Posted: Wednesday, September 5, 2007 12:00 am
CORVALLIS - The traditional emphasis on dense, fast-growing, conifer-dominated forests in the Pacific Northwest raises questions about the health of dozens of animal species that depend on shrubs, herbs and broad-leaf trees, a new analysis by Oregon State University and the U.S. Geological Survey suggests.
At least 78 vertebrate species have been documented that require, in one way or another, the food or habitat provided by non-coniferous vegetation, and may be at increasing risk whenever forest management reduces the prevalence of these shrubs or trees, or specifically targets them for removal.
The study was just published in Forest Ecology and Management, by Joan Hagar, an affiliate faculty member of the Department of Forest Science at Oregon State University, and a wildlife biologist with the Forest and Rangeland Ecosystem Science Center of the U.S. Geological Survey, which funded the study.
Natural forests of the Northwest, Hagar said, have always been dominated by conifers. But they also provided a continuity of trees that are young and old, short and tall; diverse shrubs, especially in the early stages of forest regrowth; gaps, snags and cavities; a dozen or more hardwood tree species; and possibly hundreds of grass and herbacious plant species.
In contrast, the report said, a managed forest is planted very densely with conifer trees, which dominate the forest within a short time. Broad-leaf trees and shrubs are often suppressed with herbicides or other management techniques. Even when new forestry techniques are used to encourage a diversity of trees with different sizes and ages, the undergrowth trees are usually conifers.
"Historically, forests contained significant amounts of alder, big leaf maple, white oak or vine maple," Hagar said. "The undergrowth would feature vegetation species such as California hazel, ferns, Oregon-grape, salal, many other types of shrubs and herbs."
Even when the primary goal of a private or public forest is sustainable timber production, Hagar said, the lack of historic tree diversity, shrub and vegetation species may have long-term impacts on forest health, including ability to resist disease, soil function and fixation of nitrogen. An illustration of this concern is a current epidemic of Swiss Needle Cast, a tree disease occurring in areas that used to have many diverse tree and shrub species, but which have been largely converted to a monoculture of Douglas fir.
For the Democrat-Herald