Many forest animals eat grass, though fewer than you might expect. Most forest-dwelling mammals are browsers, meaning they prefer leaves, twigs, bark, and shrubs over grass. But several species rely on grass as a significant part of their diet, especially in forest clearings, meadows, and along woodland edges where grasses grow in available sunlight.
Large Grazers in Forest Habitats
Elk are the most prominent grass-eaters in North American forests. They graze heavily in meadows, forest clearings, and along riparian areas, with grass making up well over 25% of their annual diet. During summer months, elk spend much of their time in open patches within forests where grasses are abundant, then move into denser tree cover for shelter.
Bison, including wood bison that inhabit boreal forests, also consume large quantities of grass. Wood bison shift their diet dramatically by season. In winter, grasses and grass-like plants make up about 44% of what they eat, alongside woody browse. By summer, though, grass drops to less than 1% of their diet as they switch almost entirely to leafy plants and browse. This kind of seasonal flexibility is common among forest herbivores and depends heavily on what’s available and nutritious at any given time.
Bighorn sheep, which inhabit mountainous forests and alpine meadows, are consistent grass-eaters year-round. Red deer (the European relative of elk) fall into the “mixed feeder” category, switching between grass and browse depending on location and season.
Deer Are Mostly Browsers, Not Grazers
White-tailed deer and mule deer live in forests throughout North America, but grass is a relatively small part of their diet. Both species eat less than 25% grass, preferring the leaves, buds, and twigs of woody plants along with forbs like wildflowers and clover. Moose take this even further. They are classified as true browsers, feeding on willow, birch, and aquatic plants while largely ignoring grass altogether.
This distinction between grazers and browsers comes down to behavior more than anatomy. Scientists once believed the two groups had fundamentally different digestive systems, but more recent analysis shows the real difference is in how they forage. Grazers tend to increase their intake rate as food becomes more available, while browsers maintain a steadier, more selective feeding pattern regardless of abundance. In practice, this means deer in a forest meadow will pick through the vegetation carefully for their preferred plants, while elk in the same meadow will sweep through the grass more efficiently.
Small Mammals That Depend on Grass
Voles are among the most dedicated grass-eaters in forest ecosystems. Prairie voles and meadow voles live in grasslands and old fields near forest edges, and grasses and sedges form the core of their diet. In feeding trials, prairie voles showed strong preferences for perennial ryegrass and orchard grass, while meadow voles favored tall fescue and smooth brome. Both species also eat clover, alfalfa, and dandelion, but grassy shoots are their staple food.
Eastern cottontail rabbits eat grass too, though they’re less specialized. In summer, cottontails feed on a mix of grasses and broad-leaved plants. In winter, they shift heavily toward woody plants like bark and twigs. Feeding trials found that cottontails moderately preferred several grass species, including tall fescue, timothy, and Kentucky bluegrass, but didn’t rank any grass as a top-choice food the way voles did. Rabbits are generalists that use whatever a forest edge provides.
Black Bears Eat Grass in Spring
One of the more surprising grass-eaters in the forest is the black bear. After emerging from their dens in spring, black bears eat enormous quantities of grass and herbaceous plants. One study found that grasses and herbaceous plants made up 90% of black bear diet in spring. The reason is simple: fresh young grass is one of the first green foods available after winter, and at that stage it’s tender and relatively easy to digest.
As spring turns to summer, bears largely abandon grass. Maturing grass develops more crude fiber, which bear digestive systems handle poorly compared to ruminants like elk or deer. Bears shift to berries, fruits, and seeds, which are packed with easily accessible carbohydrates. So while bears technically eat grass, they do it only during a narrow seasonal window when better options haven’t appeared yet.
How Grass-Eaters Digest Tough Plant Fiber
Grass is difficult to digest. Its cell walls are reinforced with cellulose, a tough structural compound that most animals can’t break down on their own. Forest animals that eat grass regularly have evolved one of two main strategies to handle this.
Elk, deer, bison, and bighorn sheep are ruminants. They have a multi-chambered stomach where microbes produce an enzyme that breaks cellulose into simpler compounds. Those microbes then convert the broken-down material into fatty acids that the animal absorbs as energy. The microbes also generate B vitamins as a byproduct, giving ruminants a nutritional bonus from their symbiotic gut bacteria. This is why ruminants can thrive on a grass-heavy diet that would leave other animals malnourished.
Horses, which sometimes graze in forest clearings, use a different approach. They’re hindgut fermenters, meaning the microbial breakdown happens in an enlarged section of the large intestine rather than the stomach. The result is similar: microbes process cellulose and produce fatty acids absorbed through the intestinal wall. This system is less efficient at extracting nutrients from each mouthful, which is why horses need to eat more volume than a similarly sized ruminant.
Voles and rabbits fall somewhere in between. Rabbits practice coprophagy, re-eating specialized droppings to extract additional nutrients from plant material that passed through too quickly the first time. Voles have an enlarged cecum (a pouch at the junction of the small and large intestines) that houses cellulose-digesting microbes, giving them a simplified version of the hindgut fermentation system.
How Grazing Shapes the Forest
Animals that eat grass and other plants in the forest understory play a measurable role in shaping which plants survive and which don’t. Deer, for instance, tend to browse on the most fast-growing, competitive plant species. By keeping those dominant species in check, they create space for slower-growing plants that would otherwise be crowded out. Research in temperate forests found that moderate deer browsing actually increased seedling diversity because deer consumed enough of the dominant species to let subdominant ones survive, without killing off the preferred species entirely.
The relationship works in both directions. Mixed plant communities withstand herbivore pressure better than single-species patches. In experimental plots, monocultures suffered 53% more intense damage from deer browsing than diverse plant communities did. Less palatable species in a mixed stand essentially shield their neighbors, spreading the impact of grazing across many species rather than concentrating it on a few. This feedback loop, where grazers maintain diversity and diversity buffers against overgrazing, helps explain why forests with moderate herbivore populations tend to have richer, more varied understories than those where grazers have been removed or become overabundant.