A quick shout-out for Oak Tree: Nature’s Greatest Survivor, shown on BBC 4 this week (and available for another 25 days on iPlayer) – a 90-minute documentary detailing a year-long study of a single 400-year-old oak in Oxfordshire. The film was presented by entomologist George McGavin, who promised that ‘You’ll never look at an oak tree the same way again.’ Too true: McGavin took us on an engrossing tour of the oak (literally so, by climbing the tree, and even sleeping in its uppermost branches!), guiding us through its biology and cultural significance.
The film documented research carried out by a team from Oxford University where McGavin once taught zoology. The idea was to monitor the tree’s progress through one year, investigating its complex and sophisticated biology, and learning how it adapts to the changing seasons.
The chosen tree was a 400 year-old native of Wytham Woods outside Oxford. As the seasons unfolded it was filmed, scanned and measured using the latest scientific technology. The research team discovered that this one mature oak possessed 700,000 leaves, covering the area of three tennis courts and weighing 10 tons. During the year it was monitored, the tree added 230kg of new growth and soaked up 58,822 litres of water. Most importantly for us, it pumped out 230,000 litres of oxygen, sufficient to support one human being for a whole year.
Beginning in the autumn, McGavin observed as the research team meticulously picked away the soil below an oak tree to reveal the extent of its root system and demonstrate how its roots extract precious resources from the soil. In winter, he investigated the strategies the tree uses to survive gales and bitter frosts, and the celebrated of its timber. Visiting Salisbury Cathedral he discussed the oak’s vital role in architecture, and revealed the astonishing cat’s cradle of giant oak timbers that support the spire.
Spring, found McGavin investigating how the oak spreads its pollen through the countryside in order to procreate (each tree produces both male and female pollen). In summer, he climbed into the uppermost storey of the tree’s branches to gather a sample of the hundreds of insect species that depend on the tree (a high-powered microscope was required to see many of them).
Humans, too, rely on the oak for sustenance. We learned this when McGavin visited the world’s largest whisky collection and discovered that whisky gets its unique flavours from the oak wood barrels in which it’s matured. The man he spoke to there gave him a technically-detailed lecture on how this was achieved, before kindly allowing him to sample a shot.
At the heart of a vast interconnected web of life, an oak doesn’t just sustain the many species it hosts, it depends upon them to help disperse its acorns, such as the jays and squirrels that bury them as a future food store and then forget where they left them. One acorn was the subject of an impressive sequence of time-lapse filming during which we witnessed the staggering, primeval force of the embryonic tree.
There was a time when humans were just as useful as squirrels and jays in helping spread the species. In the 17th and 18th century, McGavin reported, there was a frenzy of oak planting in Britain. The reason was simple: Britain had the world’s most powerful navy and nearly all her ships were made of oak. He showed us round the HMS Victory, Lord Nelson’s flagship, famed for helping defeat the French fleet at the battle of Trafalgar, to demonstrate just how much oak timber was needed for a fighting ship. The Victory is perhaps one of the most ambitious vessels ever created from oak timber: the product of almost 6,000 trees, shaped and sculpted by Britain’s finest shipwrights.
That we needed oaks for the timber that sustained the British navy might be old news, but I was truly surprised to discover that without the tiny gall wasp, very few manuscripts from medieval times onwards would have survived. It seems the oak tree provided the most important ink in Western civilisation.
As McGavin observed, an early version of the well known saying, ‘mighty oaks from little acorns grow’, can be found in Geoffrey Chaucer’s Troilus and Criseyde written in 1374. But, he queried, what was it written with?
The really surprising answer is that it is all due to the strange, tumour like growths that spread across an oak tree in summer, as tiny gall wasps lay their eggs in emerging acorns. McGavin said that recent research indicates that the wasps may actually be altering the oak’s DNA, genetically engineering it to grow a nursery and larder for their developing young.
But take some oak galls, crush them and mix them with water, iron sulphate and gum Arabic, and the tannin-rich gall is transformed into a cheap and extremely long lasting ink. In the National Archive at Kew, McGavin discovered that over 1,000 years of British history were written in the ink.
This was a truly absorbing documentary, which explored the oak tree and its cultural significance in more depth than Fiona Stafford had time to do in her 15-minute essays for BBC Radio 3 a couple of years back. I love oak trees, not least because here in Liverpool I’m lucky enough to be able to visit, whenever the mood takes me, one of the oldest oaks in the country – the Allerton Oak.