Hemlocks play an important role in the ecology and hydrology of mountain ecosystems. They offer critical habitat for birds. As many as 90 species can be found in hemlock forests. A few, mostly songbirds, seem particularly associated with hemlocks: the black-throated green warbler, the Blackburnian warbler and the Acadian flycatcher. Some warblers nest nowhere else.
Hemlocks do best in moist ground and, while they are found from swamps to ridges, they are especially common along streams where they play a major role in stream ecology, helping to soften temperature extremes, creating structure in stream courses, offering a rich breeding ground for the invertebrates that fish feed on.
Hemlock-dominated watersheds supported more aquatic invertebrate (insect) species than streams draining hardwood forests. Fifteen aquatic insect species were strongly associated with hemlock and three species were found only in hemlock streams. Brook trout were two and a half times as likely to occur in hemlock streams as in hardwood streams, and were twice as abundant in hemlock streams.
So if there are brook trout in your favorite mountain stream, thank a tree–most likely a hemlock. In all, according to some experts, hemlock forests are home to upwards of 120 vertebrate species as well. Hemlocks are a favored browse species for white-tailed deer, a dietary preference that can inhibit hemlock regeneration as deer nip off new growth.
Read about the role hemlocks play in the Great Smoky Mountains National Park here.