Life zones in Alaska range from grasslands, mountains, and tundra to thick forests, in which Sitka spruce (the state tree), western hemlock, tamarack, white birch, and western red cedar predominate. Various hardy plants and wild flowers spring up during the short growing season on the semiarid tundra plains. Species of poppy and gentian are endangered.
Mammals abound amid the wilderness. Great herds of caribou migrate across some northern areas of the state. Moose move within ranges they establish, but do not migrate seasonally or move in herds as do caribou. Reindeer were introduced to Alaska as herd animals for Alaska Natives, and there are no free-ranging herds in the state. Kodiak, polar, black, and grizzly bears, Dall sheep, and an abundance of small mammals are also found. The sea otter and musk ox have been successfully reintroduced. Round Island, along the north shore of Bristol Bay, has the world's largest walrus rookery. North America's largest population of bald eagles nest in Alaska, and whales migrate annually to the icy bays. Pristine lakes and streams are famous for trout and salmon fishing. In all, 386 species of birds, 430 fishes, 105 mammals, 7 amphibians, and 3 reptiles have been found in the state.
Seven species listed as endangered by the US Fish and Wildlife Service as of August 2003 included the Eskimo curlew, short-tailed albatross, leatherback sea turtle, steller sea-lion, and bowhead, finback, and humpback whales. Three species listed as threatened included the spectacled eider, Steller's aider, and Steller sea-lion. Numerous species considered endangered in the conterminous US remain common in Alaska.