Old trees can outlive anything, except humans
Trees possess a quality that humans had once attributed to gods: They don’t age. Or as forest ecologist Nathan Stephenson says, there’s a growing school of thought that trees don’t undergo senescence, a programmed slide towards 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, a scientist emeritus with the USGS.
Someone once did a calculation 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 5, and some lucky ones would live thousands of years.
Most trees don’t survive the sapling stage, and of those that reach adulthood, most never reach their 1000th 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 is growing in a remote spot – unmeasured, unknown and unnamed.
Among known trees, the oldest grow in California’s White Mountains. They’re called bristlecone pines – mid-size trees, with gnarled branches that look like driftwood.
The living bark and needles cover a few strips. Bristlecones have been measured at ages close to 5000 years.
The oldest ones take root in the harshest environments – the driest, windiest, roughest mountains with the chalkiest soils – places inhospitable to predators, beetles, microbes and smaller plants that build up brushfire fuel.
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 a drill. When the instrument got stuck in the tree, he called the Forest Service for help. They said there were plenty of old trees like this and cut it down. Later, the scientist discovered to his horror that it was nearly 5000 years old.
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 souvenir.
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 about 5400 years.
Alerce Milenario is charismatic and attracts tourists who trample its roots. Climate change it can handle, but it’s not adapted to being loved to death.
New Zealand’s oldest tree, a Northland kauri called Te Matua Ngahere, is estimated to be about 2000 years old. It’s smaller than New Zealand’s largest tree, Ta¯ ne Mahuta.
Of course, global warming is cause for alarm even if it spares the toughest, oldest trees. The most weather-hardened gods, looking down from their Olympus, won’t miss us.