What if forests are doing much more for the climate than we ever imagined? A new study shows that some forests quietly store huge amounts of carbon, far more than scientists once believed.
This discovery changes how people understand climate change and the role forests play in fighting it.
Old-growth forests hold hidden carbon
A major study published in the journal Science reveals that old-growth forests in Sweden store much more carbon than managed forests.
Researchers from Lund University and Stanford University found that these untouched forests store 78 to 89 percent more carbon. This carbon exists in living trees, dead wood, and even deep in the soil.
“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,” said Anders Ahlström from Lund University.
This finding shows that the real value of forests goes far beyond what people see above ground.
A decade of research
Researchers spent nearly ten years collecting data. First, the team had to identify old-growth forests across Sweden because no national map existed. These forests had little or no human disturbance.
After mapping, the team carried out fieldwork across the country. Scientists dug nearly 220 soil pits, each reaching one meter deep. This helped measure how much carbon was stored underground.
The team also studied more than 200 forest plots and combined the data with national forest records and advanced models.
This detailed work created one of the most complete pictures of forest carbon storage ever produced.
Soil stores more than trees
Many people think trees hold most of the carbon in a forest. This study proves that idea is incomplete. The soil beneath old-growth forests stores a huge share of carbon.
“There’s far more carbon in the soil than in the trees in these old-growth boreal forests,” noted Rob Jackson from the Stanford Doerr School of Sustainability.
In some areas, soil holds about 64 percent of the total carbon. Trees store about 30 percent, while dead wood stores the rest.
This means that damage to forest soil can release large amounts of carbon into the atmosphere.
Managed forests fall short
Managed forests often replace old-growth forests. These forests usually contain one type of tree and are grown for timber. While these forests still store carbon, the amount is much lower.
The study shows that even when counting carbon stored in wood products like paper and bioenergy, managed forests still store far less carbon.
“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,” noted Didac Pascual from Lund University.
Most wood products do not last long. Paper and bioenergy release carbon back into the air quickly.
A much bigger climate impact
The difference between old-growth and managed forests is far greater than earlier estimates. Researchers found that the gap is 3 to 8 times larger than what scientists previously thought.
This difference equals about 211 years of Sweden’s current fossil carbon dioxide emissions. In simple terms, old-growth forests store an amount of carbon that would take centuries of emissions to match.
If Sweden restored managed forests to match old-growth levels, nearly 8 billion tons of carbon dioxide could stay out of the atmosphere. This shows how powerful forests can be in slowing climate change.
Forest loss is happening fast
Despite their value, old-growth forests continue to disappear. In Sweden, these forests have been lost at a rate of 1.4 percent per year between 2003 and 2019. This rate is even higher than the loss of primary forests in parts of the Amazon.
Tracking this loss is difficult in northern regions. Managed forests and natural forests often look similar from space because they contain the same types of trees like spruce and pine.
“Unfortunately, the logging of primary forests in Sweden continues,” said Anders Ahlström. This ongoing loss reduces the planet’s ability to store carbon.
Why old forests matter
Old-growth forests act as a natural reference. These forests show what ecosystems look like without human interference. By comparing them with managed forests, scientists can understand how land use changes affect carbon storage.
“Comparing carbon storage in old-growth and managed forests is crucial, because contemporary measurements of carbon uptake can miss large historical carbon losses,” said Ahlström.
This long-term view helps scientists understand the full impact of human activity on forests and climate.
Protecting forests for the future
The study carries an important message for climate action. Protecting old-growth forests can offer stronger climate benefits than expected. Allowing damaged forests to recover can also help store more carbon over time.
“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,” said Didac Pascual.
Scientists are now studying what makes these forests so effective. One idea focuses on microbes in soil that help store carbon. Understanding this process could help improve managed forests in the future.
This research shows that forests are not just trees. Forests are powerful carbon storage systems, and protecting them may be one of the most effective ways to fight climate change.
The study is published in the journal Science.
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