Fens are a type of mire, or a peat-accumulating wetland, and are most commonly found in boreal and subarctic regions. Because surface water percolates slowly through fens (that is, they are minerotrophic), they are relatively well supplied with nutrients and alkalinity, and are only slightly acidic. Consequently, fens are relatively productive, and they are non-acidic or only slightly acidic. Fens have a plant community dominated by short-statured graminoids, especially sedges and rushes, some shrubs, and species of peat-moss (Sphagnum spp.) that do not prefer acidic habitats. Because they are not very productive, fens support relatively small populations of animals, although their associated open-water habitat may be used by breeding ducks, geese, and cranes.