Although white pine first brought loggers to northern Wisconsin, another evergreen giant – hemlock – actually outnumbered white pine at the time. Today, travelers driving across large parts of the Northwoods may see only scattered hemlocks or small, isolated groves.

What ecologists and foresters call the hemlock-hardwood forest once spread over much of the upper Great Lakes region. After logging in the last century, the pines and the hardwoods – birch, aspen, oak and especially maple – came back strong. Hemlock did not.

The Eastern hemlock was the most common tree that surveyors noted in northern Wisconsin in the 1840s, according to Craig Lorimer, a University of Wisconsin-Madison forest ecologist. Based on 19th-century surveyors” records that UW-Madison landscape ecologists have compiled, hemlock was more common than any of the hardwoods. It made up 14 percent of the “witness” trees surveyors recorded as reference points when locating township markers.

The hemlock, which can live up to 500 years and reach 100 feet, casts little shade in Wisconsin today. And hemlock could decline further without special precautions, Lorimer says.

Hemlock trees face a double whammy. In winter and spring, deer are often attracted to hemlock”s green foliage when most other vegetation is dormant. They can browse seedlings to within inches of the forest floor. So when logging or windstorms create openings, fast-growing hardwoods usually overtop and suppress hemlock.

Lorimer has conducted several research projects to clarify the ecology of this once-dominant tree and learn how to encourage its success. He has studied an old-growth forest in Upper Michigan where hemlocks survive to an average age of 300 years. And recently he and a student studied how well young hemlock can compete with other trees in small forest openings. (See sidebar.)

“Although hemlock has not traditionally been a highly valued species for lumber or pulp, it is important aesthetically and for biological diversity in northern forests,” says Lorimer, a member of the Department of Forest Ecology and Management in the College of Agricultural and Life Sciences.

To restore natural plant communities and encourage biological diversity, ecologists, wildlife managers and foresters increasingly are focusing on the mosaic of habitat types present in North America before European settlement. Ecologists want to make sure those habitats – be they old-growth forests, young forests, wetlands or open areas – are well represented in today”s landscape. Hence the concern over hemlock.

Lorimer says that Wisconsin has little remaining old-growth forest habitat, particularly hemlock stands. But he says that turning most of our forests into old growth isn”t the solution to problems with biological diversity.

“A vast landscape of homogeneous old-growth forest is not necessarily a good thing for biological diversity,” Lorimer says. “For example, ecologists have identified 74 species of migrant birds that depend upon young forest habitat.”

Wildlife biologists are concerned that many areas in the East are becoming an overly uniform landscape of mature forest that is missing the range of age classes that was common before settlement. Lorimer says that their concern prompted two recent scientific conferences.

“The best thing for biological diversity would be a large landscape with all stages of forest development, including some old growth with trees of different ages,” Lorimer says. “Old-growth hemlock stands, for example, are good for some species but not others.”