GRASSLAND DIVERSITY LOSS TO CUT CO2 UPTAKE BY 15%

 Why In News?

Researchers from Potsdam Institute for Climate Impact Research (PIK) warn that losing plant functional diversity in managed grasslands could reduce global carbon dioxide uptake through photosynthesis by up to 15% by 2050.

Highlights of The Study

Global Impact

• Global Productivity Drop: By mid-century, grasslands with reduced functional plant diversity are projected to absorb 15% less CO2 through photosynthesis compared to communities where diversity is maintained.

• Decline in India and Paraguay: Equatorial regions face the most acute reductions; grasslands with strongly reduced functional diversity in India and Paraguay could experience up to a 50% drop in Gross Primary Productivity (GPP).

• Carbon Deficit: Under a low-emissions scenario keeping warming below 2 °C, low-diversity grasslands will sequester 11 billion tonnes less CO2 per year by 2050. This carbon uptake deficit is equivalent to losing a productive grassland area the size of the Arctic Tundra.

• Long-Term GPP: By 2100, global grassland GPP in low-diversity scenarios (FD−) drops to 20 petagrams of carbon per year under low emissions, compared to 25 petagrams per year under high emissions.

Conceptual & Ecological Mechanisms

• Functional Diversity: High functional diversity (FD+) serves as an "ecological insurance policy". When climate stress impairs dominant plant species, stress-tolerant or ruderal plant types step in to sustain photosynthetic activity and ecosystem productivity.

• Functional Plant Strategies: The study modeled plants across three primary ecological strategies:

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1. Competitors: Rapid growers that utilize resources efficiently under stable conditions.

2. Stress-Tolerant Plants: Species with robust tissues capable of enduring climate extremes.

3. Ruderals: Fast-growing opportunistic plants that thrive during favorable periods between environmental disturbances.

• Failure of Monoculture Compensation: Removing non-dominant species frees up soil resources for remaining dominant plants, leading to minor localized gains; however, these gains fail to compensate for the net loss of stress-tolerant and ruderal functional types.

Socio-Economic & Ecosystem Impacts

• Threat to Agro-Pastoral Livelihoods: Lower plant diversity directly reduces dry matter forage availability, threatening livestock grazing systems and the livelihoods of pastoral communities, particularly across the Global South.

• Depletion of Soil Organic Carbon (SOC): Simplified plant communities contribute significantly less organic matter to the soil, depleting Soil Organic Carbon (SOC) stocks and weakening long-term subterranean carbon storage.

What Is Grassland?

A grassland ecosystem is an open landscape dominated by herbaceous non-woody vegetation (primarily true grasses, sedges, and rushes) where tree canopy cover remains below a regional ecological threshold.

Transitional Landscape: Grasslands function as transitional biomes situated between arid deserts and dense forest ecosystems in regions where annual rainfall is insufficient to support forest canopy growth.

Global Extent: Grasslands constitute the single most extensive land cover on Earth, occupying roughly 25% to 40% of the ice-free terrestrial surface across diverse climatic zones.

Major Ecological Classifications:

• Tropical Grasslands (Savannas): Located in warm tropical belts experiencing distinct dry and wet seasons (receiving 50 to 150 cm annual rainfall); characterized by open grass cover with scattered shrubs or fire-adapted trees like acacias and baobabs.

• Temperate Grasslands: Situated in mid-latitude regions with extreme seasonal temperatures (hot summers and cold/freezing winters) receiving 25 to 75 cm of annual precipitation; dominated by treeless plains with deep, highly fertile soils.

Grassland Around the World

Grassland biomes are distributed across all continents except Antarctica. The major global grasslands categorized by region and type include:

A. Temperate Grasslands

• Prairies (North America - USA & Canada): Flat to rolling plains with highly fertile soils used extensively for commercial wheat, corn, and livestock farming.

• Steppes (Eurasia - Russia, Ukraine, Kazakhstan): Semi-arid, treeless plains dominated by short, drought-resistant grasses.

• Pampas (South America - Argentina, Uruguay, Brazil): Humid, nutrient-rich plains supporting cattle ranching, alfalfa cultivation, and wheat production.

• Veld (Southern Africa - South Africa, Zimbabwe, Botswana): Rolling high-altitude plateaus utilized for maize farming and sheep/cattle rearing.

• Downs (Australia - Queensland & New South Wales): Semi-arid rolling plains dominated by drought-resistant Mitchell grass; major hub for sheep (Merino wool) and cattle grazing.

• Canterbury Plains (New Zealand): Temperate plains dominated by tussock grasses, extensively managed for sheep and dairy farming.

• Pustaz (Hungary): Flat, treeless plains forming part of the Eurasian Steppe, known for rich black soils and sugar beet/wheat cultivation.

• Manchurian Grassland (Northeastern China & Inner Mongolia): Temperate plains experiencing hot summers and cold winters.

B. Tropical Grasslands (Savannas)

• African Savanna (Sub-Saharan Africa): Expansive grassy plains interspersed with acacia and baobab trees supporting major megaherbivore and predator populations.

• Llanos (Venezuela & Colombia): Seasonally flooded tropical grasslands with gallery forests near river systems.

• Campos (Brazil, Uruguay, Paraguay): Tropical to sub-tropical rolling pastures used for livestock grazing and grain crops.

• Australian Savanna (Northern Australia): Tropical open grasslands with scattered eucalyptus trees adapted to seasonal dry seasons and fires.

Significance of Grasslands

Terrestrial Carbon Storage: Grasslands store up to 34% of total global terrestrial carbon. Up to 90% of this carbon is anchored underground in deep root networks and Soil Organic Carbon (SOC), creating a subterranean carbon sink far more resilient to fire and drought than aboveground forest biomass.  (Source: World Resources Institute)

Biodiversity Hotspots: Grassland and savanna biomes account for nearly one-third of global Key Biodiversity Areas. Certain temperate grasslands exhibit extreme micro-diversity, hosting up to 90 plant species per square meter. c

Hydrological Regulation & Water Security: Extensive root architectures act as natural water filters, promote rainwater infiltration to recharge groundwater reservoirs, regulate river flow to mitigate flood risks, and prevent soil erosion.

Livelihoods & Food Security: Over 1 billion people globally—including pastoralists, smallholders, and Indigenous communities—depend directly on grasslands and rangeland livestock for food security, income, and cultural identity. (Source: World Resources Institute)

Microclimate & Albedo Regulation: High surface albedo allows grassy vegetation to reflect solar radiation, providing localized land surface cooling.

Conclusion

Protecting and restoring grassland plant diversity is vital to safeguard subterranean carbon sinks, water systems, and pastoral livelihoods.

Source: DOWNTOEARTH