Grasslands play a bigger climate role than many realise. New research highlights why changes within these ecosystems could have far-reaching consequences for carbon storage and rural livelihoods.
A major decline in plant diversity could significantly weaken the ability of grasslands around the world to absorb carbon dioxide from the atmosphere, according to a new study by researchers from the Potsdam Institute for Climate Impact Research (PIK) and Kiel University (CAU).
Published in PNAS, the research projects that grasslands such as meadows and pastures may take up about 15 per cent less carbon dioxide through photosynthesis by the middle of the century if plant diversity continues to decline. The study also found that in some of the most heavily affected regions, carbon sequestration could be reduced by as much as 50 per cent even in a world where warming remains below 2 degrees Celsius.
Researchers identified some of the strongest productivity losses around the equator, particularly in Paraguay and India. In those locations, gross primary productivity (GPP), a measure of carbon absorbed by vegetation through photosynthesis, was projected to be up to 50 per cent lower under conditions of reduced plant diversity. Meanwhile, parts of Africa north and south of the equator, along with Spain, showed increases of up to 20 per cent under the same scenario.
Lead author Stephen Wirth of PIK said climate change may reduce the productivity of plant species that currently dominate many grasslands. However, maintaining diverse plant communities allows species that are better suited to changing conditions to expand and help offset declines.
He noted that the effects stretch beyond photosynthesis alone. Reduced plant diversity can lower forage availability for grazing animals, threaten incomes linked to livestock production and decrease the amount of carbon stored in soils.
Diversity Found To Strengthen Grassland Resilience
To examine future outcomes, researchers developed a model grouping grassland species into three ecological strategies: competitors, which grow quickly and make efficient use of resources; stress-tolerant plants, which survive harsh conditions through robust structures; and ruderals, which rapidly establish during favourable periods between disturbances.
The team assessed two key ecosystem functions, gross primary productivity and soil organic carbon stocks. Simulations covered the period from 1850 to 2100 and drew on climate data from five general circulation models. Researchers tested both a low-emissions pathway, SSP1-2.6, where warming stays below 2°C, and a higher-emissions pathway, SSP3-7.0, associated with approximately 4°C of warming.
In the high-diversity scenario, existing plant types remained while new types could establish themselves. The low-diversity scenario retained only dominant plants and prevented new types from emerging.
According to the findings, diverse grasslands acted as a form of ecological insurance. Communities with greatly reduced diversity were more vulnerable when dominant species reached their biological climate limits.
The study estimated that under 2°C of warming, grasslands with sharply reduced diversity would absorb roughly 11 billion tonnes less carbon dioxide annually through photosynthesis by 2050 than grasslands where diversity was preserved. Researchers said that reduction would be comparable to losing an area of average-productivity grassland roughly equivalent in size to the Arctic Tundra.
The modelling also showed declines in soil carbon storage and forage production in low-diversity landscapes. Although remaining dominant species often became more productive after other plant types disappeared, those gains generally failed to offset losses resulting from the removal of stress-tolerant and ruderal plants.