Primary forests store much more carbon than managed forests
Swedish primary forests store 83 percent more carbon than managed forests, according to new research from Lund University in which doctoral students from the University of Gothenburg participated. The difference is significantly greater than previous estimates and is primarily due to large carbon stores in the soil.
The study, published in the scientific journal Science, is the most comprehensive assessment to date of how much carbon is stored in Swedish old-growth, primary forests. The results show that primary forests store 78–89 percent more carbon than managed forests in living trees, dead wood, and in the soil to a depth of 60 centimeters.
The soil stores the most carbon
“The most surprising finding is just how much carbon is stored in the soil of primary forests. The carbon stored in the soil there is equal to all the carbon in managed forests—trees, dead wood, and soil combined,” says Anders Ahlström, a researcher at Lund University.
The study took nearly ten years to complete. Since there was no national map of primary forests, the researchers first had to identify and map forests that had been little or not at all affected by direct human activity. Extensive fieldwork was then carried out across the country, including the digging of nearly 220 test pits one meter deep to measure carbon storage in the soil.
Time-consuming work
“It was time-consuming but enjoyable work, especially in primary forests, which are often more remote and where the terrain can be more difficult to navigate,” says Ulrika Ervander, a doctoral student at the University of Gothenburg who has helped map carbon storage in primary forests throughout Sweden.
The total difference in carbon storage between primary forests and managed forests—including carbon stored in wood products—is approximately 3 to 8 times greater than previous estimates. This is equivalent to about 211 years of Sweden’s current fossil carbon dioxide emissions and is roughly 1.5 times all fossil emissions since 1834.
Short-lived products
“The amount of 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 of these products are short-lived, such as paper and bioenergy, where the carbon quickly returns to the atmosphere,” says Didac Pascual, a researcher at Lund University.
Primary forests serve as a reference for what Swedish forests would have looked like without forestry and land use. The difference in carbon storage between primary forests and today’s managed forests reflects the cumulative effect of direct human land use. All carbon uptake and losses since the late 1800s—and in particular since the 1950s, when today’s large-scale forestry was established—are included.
Primary forests as a reference
“Comparing carbon storage in primary forests and managed forests is crucial, as current measurements of carbon uptake may overlook significant historical carbon losses. Carbon storage provides the full picture over time. Primary forests serve as a reference for understanding how forestry affects ecosystems and the carbon balance,” says Anders Ahlström.
The findings are relevant to the discussion on the role of forests in the climate transition. The significant differences in carbon storage mean that a conversion from natural forest to managed forest results in much greater losses of stored carbon or potential carbon sequestration than previously estimated. This affects calculations of the climate benefits of forest products, such as bioenergy and building materials.
Benefits in Old-Growth Forests
“The conversion of primary forests and other natural forests reduces the landscape’s carbon storage more than previously thought. Protecting remaining old-growth forests and allowing unmanaged forests to recover can yield significantly greater climate benefits than previous studies have shown. Furthermore, a large portion of the clear-cutting that takes place each year occurs in forests with a relatively high degree of naturalness,” says Didac Pascual.
Study in Science: ”Higher carbon storage in primary than secondary boreal forests in Sweden”
Contact info: Anders Ahlström, Senior lecturer at Lund University, email: anders.ahlstrom@mgeo.lu.se