As National Tree Week approaches, plant experts share fact and folklore with Rita de Brún about the beauteous arboreal survivors that surround us.
At any time of the day or year, trees are a sight to behold. But with National Tree Week kicking off on Saturday March 21, we’ve an added excuse to pay tribute.
As a long-living species, many trees have borne witness to times of war and peace, the birth and toppling of nations, and everything in between.
Like elderly community members, they have a lot to teach us about the art of survival and the benefit of sharing for the common good.
Of course, trees don’t have to be long-lived to be interesting. On the African Savanna, acacias are the firm favourite food source for giraffes. Since the animals are undeterred by its sharp spindly thorns, the trees have another line of defence: Once a giraffe starts nibbling its leaves, the trees release tannins which make their leaves taste sour.
Cleverly, they then message neighbouring trees to alert them to the browser threat. In response, they too release tannins.
It’s a clever defence technique, which stops the browsers in their tracks. But it’s not entirely successful. As defence messages between acacias only travel so far, the giraffes’ instinctive response is to amble just beyond the defence zone. There, they continue browsing on their favourite foliage.
While we tend not to graze on their leaves, we’re familiar with the beauteous appeal of trees.
While we might marvel at the sensation of bark on fingertips, leafy canopies lit by sunbeams and the silhouette of winter-bare branches stark against the sky, our awe belongs elsewhere.
One who knows much about tree behaviour is Crann director Dr Diarmuid McAree. He was chief forestry inspector at the Irish Forest Service before retiring.
He’s now a consultant, a role that regularly takes him before the United Nations.
Recalling working in the forests of Canada he says: “When beetles would attack, trees would trigger a defence mechanism. They’d give off chemicals to deter the insects. They’d lose needles, close down their breathing tubes and exude resin. When stressed, they use the wood wide web to connect to one another and send warning messages.”
While clearly passionate about trees Dr McAree is not given to romanticising their essence.
When I ask whether it’s true that when an old tree dies, its elderly neighbour often dies shortly afterwards, I hope he’ll reveal that tree sentiment played a role, but it wasn’t to be: “There are good fungi and bad,” he began.
“If bad fungi play a part in the death of one tree, it’s hardly surprising that the one beside it will go too.” On the topic of alien tree species, he declares that he’s ‘not botanically racist,’ then cautions about the importance of planting the right trees in the right places.
“If it is ecologically appropriate, socially acceptable and environmentally sound to do so, then plant the tree,” he says.
When asked about the importance of planting native species, Dr Eoin Lettice, plant scientist and lecturer at University College Cork, replies: “I’m perfectly glad to promote native tree planting. But at UCC the trees were planted as a teaching and research tool.” He then talks passionately about those trees, advising that the giant sequoia or redwoods there are just 27 and 30 metres tall, being 140 or 150 years old.
“Given that these trees can reach 90-100 metres and live to be one thousand years old, ours are just babies,” he says.
Of the Monterey Pines growing on the UCC campus, he says: “In a wild or forest fire, they’d pop their seeds. Heat pops the cones. Seeds land on the ground. Some are destroyed, but a thick outer coating enables some to survive and grow into new trees. They’d be the first survivors, the first organisms to come back and thrive. They use the rich nutrients left behind from the fires to help with that process.
“Yews are interesting as well,” he says. “There are two main types, the Irish yew and the common or English yew. The Irish yew is a strange mutation: first noticed in Co Fermanagh for being tall and statuesque. Nowadays, all Irish yews are cuttings propagated from that one individual tree.”
He’s a born storyteller: “There’s an old myth that yews protect graveyards. What’s more likely to be the truth is that because they are poisonous, animals don’t eat them. They’re often the graveyard plant of choice in a bid to keep animals away”.
Trees are veteran survivors. Their nurturing nature doubtless plays a role, as if it takes a village to raise a child it sometimes takes a forest to raise a sapling.
Deprived of the sunlight they need to grow in dense forests, their survival often comes courtesy of the nutrients channelled into their roots by not only their mothers but neighbouring trees as well.
“We are still finding new trees, making new botanical discoveries,” says Dr Mary Forrest, an associate professor at UCD. “In 1994 the Wollemi Pine was discovered in Sydney. It was known from fossil records to have lived 40 million years previously and was thought to be extinct.”
That discovery caused quite the stir. One academic remarked at the time that the find was ‘the equivalent of finding a small dinosaur still alive on Earth.’
The conversation then turns closer to home, and Dr Forrest tells me then, that the cherry, rohan and our native hawthorn all need a period of cold to ripen. “They might fall to the ground to get a period of winter frost,” she says. “Then the seed will germinate.” Then, ever the pragmatist she adds: “Of course in nurseries they put the seeds in fridges to get around the required cold period.
“Eucalyptus has another way of germinating,” she continues. “Commonly called gum trees, they are native to Tasmania. You’d have no idea there’s a seed inside the woody capsules until fire makes them break open. The heat triggers germination.
“In Ireland, you will see them growing between Waterford and Cork and Kerry. You will see them at Fota. Here it would be a period of cold that would trigger germination. The same in Europe. But in the heat of Australia where bushfires are common, fire is part of their natural occurrence, so their seeds break open when there are fires.”
We talk then about how Ireland’s history is wrapped up in trees and what old trees are likely to have witnessed in their lives. She tells me she has ‘been to the Áras looking at trees’ and how Queen Victoria planted some here.
“Go to Glengarriff, Kilmacurragh or Curramore and consider what the trees there have lived through, the changes. They were there before electricity and motor cars. We have to marvel at the trees, at their ability to grow in the ground and look after themselves in the ways they do.”
They do look after themselves, but with our planet-destroying habits, we humans are not making it easy for them to thrive.
In recent weeks, a Leeds University study, published in the journal Nature, shows that tropical forests are absorbing less carbon dioxide from the air than they did in the 1990s. Back then, trees cleaned 46 billion tonnes of carbon from the air — a figure that plummeted to just 25 billion tonnes in the last decade.
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