The typical industrial forests of the Northwest, with their concentrations of evergreen trees, can be bad for wildlife that depend on other types of trees and plants for survival, according to a study by the federal government.
The study by the United States Geological Survey focused on managed forests that are planted densely with conifers - cone-bearing evergreens such as pines and firs - which dominate the forest within a short time. Broadleaf trees and shrubs are often killed with herbicides soon after the forest is planted, to diminish competition.
The natural forests of the Northwest have always been dominated by conifers. But they also have had trees of varying ages and sizes along with a diversity of shrubs, hundreds of different plant species and perhaps a dozen or more kinds of hardwood trees, according to the study's author, Joan Hagar, a USGS wildlife biologist.
And 78 vertebrate species in Oregon and Washington rely on a diversity of plants in the forest to survive, Hagar found. The northern spotted owl, for instance, gets 90 percent of its diet from small mammals that live off nonconiferous vegetation.
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The study says that planting conifers less densely, thinning more and spraying less all would contribute to a broader variety of vegetation.
Mike Mosman, vice president of Port Blakely Tree Farms, a family-owned company based in Tumwater, said even managed timberlands are diverse. By law, they include buffers along streams and other sensitive areas that are not planted with conifers. That maintains some diversity of habitat across the landscape.
And while managers spray with herbicides to allow newly planted forests to get going, once the trees are established, the underlying vegetation grows back, he said. "You can't think of it as the cornfields of Kansas; it's a more diverse landscape."
Even so, Mosman said, managed forests aren't intended to mimic natural ones.
"Compare it to a garden," he said. "If you have a quarter-acre garden, and you have five clumps of lettuce, you are not going to do very well."