's old-growth forests existed when this project began. The research team at Lund University first had to identify and catalog forests that had been minimally disturbed, or not disturbed at all, by human activity. That alone took years. Then came the fieldwork: nearly 220 soil pits dug to a depth of one meter across the country, measuring carbon content at various depths alongside assessments of living trees and dead wood.

The results, published in Science, constitute the most comprehensive carbon inventory of Swedish old-growth forests to date. Primary forests store between 78% and 89% more carbon than managed forests when accounting for living trees, dead wood, and soil down to 60 centimeters.

Where the carbon actually lives

The biggest surprise was underground. Anders Ahlstrom, a researcher at Lund University's Department of Environmental and Earth Sciences, noted that the soil carbon in old-growth forests alone equals the total carbon in managed forests across all compartments. This is not a marginal difference. It is a structural one.

Why does soil matter so much? In boreal forests, decomposition is slow. Dead organic material accumulates over centuries, building deep carbon-rich layers. When forests are logged and replanted, the disruption to these soil systems, through plowing, drainage, and the removal of dead wood, releases carbon that took hundreds of years to store. And the replacement is not equivalent: most harvested wood ends up as short-lived products like paper and bioenergy, where the carbon cycles back into the atmosphere quickly.

Didac Pascual, a researcher on the team, put it plainly: carbon stored in wood products from harvested forests does not compensate even for the difference in dead wood, let alone the larger gaps in living trees and soil.

The scale of what has been lost

The total carbon storage difference between old-growth and managed forests across Sweden is staggering. It corresponds to approximately 211 years of the country's current fossil carbon dioxide emissions. Another way to frame it: roughly 1.5 times all fossil emissions Sweden has produced since 1834.

Previous estimates of this gap were 2.7 to 8 times smaller than what the new data shows. The discrepancy matters because climate models and national carbon accounting frameworks rely on these numbers. If the baseline is wrong, every calculation built on it, including the projected climate benefits of bioenergy and timber products, shifts accordingly.

What old-growth forests reveal about managed ones

Old-growth forests serve as a reference point: they show what Swedish forests would look like without human management. The difference between them and today's managed stands reflects the cumulative effect of land use changes, primarily since the late 1800s, and accelerating sharply after the 1950s when industrial-scale forestry became standard practice.

Ahlstrom emphasized that comparing carbon in old-growth and managed forests is essential because contemporary measurements of carbon uptake, the kind typically used in national inventories, can miss large historical losses. A managed forest might be absorbing carbon right now while still holding far less total carbon than the old-growth forest it replaced. Carbon storage, rather than carbon flux, gives the full picture over time.

The limits of this analysis

This study focused on Sweden, and boreal forests vary significantly across their range in Canada, Russia, Finland, and Alaska. The specific numbers cannot be directly extrapolated to other countries without similar fieldwork. Soil carbon dynamics depend on local climate, tree species, management history, and soil type.

The study also does not track exactly which management practices cause the most damage. Drainage, plowing, prescribed burns, and the loss of beneficial soil fungi may all play roles, but disentangling their individual contributions requires further investigation.

A large portion of annual clear-cutting still targets primary forest

Despite these findings, logging of old-growth forests continues in Sweden. Pascual noted that protecting remaining primary forests and allowing unmanaged forests to recover could deliver substantially greater climate benefits than earlier studies suggested. The implication is clear, if uncomfortable for a country whose economy is deeply tied to its forestry industry: the climate math of converting natural forests into managed plantations needs to be recalculated.