Two conservation groups have threatened to sue the U.S. Forest Service over a long-debated timber sale to reduce fire hazard around Lemolo and Diamond lakes. Eugene-based Cascadia Wildlands and Portland-based Oregon Wild contend the Umpqua National Forest timber sale would harm the threatened northern spotted owl. They announced Wednesday they plan to go to court if the Forest Service doesn’t modify its D-Bug Hazard Reduction Sale to avoid destroying spotted owl habitat. The timber sale is intended to reduce fire danger to popular recreation areas by thinning mountain pine beetle-infested trees. The plan originally called for removing fire-prone dead and …