What’s captured people’s attention about the Washburn fire raging in Yosemite isn’t just its size or scope, but the fact that it threatens a giant Sequoia with a name, Grizzly Giant, and an extreme age: It’s almost 3,000 years old.
The oldest trees have scientific as well as sentimental value. There’s something alarming about the thought that anything hardy enough to live through multiple millennia could now be in trouble. As it turns out, climate change is not even the worst hazard the oldest trees face.
Trees possess a quality that humans had once attributed to gods: They don’t age. Or as forest ecologist Nathan Stephenson puts in a more scientifically accurate way, there’s a growing school of thought that trees don’t undergo senescence, a programmed slide toward decline and death that puts a limit on the lives of animals. “They die from accidents, like getting attacked by bark beetles, getting burned in a fire … getting infected by a pathogen,” said Stephenson, who is a scientist emeritus with the USGS Western Ecological Research Center.
Someone once did a calculation, he said, that if humans didn’t senesce but only died when our luck ran out, the average lifespan would be about 700 years. Some unlucky people would die at five, and some lucky ones would live thousands of years.
Trees, including giant Sequoias, don’t have life expectancies of 3,000 or more years. Most never survive the sapling stage, and of those that reach adulthood, most never get to their 1,000th birthday. But a few can last thousands of years.
The only way to ascertain the age of a living tree is to take a pencil-thin section from the trunk and count the rings. While scientists can pick up clues about which trees are likely to be very old, it’s almost inevitable that the oldest tree in the world is growing in a remote spot — unmeasured, unknown and unnamed.
But among known trees, the oldest grow in an arid set of jutting peaks called the White Mountains, near California’s border with Nevada. They’re called bristlecone pines — mid-size trees, with gnarled branches that look like long-dead driftwood. The living bark and needles cover just a few strips and patches of the mostly dead wood. Bristlecones have been measured at ages close to 5,000 years, having sprouted from seeds when humans were just inventing writing on clay tablets.
The oldest ones take root in the harshest environments — the driest, windiest, roughest mountains with the chalkiest soils — places inhospitable to predators, tree-eating beetles, tree-rotting microbes and smaller plants that might build up brushfire fuel.
The ones that live in nicer spots, such as the lower-elevation hills of Death Valley, are more vulnerable, and indeed, some of those are now dying, suffering from beetle infestations and other side effects of human-generated climate change.
The very oldest trees are good at standing up to changes in climate — that’s one of their superpowers — but there are some threats that even they can’t endure.
The world’s oldest recorded tree, called Prometheus, was killed in 1964. A scientist tried to take a core sample using drill called an increment borer. When the instrument got stuck in the tree, the researcher called the Forest Service for help. They said there were plenty of old trees like this one and called in a crew with a chainsaw to cut it down. After the fact, the scientist, who was a graduate student at the time, counted the rings and discovered to his horror that it was nearly 5,000 years old. They’d just chopped down the world’s oldest tree.
The current oldest living tree, a bristlecone called Methuselah, endured the extraction of a tree ring core without harm, but spent years getting torn apart by tourists wanting a piece of bark. Now scientists try to keep its location secret.
Similar problems afflict a tree in Chile called Alerce Milenario, a cyprus scientists recently announced as a new contender for the world’s oldest tree. It’s not the official record holder yet because it’s rotten and has lost some of its rings, and so the scientists had to estimate its age, which they claim is around 5,400 years. Alerce Milenario is a charismatic giant tree and attracts tourists who are trampling its roots. Climate change it can handle, but it’s not adapted to being loved to death.
And for the giant Sequoias, there’s another threat. Stephenson said that the trees are well adapted to a natural cycle of fire, but not to the kinds of megafires that result when humans suppress fire for decades, allowing an explosive buildup of small trees, brush and other fuel. When those finally catch, flames can rise more than 100 feet and burn the crowns. He said fires have killed 13% to 19% of all the giant Sequoias in the last few years alone. Our current period of global warming and Southwestern drought are also contributing risk factors for megafires.
And of course, global warming is cause for alarm even if it spares the toughest, oldest trees. The more enduring threat of climate change is the collapse of complex ecosystems. It will leave us in a diminished world, a world less able to provide food and clean water to billions of humans. The most weather-hardened gods, looking down from their Olympus, won’t miss us.