Grassland

• 1. Introduction

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  Grassland covers somewhere between 31 and 69 percent of the Earth's land area, a span so wide it reveals how hard the thing is to even define. Grassland is an area where grasses dominate the vegetation, with sedges, rushes, legumes like clover, and other herbs mixed in. It grows naturally on every continent except Antarctica, and it reaches into most of the planet's ecoregions. One of the largest biomes on Earth turns out to be one of the most contested. Why do these open spaces resist a single definition? How did a meadow in Estonia come to hold 76 species of plants in one square meter? And why have nearly 90 percent of Europe's semi-natural grasslands vanished within a single century? The answers move underground, into deep soil, into fire, and into the long history of who tends these lands.

• 2. Many Names, Many Definitions

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  Any plant community in which grasses or legumes make up the dominant vegetation can count as grassland, according to one of the definitions cataloged for the term. Another, from the Pilot Assessment of Global Ecosystems in 2000, frames grasslands as terrestrial ecosystems dominated by herbaceous and shrub vegetation and maintained by fire, grazing, drought, or freezing temperatures. A third, from Stiling in 1999, draws the line by rainfall: a region with enough average annual precipitation, 25 to 75 centimeters, to support grass.

  Natural, semi-natural, and agricultural grasslands form the three broad types. Semi-natural grasslands exist as a result of human activity such as mowing or livestock grazing, while natural processes maintain their environmental conditions and species pool. Hay meadows are one common example. Some descriptions call them among the world's most biodiverse habitats on small spatial scales, formed over centuries through extensive grazing and mowing, and in modern times kept up without pesticides or fertilisers. The persistence of these definitions side by side points to a deeper tension between what nature builds and what human hands maintain.

• 3. How Grasslands Came To Be

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  Coprolites of fossilized dinosaur feces have been found containing phytoliths of grasses, including grasses related to modern rice and bamboo. The graminoids became widespread toward the end of the Cretaceous period, ranking among the most versatile of life forms. Long before open plains spread across continents, grasses were already present in the diets of dinosaurs.

  Mountains rising in the western United States during the Miocene and Pliocene epochs, across roughly 25 million years, created a continental climate that favoured grassland evolution. The first true grasslands appeared around 5 million years ago, during the Late Miocene in the New World and the Pliocene in the Old World. Existing forest biomes declined as grasslands spread.

  Europe's grasslands have existed throughout the Pleistocene, the last 1.8 million years, which produced wide variability across the continent. Steppe-tundra dominated Northern and Central Europe, while more xerothermic grasslands occurred in the Mediterranean area. Within temperate Europe, the exchange of species and genetic material between biomes made the range of types both wide and unique.

  Semi-natural grasslands first appeared when humans began farming, clearing forests in Europe for agriculture. Ancient meadows and pastures suitable for cultivation became these new grasslands. Yet evidence also points to natural grasslands persisting locally in Europe through the pre-Neolithic Holocene, originally maintained by wild herbivores. As grazing animals and later mowing farmers removed plants, other plant species came to co-exist alongside, and biodiversity evolved. Most of these areas were eventually turned into arable fields and disappeared, as a steady decrease in organic matter locked them into permanent cropping.

• 4. Life In The Sward

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  Seventy-six species of plants were recorded in a single square meter on a meadow in Estonia, a European record for such density. Semi-natural grasslands hold many wild plants, including grasses, sedges, rushes, and herbs, with up to 25 plant species packed into 100 square centimeters. Chalk downlands in England can support over 40 species per square meter. These figures explain why semi-natural grasslands are called among the most species-rich ecosystems in the world.

  Grassland birds include specialists such as the snipe and the little bustard, alongside a rich invertebrate fauna tied to the wild-plant diversity of unimproved grasslands. Pollinators rely on these habitats too, which has drawn many recent conservation efforts. Original North American prairie grasslands and lowland wildflower meadows in the UK are now rare, and their associated wild flora is equally threatened.

  Agriculturally improved grasslands, the kind that dominate intensive modern farming, are usually poor in wild plant species. Fertilizing, weed killing, plowing, or re-seeding destroyed the original diversity. Sown monocultures of cultivated grasses and clovers, such as perennial ryegrass and white clover, replaced the wild communities. Almost 90 percent of Europe's semi-natural grasslands no longer exist, a loss driven by political and economic reasons across the 20th century. Those in Western and Central Europe have almost disappeared completely, with a few left in Northern Europe, and a large share of red-listed species are specialists of exactly these vanishing habitats.

• 5. The Creatures Of The Plains

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  Jaguars, African wild dogs, pronghorn, black-footed ferret, and plains bison are among the great aggregations of large animals that grasslands support, the largest such gatherings on Earth. The list runs on through the African elephant, Sunda tiger, black rhino, white rhino, greater one-horned rhino, Indian elephant, swift fox, and mountain plover. Lions and cheetahs hunt in the grasslands of the African savanna.

  Mites, insect larvae, nematodes, and earthworms inhabit soil that can reach 6 meters underground in undisturbed grasslands on the richest soils of the world. These invertebrates, together with symbiotic fungi, extend root systems, break apart hard soil, and enrich it with urea and other natural fertilizers. They trap minerals and water and promote growth, and some fungi make plants more resistant to insect and microbial attacks.

  The blue wildebeest, American bison, giant anteater, and Przewalski's horse count among the typical large mammals, while grassland in all its forms supports mammals, reptiles, birds, and insects alike. Removing key species such as buffalo and prairie dogs in the American West, and introducing invasive species like cane toads in northern Australia, has disrupted the balance and damaged other species. Elephants, bison, and lions have long drawn hunters, and where hunting goes uncontrolled or illegal, species can become extinct.

• 6. Carbon Below The Surface

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  About twenty percent of global soil carbon stocks are held in grasslands, stored not in leaves but in roots and soil underground. Herbaceous vegetation dominates these systems, and above-ground biomass carbon is short-lived because of grazing, fire, and senescence. Grasses often account for 60 to 80 percent of the biomass carbon, with extensive fibrous root systems extending several meters down. Soil carbon makes up about 81 percent of the total ecosystem carbon in grasslands, producing deep, fertile soils high in organic matter.

  Precipitation sets the ceiling on plant productivity, so carbon stocks are highest where rainfall is heaviest, such as the high grass prairie of the humid temperate United States. As annual temperatures rise, grassland carbon stocks fall through increased evapotranspiration. Soil disturbances, vegetation degradation, fires, erosion, nutrient deficiencies, and water shortages have all caused large losses of organic carbon.

  Good grassland management can reverse historical soil carbon losses, and the link between improved biodiversity and carbon storage is a subject of research. There is no firm agreement on how much carbon grasslands can store, partly because different methods measure soil organic carbon differently and datasets remain limited. Carbon accumulation in soils shifts significantly over time, so a single point-in-time measurement leaves the evidence base thin.

• 7. Vanishing Ground

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  Global losses from grassland degradation are estimated at over $7 billion per year, placing grasslands among the most threatened ecosystems. According to the International Union for the Conservation of Nature, the most significant threat is human land use, especially agriculture and mining. Misclassification, poor protection, and cultivation all add to their vulnerability. To feed a growing population, most of the world's grasslands are converted into fields of corn, wheat, or other crops, and even largely intact systems like the East African savannas face loss to agriculture.

  Misguided afforestation can harm grasslands, including efforts tied to the global push for carbon sequestration. A map created by the World Resources Institute with the IUCN identifies 2 billion hectares for potential forest restoration, and it has been criticised for including 900 million hectares of grasslands. Non-native grasses are expected to keep outperforming native species under the warmer, drier conditions that climate change brings.

  Land management itself can drive loss. A study in Brazilian Subtropical Highland Grasslands found that grasslands without traditional management, which uses fire every two years and extensive cattle grazing, can disappear within 30 years. Inside protected areas where fire was banned and cattle grazing prohibited, grasslands were quickly replaced by shrubs. Land cover figures sharpen the picture: in 1960 semi-natural grassland covered 18.8 percent of the land studied, more than the 15.8 percent under arable. By 2015 forest cover had risen to 50.8 percent and arable to 20.4 percent, while semi-natural grassland fell to 10.6 percent. A quarter of semi-natural grassland was lost through intensification, converted into arable, pasture, and forest.

• 8. Tending And Restoring

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  Rangelands account for an estimated 70 percent of the earth's landmass, and many cultures, including those of the United States, are indebted to the economics they offer. Grazing animals, tourism, clean water and air, and energy extraction all flow from these grass-dominated arid and semi-arid lands, studied under rangeland management. Woody encroachment, the expansion of woody plants at the expense of the herbaceous layer, affects vast areas through a mix of fire exclusion, overstocking, overgrazing, and rising atmospheric CO2.

  Understanding of restoration options remains limited despite growing recognition of grassland importance, and the cost of restoration is highly variable with scarce data. Prescribed fires, careful management of livestock and wild herbivores, tree cutting, shrub removal, invasive species control, and reintroduction of native grasses and forbs by seeding or transplant all feature among the methods. Overcoming seed limitation stands out as a main challenge.

  Grasslands provide marketed and non-marketed ecosystem services fundamental to the livelihoods of an estimated one billion people globally. For 2021 to 2030, the United Nations General Assembly has proclaimed the UN Decade on Restoration through a joint resolution by over 70 countries, led by the United Nations Environment Programme and the Food and Agriculture Organization. The Everglades of Florida, the world's largest rain-fed flooded grassland, holds 11,000 species of seed-bearing plants, 25 species of orchids, 300 bird species, and 150 fish species, a measure of what such restoration stands to protect.