The bizarre trees that ‘milk' clouds and start lightning storms

Telegraph

20-07-2025

Thanks to Harriet Rix and her sublime book, The Genius of Trees, I have seen and relished the world the day before the Chicxulub asteroid hit. I have smelled its perfumes, and squelched through its hot boggy litters, and dodged its foot-long dragonflies. And I have seen the day after, too, 'when all was darkness and confusion, mushrooms and rot'.
Rix's book explains how over millennia, trees have shaped the earth and been shaped by it. (They allowed for the existence of those monster dragonflies by saturating the atmosphere with oxygen, for starters.) Trees thrived before Chicxulub, Rix tells us, but afterwards, their 'green shade became a grey gloom' as a dust cloud blotted out the sun for two years. The Amazon became a death zone. Gymnosperms – meaning pines and monkey puzzles – were utterly outmanoeuvred by flowers, which could survive by bouncing light about themselves between water droplets. (Through Rix's luminous descriptions, I pictured this as a microscopic pinball game played with light, where the winner inherits the Earth.)
Her book is a dazzling series of lectures which explore how trees shape water, soil, fire, air, fungi, animals and people. Like an early Robert MacFaralane narrator, Rix refuses to put herself much in the picture, but through the scenes we glimpse an Indiana Jones figure who is both an eminent, travelling scientist and a born writer. She describes the 'stately galliards' of coniferous trees taking over after the asteroid's destruction. To Rix, they arrive in 'a mass tango, angular and fluid'. On the Canary island of La Gomera, we encounter trees that not only make clouds, but farm and milk them, seeding the air with compounds which cause water molecules to cluster around them, 'until like a small planet, it falls as rain'.
She also travels to the environs of Quetta to look at the Ziarat junipers, guarded by Balochi rangers in one of the world's deadliest zones of human conflict. Here, wild ephedra is easily and popularly synthesised into methamphetamine (do you prefer your Taliban on opium or speed?) Rix is completing a spreadsheet on juniper carbon capture when she's reassured that she won't be kidnapped, as long as she visits their food market twice.
And by the time we have watched the beautiful Zelkova abelicea on Crete turn red when the first frosts fall, and have paddled up the Curicuriari, an Amazon river, to meet a rare duraka tree, it becomes clear that Rix's world is astounding.
There are some mountains in deep, rural China where 18 species of tree are currently in a pitched brawl, using poison, shade, theft, disease, fire, misdirection, brute force and lighting on each other. This is normal tree behaviour, and it's a salutary experience, having been near woods most days of my life, to realise that I had little idea what I have been looking at.
In their battles, trees lace the air with flammable gases, strew kindling, douse everything in the pyromaniac's molecule, oxygen, and gather clouds to encourage lightning strikes, which they have put up conductors to catch. Then, whoosh: their competition is vaporised, their insect pests barbecued, their fungi put in their place, their seed children pre-fertilised (lovely ash) and suddenly, there's a lot more sunlight to eat. When you see Greek islands scorched, know there is a pine or eucalyptus somewhere rubbing its roots together.
Trees can change 'their entire habit of growing in one or two generations'. We know when the land-bridge between Britain and Ireland went (the sunken kingdom of Cantre'r Gwaelod under Cardigan bay) because lime trees, spreading slower than pioneer species, did not make it out of Wales. The climate in Ireland tipped from Arctic to temperate in just 10 years.
The book is often alarming but Rix is also funny. Oak die-back happens, in Rix's eyes, when the trees' 'farthest fungi' have 'lost their love of adventure, their passion for the quest'. You feel delightedly child-like, and not just while being shown how a member of the avocado family seeds a cloud with a hexagonal ring of carbon.
The mysteries stalking science and Rix's pages are telling. We still do not know how trees' roots appear to be able to 'hear' or sense water. It might be vibration. What's the real evolutionary relationship between the Joshua Tree of the Mojave Desert, the giant sloth with the mushroom-alcohol body odour, and the sloth's on-board moth? Only time, and Harriet Rix, can tell. Non-fiction rarely sees a debut like The Genius of Trees. It is a true masterpiece.