SEQUOIA NATIONAL PARK, California — High in the evergreen canopy of General Sherman, the world’s largest tree, researchers searched for evidence of an emerging threat to giant sequoias: bark beetles. The climbers descended the towering 2,200-year-old tree with good news on Tuesday. “The General Sherman tree is doing fine right now,” said Anthony Ambrose, executive director of the Ancient Forest Society, who led the expedition. “It seems to be a very healthy tree that’s able to fend off any beetle attack.” It was the first time climbers had scaled the iconic 275-foot (85-meter) sequoia tree, which draws tourists from around the world to Sequoia National Park. Giant sequoias, the Earth’s largest living things, have survived for thousands of years in California’s western Sierra Nevada range, the only place where the species is native.