Old-growth forests store a lot more carbon than managed forests

Peer-Reviewed Publication

Lund University

News Release 19-Mar-2026

Swedish old-growth forests store 83 percent more carbon than managed forests, according to a new study from Lund University. The difference is substantially larger than previous estimates and is mainly due to large carbon stocks in the soil.

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The study, published in the scientific journal Science, is the most comprehensive mapping of how much carbon is stored in Swedish old-growth forests to date. The results show that old-growth forests store 78–89 per cent more carbon than managed forests in living trees, dead wood, and in the soil down to a depth of 60 centimetres.

“The most surprising result is the large amounts of carbon stored in the soil of old-growth forests. It is the same amount as all the carbon in managed forests - trees, dead wood, and soil, combined,” says Anders Ahlström, researcher at the Department of Environmental and Earth Sciences at Lund University.

The work behind the study took nearly ten years. Because there was no national map of old-growth forests, the researchers first had to identify and map forests that had been very little affected, or not affected at all, by direct human activity. Extensive fieldwork was then carried out across the country, including nearly 220 soil pits dug to a depth of one meter to measure carbon storage in the soil.

The total difference in carbon storage between old-growth forests and managed forests -including carbon stored in wood products - is about 3 to 8 times greater than previous estimates. This difference corresponds to approximately 211 years of Sweden’s current fossil carbon dioxide emissions, or about 1.5 times all fossil emissions since 1834.

“Carbon stored in wood products from harvested forests is relatively small and does not even compensate for the difference in dead wood, let alone the differences in living trees and soil. This is because most products are short-lived, such as paper and bioenergy, where the carbon quickly returns to the atmosphere,” says Didac Pascual, researcher at the Department of Environmental and Earth Sciences.

Old-growth forests serve as a reference for what Swedish forests would look like without forest management and land use. The difference in carbon storage between old-growth forests and today’s managed forests reflects the combined effect of direct human land use, all carbon gains and losses—primarily since the late 1800s, and especially since the 1950s when today’s large-scale forest management was established.

“Comparing carbon storage in old-growth and managed forests is crucial, because contemporary measurements of carbon uptake can miss large historical carbon losses. Carbon storage shows the full picture over time. Old-growth forests serve as a reference for understanding how forest management affects ecosystems and the carbon balance,” says Anders Ahlström.

The results are relevant to discussions about the role of forests in the climate transition. The large differences in carbon storage implies that converting natural forests into managed forests leads to much greater losses of carbon or potential carbon uptake than previously estimated. This affects calculations of the climate benefits of forest products such as bioenergy and building materials.

“Converting old-growth forests reduces the landscape’s carbon storage more than previously believed. Protecting remaining old-growth forests and allowing unmanaged forests to recover could provide substantially greater climate benefits than earlier studies have shown. A large portion of the clear-cutting that occurs each year takes place in old-growth forests,” concludes Didac Pascual.

A ‘shocking’ carbon discovery in Sweden’s forests

A new study finds old-growth forests in Sweden store far more carbon than the industrial tree plantations that are rapidly replacing them, with soil accounting for most of the difference.

Peer-Reviewed Publication

Stanford University

News Release 19-Mar-2026

The world’s northern forests act as massive carbon vaults, locking away greenhouse gases in spruce, pines, and needle-covered soils. But industrial logging is quickly eroding their ability to mitigate climate change, according to a major new study led by scientists at Lund University and Stanford University. The biggest losses are happening in soils beneath the forest floor. 

Working in Sweden, researchers mapped old-growth forests across the country and then measured carbon at more than 200 forest plots over the course of three years. They then combined the field data with decades of national forest and soil carbon inventory data and statistical models. The result is a first-of-its-kind analysis quantifying carbon in vegetation, dead wood, soil, and harvested timber. 

Their findings, published March 19 in Science, reveal a stark gap. Undisturbed primary forests store 72% more carbon per acre than the managed forests that are replacing them, typically with single-species plantations. That figure gives managed forests credit for all the carbon stored in goods made from harvested wood, including bioenergy, paper, and building materials. Excluding harvested wood products, primary forests store 83% more carbon per acre.

The difference is 2.7 to 8 times larger than current official estimates. To put that in perspective, restoring carbon storage in Sweden’s managed forests to the level maintained by primary forests would mean keeping nearly 8 billion tons of carbon dioxide out of the atmosphere. That’s equivalent to Sweden’s cumulative emissions from burning fossil fuels over the last two centuries and hundreds of times larger than the country’s current annual fossil CO2 emissions. 

Boreal forests under threat

The researchers were surprised to find the biggest difference lies in the soil. “There’s far more carbon in the soil than in the trees in these old-growth boreal forests,” said Rob Jackson, a senior author of the study and professor of Earth system science at the Stanford Doerr School of Sustainability. The carbon storage capacity that an old-growth forest loses once it’s been heavily furrow-cut and logged can’t easily be recovered, he said. “The loss of soil carbon through industrial management is persistent and shocking.”

In lowland primary forests, the researchers found the top meter of soils contained roughly 64% of total carbon in an average plot, compared to about 30% in live trees and 6% in dead wood. 

Previous research has shown that between 2003 and 2019, Sweden lost unprotected old-growth forests to clear-cutting at a rate of 1.4% per year, or six times the current rate of loss of primary forests in the Brazilian Amazon. 

Similarly rapid loss of primary forests may be widespread across the planet’s boreal regions, but it is often harder to track than tropical deforestation. While satellite sensors can easily distinguish oil palm plantations from primary rainforest, native spruce, pine, and birch dominate both old-growth and managed stands in the north, making them appear similar from space. 

“Unfortunately, the logging of primary forests in Sweden continues,” said study author Anders Ahlström, who spearheaded work on the research over the past eight years – first as a postdoctoral scholar in Jackson’s lab at Stanford and then as a senior lecturer at Lund University in Sweden. “Our results show that protecting the few primary forests that remain has a much larger potential to slow climate change than previously thought. Restoring sites degraded by industrial forestry could also boost biodiversity and store even more carbon.”

Overlooked value of old-growth forests

Around the world, nations are counting on forests to help them meet climate commitments. Most models used to construct pathways that stabilize global temperatures assume increased use of northern forests, especially for bioenergy production. 

But if managed forests and plantations store less than half as much carbon as the old-growth boreal forests they replace, as the new study suggests, those projections may overestimate climate benefits from forest-derived biofuels, especially if slowly growing boreal forests take centuries to accrue those benefits. They may also miss the value of protecting old-growth forests or improving forest management. 

“Some of the changes we found are intuitive – that the primary forests have larger trees and hold more dead wood. But we weren’t sure what to expect from the soils,” said lead study author Didac Pascual, a postdoctoral scholar at Lund University. “We learned that primary forests stored more carbon in their soil alone than managed forests do in trees, dead wood, and soils combined.”

Understanding what drives carbon storage

Major questions remain, including how much specific forest management practices may contribute to carbon storage capacity. Drainage ditches, plowing, and prescribed burns may all play a role, as could the loss of beneficial fungi in soil that can help trees take up nutrients. The researchers will need those answers before extrapolating the results from Sweden to other boreal regions across Canada, Russia, and Alaska.

Based on the results published in Science, Jackson and Ahlström are now working with Stanford biologist Kabir Peay to understand what drives carbon storage in old-growth forest relics in Sweden and across Scandinavia. One possibility is that old-growth forests harbor a greater variety of microbes in tree roots and soil. The team wants to know whether microbe-driven mechanisms could be transplanted elsewhere. 

“Our goal is to understand what makes the fungi and bacteria in these old-growth forests unique,” Peay said. This knowledge could potentially then pave the way for using microbes to speed up the transition of managed forest soils to a state where they lock away more carbon, “without having to wait centuries for old-growth forests to develop naturally.”

Acknowledgements: 

Jackson is the Michelle and Kevin Douglas Provostial Professor at Stanford. He is also a senior fellow at the Stanford Woods Institute for the Environment and the Precourt Institute for Energy, which are both part of the Doerr School of Sustainability. Peay is a professor of Earth system science, the director of the Earth Systems Program, and senior associate dean for education in the Doerr School of Sustainability. He is also a senior fellow at the Woods Institute and a professor of biology in the Stanford School of Humanities and Sciences. 

Study co-authors not mentioned above are affiliated with Lund University, Stockholm University, CSIRO Environment, the U.S. Geological Survey, Oregon State University, Biokonsult, China University of Geosciences, Gothenburg University, and Würzburg University.

This research was supported by The Crafoord Foundation, Swedish Research Council, BECC, Carl-Tryggers Stiftelse, Stiftelsen Extensus, Stiftelsen Längmanska kulturfonden, the Royal Physiographic Society of Lund, P.O. Lundells stiftelse, Jan Hain stiftelse för vetenskaplig teknisk forskning inom miljö och klimat, EU H2020 Climb-Forest, MERGE, a Blaustein Award to AA from Stanford’s Earth System Science Department, and the Stanford Sustainability Accelerator, which is based at the Doerr School of Sustainability.