Methuselahs: Bristlecones and Date Palms
BRISTLECONE PINES, by common consent the oldest trees on earth, seem not so much old as stone dead. The snags of contorted wood that grow in the high mountains of south-western North America have the look of fossil trees, bleached to the colour and texture of the shattered dolomite rock round their roots.
There are three species of bristlecone (named from the prickles on the female cones) growing in the arid highlands between Utah and New Mexico, at altitudes between 5,600 and 11,000 feet. In this extreme habitat of long, cold winters, low rainfall and high winds, bristlecones have few competitors and are supremely well adapted. Their wood is dense and resinous, and resistant to invasion by wood-boring insects and fungi. The roots are shallow and spread wide, to give support against the wind and rapid access to surface water. The needles are coated with wax to reduce moisture loss, and can hang on the tree for up to forty years. But the bristlecones’ major strategy for survival into extreme old age is, counter-intuitively, to take itself very close to death. As an already ancient tree edges into venerability much of the wood dies back, often leaving just a wisp of living tissue connecting the roots to a handful of twigs. Effectively it has become torpid, embalmed, reducing its growth – and therefore its needs – to almost nothing. The stresses of old age in bristlecones are purely climatic, not metabolic. The heartwood is so dense and desiccated that instead of rotting it is eroded like stone, by frost and gale-driven rock dust.
The species capable of reaching the greatest age is Pinus longaeva, and in 1957 Edmund Schulman discovered a specimen in the White Mountains of Inyo County, California, which he was able to give an age of exactly 4,846 years. By drilling an unbroken core from the heartwood he’d counted the annual rings through a microscope. At that moment it was the oldest accurately dated tree in the world, and was promptly dubbed Methuselah. (The Fortingall yew may be older but that can never be proven.) A few years later an even older tree was found nearby by a graduate geography student from the University of Carolina. Donald Rusk Currey was studying how clues to climate and even year-by-year weather are preserved in tree rings (warm wet summers produce wide rings, for instance) and bored a routine core from a tree which on his schedule was labelled as WPB-114. What he didn’t know was that it was one of the most celebrated bristlecones, with its own name – Prometheus – given by local tree enthusiasts in the early 1950s. Unfortunately Currey’s specialised drill got stuck in the trunk. Without it he couldn’t continue his research project. So with the bravura of a frontier lumberjack, he simply cut the tree down. The story goes that he took a slice of the trunk back to his motel and sat outside in the sun to count the annual rings. There were 4,844, but he thought the tree might be older than this, as his section wasn’t from the base of the tree. He imagined it might exceed 5,000 years. Whatever its exact age, at the moment of its summary execution Prometheus then succeeded Methuselah as the oldest known tree in the world. (Both it and the still surviving Methuselah were beaten in this not wholly edifying league table by the discovery in 2013 of a bristlecone from the same area with 5,065 annual rings.)
Death from dendrological drill is unlikely to happen to any of the now much more securely protected ancient bristlecones. But their future looks uncertain nonetheless. Climate change is raising the average temperature of their alpine redoubts. The prolonged frosts that killed off predatory insects are now less frequent. A new fungal disease from Asia, blister rust, has joined the list of invasive parasites that seem to have a particular taste for trees, and is attacking bristlecone saplings. P. longaeva seeds well, and its populations are widely scattered, so the species is not under serious threat. But Champion Trees, as they are known in the USA, attract human champions, who are interested not so much in the survival of the species as prolonging the life and exact genetic essence of the veterans. There is a whiff of arboreal eugenics here, and a nostalgic sense of heritage which believes that the best lies in the past. The ideology of veteran tree conservation – certainly in the USA – still echoes with the nineteenth-century conviction that the anciently pristine may be the God-given route to the future.
In the 1990s a Michigan nurseryman called David Milarch began a project to clone Champion Trees, including the ancient bristlecones. Uncannily, he’d been prompted by visions almost identical to those experienced by Allen Meredith before he began his research on ancient yews. Milarch had an out-of-body experience during acute liver failure, and for months afterwards had early morning visitation by ‘light beings’. ‘The big trees were dying, they told him, it was going to get much worse, and they had an assignment for him.’ His mission resolved into one of cloning the big trees and planting them across the USA. They were a unique biological legacy, he believed, and humankind needed them. Milarch’s own reasoning was disarmingly down to earth. ‘[T]hese are the supertrees,’ he said in an interview, ‘and they have stood the test of time. Until we started cloning the nation’s largest and oldest trees, they were allowed to tip over, and their genes to disappear. Is that good science? If you saw the last dinosaur egg, would you pick it up and save it for study or let it disappear?’ Alas, for all his good intentions, Milarch’s science isn’t too good either. Size and old age clearly indicate past success in surviving the ‘tests of time’. But they do not predict an ability to survive the tests of the future, which may be very different. New exotic diseases and climatic anomalies are multiplying. The Champions’ survival may also have resulted from a lucky combination of site and historical experience, and a clone transplanted to a new situation might have no such luck. Nor do genes wholly ‘disappear’ if an individual tree dies. They’re retained in its relations and the offspring it may have been generating for thousands of years, and which might hold not only the genes which contribute to longevity, but others temporarily in recession (for enduring a warmer climate perhaps). The dinosaur’s egg is an unfortunate comparison too, as nature invented sex (and eggs) precisely to ensure plenty of gene swapping, and broods of offspring with a wide mix of potential responses to unpredictable situations.
The seeds of old trees would be considered part of their legacy if they weren’t so lacking in the monumental splendour of their parents. Many can live for great ages (though what ‘live’ means in the case of a dried-out husk is an interesting question), carrying potential templates not just of the particular tree that bore them, but of all its ancestors.
The longest proved dormancy for a seed is for a date discovered in the ruins of the ancient Israeli settlement of Masada. The remains of this city had lain undisturbed for nearly 2,000 years before they were excavated by archaeologists in the 1960s. In the deepest layers the diggers discovered a cache of provisions: grain, olive oil, wine, pomegranates and a generous hoard of dates from the extinct Judean palm, so perfectly preserved that scraps of fruit flesh still clung to the seeds. Four decades later, after museum workers had cleaned and catalogued the dates, someone decided to plant one. It was a shock and a thrill when the workers noticed a lone shoot sprouting from one of the pots. By 2012 it was ten feet tall, and sharing the name Methuselah with the unrelated dwarf pine halfway across the globe. Alas, this may be only a temporary resurrection. Methuselah has flowered, but proved to be a male tree. Unless a female fossil date can be found no future generations of Judean palms will follow.
The bleached trunk of a dead bristlecone pine, Inyo National Forest, California.
The foliaged trees beyond may be thousands of years old.
Dormancy is an extraordinary phenomenon both botanically and philosophically. No one is yet sure how it works, or what exactly it means. It may be a purely physical trick, depending on the seed’s coat mummifying its life processes until it is struck by just the right combination of light and temperature. Yet the seeds of some species (e.g. the field poppy) appear to be programmed to germinate far in the future, as an insurance policy. Do they contain some so-far undetected bio-electric timer? And what might be a botanical pathologist’s verdict on the existential status of a dormant seed? Can it be said to be truly alive without any discernible metabolic activity? The answer given by one American seedbank botanist, Chris Walters, is: ‘If seeds are alive but aren’t metabolising, then maybe we need to rethink our definition of what it means to be alive.’