Grassland plant diversity loss could cut CO₂ uptake 15% by 2050, model projects

Researchers at the Potsdam Institute for Climate Impact Research and Kiel University reported on 8 October that a global vegetation model projects roughly 15% less photosynthetic CO₂ uptake by grasslands in 2050 if plant diversity is severely reduced, compared with grasslands retaining diversity. The difference matters for meadows and pastures worldwide, but it describes a scenario, not a decline already observed or one shown to be inevitable.

The study, led by Stephen Björn Wirth and published in the Proceedings of the National Academy of Sciences, compared grasslands with maintained plant diversity against grasslands with strongly reduced diversity. The researchers examined warming scenarios below 2°C and around 4°C. Their account describes the assumed loss of diversity as extreme; it does not establish how likely that loss is by 2050.

How much CO₂ uptake could grasslands lose?

Under the below-2°C warming scenario, the model projects that low-diversity grasslands would take up about 11 billion tonnes less CO₂ through photosynthesis per year in 2050 than grasslands retaining diversity. The researchers compare that difference with the productivity of an area of grassland roughly the size of the Arctic tundra. Both comparisons describe the gap between modeled futures, rather than an observed change from today's uptake.

The projected gap is uneven. In some tropical and subtropical regions, grasslands with strongly reduced diversity take up as much as 50% less CO₂ than those retaining diversity. Co-author Susanne Rolinski said remaining plants could compensate for losses in some places and productivity might even increase there. Across the globe, however, the model favors maintained diversity under both warming scenarios.

Why plant diversity may affect grassland productivity

Wirth said climate change could reduce the productivity of plants that currently dominate pastures and meadows. Where diversity is maintained, other plants better able to cope with the changing conditions may become more prominent and help limit the decline, he said. That proposed response helps explain why the model compares plant communities, rather than treating all grassland vegetation as interchangeable.

Separate experimental work supports a relationship between diversity and productivity, though it does not verify the new model's global 2050 figures. A 2026 synthesis of 75 biodiversity experiments across grasslands and forests found that diversity most strongly enhanced productivity during extreme drought in more arid grasslands. Under those conditions, the reported effects were limited in forests, showing that the response depends on the ecosystem and climate stress involved.

An earlier synthesis of ten years of the globally distributed Nutrient Network experiment reported that species diversity promotes grassland productivity and stability. It also found that nutrient supply and herbivory affect diversity by changing the composition of plant communities. These experimental findings provide context for the new projection, while leaving open how closely any particular future grassland will match the model's assumptions.

What the projection leaves uncertain

The researchers caution that the size of the projected effects is uncertain because their model simplifies plant traits and interactions. The strongly reduced-diversity scenario tests what a substantial loss could mean; the available account gives no probability that grasslands worldwide will follow it. Regional differences also matter: a global average can conceal places where remaining species compensate for losses.

Wirth said reduced photosynthesis could be accompanied by less forage for grazing animals, with potential consequences for people who depend on livestock. The account supplies no quantified forage or livelihood outcome, so those remain possible effects identified by the researcher, not results measured by the study. Kiel University co-author Friedhelm Taube called for management that preserves diversity and prevents overgrazing, alongside agricultural policies supporting farmers' adaptation. Those are recommendations drawn from the findings, not demonstrated effects of a particular policy.