The Unofficial Book Club no 5

Trees, Peter A Thomas, New Naturalist 145, HarperCollins, 505 pp, £65 hbk

I’m ashamed it’s taken so long to review this fabulous title by Peter Thomas. My excuse was that I have a small library of books on trees. I’ve even reviewed a modest shelf of great past titles (Oak, William Bryant Logan 2005; Woodlands, Oliver Rackham 2005, The Secret Life of Trees, Colin Tudge, 2005). I’ve ploughed my way through Meigg’s classic Trees and Timber in the Ancient Mediterranean World, not to mention a half dozen other tree-centred works by Rackham; so what could I possibly learn from a new book on the subject?

Turns out, a very great deal. Almost every page reveals something I didn’t know or properly understand. The previous titles that I’ve mentioned deal to a large extent with trees as cultural entities, or on the habitats they comprise. This is not Thomas’ main goal. He does branch off to take in any number of arboreal side issues, but first and foremost he gives us the latest research on trees as biological organisms. His book is about what makes trees work. How they overcome challenges, survive, thrive and dominate our world. Along the way he reveals just what extraordinary beasts they are, some living for 5,000 years (bristlecone pine) while others are the largest organisms ever to have flourished on Earth (giant sequoia) . And they are still here.

When I reflect there really are very few books like it; and certainly not written for a general audience (I dare you to grind through The Evolutionary Biology of Plants, Niklas, or Diversity and Evolution of Land Plants, Ingrouille, which are learned but tough) For the last few months Trees has been a constant companion, inspiring a number of related forays. So my review is part reflection on Thomas’ achievement, and partly a celebration of trees in about 20 images.

To give a small flavour of the book’s revelations, I didn’t know that trees grow mainly at night, that a single mature deciduous specimen sets out a tent of leaves that covers the equivalent of 350 square kilometres; that in the course of a year a big deciduous specimen takes up something like 40,000 litres of water. In one day it can use 220 litres, or 364 pints!

Another element we can overlook is how astonishingly successful trees are. Although their earliest ancestors arose roughly 400 million years ago, the majority of the plants clothing the Earth, arguably the most widespread and successful set of organisms ever, creating the world’s richest environments, are called angiosperms, which appeared in the age of dinosaurs, a mere 100 million years ago. Almost all deciduous trees, such as these autumn beeches in Chee Dale below, are angiosperms. By the late Cretaceous (90m years ago) elms, birches, laurels, maples, oaks and willows were all flourishing.

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We often credit trees as the primary suppliers of oxygen – the element that shapes almost the entirety of life – yet neither trees nor plants invented photosynthesis. True thanks must go to the earliest ancestors of bacteria, which stumbled on the innovation of turning sunlight to sugar more than 2,500 million years before trees even existed. Marine phytoplankton are still generating as much as half of the planet’s oxygen today, yet there is no mistaking the astonishing engineering achievement of tree leaves. Here’s a single beech leaf in close up.

Thomas may go deeply into the inner processes of trees, but he delights to mention that trees also shape cultures and even whole civilisations. Apparently, 1.6 billion people – 20 per cent of the world population – still rely on trees. Coffee, tea and palm oil, the latter apparently in half the products in our supermarkets, are just three ‘small’ indicators of their universality in modern life. Meanwhile, spices like cinammon and nutmeg were historical triggers for the European imperial project. (Although I like to imagine how a single insect – the silk moth – and ‘mere’ soil, deployed respectively in Indian silk manufacture and China’s famous china products, were drivers of European world exploration, global trade and conquest.)

Below are a few reminders of the many practical arboreal applications: in their roles as shade, coolness, beauty, absorbers of urban pollution (eg: plane trees arched over Lisbon’s downtown area), as acorn fodder for Spain’s famous charcuterie products; as cork to keep intact our favourite tipple; as sources of fruit or seed (eg: rowan berries a staple for Britain’s winter birds) and as building materials for human construction everywhere (eg: the Scottish conifer plantation below, however, represents the very worst in misguided forestry.)

Yet Thomas’ main achievement is to offer us the most comprehensive and detailed analysis of how trees live. There are sections devoted to seasonal challenges – how they grow in early spring and their responses to high summer, especially where and how to source water, given that they comprise over 80 per cent H2O. Some trees in dry landscapes, for example, are moving, over a single night, 80 litres from the deep root to the canopy. There are also sections on how trees propagate through flowers, fruits and seeds, and who are the main collaborators in these various reproductive strategies.

I found the best way to enjoy so long and heavy a book (it’s 1.4 kg) with relatively small font was to read it as a sequence of random chapters. There is a separate section on pests and pathogens, which is deeply pertinent here in Derbyshire, given that we are losing millions of trees because of ash-dieback disease. The latter is every bit as bad as the so-named Dutch elm disease in the 1970s and has spread partly because of our supremely lax attitude to biosecurity in Britain. (Incidentally, one of the most striking aspects of ashwoods is their reluctance to leaf until almost high spring. Look how there is not the slightest hint of greenery, yet this photo was taken on 29 April ’21).

Given their own highly complex architecture, each tree is a kind of engineer of its own parts. Thomas tackles in detail the fine balance act that it must achieve to match inputs to outputs. One of the strategies that has received a lot of attention recently is trees’ capacity to collaborate with micorrhizal fungi now popularised as the ‘wood-wide web’. Trees essentially form symbiotic partnerships with the subterranean mycelia of mushrooms. The fungi are sending upwards water and nutrients in exchange for a downward transfer of sugars made through photosynthesis. These relationships have given rise to popular notions of a sort of idealised woodland communism. I like the way in which Thomas ever-so-gently debunks this simplistic version of nature.

As I mentioned, I seem to have spent a lot of time recently reflecting and celebrating trees. Here is a little of the results. Before I take leave of Peter Thomas and his inspiring company I should add that Christmas is upon us. I couldn’t think of a finer present for someone than his superb book. And if the person you have in mind loves trees, they will cherish them more on reading it.

My images above, clockwise from top-left, show the magnificent Oriental plane trees on a Greek river, about which I have written here. (Not only is each a kind of independent engineer, levering up resources to meet its downward distribtion of sun-sourced carboydrates, but the planes keep intact the entire riverine ecosystem. Once again, the inadvertent transfer of pathogens by our own species is threatening these magnificent citizens of Arcadia.) Next comes The Old Lady of Moccas Park described here (getting a big hug from yours truly). A birchwood in Scotland, then a trio of images of beechwoods in the Peak District: which I have described here and here.

The photos hereafter are simply a gallery of some much-loved specimens with captions. But perhaps it remains for me to point out that Christmas is upon us. I couldn’t think of a better present for anyone who enjoys trees than this book. I promise: Peter Thomas will encourage you to love them even more.

Above is one of the oldest sallows in Britain that lies on one of the main roads west of Inverness (further described here). I often feel tempted to photograph veteran trees in black and white. Somehow their age and venerability, not to mention their architectural structure, seem to be captured better. To me this sallow has an arachnid-like form and has managed to cross an entire stream and start growing on both sides simultaneously. Sometimes trees are more like animals than vegetation.

Here (clockwise from top left) are some of the oldest trees I have ever seen. Top left and right are parts of the Doveridge yew, the oldest tree in Derbyshire and possibly 1,200 years old. Next is Maria leaning upon the ample knee of a glorious sweet chestnut in Gloucestershire. Author and naturalist Peter Marren wears the 1100-year-old Big Belly Oak in Savernake, Wiltshire as a sort of hat. Finally bottom left is the Major Oak in Sherwood Forest, perhaps Britain’s most-visited single tree.

Above is the tree as life inspiration and personal hero. This is a juniper that I photographed earlier in the year. It’s growing, and has done possibly for hundreds of years, on the very edge of oblivion. Its true jeopardy and full heroism is better revealed in the picture on the right (look smack at the centre), because the tree lives on the lip of the deepest gorge in the world, Vikos Gorge in Zaghoria. Below it lies a 500m drop.

Last but not least is a montage of hawthorn in all its magnificent parts. I don’t do favourites very often, but if I had a favourite tree then this is perhaps it. Without hawthorns Derbyshire would often be merely rock and grass.