Shrubs and trees empty subarctic soil carbon
At a Swedish subarctic treeline, shrub and birch plots stored far less soil organic carbon than nearby heaths and respired that carbon faster, implying woody expansion can accelerate soil C loss.
Source
Rapid carbon turnover beneath shrub and tree vegetation is associated with low soil carbon stocks at a subarctic treeline
Study at a glance
- Design
- Cross-sectional — Space-for-time forest–heath transects comparing SOC and respiration under shrub expansion
- N
- N=19 · 12 Abisko + 7 Vassijaure forest–heath transects
- Population
- Subarctic treeline heath, shrub, and birch forest plots in northern Sweden
- Outcome
- Soil organic carbon stocks and respiration rates across vegetation types
Structured fields used in claim comparison tables when every cited study has a complete layer.
What they did
Authors sampled 12 Abisko and 7 Vassijaure forest–heath transects, measured organic and mineral SOC, chamber respiration, and ectomycorrhizal hyphal in-growth bags along heath–shrub–forest plots, using space-for-time as a shrub-expansion analogue.
What they found
At Abisko, organic-horizon SOC was 7.03 kg m⁻² on heath vs 2.98 (shrub) and 2.04 (forest). Total SOC fell from 9.01 to 4.51 kg m⁻² heath to forest. Shrub plots had the highest respiration; per kilogram of organic SOC, shrub and forest plots respired about three times heath rates. Hyphal in-growth rose from heath to forest edge.
The limits
What it doesn't show
Space-for-time cannot prove future shrub advance will lose the same carbon; moth defoliation likely understated forest ECM growth; root C was not fully inventoried; permafrost and waterlogged tundra may respond differently.
Key terms
- SOC
- Soil organic carbon stored in organic and mineral horizons.
- Ecotone
- Transition zone—here from ericaceous tundra heath through deciduous shrubs into mountain birch forest.
- Positive priming
- Input of fresh plant carbon that stimulates microbes to decompose older soil organic matter.
- Ectomycorrhiza (ECM)
- Fungal symbionts of birch and dwarf birch that can exude enzymes targeting soil organic matter.
- Space-for-time substitution
- Using spatial vegetation transitions as analogues of expected climate-driven succession.
Flashcards
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Quiz yourself
Where was soil organic carbon highest?
Common questions
Where is SOC highest?
Ericaceous tundra heath, not the more productive shrub or forest plots.
Do shrubs behave like forest?
Yes—similarly low SOC and fast turnover compared with heath.
Is respiration higher under shrubs?
Highest absolute rates at shrub plots; highest per-SOC rates at shrub and forest.
What fungi were measured?
ECM hyphal in-growth in sand bags, rising from heath to forest edge.
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