Climbing the world’s biggest tree

HIGH in the Sierra Nevada, in Calaveras Big Trees State Park, the last rays of the day are turning the topmost branches of a giant sequoia golden brown. The bark, much thinner up here than it is lower down the trunk, appears to be flowing around the massive boughs in liquid whorls of pink, brown and cream. It is rough to the touch and exquisite, especially viewed with the sniper-like focus that comes with bright sunlight, high adrenalin and the extreme exposure of the perch.

Swaying just perceptibly in a light breeze, the sequoia is over 83 metres high, about the height of a 27-storey building. Anthony Ambrose, a tree-climbing botanist from the University of California, Berkeley, estimates the tree—which he has named Munz, after a celebrated 20th-century botanist—is around 1,500 years old. That is middle-aged for a sequoia. The oldest known specimen, measured by the rings in its stump, was more than 3,200 years old when it fell—so already 700 when work was begun on the Parthenon. The surrounding pines, which appeared vast from the ground, are mere weeds by comparison. Looking straight down in the fading light, through a murk of green needles and hulking boughs, the forest floor is too distant to make out.

The massiveness of the sequoia, a species of cypress which is endemic to just 75 groves in the Sierra Nevada, is not easy to comprehend. That is in part because it is rather hard to observe. Up close, the viewer gawps at the vastness of the trunk, a great pillar rising into the sky, typically branchless for almost half the tree’s length. The bole of the biggest living sequoia, the General Sherman tree, is over 30 metres (100 feet) in circumference; it takes 17 adults with their arms outstretched to encircle it. Yet to see the tree’s distant crown, a mass of huge and shaggy boughs, curling downwards under their own weight, it is necessary to stand much further back. Excluding some subterranean fungi, the sequoia is the biggest organism ever known to have existed.

Twizzling in mid-air

Mr Ambrose, a 47-year-old scientist with a watchful manner and diamond stud glinting in one ear, is one of a tiny cabal of botanists whose research mingles science with extreme sports. He has climbed several hundred giant sequoias (Sequoiadendron giganteum) and coastal redwoods (Sequoia sempervirens)—another California species, slightly taller than the giant sequoia but usually more slender—over the past decade. Yet his wonder is undimmed. “God, I love these trees!” he exclaimed periodically, on a field-trip in November, while unpacking climbing gear, fiddling with solar panels and trying to take his mind off the wreckage some curious bears had made of some of his humidity sensors.

He and his colleague, Wendy Baxter, had come to Calaveras to take down some instruments they had installed in a pair of trees, part of a six-year study into the microclimates of sequoia groves. It was a fine autumn day. A pale blue sky showed through the forest’s old-growth conifers—sugar and ponderosa pines, Douglas firs and incense cedars—as the researchers tramped over dry ground, carpeted with dead needles and cones. At the study site they set to work with quiet efficiency, sorting out ropes and carabiners. Mr Ambrose and Ms Baxter are partners as well as colleagues, which is not uncommon among tree-climbing scientists. The most celebrated, Steve Sillett, who pioneered canopy research in giant trees, also met his wife clambering aloft. Mr Sillett is known among his peers for opening a new realm of tree science. But he is perhaps most famous, thanks to “The Wild Trees”, a book about redwoods by Richard Preston, for having got married and had sex in a tree. It was a perilous undertaking.

For those without amorous intent, the most dangerous part of climbing a giant tree is the first ascent, which is carried out, Swiss-Family-Robinson-style, by first shooting a crossbow bolt with fishing-line attached to it over the highest possible branch. Once the bolt is retrieved, a length of yarn is run up after the line. A rope is then run up after the yarn.

One end of the rope is made fast to a nearby tree. The other hangs free to the ground, where it can be clipped onto and climbed up, using grips that can be slid up the rope but not down it. One grip is attached to a climbing harness, another to a pair of foot slings. By sliding one up after the other, first the foot grip, then, after lurching to full height in the slings, the hand grip, the climber rises up the rope.

As the lowest branch of the Munz tree is 35 metres off the ground, this at first involves a lot of twizzling in mid-air, a metre or two from the tree, as the forest floor falls sickeningly away. At around 10 metres, or the height of a three-storey building, the vastness of the trunk, with its massive bark flutes, runnels and crevasses, the skinniness of the rope, and the extreme exposure of the climb become powerfully evident. There are 73 metres to go.

Mammoths and mothers

The first reports of monster trees out West, sent by the European trappers and gold prospectors who flocked to California in the mid-19th century, carried a familiar ring of dragons and sea monsters. They sounded incredible. Then, between 1853 and 1855, sections of bark were cut from two colossi in Calaveras, the Mammoth Tree and the Mother of the Forest, and exhibited in San Francisco, New York and London. The husk of the Mother was celebrated as the “eighth wonder of the world”; over 7,000 New Yorkers went to see it on the first day of its display. Even then the New York Times was doubtful: “We have no assurance, from seeing this clothed skeleton, that the tree was actually so large,” it opined.

Felling the Mammoth had taken five men working with drills and wedges almost a month. The tree’s stump was used as a dance-floor, big enough to accommodate 40 people. The biggest part of its fractured bole was used as a bowling alley. Thus did the sequoia enter American culture, as a tall story, a popular attraction and, in due course, a source of intense national pride.

At a time of territorial expansion, America’s natural bounty struck some as a God-given substitute for the ancient culture which was the only thing the country seemed to lack (if, that is, you ignored its native American heritage, as most Americans did). For John Muir, a Scottish-American naturalist who lived in the Sierra Nevada and introduced it to the world in his florid writings, the sequoias were “nature’s masterpiece”. Indeed, they were like the Parthenon, with “massive columns from the swelling instep to the lofty summit dissolving into a dome of verdure”.

This exalted status, unusual for a plant, would ensure for the sequoia an important role in two historic debates that began around this time, in both of which Muir had a hand. One was over the competing claims of development and conservation, especially in the West. The other concerned the acceptance by American scientists of Darwinism.

By the time the Mother was shown to New York the rate at which America’s forests were being cleared for fuel and timber was already worrying some people. The sequoia exhibits added a less utilitarian concern. Cutting down such giants was wrong in itself, an act of national self-harm, sacrilegious even, and must be stopped. “Unless the Goths and Vandals are arrested in their work, the destruction of the incomparable forest will probably go on till the last vestige of it is destroyed”, the New York Herald railed in December 1855. “The state of California and the Congress of the Union should interpose to preserve these trees, as the living proofs that the boasted monarchs of the wood of the Old World are but stunted shrubbery compared with the forest giants of our own country.”

“I wish I were so drunk and Sequoical that I could preach the green brown woods to all the juiceless world”

It would be long before this notion seriously threatened Americans’ sense of manifest destiny. In the second half of the 19th century loggers felled around a quarter of the sequoias. It was rarely worth the effort involved. Unlike fine redwood timber, sequoia wood is too fibrous and brittle to be much use for anything except matchsticks and fence-posts. Partly for the same reason, the trees also tended to shatter when felled; it was reckoned that half of any felled giant was thus wasted.

Not until 1909, after nearly 1.5m people signed a petition beseeching President Theodore Roosevelt to intervene, was the Calaveras grove purchased by the federal government to prevent it being logged. Yet slow though it may have been to grow, the conservation movement behind that petition was nonetheless rooted in the husk of the Mother. John Conness, a senator from California, referred to that very tree when urging his fellow senators to pass a bill to protect the nearby Yosemite Valley in a speech now considered a milestone in American conservation. The bill in question, he argued, would at least “preserve one of these groves from devastation and injury”, which, again, national pride demanded. Even more than the painful felling of the Mother, Conness seemed motivated by his sense of pique at “the English who saw it [and] declared it to be a Yankee invention”, not, as the good senator understood the fallen tree, a “specimen of American growth”.

Muir, one of the most celebrated Americans of his time, added impetus to the conservationist movement. The son of a Presbyterian preacher, who, at the age of 11, could recite most of the Bible by heart, he became an evangelist for nature. He believed that wilderness, uncorrupted by civilisation, revealed God. “Do behold the King in his glory, King Sequoia!” he wrote, “Some time ago I left all for Sequoia and have been and am at his feet; fasting and praying for light, for is he not the greatest light in the woods, in the world?” By soaking sequoia cones in water, Muir brewed for himself an arboreal communion wine: “I wish I were so drunk and Sequoical that I could preach the green brown woods to all the juiceless world, descending from this divine wilderness like a John the Baptist…crying, Repent, for the Kingdom of Sequoia is at hand!”

He got his wish. In 1903 Roosevelt spent three days with him in Yosemite, staring at its sequoias, and the preacher convinced the president of the need for preservation. Roosevelt signed into existence five national parks, 18 national monuments, 55 national bird sanctuaries and wildlife refuges and 150 national forests. Muir’s vision of wilderness preservation was not unchallenged; a rival “conservation” movement, led by Gifford Pinchot, the first boss of the United States Forest Service, argued for America’s natural resources to be protected for sustainable exploitation, rather than for their own sublime sake. But when it came to the “gigantically wasteful lumbering of the great Sequoias” Pinchot was with Muir: “I still resent the practice of making vine stakes hardly bigger than walking-sticks out of these greatest of living things.”

An earlier trip to the sequoias with Muir, undertaken in 1872 by Asa Gray, a celebrated botanist, was influential in a different way. A friend and advocate of Darwin, Gray argued that natural selection was consistent with a divine creator. Having rehearsed his views with Muir, who, with some quirks, broadly accepted them, Gray outlined them in an influential speech he delivered soon after on the distribution of trees in the present and the past, making the sequoia his prime example. As the world changed, Gray argued, so its flora did, with species sometimes adapting well and sometimes being out-competed by others. The sequoia had not fared well since the most recent ice age. Having once been widespread, changes in its range had left it only restricted areas to grow in, and in these territories lesser species that reproduced faster, such as sugar pines and incense cedars, could “overpower” it. “Certain if not speedy”, Gray expounded, “is the decline of a race in which a high death rate afflicts the young.”

A tree for all seasons?

Mr Ambrose’s climate study is in a way testing Gray’s hypothesis—but in the more recent context of anthropogenic warming. The work received particular attention (and a dollop of needed funding) in 2014, near the height of California’s now five-year drought, after half the foliage on some sequoias suddenly died. Mr Ambrose found that the affected trees were in fact no worse off than apparently healthy ones. Though water-stressed, all the sequoias were to some degree mitigating the effects of the drought by shedding foliage and shutting off some of their stomata to conserve water. It is a trick sequoias turn out to be especially good at, which illustrates a paradoxical truth about the giants. Coeval with dinosaurs, once widespread across the northern hemisphere, but now reduced to refugia that cover a total range of just 150 square kilometres (38,000 acres), they are plainly sensitive to climate change. Yet they are also extremely resilient.

Some of their defences against the buffeting of geological time were revealed during your correspondent’s ascent of the Munz tree. The shaggy thickness of its bark, up to a metre deep, and, as the rope angled in towards the trunk, not uncomfortable to bounce off, protects it against the fiercest wildfires. This was especially apparent in the crown, where a fold of pinkish new growth was slowly overlapping a branch killed by fire. The damage had been done, Mr Ambrose estimated, 200 years ago; the heat of the blaze, raging at the height of a modest skyscraper, must have killed most of the trees in the forest at the time.

Besides a few ants and spiders, the tree was also surprisingly devoid of creepy-crawlies. The sequoia’s tannin-rich wood is unappetising, which has spared it from another warming-related blight, the bark beetles and other pests currently ravaging America’s West. In the Sierra Nevada, more than 66m trees are estimated to have been killed by bugs and drought since 2010.

Sequoia wood resists rot; scratch away the muck and charcoal from a stump which took root three millennia ago and the wood beneath is intact. As a result the trees are not particularly welcoming to other plants, either. In their more humid, coastal conditions, redwood canopies tend to be thick with epiphytic lichens, bryophytes and even small trees, growing in pockets of rotted wood. The Munz tree was barren by comparison: a stunted sugar pine, sprouting from a fire scar about 50 metres up, was its only large epiphyte.

With such advantages, the sequoias are playing only a minor role in a third great public debate, over climate change. Even as the pines succumb to beetles and the firs go up in smoke, the giants look able to endure—at least for a while. Yet there will be a limit to that. Sequoias need vast quantities of water; Mr Ambrose and Ms Baxter calculate they use more than two tonnes a day in summertime. And there are multiple indicators, including drought, dieback, shrinkage of the Sierra Nevada’s snowpack and a slight retreat of the sequoia’s southern range, to suggest such volumes could soon be unavailable to them. “I worry about them. I worry about them a lot,” said Mr Ambrose, working deftly to dismantle his scientific rig from the very top of Munz, while being peppered with journalistic questions from a neighbouring branch.

At that highest point on the tree, illuminated in crystalline detail by the explosive last rays of the dying sun, I noticed a single thread of spider’s silk. It was snagged on a piece of bark, and trembling in the delicate breeze. It was powerfully beautiful. It also seemed for all the world like a sign.