Widespread sink limitations on forest biomass growth in the Northern Hemisphere
Bibliographic record
Abstract
Forests, which sequester atmospheric CO2 in the form of biomass within long-term reservoirs, are critical to the global land carbon sink. Current land surface models assume a strong coupling between photosynthesis and plant biomass changes, with carbon supply (i.e., carbon assimilation though photosynthesis) has been considered the main driver of plant biomass growth (‘source limitation’). However, the potential for sink limitations to constrain plant biomass growth, where plant biomass change become decoupled from photosynthesis, has been raised and supported by free air CO2 enrichment (FACE) experiment, inventory and tree ring evidence.In this study, we relied on high spatial resolution satellite-based retrievals of above-ground biomass (AGB) and vegetation primary productivity (GPP), to quantify the extent of decoupling between plant photosynthesis and biomass growth at the ecosystem scales over the past decade in the Northern Hemisphere (from 35ºN to 90ºN). We found that the fraction of decoupled area in non-intact forest is 66 ± 9%, significantly higher than in the intact forest. Extensive decoupling was observed across Europe, Russia and Canada. This spatial pattern was verified using multiple satellite-derived and inventory-derived AGB, and GPP data from P model. To investigate the drivers of decoupling, we built a generalized additive model to predict spatial variations in decoupling fractions within non-intact forests. The model suggests that harvest and logging account for most of the decoupling in Europe, while wildfires in Siberia may promote a recovery of coupling due to rapid vegetation regrowth. More importantly, even in intact forests, 56 ± 13% still exhibited the decoupling signals. In western Russia, this decoupling appears to be driven by droughts, likely due to carbon allocation shifts to support metabolism and critical plant functions, thereby constraining biomass growth. In western Canada, decoupling was found in in old-growth, or dense intact forests, where high decomposition, competition, or mortality may result in stable or declining forest biomass over time. Our analysis provides a geographic overview of regions experienced sink limitations to forest biomass growth, as well as insights into the mechanisms regulating terrestrial carbon sequestration. These findings represent a critical step toward improving process-based models and enhancing predictions of terrestrial carbon dynamics under future climate change scenarios.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".