Grassland

Grasslands are vast terrestrial ecosystems where grasses and legumes are the dominant vegetation.

These biomes are incredibly widespread, covering between 31% and 69% of the Earth's total land area. You can find them on every continent except Antarctica. A grassland is defined by its specific environment and plant life. These areas usually receive between 25 and 75 cm of average annual precipitation. This amount of rain is enough to support grass but not enough for thick forests. They are maintained by natural forces like fire, grazing, drought, and freezing temperatures.

There are three primary types of grasslands: natural, semi-natural, and agricultural. Natural grasslands exist without human interference. Semi-natural grasslands are a very common subcategory. These form through human activities like mowing or livestock grazing. While humans influence them, natural processes still maintain the species pool. These areas are often among the most species-rich ecosystems in the world. For example, some meadows in Estonia have recorded 76 plant species in just one square meter.

In contrast, agricultural grasslands are often modified by humans. These are frequently turned into monocultures, where only one type of plant is grown. This process often uses fertilizers and pesticides, which can reduce the original plant diversity.

Grasslands have a deep evolutionary history spanning millions of years. Graminoids, or grass-like plants, became widespread toward the end of the Cretaceous period. Scientists have even found fossilized dinosaur feces, called coprolites, containing bits of early grass relatives.

Around 5 million years ago, the first true grasslands appeared in the New and Old Worlds. This happened as forest biomes began to decline. In the western United States, the rise of mountains during the Miocene and Pliocene epochs helped create a climate perfect for grass. Following the Pleistocene ice ages, grasslands expanded in hotter, drier climates. They became a dominant land feature across the globe over 1.8 million years ago.

The biology of a grassland involves a complex web of interactions. Perennial grasses have extensive, fibrous root systems. These roots form thick mats that hold the soil firmly in place.

In undisturbed areas, the soil can reach depths of 6 metres. Deep in the soil, invertebrates like earthworms, mites, and insect larvae live. These creatures, along with symbiotic fungi, help the ecosystem thrive. They break apart hard soil and add natural fertilizers like urea. Fungi can even help plants resist attacks from microbes or insects. This underground activity creates deep, fertile soils with high organic matter.

Animals in the grasslands often live in massive groups. Grasslands support some of the largest aggregations of large animals on Earth. You might see African elephants, plains bison, or white rhinos in these habitats.

Predators like lions, cheetahs, and jaguars also rely on these open spaces.

The vegetation can vary from short grasses to tall prairies. Some grasslands, known as savannas, include scattered trees and shrubs. These include the dehesa and montado regions in Spain and Portugal. However, the removal of key species like prairie dogs can disrupt the entire ecological balance.

Grasslands provide essential services that support about one billion people globally. One of their most important roles is carbon sequestration, which is the process of capturing and storing carbon.

Grasslands hold about 20% of the world's soil carbon stocks. Most of this carbon is stored underground in the roots and soil. In fact, soil carbon accounts for approximately 81% of the total ecosystem carbon. This happens because the underground biomass is much larger than the visible plants above. By storing carbon in the soil, grasslands help regulate the Earth's climate.

Despite their importance, grasslands are among the most threatened ecosystems. Many have been lost to agricultural improvement, such as plowing or fertilizing. In Europe, nearly 90% of semi-natural grasslands disappeared during the 20th century. This loss happened due to various political and economic reasons. When grasslands are converted to intensive farming, they often lose their wild plant diversity. This affects many "specialist" species, including certain birds and pollinators. Protecting these lands is vital for maintaining global biodiversity and managing the planet's carbon.