Traditional Emphasis on Dense Conifer Forests Questioned

Traditional Emphasis on Dense Conifer Forests Questioned



Aug. 2007  - The traditional emphasis on 
dense, fast growing, conifer forests in the Pacific Northwest raises 
questions about the health of dozens of bird and animal species that 
depend on shrubs, herbs and broadleaf trees, suggests a new analysis by 
Oregon State University and the U.S. Geological Survey. 
Conifers are evergreen trees such as fir and cedar that dominate the 
forests of the Pacific Northwest. 
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. 
At least 78 vertebrate species have been documented that require the food 
or habitat provided by non-coniferous vegetation, and may be at risk 
whenever forest management reduces the prevalence of these shrubs or 
trees, or targets them for removal. 
Among these species of concern are three birds, one amphibian, and five 
mammals that already have federal or state status as threatened or 
endangered. 
Declines of western bluebirds have been linked to reduction of available 
nest sites. Similarly, a major threat to the willow flycatcher is 
destruction of shrubby vegetation. 
Mountain quail populations have declined due to loss of upland shrub 
habitats, plant species diversity and loss of woody vegetation in riparian 
zones. And a major threat to Columbian white-tailed deer has been removal 
of "brush" during logging or agricultural development. 
In similar fashion, 90 percent of the diet of the northern spotted owl is 
composed of small mammals that are associated with non-coniferous 
vegetation. 
Many species rely on a diversity of grass, herb, shrub and tree species 
for their energy needs, the report said. Fruits from deciduous trees and 
shrubs are a critical resource for migrant birds. 
Rodents cache seeds and nuts to get through the winter. Many species of 
insects depend on specific host plants, and in turn form the diet for many 
birds and some mammals. And in the conifer forests of western Oregon, 
hardwood trees support the abundance of 69 percent of the butterflies and 
moths. 
"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. And this type of vegetation, 
in turn, provides the habitat and food base for many wildlife species." 
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. 
Hagar said management options for a wider diversity of vegetation and the 
wildlife species that depend on it include slower rates of conifer 
re-establishment, less-dense conifer plantations, more thinning of 
over-stocked forests, and less control of shrubs or other vegetation. It 
may take a decade or more, she said, for shrubs, herbs and broad-leaf 
trees to recover. 

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