PIK: losing plant diversity could cut grasslands' CO2 uptake by 15%

Grasslands worldwide could absorb considerably less CO2 if their plant diversity is lost, according to a study by the Potsdam Institute for Climate Impact Research (PIK) and Kiel University published on 7 October 2026 in PNAS. The lead author is Stephen Wirth of PIK. The team used the global vegetation model LPJmL-CSR, which simulates three basic plant strategies: competitive, stress-tolerant and ruderal, or fast-spreading. It compared two scenarios, maintained diversity and an extreme loss of diversity, under warming below 2C and around 4C.

With strongly reduced diversity, grasslands would absorb about 15% less CO2 through photosynthesis in 2050. Under warming below 2C, that amounts to about 11 billion tonnes of CO2 less per year. Tropical and subtropical grasslands are hit hardest, especially in South America and South Asia: in parts of Paraguay and India, photosynthesis is up to 50% lower. Soil carbon stocks also decline. In parts of Africa and Spain, by contrast, productivity rises slightly as the remaining plants compensate. "Globally, however, the benefits of maintaining diversity prevail in both climate scenarios," said senior author Susanne Rolinski of PIK.

This is a model projection, not measured data. The model reduces hundreds of species to three strategies and tests an extreme collapse of diversity, so real-world losses would likely fall between the two scenarios and the exact figures are uncertain. The 11 billion tonnes refer to uptake through photosynthesis, not the net carbon balance. The authors recommend management that preserves diversity and prevents overgrazing, along with farm policy that helps farmers adapt, particularly in the Global South. "We need management practices that preserve existing diversity over the long term," said Friedhelm Taube of Kiel University.