They are considered to be the second largest rodent in the world. The subspecies nigra is thought to have 10 populations within its geographic range, totaling 100 animals. Diet. Further nutrients are recovered in the form of fecal pellets that the beaver will re-ingest. Mountain beavers are herbivorous animals; their diet includes forbs, grasses, and even ferns such as sword fern and bracken fern. In summer they prefer sword ferns, bracken, leaves and various herbaceous plants. Anything plant-based is potential beaver food.
The IUCN Red List resource estimates the global Mountain beaver population size from 10,000 to over 1,000,000 individuals.

They also eat roots, grasses and aquatic plants, and in captivity they even eat leafy greens and mixed vegetables. Researchers are unsure of the exact composition of the diet of this species. The composition of the diet of mountain beavers differs depending on the sex and age of the individual and the season. The beaver (Castor) is a large semi-aquatic rodent with the nocturnal nature. This article unleashes some of the significant beaver diet facts that are not common. Diet of the Mountain Beaver.
We do know that they feed on young trees and eat the bark of older trees. Mountain beaver do not hibernate and, in winter, eat conifer needles, leaves, tender twigs and bark, often climbing 2.5 m up shrubs and trees to clip leaders and branches. These clever engineering animals eat the bark right off trees they fell for building dams and lodges, along with twigs, buds and leaves. These animals are well reputed to build dams, lodges, and canals. This rodent is an herbivore, which means that they eat only plants. They also eat ferns and other small shrubs.

Mountain beaver is a very widespread, common species. Beavers will eat bark from hardwood trees such as birch, aspen, willow, cottonwood, and adler.