One square metre of Estonian meadow held 76 plant species
Old meadows shaped by centuries of grazing and mowing rank among the most species-rich habitats on the planet; a single square metre in Estonia set a European record with 76 plant species. Yet nearly 90 percent of Europe's semi-natural grasslands vanished during the 20th century, ploughed, fertilised or reseeded out of existence.
Grasslands grow naturally on every continent but Antarctica and, depending on the definition, cover somewhere between 31 and 69 percent of Earth's land. They thrive where yearly rainfall lands roughly between 500 and 900 millimetres, and are held in place by fire, grazing, drought or frost that keep trees from taking over. Grasses spread late in the Cretaceous; fossilised dinosaur dung contains microscopic traces of grasses related to modern rice and bamboo. True grasslands, though, appeared only about 5 million years ago, as forests shrank.
Semi-natural grasslands are a human and animal collaboration. When early farmers cleared European forests, grazing and hay-making created meadows and pastures whose plants were wild but whose survival depended on the routine of cutting and browsing. Such unimproved grassland can pack 25 species into 100 square centimetres, and English chalk downland supports over 40 per square metre. Most has since been converted to crops or sown with monocultures such as ryegrass and white clover, which are poor in wild species. Survivors now cling mainly to land too awkward to farm, and many red-listed species depend on them.
Grasslands host the greatest gatherings of large animals on Earth, from bison and pronghorn to elephants, rhinos and lions. Beneath them, in the richest undisturbed soils, worms, mites and fungi can work as deep as 6 metres, extending roots and fertilising the ground. Removing key species such as prairie dogs, or introducing invaders like cane toads in northern Australia, can unravel these webs.
The hidden treasure is carbon. Grasslands store about twenty percent of global soil carbon, mostly underground in dense fibrous roots, so soil holds about 81 percent of their total ecosystem carbon. Good management can reverse past losses, though scientists disagree on how much carbon grasslands can ultimately hold, partly because measurement methods differ. Around one billion people depend on grassland services for their livelihoods.
Source: Grassland
