The giant sequoia is so enormous that it was once believed to be indestructible. High in California’s southern Sierra Nevada mountains, the oldest trees – known as monarchs – have stood for more than 2,000 years. Today, however, in Sequoia national park, huge trunks lie sprawled on the forest floor, like blue whale carcasses stranded on a beach. Many of these trees were felled by a combination of drought and fire. But among the factors responsible for the rising toll is a tiny new suspect: the bark beetle. …“This is a global phenomenon but it is also a complicated story,” says Prof Diana Six, a forest entomologist at the University of Montana. …“If the beetles kill a bunch of trees and they grow back, it’s not such a big deal,” she says, but adds: “If the conditions won’t allow regeneration, that is not just serious for carbon sequestration – think about the wildlife that’s going to go: a big extinction.”