The research team undertook an extensive empirical campaign in Sweden, combining detailed field measurements from over 200 forest plots with historical national forest and soil carbon inventory datasets spanning several decades. This integrative approach allowed for precise estimations of carbon stocks not only in the biomass of live trees and dead wood but also in the often-overlooked soil layers as well as in harvested wood products such as bioenergy materials, pulp, and timber. Their analysis demonstrated that intact old-growth forests retain approximately 72% more carbon per acre than the secondary forests commonly managed through industrial silviculture. Notably, this figure includes carbon accounted for in harvested wood products; excluding these products enhances the carbon storage differential to an astonishing 83% per acre advantage in primary forests.

Such a significant discrepancy starkly contrasts with prior official assessments, which have substantially underestimated the carbon sequestration gap between primary and managed forest ecosystems. To contextualize the magnitude, restoring Sweden’s managed forests to emulate the carbon storage of primary forests could avoid the release of nearly eight billion metric tons of CO₂, mirroring the cumulative fossil fuel emissions of Sweden over the last two centuries. This revelation positions boreal forest conservation as a linchpin in climate mitigation strategies, offering potential benefits that dwarf current national emission reduction targets. Crucially, these findings challenge prevailing assumptions that managed forest plantations reliably substitute for natural old-growth stands in climate models and carbon accounting frameworks.

Among the most startling outcomes of this work is the discovery that forest soils are the dominant carbon reservoirs within boreal woodlands—a fact that has received inadequate attention until now. The researchers found that in undisturbed primary forests, roughly two-thirds of the total ecosystem carbon resides within the upper meter of soil, whereas live tree biomass accounts for about one-third and dead wood a mere fraction. This soil carbon is intricately linked to microbial communities, root networks, and complex organic matter stabilization processes that can be drastically disturbed by mechanical soil disruption typical of industrial forestry. Practices such as scarification, plowing, and drainage ditch construction dramatically degrade soil structure and diminish its carbon sequestration functions, leading to persistent losses that forest regeneration alone cannot readily offset.

Sweden’s boreal forests have experienced an alarming reduction of unprotected old-growth areas at a rate of approximately 1.4% annually between 2003 and 2019. This deforestation pace is approximately six times higher than that observed in the Amazon’s primary rainforest, underscoring the urgency to address forest conservation in temperate and boreal zones, which traditionally receive less global attention than tropical regions. The difficulty lies in monitoring these forest changes using satellite remote sensing, as managed and old-growth boreal stands often consist of the same native tree species, rendering visible distinctions minimal from aerial perspectives. This obscurity has impeded effective policy responses and conservation efforts based on accurate deforestation data in these northern ecosystems.

The persistence of logging in Sweden’s remaining primary forests signifies ongoing risks to their ecological integrity and climate function. According to the study’s senior author Rob Jackson, Professor of Earth System Science at Stanford, the loss of soil carbon caused by industrial forestry is both substantial and enduring. The research indicates that safeguarding the limited remnants of primary forests is imperative not only for climate mitigation but also for preserving biodiversity and ecosystem resilience. Furthermore, the restoration of degraded forest lands offers a promising avenue for enhancing carbon storage and ecosystem services but requires a nuanced understanding of the specific management techniques that influence soil carbon dynamics.

This study also interrogates the assumptions embedded in many climate-scenario models which assume a net benefit from bioenergy production sourced from northern forests. If, as the data suggests, managed plantations store less than half the carbon of the old-growth forests they replace, the projected climate benefits from substituting fossil fuels with biomass energy may be substantially overstated, especially given boreal forests’ slow growth rates. This realization calls for a recalibration of climate policies and renewable energy strategies that rely heavily on forest bioenergy, promoting greater emphasis on conservation and improved silvicultural practices instead.

Lead author Didac Pascual, a postdoctoral scholar at Lund University, emphasized the surprising magnitude of soil carbon differences, noting that primary forest soils alone store more carbon than the combined pool of trees, dead wood, and soils in managed forests. This underscores the complexity of belowground carbon processes and signals the need to integrate soil health as a priority in forest management and climate mitigation frameworks. Addressing this challenge requires collaborative research spanning ecology, microbiology, and forestry science.

Looking ahead, the study’s authors aim to dissect the mechanisms underpinning high soil carbon storage in primary boreal forests. Collaborating with Stanford biologist Kabir Peay, the team is exploring the role of diverse microbial communities, including fungi and bacteria within tree roots and soil matrices, in enhancing carbon sequestration. They hypothesize that unique microbial assemblages in old-growth forests contribute to soil carbon stabilization, and understanding these relationships could unlock biotechnological solutions to accelerate carbon accumulation in managed forest soils. Such insights would enable a faster transition to carbon-rich forest ecosystems without waiting centuries for natural old-growth conditions to develop.

Professor Kabir Peay highlighted the transformative potential of this microbial approach, stating that harnessing soil microbes may revolutionize forest restoration by enabling enhanced carbon sequestration and ecosystem resilience. This avenue of research offers innovative strategies to reconcile timber production with climate goals, emphasizing synergistic interactions between soil biology and forest management practices. It points toward a future where microbial ecology becomes a cornerstone of sustainable forestry.

The broader implications of this research resonate beyond Sweden and boreal regions, extending to global efforts to meet ambitious climate targets. As northern forests represent one-third of the world’s forested land area, integrating these findings into international forest conservation policies is critical. The results advocate for prioritizing the protection and restoration of primary forests to maximize carbon sequestration and biodiversity preservation. They also underscore a pressing need to revise carbon accounting methodologies to incorporate soil carbon losses induced by contemporary forestry practices.

This landmark study ultimately redefines our understanding of boreal forest carbon dynamics, spotlighting the profound, previously underestimated role of soils and microbial life in climate regulation. By revealing the persistent and substantial carbon deficits caused by industrial forestry, it challenges policymakers, conservationists, and land managers to rethink conventional approaches. The future of boreal forests, and their capacity to mitigate climate change, hinges on embracing innovative, multidisciplinary strategies that honor the complex, living systems beneath the forest floor.

Subject of Research: Carbon storage capacity in primary versus managed boreal forests in Sweden, with a focus on soil carbon dynamics and the impacts of industrial forestry on carbon sequestration.

Article Title: Higher carbon storage in primary than in secondary boreal forests in Sweden

News Publication Date: 19-Mar-2026

Web References:

• https://doi.org/10.1126/science.adz8554
• https://sustainability-accelerator.stanford.edu/project/hidden-sink-old-growth-fungi-carbon-solution
• https://news.stanford.edu/stories/2024/10/tapping-into-the-fungal-network
• http://woods.stanford.edu
• http://energy.stanford.edu
• http://sustainability.stanford.edu

References:
Jackson et al., “Higher carbon storage in primary than in secondary boreal forests in Sweden,” Science, 2026. DOI: 10.1126/science.adz8554.

Image Credits: Philippe Roberge

Keywords: Boreal forests, carbon storage, soil carbon, old-growth forests, forest management, industrial logging, climate change mitigation, microbial ecology, Sweden, forest conservation, carbon sequestration, bioenergy

The research team conducted an extensive soil sampling campaign, analyzing 595 plots across south-central Norway’s Trillemarka and Varaldskogen forest regions. By examining both organic layer carbon and charcoal carbon stocks, the study breaks new ground in distinguishing how different forest compositions—specifically pine versus spruce—modulate soil carbon reservoirs. Soil samples were meticulously processed, and advanced statistical techniques, particularly Structural Equation Modeling (SEM), were employed to dissect the causal relationships among vegetation structure, hydro-topographic attributes, and intrinsic soil properties.

One of the landmark discoveries of this study is that pine-dominated forests consistently harbor greater organic layer carbon stocks compared to spruce-dominated areas. This discrepancy underscores the differential litter input, root turnover, and decomposition dynamics associated with these tree species, suggesting pine forests contribute more substantially to long-term carbon sequestration in soil organic matter. However, when it came to charcoal carbon—carbon sequestered in pyrogenic black carbon forms resulting from past fires—the patterns were more spatially and compositionally variable.

Intriguingly, in the Trillemarka region, pine forests showed significantly elevated charcoal carbon accumulations relative to spruce forests, a differentiation absent in Varaldskogen where charcoal carbon stocks were comparable across forest types. This geographic heterogeneity likely reflects divergent fire regimes, historical fire frequencies, and post-fire vegetation succession pathways. Notably, charcoal carbon stocks were positively correlated with increased fire frequencies spanning the last six centuries, reinforcing the notion that fire acts as a critical source of stable carbon in boreal soils.

The team’s SEM analysis elucidated several key environmental drivers exerting dominant controls on organic layer carbon stocks. Vegetation composition, terrain slope, and soil moisture emerged as primary variables. Soils under pine forests on gentler slopes with higher moisture content exhibited enhanced carbon accumulation, highlighting the importance of microclimate and topographic context in modifying soil organic matter stabilization. Terrain slope influences drainage and erosion processes, indirectly shaping organic matter retention, whereas soil moisture regulates microbial activity and decomposition rates.

Charcoal carbon stocks, distinct from bulk organic carbon, were principally influenced by the thickness of the organic layer. Thicker organic horizons provide greater substrate for charcoal deposition and protection from mineralization, thereby enabling longer-term carbon persistence. Additionally, the study uncovered a strong effect of microtopography; microsite depressions in the forest floor served as charcoal sinks, accumulating greater amounts than adjacent well-drained micro-elevations. This spatial variability highlights the heterogeneity of carbon stabilization mechanisms at microscale levels.

From an ecological and climate mitigation standpoint, the research offers profound implications. Understanding the nuanced drivers of carbon pools within boreal forests can inform predictive models that forecast carbon fluxes under different fire regimes and forest management scenarios. Forest managers could harness this knowledge to optimize silvicultural practices aimed at maximizing soil carbon storage—such as promoting pine species in specific topographies or adjusting fire management policies to align with carbon sequestration goals.

Yet, the study also underscores the complex nature of soil carbon dynamics in boreal ecosystems, cautioning against oversimplified generalizations. As Dr. Vilde L. Haukenes notes, “The organic soil and charcoal carbon stocks are highly context-dependent, shaped by a multitude of interacting factors. What produces positive carbon outcomes in one region may not be universally applicable elsewhere.” This regional variability necessitates more granular, localized studies to devise management strategies tailored to specific landscape conditions and disturbance histories.

Moreover, the linkage between fire history and carbon stocks is especially significant given the projected increase in wildfire prevalence and severity due to climate change. While fire events release substantial carbon into the atmosphere, they also contribute to enduring charcoal carbon pools that may represent a stable carbon sink if preserved within soils. Balancing wildfire management to mitigate emissions while recognizing fire’s role in soil carbon formation represents a nuanced ecological challenge.

Technological advances underpinning this study, such as the use of Structural Equation Modeling, facilitate the disentangling of multifactorial environmental influences on soil carbon. SEM accommodates complex, interrelated cause-and-effect pathways, providing a robust framework for ecological investigations involving intertwined biotic and abiotic drivers. This methodological approach sets a precedent for future studies aiming to capture the multifaceted nature of ecosystem carbon dynamics.

The investigation also sheds light on the importance of soil physical properties and hydrological settings. Soil moisture and organic layer thickness do not merely regulate decomposition and carbon inputs but also mediate redox conditions affecting microbial activity and carbon stabilization. Microtopography’s effect illustrates how fine-scale landscape features modulate these processes, emphasizing that spatial heterogeneity must be accounted for in carbon budget assessments.

This study marks a significant step forward in boreal forest carbon research by integrating fire ecology, vegetation dynamics, and soil science into a cohesive explanatory model. It challenges forest ecologists and climate scientists alike to rethink carbon cycling paradigms and addresses the pressing need to incorporate detailed environmental variability into large-scale carbon accounting efforts. In doing so, it lays the groundwork for more effective and regionally appropriate forest management policies that leverage natural processes to bolster climate mitigation.

As boreal forests continue to respond to accelerating environmental changes, the insights generated by this research offer a timely contribution. Enhancing our mechanistic understanding of how different forest types and fire histories influence carbon storage is vital for forecasting ecosystem responses and guiding sustainable stewardship. The delicate balance between disturbance and carbon retention revealed here will shape how humanity manages some of the planet’s most extensive and carbon-rich terrestrial biomes in the decades to come.

Subject of Research: Drivers of organic layer and charcoal carbon stocks in boreal pine and spruce forests with differing fire histories

Article Title: Disentangling drivers of organic layer and charcoal carbon stocks in boreal pine and spruce forests with different fire histories

News Publication Date: 8-May-2025

Web References:

• Forest Ecosystems Journal: https://www.sciencedirect.com/journal/forest-ecosystems
• Norwegian University of Life Sciences (NMBU): https://www.nmbu.no/en
• Norwegian Institute of Bioeconomy Research (NIBIO): https://www.nibio.no/en

References:
DOI: 10.1016/j.fecs.2025.100334

Image Credits: Vilde L. Haukenes, Johan Asplund, Line Nybakken, Jørund Rolstad, Ken Olaf Storaunet, Mikael Ohlson

Keywords: Boreal forests, soil carbon stocks, organic layer carbon, charcoal carbon, fire history, pine forests, spruce forests, structural equation modeling, hydrotopography, microtopography, carbon sequestration, climate change mitigation