Key factors shaping soil carbon storage in boreal forests revealed

Key factors shaping soil carbon storage in boreal forests revealed
by Riko Seibo
Tokyo, Japan (SPX) Jun 17, 2025

Boreal forests, spanning much of the northern hemisphere, are essential carbon sinks, holding between 25% and 40% of the world's terrestrial carbon in their soils. Yet, the factors controlling how much carbon these soils retain remain complex. A new study from researchers at the Norwegian University of Life Sciences and the Norwegian Institute of Bioeconomy Research, published in Forest Ecosystems, sheds light on the interplay of forest type, fire history, and soil conditions in determining carbon stocks.

The team analyzed soil samples from 595 forest plots across two sites in south-central Norway-Trillemarka and Varaldskogen. Using structural equation modeling (SEM), they examined how vegetation composition, terrain features, and soil characteristics affect both organic layer carbon and charcoal carbon storage.

Findings indicate that pine forests consistently store more carbon in their organic layers than spruce forests. Charcoal carbon levels, by contrast, were more variable. In Trillemarka, pine forests had higher charcoal carbon stocks compared to spruce forests. However, in Varaldskogen, both forest types showed similar levels. Fire history also emerged as a critical factor: both organic and charcoal carbon stocks increased with fire frequency over the past six centuries.

Key drivers for organic carbon stocks include vegetation type, terrain slope, and soil moisture. Charcoal carbon was mainly influenced by organic layer depth. Depressions in the terrain, or microtopographic lows, were associated with greater charcoal accumulation than drier, elevated areas.

These insights carry important implications for climate strategies and sustainable forestry. By understanding the conditions that enhance soil carbon storage, forest managers can better support carbon sequestration efforts. The study also highlights the need for localized management, as emphasized by Dr. Vilde L. Haukenes: "Boreal forests are highly variable, and what works in one region may not be effective in another."

The researchers caution against generalizing results across all boreal regions, noting that relationships between organic and charcoal carbon pools are often context-dependent.

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