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Friday 19 April 2019

Ann Fitzgerald: So much to learn from root and branch look at life of an ancient oak

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Ann Fitzgerald

Ann Fitzgerald

Everyone should watch the film, Oak Tree - Nature's Greatest Survivor, which was recently aired on BBC 4.

Part scientific documentary, part historical investigation, it tracks the dramatic life of a specific oak, in Wytham Woods near Oxford, over the course of a year.

It was first shown in 2015, which would be a long time ago if you were a Kardashian, but not for a tree that was laying down its roots when Newton discovered gravity (1687).

The presenter is an entomologist named George McGavin, who strikes just the right note of expertise and awe.

Through the use of lasers, we learn that this oak has some 700,000 leaves, while many human hours removing every crumb of soil from the roots of a young tree expose lengths of mycorrhizal fungi threads that would stretch around the world.

I was amazed at how responsive the oak is to changes its environment.

So, in autumn, chemical messengers (like the hormones associated with some of our own biggest changes, puberty and pregnancy), flow through the branches telling the oak to break down pigments in the leaves to conserve precious water and energy for winter.

Equally incredible is how the tree responds to predator attacks at its most vulnerable, in summer, when covered in soft, young leaves.

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One of its fiercest foes is the winter moth caterpillar, which can eat 27,000 times its own weight in oak leaf.

If the oak did not respond, it would struggle to survive.

But, when the larva is eating, it dribbles saliva. The oak senses this chemically and sends out 'wound' hormones to other parts of the tree, telling it to turn on its defence system, to produce species-specific poisons. The tree is essentially talking to itself.

The oak then encounters its strangest and most sophisticated group of foes, the gall wasp, which lays its egg in a female oak flower. Instead of developing into an acorn, this then grows into a tumour-like gall, a perfect nursery for its grub to develop.

There are several hundred species of gall wasp, each with its own shape of gall.

We learn that one type of oak gall was the basis for our recorded history for over 1,400 years, from the fifth century on.

Crushed, then mixed with water, iron sulphate and gum Arabic, the tannin-rich gall is transformed into a cheap and extremely long-lasting ink.

It was used in the Magna Carta, the American Declaration of Independence, Mozart's music, the letters of Charles Darwin, even in the drawing of Da Vinci's Vitruvian Man.

There is a lot of coverage of the various connections between the oak and humans, in particular in construction, where it is prized not just for its strength and durability but also its curved limbs, especially in its most famous use, shipbuilding.

During the 17th and 18th centuries, Britain had the biggest navy in the world, and nearly all the ships were made of oak. This includes the flagship of Lord Nelson, the Victory, the product of almost 6,000 oak trees.

Many great buildings have also been born out of oak, including Salisbury Cathedral, while we also learn of its role in flavouring Scotch whisky.

During the year, the Wytham Woods oak added 230kg of new growth. It also pumped out 230,000 litres of oxygen, sufficient to support one human being for the period.

The footage is beautiful and the choice of accompanying classical music, superb. My favourite bit is a time-lapse clip of an acorn germinating to the sound of Strauss, somehow managing to look like a ballerina.

Fascinating and uplifting, the film also gives so much insight into nature and to biological inter-relationships that we could apply to our own lives.

For those who can't access the BBC player, the film is on Youtube.

As George McGavin says at the start: "You will never look at an oak in the same way again."

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