Three years ago I planted twelve multi-stemmed silver birches on the slopes of my ground, a tree native to Scotland. They are the kind that has the bark peel off and rolls up as it grows. I removed alien trees whose roots were thin and spread outward, not down to keep a tight hold of the earth and sustenance. The birches were 12-feet tall when they arrived and in huge heavy pots, a killer to drag down a hill and drop into a pre-dug planting hole. They are 20-feet or more now. Not one died. I think I have planted over thirty others kinds of trees, including Douglas firs.
A few years back it was my luck to visit the Giant Redwoods north of San Francisco, an experience never forgotten. Those trees justify the over-used adjective awesome! They can live for over 1,500 years and surpass 300 feet in height, their massive girth one of nature’s wonders. We have a few in Scotland The oldest two coast redwood trees are at Rossie Priory in Perthshire, and at Smeaton House, East Lothian and planted in 1845 and about 1844 respectively.
In the contuinuing series on Climate Change, Michael Viney, the Irish Times environmental journalist, explains why the the giants of California are so important to the Earth’s existence – they can remove a lifetime of carbon from the atmosphere. (As usual, items in blue link to other articles or reseach papers.)
EARTH’s FRIENDLY GIANTS
The rope climber in my illustration are ascending one of the tallest trees on Earth, Sequoiadendron giganteum, otherwise the giant redwood, growing in the dense rainforest of northern California. I hope it’s still alive and not one of thousands already killed by the heat of the infernos.
The plight of California’s great sequoias made the world’s front pages recently as the largest known tree on the planet, the General Sherman, had its huge base wrapped in foil. This was meant to offer some protection as the latest blaze headed towards its forest in the Sequoia National Park.
Little known at that point was the full toll of redwoods in fire that had swept through 20 groves in the Sierra Nevada last year – a loss now put, from satellite imagery, at 7,500 to 10,600 trees. Many were comparatively young as sequoias go (just a few centuries), but among them, in groves where fire burned hottest, were trees aged in thousands of years.
To stay alive so long has meant surviving many of the blazes regularly begun by lightning. With bark 2ft (60cm) thick. sequoia can survive if even 5 per cent of its crown remains unscorched, but the intensity of the new fires can be all-consuming, the heat killing even the seeds in their cones.
The fluted, massive cylinder of the General Sherman weighs some 1,500 tonnes, but its height of 275ft (83.82m) falls well short of the 350ft (106.68m) that marks the class of tallest redwoods on Earth.
I switch back to feet for these incredible spires because that’s the way they take shape in my mind and because it’s the usage of the wonderful book in which I found the climbers of my drawing. The Wild Trees was published in 2007 in the US, and I had just enjoyed it for a second time when the menace to General Sherman became news.
Its author, Richard Preston, a writer of New Yorker quality, came to learn of the remarkable group of wild tree climbers and naturalists devoted to scaling the sequoias. In the uppermost crowns they discovered a new botanical ecosystem. In hanging gardens of ferns, mosses and lichens, branches fuse with each other to make walkways between the trees, creating strange and magical canopies.
Preston shares the committed and dangerous lives of the climbers in unexplored canyons of the Sierras. The valleys are tangled with rocks and huge fallen trunks, setting obstacles to finding tallest trees that have never been climbed or named.
In 2006 Preston joined in the first ascent and measurement of Hyperion, the newest tallest tree in the world at 379.1ft (115.5m). Its location is still unpublicised to protect it the thousands of footsteps that would trample the soil at its base.
Along with an historically moist climate and rich soil, the reason for California’s exceptional groves of redwoods is their forested togetherness. Their roots fan out to mingle with each other and the close sharing of light draws them up towards the sky.
There is a theoretical limit to tree height. It was recently projected as the point, somewhere between 400ft (131.92m) and 426ft (129.8m), where the energy from leaf photosynthesis is outweighed by the pull of gravity in drawing water up from the roots. (The Dublin Spire, in comparison, is 390ft/118m.)
When sequoias reached Britain in the 1850s (the trees renamed as Wellingtonias) their one-guinea seedlings were widely planted. Rarely set in groves, they grew fast but lonely, short and fat and thirsty for regular water.
The Irish experience
In Ireland, sequoias took the fancy of big house planters, notably Viscount Powerscourt. A lone specimen below the waterfall has a beautiful shape, reaching just over 150ft (45.72m).
Today, the biggest grove of giant redwoods outside of California is beginning to take shape on 20 acres of the grounds of Birr Castle in Co Offaly. Launched by the present Earl of Rosse in 2016 in partnership with Crann, the project aims at a final grove of 1,000 giant and coastal redwoods, underplanted with shade-tolerant native Irish trees.
The first growth of the redwoods is four years into a potential 1,200 year life cycle. Their numbers will increase as more sponsors respond to the project’s elaborate website (giantsgrove.ie).
Giant sequoias can also inspire as absorbers of man-made carbon: General Sherman is already credited with removing 1,500 tonnes of it from the atmosphere. A UK project called One Life One Tree calculates that growing a sequoia to a trunk diameter of 3 metres will make up for one person’s lifetime carbon footprint.
An online search for giant sequoias to plant in Ireland found the Clarinbridge Garden Centre in Co Galway offering a 45cm seedling in a pot for €28.99. Not the best choice, perhaps, for your front lawn.