The world’s largest living species, native to California’s Sierra Nevada, faces a two-pronged risk from declining snowpack and rising temperatures. The threat to sequoias mirrors a growing danger to trees worldwide, with some scientists saying rapid warming this century could wipe out many of the planet’s old trees. Few living things seem as permanent as the giant sequoia trees of California’s Sierra Nevada. The largest species of flora or fauna on Earth, these towering redwood trees have held sway for millions of years in a narrow band of their native mountain habitat. With heights reaching 300 feet and girths as large as 150 feet, some sequoias can live in excess of 3,000 years before being naturally toppled by a combination of weather and gravity.