Peter Gould, a research forester at the U.S. Forest Service's Pacific Northwest Research Station in Portland, Ore., said fire suppression programs, conifer and invasive plant encroachment and land use changes have resulted in the loss of as much as 99 percent of the oak communities historically present in some areas of the region.

The study's findings indicate that if oaks are to be successfully restored, more aggressive management is needed within the next several decades.

"In areas where conifers have encroached into oak woodlands and savannas, about two-thirds of the remaining oaks were predicted to die over a 50-year period unless the conifers are removed," said Gould, lead author of the report.

An electronic copy of the report is available at http://www.fs.fed.us/pnw/pubs/pnw_gtr745.pdf. Print copies will be available May 30.