Elevated CO₂ Boosts Wisconsin Forest Growth by 39% Over 11 Years, Ozone Cuts Gains
Researchers found that raising CO₂ levels around a Wisconsin forest for 11 years increased net primary productivity by 39%, while added ozone reduced it by 10%.
From 1998 to 2009, the Aspen-FACE study altered the atmosphere surrounding forest plots in Rhinelander, Wisconsin, applying elevated carbon dioxide, elevated ozone, or both to natural aspen-birch-maple communities. After 11 years, plots receiving extra CO₂ produced 39% more cumulative net primary productivity and stored 11% more ecosystem carbon, largely driven by tree growth in stems, branches and roots. In contrast, elevated ozone reduced cumulative productivity by 10% and ecosystem carbon by 9%, partly due to a 21% drop in canopy nitrogen.
When both gases were applied together, the net carbon balance did not differ significantly from control plots, indicating opposing effects without a clear interaction. Follow-up modelling by the USDA Forest Service confirmed CO₂ as the primary driver of biomass gains across landscapes, while ozone imposes a notable negative offset. The findings highlight that rising CO₂ can enhance forest carbon uptake, but concurrent air pollutants may limit that potential.
Why it matters
It reveals how CO₂ rise and ozone pollution together could affect forests' capacity to sequester carbon.
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