The Arctic tundra is an extreme biome defined by permanently frozen subsoil, known as permafrost, and a short, cold growing season. This harsh environment limits plant life primarily to low-growing forms like mosses, lichens, and dwarf shrubs. Arctic mosses, which are non-vascular bryophytes, form dense, insulating carpets across the landscape, acting as a foundational species in this fragile ecosystem. These resilient plants thrive despite the frigid temperatures and high winds, setting the stage for the limited food web that sustains the region’s herbivores.
The Unique Role of Arctic Moss in the Tundra Diet
The consumption of Arctic moss is often a nutritional compromise for tundra animals, rather than a preference. Moss is a challenging food source due to its low overall digestibility and high fiber content, which can be as much as 80% in some species. Furthermore, many bryophytes contain anti-nutritional compounds that deter consumption.
Despite these drawbacks, the sheer abundance of moss makes it a crucial resource, particularly during the long, dark winter months. When more palatable vascular plants, like sedges and grasses, are covered by thick snow or dormant, moss becomes a readily available survival food. For many herbivores, consuming moss is an unavoidable consequence of foraging when preferred plant matter is scarce.
Large Mammalian Grazers and Their Moss Consumption
Among the largest herbivores of the Arctic, Caribou and Musk Oxen rely on moss as a winter dietary component. While their primary winter food is typically lichen, moss becomes a significant fallback when lichens are inaccessible or depleted. The presence of moss fragments in the feces of these ruminants often signals a period of low availability of their favored forage.
These large grazers possess specialized digestive systems, including a multi-chambered stomach, that facilitate microbial fermentation necessary to break down the tough cellulose and lignin in mosses. Even with these adaptations, moss provides a low nutritional return, and its consumption may represent a net energy cost. Beyond consumption, their grazing and trampling activities reduce the thickness of the moss layer. This reduction allows more solar energy to reach the soil, increasing the ground temperature and potentially extending the growing season for vascular plants.
Small Mammals and Avian Species Utilizing Arctic Moss
Smaller tundra inhabitants, including Lemmings and Voles, depend on Arctic mosses, often using them for both sustenance and shelter. Lemmings are herbivores that feed on a variety of vegetation, and while they are not strictly moss specialists, they readily consume mosses, grasses, and sedges. The continuous growth of their incisor teeth allows them to process this tough, fibrous forage.
In some areas, species like the Wood Lemming are almost entirely dependent on one or two moss species. Lemmings often forage beneath the snow, where mosses are a consistent food source throughout the winter. Their cyclical population booms can lead to heavy grazing pressure, significantly impacting the local moss micro-ecosystem. Mosses also serve a crucial non-dietary function, used extensively as insulating material for their winter nests and burrows.
Avian species, particularly certain waterfowl, also incorporate moss into their diet. The Barnacle Goose, for example, feeds heavily on mosses during the winter months when grasses are less available. In regions like Svalbard, moss can become a substantial part of their cold-season diet.
Other birds, such as the Ptarmigan, may also consume mosses, often targeting the softer parts or incidentally ingesting them while feeding on other low-growing plants. Certain goose species have been observed to specifically target the spore-producing capsules of mosses. This consumption by both small mammals and birds highlights the role of moss as a foundational food resource across multiple trophic levels in the challenging Arctic environment.