Plant Regrowth as a Driver of Recent Enhancement of Terrestrial CO₂ Uptake

The increasing strength of land CO₂ uptake in the 2000s has been attributed to a stimulating effect of rising atmospheric CO₂ on photosynthesis (CO₂ fertilization). Using terrestrial biosphere models, we show that enhanced CO₂ uptake is induced not only by CO₂ fertilization but also an increasing uptake by plant regrowth (accounting for 0.33 ± 0.10 Pg C/year increase of CO₂ uptake in the 2000s compared with the 1960s–1990s) with its effect most pronounced in eastern North America, southern-eastern Europe, and southeastern temperate Eurasia. Our analysis indicates that ecosystems in North America and Europe have established the current productive state through regrowth since the 1960s, and those in temperate Eurasia are still in a stage from regrowth following active afforestation in the 1980s–1990s. As the strength of model representation of CO₂ fertilization is still in debate, plant regrowth might have a greater potential to sequester carbon than indicated by this study.