Open water and freshwater marshes occupy 40,000 acres of the refuge, Extensive areas of willow, trees and grasses are found on an additional 21,500 acres on higher ground. Common trees growing in the hardwood forest are aspen, bur oak, green ash, elm and box elder. Two black spruce-tamarack bogs with associated bog lakes comprise a 4,000 acre wilderness area. Today there are 74 resident species within the state. Mammals on the refuge range in size form the small pygmy shrew to the large Northwestern moose.
Mammals are important in the ecology of the refuge.
Herbivores such as mice, squirrels, rabbits, hares, muskrats and deer change plant food energy into animal protein which then becomes available to predators such as mink, gray wolf, hawks and owls. Some of the mammals such as raccoon, red fox and coyote play the role of scavangers, as well as predators. Many mammals are fairly common and are most active during early morning or late evening. Others are rare, secretive, or appear only at night. Mammals select habitat which provides good cover making observation more difficult than birds.