Grasslands cover somewhere between 30 and 40 percent of Earth’s land surface, depending on which vegetation types get counted. That range is not a sign of sloppy science; it reflects genuine disagreement about where to draw the line between a grassland, a savanna, a shrubland, and a sparse woodland. Even the lower estimate makes grasslands one of the planet’s largest biomes, rivaling forests in total area and quietly underpinning much of the world’s food production, water supply, and carbon storage.
Why the Estimates Vary So Much
When researchers try to pin down a single number for global grassland coverage, the answer keeps shifting because the definition of “grassland” is not standardized across disciplines. A plant ecologist studying temperate prairies, an African savanna specialist, and a remote-sensing scientist mapping land cover from satellite data may all be talking about different things when they use the word.
One widely cited figure puts grasslands at up to 40 percent of Earth’s terrestrial area.1PubMed Central. Grassland biodiversity That estimate generally includes tropical and subtropical savannas, temperate grasslands, montane meadows, tundra grasslands, and some shrub-grass mosaics. A more conservative figure of about 30 percent tends to emerge when researchers narrow the definition to exclude the woodier savannas or count only landscapes where grasses clearly dominate the ground layer. One global review used that 30 percent figure while emphasizing the carbon stored belowground in grassland soils. The gap between 30 and 40 percent is largely explained by whether tropical savannas with scattered trees get lumped in or treated as a separate biome.
Formal classification efforts have tried to bring order to this. One biogeographic mapping study defined a grassland as a non-wetland area with at least 10 percent vegetation cover, dominated by grasses and forbs, where any tree canopy is sparse and short.2Journal of Biogeography. Distribution mapping of world grassland types Under that kind of framework, a savanna with 30 percent tree cover and a thick grass understory might qualify, but a dry woodland with the same tree cover and little grass might not. The boundaries are real ecological gradients, not neat lines, which is why the global number keeps moving.
Where Grasslands Are Found
Grasslands are not confined to one climate zone or continent. They span the tropics, the temperate midlatitudes, and even parts of the subarctic. What unites them is not temperature or rainfall but a vegetation structure dominated by grasses, maintained by some combination of climate, fire, and grazing.
Tropical savannas alone cover around 20 percent of the global land surface, making them the single largest grassland category.3Current Biology. Tropical savannas and dry forests These landscapes stretch across sub-Saharan Africa, central Brazil, northern Australia, and parts of South and Southeast Asia. Rainfall in savannas varies enormously, from around 300 millimeters per year in the driest African savannas to 2,500 millimeters in parts of South America. Half of the global tropics experience a seasonally dry climate, and research and conservation attention have historically focused on tropical rainforests at the expense of these vast grassy ecosystems.4PubMed. Tropical savannas and dry forests
In temperate regions, the major grassland systems go by different names. The Eurasian steppe extends from Central and Eastern Europe through Central Asia to northern China, forming one of the largest continuous terrestrial habitats on Earth.5Flora. Climate, landscape history and management drive Eurasian steppe biodiversity Floristically similar grasslands also appear in North Africa, Turkey, and Iran. In North America, the Great Plains once formed a massive grassland corridor from southern Canada to Texas, though much of it has been converted to cropland. South America has the Pampas of Argentina and Uruguay, and southern Africa has its own temperate highveld grasslands. Each of these systems has a distinct climate, fire regime, and evolutionary history, but all share the basic structure of grass-dominated vegetation with few or no trees.
What Keeps Grasslands Open
One of the most persistent questions in ecology is why grasslands stay grassy rather than filling in with trees. In many grassland climates, rainfall is high enough to support woodland or even forest. The answer involves disturbance, specifically fire and grazing, which act together to suppress woody plant growth and maintain an open landscape.
Research on South American grasslands has shown that fire and grazing are mutually dependent: neither alone is enough to prevent shrubs from taking over. Together, they keep the canopy open and maintain small patches of bare soil that promote turnover among plant species.6PubMed. Fire and grazing interact to maintain open physiognomy and diversity in a South American grassland In tropical savannas, the mechanism is similar. Grasses provide fuel for fire, fire kills or stunts young trees, and large herbivores browse on woody seedlings and saplings. Remove fire or remove grazers, and many grasslands begin a slow transition toward shrubland or forest.
This is not just a theoretical concern. When those disturbance processes break down, woody plants move in. Across sub-Saharan Africa over the past three decades, woody plant cover increased significantly on roughly 7.5 million square kilometers of non-forest land, more than triple the area where woody cover declined.7Nature Communications. Drivers of woody plant encroachment over Africa In western North America, a similar pattern has unfolded: as woody shrubs encroach into grasslands, grass biomass, density, and cover decline.8PubMed. Causes and consequences of woody plant encroachment into western North American grasslands Woody encroachment is now recognized as a major driver of grassland loss globally, alongside agricultural conversion.
An Ancient Biome With a Relatively Recent Rise
Grasslands feel timeless, but in geological terms they are surprisingly young. Grasses themselves have been around for tens of millions of years, but the vast grass-dominated landscapes we see today assembled relatively recently. The evolution of grasses that use a highly efficient form of photosynthesis, called the C4 pathway, and their sudden rise to ecological dominance between 3 and 8 million years ago is considered one of the most dramatic examples of biome assembly in the fossil record.9PubMed. The origins of C4 grasslands: integrating evolutionary and ecosystem science That expansion coincided with declining atmospheric carbon dioxide levels, increased seasonality, and the spread of fire. In other words, the grasslands that now cover a third or more of the planet’s land are younger than many of the forest types they replaced.
This evolutionary history matters for conservation. Because grasslands co-evolved with fire and grazing over millions of years, many grassland species depend on periodic disturbance. Suppressing fire or removing large herbivores does not simply “protect” a grassland; it often triggers a shift toward a fundamentally different ecosystem. That distinction between disturbance-dependent and disturbance-sensitive ecosystems is central to understanding why grassland conservation is so different from forest conservation.
Carbon Storage and Climate
Grasslands store a substantial share of the planet’s terrestrial carbon, and they do it in a way that is fundamentally different from forests. While forests lock most of their carbon in trunks, branches, and leaves above ground, grasslands store the vast majority of theirs underground in root systems and soil organic matter. One estimate puts grasslands at about 34 percent of global terrestrial carbon storage, with roughly 89 percent of that carbon held in the soil.10PubMed. Soil organic carbon stock in grasslands: Effects of inorganic fertilizers, liming and grazing in different climate settings
This underground storage has a practical advantage: it is less vulnerable to fire. When a forest burns, decades or centuries of above-ground carbon can be released in days. When a grassland burns, the above-ground biomass is consumed, but the deep soil carbon stays put, and the grasses regrow within a season. In a warming world with increasing wildfire frequency, some researchers have argued that grassland carbon is more resilient than forest carbon over the long term.
The flip side is that this soil carbon is sensitive to land management. Plowing a grassland to plant crops exposes stored organic carbon to decomposition, releasing it as carbon dioxide. Overgrazing can degrade soil structure and reduce carbon inputs. Conversely, well-managed grazing can maintain or even build soil carbon, depending on the climate and soil type. The practical upshot is that grassland carbon is stable as long as the grassland stays intact, but fragile once the sod is broken.
Grasslands and the Water Cycle
Beyond carbon, grasslands play a major role in how water moves through landscapes. Their shallow root systems and permeable soils allow a significant fraction of rainfall to percolate downward and recharge underground aquifers, rather than being intercepted by tree canopies or taken up by deep roots.
A case study in Nebraska’s Sand Hills illustrates this vividly. When grassland was converted to dense pine forest, average annual groundwater recharge dropped from about 9.65 centimeters per year to just 0.07 centimeters per year, essentially zero. The trees intercepted more rainfall, transpired more water through their leaves, and rooted deeper into the soil, collectively eliminating almost all of the deep drainage that had been replenishing the aquifer beneath.11Journal of Hydrology: Regional Studies. Impact of grassland conversion to forest on groundwater recharge in the Nebraska Sand Hills The study highlighted the significance of grassland ecology for the sustainability of the High Plains Aquifer, one of the largest freshwater reserves in the world.
Similar patterns have been documented elsewhere. On China’s Loess Plateau, grasslands showed an annual recharge rate of about 26 millimeters per year, attributed to the improved water infiltration and higher soil porosity that grass root systems create.12Journal of Hydrology: Regional Studies. Discrepancy and estimates of groundwater recharge under different land use types on the Loess Plateau In semiarid rangelands of the western United States, removing deep-rooted woody shrubs and allowing grasses to reestablish has been shown to reduce root zone water uptake and increase deep drainage substantially, because the shallower grass roots leave more water available to percolate below the root zone.13Hydrological Processes. Soil water storage and rooting depth: key factors controlling recharge on rangelands
The implication is that grassland loss does not just affect biodiversity or carbon; it can fundamentally alter the water balance of a region, with downstream consequences for agriculture, drinking water supply, and streamflow.
What Has Been Lost and What Keeps Disappearing
Grasslands have been called the most threatened and least protected biome on Earth.14Conservation Science and Practice. The last continuous grasslands on Earth: Identification and conservation importance That label reflects two converging pressures: grasslands are being converted to cropland at alarming rates, and the ones that remain are under-represented in protected area networks compared to forests, wetlands, or coral reefs.
In the United States, over 2 million hectares of grassland were converted to crop production between 2008 and 2016 in the Midwest alone, with far less cropland retired or abandoned to offset the loss.15PubMed Central. Grassland-to-cropland conversion increased soil, nutrient, and carbon losses in the US Midwest between 2008 and 2016 Modeling efforts have attempted to predict where future conversion is most likely, using patterns from the past decade to identify ecoregions at greatest risk.16PubMed Central. Landscape-scale predictions of future grassland conversion to cropland or development
Globally, the picture is even starker. A spatially explicit analysis of land conversion between 2005 and 2020 found that non-forest ecosystems, which include grasslands, savannas, and wetlands, were converted at nearly four times the rate of forested land. Brazil accounted for about 13 percent of this global conversion, with Russia, India, China, and the United States each contributing roughly 6 percent.17PubMed Central. Overlooked and overexploited: Extensive conversion of grasslands and wetlands driven by global food, feed, and bioenergy demand The drivers are familiar: expanding cropland for food, feed crops for livestock, and bioenergy production. Yet because forests attract far more conservation attention and policy protection, grassland conversion often proceeds with little scrutiny.
On the other end, abandonment is also a problem, though it might not sound like one. When traditional grazing or mowing ceases, grasslands in temperate regions tend to be overtaken by shrubs and eventually trees. Research in Europe has found that both afforestation and abandonment of semi-natural grasslands lead to significant declines in biodiversity, pollination services, natural pest regulation, forage production, soil quality, and cultural landscape value.18Journal of Applied Ecology. Afforestation and abandonment of semi‐natural grasslands lead to biodiversity loss and a decline in ecosystem services and functions In other words, a grassland that is plowed under and a grassland that is simply left alone can both end up losing the qualities that made it a grassland in the first place.
Half a Billion People Depend on These Landscapes
Grasslands are not just ecological curiosities; they are working landscapes. Pastoralism, the practice of raising livestock on rangeland, is the primary land use on grasslands worldwide and the most widespread form of land use on the planet. It provides livelihoods for an estimated 500 million people and supplies about 16 percent of global food production.19PubMed Central. Pastoralism Can Mitigate Biodiversity Loss on Global Rangelands For many pastoral communities, livestock represent not just an economic activity but a cultural identity and a centuries-old relationship with the land.
Climate change threatens to disrupt these livelihoods in the places that can least afford it. Projections suggest that about half the people living in rangeland systems, roughly 376 million people, live in regions that are expected to see both declining average vegetation productivity and increasing year-to-year variability in that productivity. These same regions currently have the lowest stocking rates, the lowest meat and milk yields per hectare, and the lowest per capita incomes among rangeland communities. They also face the highest projected increases in human population density by 2050.20Environmental Research Letters. Global rangeland production systems and livelihoods at threat under climate change and variability The people who depend most on grasslands are the ones most likely to see those grasslands become less productive, while having the fewest resources to adapt.
The Protection Gap
Forests have long dominated the global conservation agenda. International climate agreements, carbon offset markets, and high-profile conservation campaigns have directed enormous resources toward protecting and restoring tree cover. Grasslands have not received comparable attention, partly because they lack the visual drama of a rainforest canopy and partly because the assumption persists that planting trees is always an ecological improvement.
That assumption can be actively harmful to grasslands. Tree-planting campaigns that target naturally treeless landscapes, whether savannas, steppes, or prairies, do not restore anything; they replace a native ecosystem with a novel one. The evidence from Europe that afforestation of semi-natural grasslands degrades biodiversity and ecosystem services is one example. The Nebraska data showing that converting grassland to pine forest essentially eliminates groundwater recharge is another. Some of the world’s most ambitious reforestation targets include land that was never forested and should not be.
Grassland conservation faces a structural disadvantage in policy as well. The conversion of non-forest ecosystems to agriculture proceeds at nearly four times the rate of deforestation, yet there is no grassland equivalent of the moratoriums and zero-deforestation pledges that have slowed forest clearing in some regions. Part of the issue is monitoring: satellite-based tracking of forest loss is well developed, while tracking the plowing of a prairie or the slow encroachment of shrubs into a steppe is technically harder and attracts less funding.
The identification of the world’s last remaining continuous grasslands has been proposed as a conservation priority, with researchers arguing that intact grassland blocks have outsized ecological value because they maintain landscape-level processes like fire spread, animal migration, and gene flow that fragmented remnants cannot support.14Conservation Science and Practice. The last continuous grasslands on Earth: Identification and conservation importance Whether those arguments gain traction in international policy circles remains to be seen, but the scientific case for treating grasslands as a conservation priority in their own right, rather than as degraded land waiting to become forest, continues to grow stronger.