Grassland ecosystems are landscapes dominated by grasses and other herbaceous plants, with too little or too seasonal rainfall for trees to become the main vegetation. They support a wide range of animals, from grazing mammals and insects to birds, reptiles, and predators. Their ecology is shaped by the close interaction among plants, herbivores, predators, soil organisms, fire, rainfall, and seasonal changes.
Grasslands occur on every continent except Antarctica. They include temperate prairies and steppes, tropical savannas, and other open habitats that differ greatly in climate and vegetation. What they share is an environment in which grasses and other low-growing plants are better adapted to the conditions than dense forests.
What makes a grassland ecosystem?
A grassland is more than an area covered in grass. It is an ecosystem in which living organisms interact with one another and with the physical environment.
Grasses are usually the dominant plants, but grasslands can also contain flowering plants, legumes, sedges, and other herbaceous species. Trees and shrubs may occur in some grasslands, particularly where rainfall is higher, but they do not dominate the landscape.
The amount and timing of rainfall are especially important. In many grasslands, precipitation is insufficient, unreliable, or concentrated in a particular season. Periodic drought can make it difficult for trees to establish and survive. Fire and grazing can also limit the growth of woody vegetation.
These conditions create an open habitat in which sunlight reaches much of the vegetation and animals can move across relatively unobstructed ground.
Why grasses are so important
Grasses form the foundation of many grassland food webs. Through photosynthesis, they use sunlight to convert carbon dioxide and water into organic compounds that store chemical energy. That plant material becomes food for herbivores and, indirectly, for the predators that feed on them.
Grasslands also have an important advantage below ground. Many grasses can survive damage to their leaves because their growth points are located close to the soil surface or below it. Their extensive root systems allow them to regrow after grazing, drought, and, in many ecosystems, fire.
A large portion of a grassland plant’s biomass can therefore exist underground. Roots add organic matter to soil as they grow and die, while soil organisms break down dead plant material and return nutrients to the ecosystem.
This connection between vegetation and soil helps grasslands remain productive even when the plants are repeatedly grazed or disturbed.
Animals that depend on grasslands
Grasslands support animals with very different lifestyles. Some depend directly on the vegetation, while others depend on the herbivores, insects, seeds, or other organisms that grasslands produce.
Grazing mammals
Large herbivores are among the most recognizable grassland animals. Bison, pronghorn, horses, zebras, antelope, and many species of deer and other grazing mammals use grasslands for food.
Their feeding habits can influence the vegetation itself. Grazing removes plant material and can change which species become more or less abundant. Different herbivores also feed in different ways. Some prefer short vegetation, while others can consume taller grasses or browse shrubs and other plants.
Smaller mammals are important as well. Rabbits, prairie dogs, ground squirrels, mice, and other rodents consume grasses, seeds, roots, and other plant material. Their burrowing can also alter soil structure and create shelter used by other animals.
Grassland birds
Open habitats provide essential feeding and nesting grounds for many birds. Grassland birds include species that spend much of their lives on the ground or in low vegetation rather than in trees.
Some feed primarily on seeds and plants, while others eat insects and other small animals. Raptors may hunt rodents and other prey across open terrain.
The structure of vegetation matters greatly to these birds. Some species need tall, dense grass for nesting, while others prefer shorter vegetation. Changes in grazing, fire, rainfall, or plant composition can therefore alter which bird species can use a particular grassland.
Insects and other invertebrates
Grasslands contain enormous numbers of insects and other small invertebrates. Grasshoppers, crickets, beetles, butterflies, moths, bees, ants, and many other organisms occupy different parts of the ecosystem.
Herbivorous insects feed on plants. Pollinating insects visit flowers. Predatory insects consume other insects, while decomposers help break down dead organic material.
Although individually small, these animals are important links between plants, predators, and nutrient cycling. They also provide food for birds, reptiles, amphibians, mammals, and other predators.
Reptiles and amphibians
Reptiles such as snakes and lizards can occupy grasslands where suitable temperatures, prey, and shelter are available. Snakes may feed on rodents, birds, amphibians, or other reptiles, while lizards commonly consume insects and other small animals.
Amphibians are more closely tied to moisture and are particularly important in grasslands that contain seasonal wetlands, streams, or other sources of water. Their presence can vary substantially with rainfall and local habitat conditions.
Predators connect different parts of the food web
Grassland predators depend on the abundance and distribution of smaller animals. Coyotes, foxes, wolves in some regions, wild cats, snakes, hawks, eagles, and owls can all occupy predator roles in different grassland ecosystems.
Predators do more than simply remove prey from the ecosystem. By feeding on herbivores and smaller predators, they influence how energy and nutrients move through the food web. Their presence can also affect where prey animals feed and how they use available habitat.
A grassland food web is therefore not a simple chain. A single plant species may be eaten by many herbivores, and those herbivores may become prey for several different predators.
Fire is a natural part of many grasslands
Fire can play an important ecological role in grasslands. In ecosystems where fires occur naturally or have long been part of the disturbance regime, periodic burning can remove accumulated dead vegetation and suppress some woody plants.
Many grasses can recover after fire because important growing tissues remain near or below the ground. Their ability to regrow gives them an advantage over plants that depend on exposed stems and branches.
Fire does not affect every grassland in the same way, however. Its effects depend on factors such as climate, season, frequency, intensity, and the plants and animals present. Some animals may benefit from newly opened areas, while others depend on taller vegetation that takes time to recover.
Grazing helps shape grassland structure
Grazing is another major ecological force. Herbivores remove vegetation, trample plants and soil, and redistribute nutrients through their movements and waste.
Moderate grazing can create a mixture of vegetation heights rather than a landscape in which every area has the same structure. This variation can provide different feeding and nesting opportunities for different animals.
Too much grazing, particularly when combined with drought or other pressures, can reduce vegetation cover and contribute to soil degradation. The ecological effects therefore depend on the intensity, timing, and environmental context of grazing rather than simply on whether grazing occurs.
Grasslands depend on their soils
Grassland ecosystems are closely connected to the soil beneath them. Dense root systems help hold soil in place and contribute organic material as roots and other plant tissues decompose.
Decomposers, including fungi, bacteria, and soil invertebrates, break down dead material. Nutrients released during decomposition can then become available to plants again.
This creates a continual cycle: plants take nutrients from the soil, animals consume plants, organisms produce waste or die, decomposers break down organic matter, and nutrients return to the soil.
Because so much grassland plant material occurs below ground, soil conditions can remain an important part of the ecosystem even when the vegetation above ground appears relatively simple.
Seasonal changes affect the entire ecosystem
Grasslands can change dramatically with the seasons. Rainfall and temperature influence when plants grow, flower, and produce seeds. Herbivores respond to changes in the availability and quality of vegetation, while predators respond to changes in prey.
In seasonal grasslands, periods of rapid plant growth can provide abundant food for herbivores. During dry or cold periods, food may become scarcer, forcing animals to migrate, move between habitats, change their diets, or conserve energy.
These seasonal cycles connect organisms that may never interact directly. A change in rainfall, for example, can alter plant growth, which affects herbivores, which in turn affects predators.
Grasslands are not all the same
The word grassland covers ecosystems with very different climates and communities.
Temperate grasslands, such as prairies and steppes, generally experience substantial seasonal temperature changes. Tropical grasslands, including savannas, are often shaped by warm temperatures and pronounced wet and dry seasons. Some grasslands occur in regions where cold, drought, poor soils, or other conditions limit tree growth.
Vegetation height, plant diversity, rainfall, fire, grazing, and soil characteristics can all vary widely among grasslands. Consequently, the animals found in one grassland may be very different from those found in another.
What happens when grasslands change?
Grassland animals depend on particular combinations of food, cover, nesting sites, water, and vegetation structure. When those conditions change substantially, the animal community can change with them.
Conversion of grassland to cropland or other land uses can remove habitat directly. Changes in fire and grazing regimes can alter vegetation structure. Invasive plants can change plant communities, while prolonged drought can reduce plant growth and water availability.
Habitat fragmentation can also separate areas that animals need for feeding, breeding, or seasonal movement. A grassland may still look open from a distance while having lost important ecological features that particular species require.
Protecting grassland ecosystems therefore involves more than preserving the visible grasses. The plants, soils, disturbance processes, water availability, and interactions among species all contribute to the habitat on which grassland animals depend.