by Colin Tudge
PENGUIN BOOKS
THE SECRET LIFE OF TREES
‘The best nature writing’ The Times
‘Page after page of astonishing tree-facts … makes us look anew at the familiar, to understand a little more of the hidden and constantly enacted miracles taking place in the woods all around us’ Sunday Times
‘Tudge’s delight in the world of trees is infectious’ Herald
‘Set to become a classic reference in the mould of Oliver Rackham’s History of the Countryside’ BBC Wildlife
‘Tudge’s gift as an author lies in being able to explain complex scientific mechanisms in language that the rest of us can understand’ Anna Pavord, Independent, Books of the Year
‘Magnificent, a minor classic … even the most knowledgeable connoisseur of nature will feel themselves in the hands of a witty and erudite guide … probably the best general purpose book on the subject published in the last decade’ Oldie
‘Inspiring, a reawakening’ Scotsman
‘Reminds us just what we spend our lives not knowing, and all of it is not only wondrous and important but entirely free’ Guardian
‘A love-letter to trees, written with passion and scientific rigour … a pleasure to read. Tudge writes with warmth and wit’ Financial Times
ABOUT THE AUTHOR
Colin Tudge started his first tree nursery in his garden aged eleven, becoming an accomplished Cacti grower by the age of eighteen and marking his life-long interest in trees. Always interested in plants and animals, he studied zoology at Cambridge and then began writing about science, first as features editor at the New Scientist and then as a documentary maker for the BBC. Now a full-time writer, he appears regularly as a public speaker, particularly for the British Council and is a Fellow of the Linnean Society of London and visiting Research Fellow at the Centre of Philosophy at the London School of Economics. His books include The Variety of Life: A Survey and Celebration of All the Creatures that have Ever Lived and So Shall we Reap. The Secret Life of Trees brings together Colin Tudge’s knowledge of trees and his fascination with them, built up from trips to the rainforest in Costa Rica, Panama and Brazil, to his time in India, Australia, New Zealand, China, the United States… and his own back garden. He is unable to choose a favourite tree, believing that variety’s the thing.
COLIN TUDGE
The Secret Life of Trees
How They Live and Why They Matter
PENGUIN BOOKS
To my grandchildren
PENGUIN BOOKS
Published by the Penguin Group
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First published by Allen Lane 2005
Published in Penguin Books 2006
Copyright © Colin Tudge, 2005
Illustrations copyright © Dawn Burford
All rights reserved
The moral right of the author has been asserted
Except in the United States of America, this book is sold subject to the condition that it shall not, by way of trade or otherwise, be lent, re-sold, hired out, or otherwise circulated without the publisher’s prior consent in any form of binding or cover other than that in which it is published and without a similar condition including this condition being imposed on the subsequent purchaser
ISBN:978-0-14-192729-9
Contents
List of Illustrations and Figures
Acknowledgements and Author’s Note
Preface
I What Is a Tree?
1 Trees in Mind: Simple Questions with Complicated Answers
2 Keeping Track
3 How Trees Became
4 Wood
II All the Trees in the World
5 Trees Without Flowers: The Conifers
6 Trees With Flowers: Magnolias and Other Primitives
7 From Palms and Screw Pines to Yuccas and Bamboos: The Monocot Trees
8 Thoroughly Modern Broadleaves
9 From Oaks to Mangoes: The Glorious Inventory of Rose-like Eudicots
10 From Handkerchief Trees to Teak: The Daisy-like Eudicots
III The Life of Trees
11 How Trees Live
12 Which Trees Live Where, and Why
13 The Social Life of Trees: War or Peace?
IV Trees and Us
14 The Future With Trees
Notes and Further Reading
Glossary
Index
Illustrations and Figures
p. 1 The Buddha receiving enlightenment under a peepul tree
p. 13 Judas tree
p. 31 Jungle scene
p. 60 Dicksonia
p. 64 The Names and Times of Ages Past
p. 71 General classification (phylogenetic tree)
p. 77 Cyad
p. 79 Ginkgo
p. 81 Young yew
p. 95 Bristlecone pine
p. 108 Juniper
p. 122 Magnolia
p. 124 Phylogenetic tree for angiosperms
p. 131 Tulip tree
p. 136 Flowering plant orders
p. 139 Dragon tree
p. 141 The Monocots
p. 150 Double coconut palm
p. 151 Young royal palm
p. 154 Bamboos
p. 156 Traveller’s palm
p. 157 Large cacti
p. 159 Phylogenetic tree for Eudicots
p. 167 Baobab
p. 169 Phylogenetic tree for the Rosids
p. 193 Banyans
p. 199 Beech
p. 204 Birch
p. 227 Handerkerchief tree
p. 229 Phylogenetic tree for the Asterids
p. 236 Cannonball tree
p. 245 Teak
p. 251 Mangroves
p. 277 Coastal redwood
p. 284 Map showing continental drift
p. 314 Coastal redwoods re-rooting themselves as silt piles up around them
p. 317 Figs
p. 328 Bat pollination
p. 331 The syconium (fruit) of a fig
p. 365 Agroforestry
Original drawings by Dawn Burford
Acknowledgements
Over the past half century I have had many illuminating conversations with a lot of people who know a great deal about trees, in at least a score of countries in every habitable continent, and it would be too exhausting to mention everyone who has helped me with this book. Over the years, however, I have been particularly informed by Professor E. R. (‘Bob’) Orskov, now at the Macauley Research Station in Aberdeen, on Third World agriculture in general and agroforestry in particular. From China, I have particular cause to thank Professor Hao Xiaojiang, director of the Kunming Institute of Botany in Yunnan, China, who introduced me to the extraordinary collection (including 100 species of magnolia) in the Botanic Garden of Kunming; and Dr Ian Hunter, director of the Inte
rnational Network for Bamboo and Rattan, Beijing. In Australia, I spent several excellent days with scientists from CSIRO both in the bush of Western Australia and in the tropical and subtropical forests of Queensland and New South Wales. In New Zealand, Keith Stewart, novelist and columnist, took me to see the kauri forests in the North Island, and introduced me to Tane Mahuta.
For the particular writing of this particular book, I am especially aware of my debt to Professor Jeff Burley, formerly head of forestry at Oxford University, who indeed inspired this whole enterprise (just as he inspired generations of foresters worldwide). Also at Oxford, Dr Stephen Harris read several of the chapters for me; Dr Nick Brown helped me on my way with comments about mahogany; Professor Martin Speight provided fine fresh insights into pests; Professor Andrew Smith instructed me in tree physiology; and Dr Yadvinder Malhi had excellent, original things to say about tropical forests and climate change. At the Royal Botanic Gardens, Kew, I was privileged to be introduced to the latest thinking on conifers by Dr Aljos Farjon. At EMBRAPA in Belém, I was treated royally and introduced to the realities of Brazilian forestry by Ian Thompson; and had particularly illuminating discussions with Dr Mike Hopkins and Dr Milton Kanashiro. In Belém, too, from Johan C. Zweede I learned at least a few of the ins and outs of tropical forest commerce. I was introduced to the Cerrado by Professor Carolyn Proença of the University of Brasilia, and by Dr Manual Cláudio da Silva Júnior of Brazil’s forestry department, while José Felipe Ribeiro took my wife and me out into the field to show us ways in which local people can make a much better living from the Cerrado than by growing yet more soya. Hugely instructive, too, as well as enjoyable, was our stay with Robin and Binka Le Breton, at Iracambi, who are seeking among other things to restore at least some of the sadly depleted Atlantic rainforest. At the Smithsonian Tropical Research Institute in Panama I was prodigiously instructed by Drs Anthony G. Coates (continental drift), Neal G. Smith (mainly birds), Stanley Heckadon-Moreno (mangroves), Egbert G. Leigh (particularly on the tropical forest on Barro Colorado Island) and Allen Herre (whose extraordinary researches on figs are a key theme in Chapter 13). Boundless gratitude to all of them, and to Beth King for fixing up the entire trip. At the Tropical Agricultural Research and Higher Education Center (CATIE) in Costa Rica Dr Bryan Finegan was wonderfully generous with his time and showed, as we stood in the rain, how physically hard as well as magical it can be to carry out research in tropical forest; while Dr Muhammad Ibrahim introduced me to CATIE’s excellent researches in agroforestry and Dr Wilberth Philips showed me the local trees. Then to India, and in particular to the vast and extraordinary campus and arboretum of the Forestry Research Institute at Dehra Dun, where I have particular cause to be grateful to FRI’s then director, Dr Palab Parkash Bhojavid, for excellent discussions and hospitality (including Christmas dinner with his family), and in particular among his colleagues to Dr Sas Biswas. In Latvia, I was introduced to the forest (and its beavers) by leva Muizniece of the British Council, Anita Upite, editor of Hunting, Angling and Nature, and Monvids Strautins, forester. I am grateful, too, to the British Council in general and to Dr Gavin Alexander in particular, who arranged some of my most illuminating trips.
Overall, I am aware of my debt to my agent, Felicity Bryan; to my editor at Penguin, Helen Conford; and to Jane Birdsell, an outstanding tidier of prose and picker-up of solecisms who has made this book much better than it would otherwise have been. Finally, the book has been much enhanced by Dawn Burford’s excellent drawings, almost all taken directly from life. Many thanks to her and to the Birmingham Society of Botanical Artists for introducing me to her. Most of all, I thank my wife Ruth, who introduced me to Oxford and organized and managed most of our travels. Without her heroic efforts I would almost certainly have petered out at Heathrow.
AUTHOR’S NOTE
The following abbreviations have been used throughout the text:
‘Judd’ refers to Walter S. Judd, Christopher S. Campbell, Elizabeth A. Kellogg, Peter F. Stevens and Michael J. Donoghue (eds), Plant Systematics (Sinauer Associates Inc., Sunderland, Massachusetts; 2nd edn, 2002.).
‘Heywood’ refers to V. H. Heywood (ed.), Flowering Plants of the World (Oxford University Press, Oxford, 1978).
Preface
Trees inspire: the Buddha received enlightenment under a peepul tree
At Boscobel in Shropshire in the English Midlands stands the Royal Oak, where the provisional King Charles II is alleged to have hidden from Cromwell’s men after the Battle of Worcester, which ended his premature attempt to restore the monarchy. Why not? All this happened only about three and a half centuries ago (1651) and oaks may live for two or three times as long as that. Robin Hood and his Merry Men are said to have feasted beneath the Major Oak in Sherwood Forest in Nottinghamshire – and so they might have, for if they existed at all it was in the time of Richard I, in the late twelfth century, and the Major Oak was alive and well at that time. A yew I met in a churchyard in Scotland has a label suggesting that the young Pontius Pilate may once have sat in its shade – ‘and wondered what the future held’. It’s an audacious claim. But the tree was there, even if Pilate wasn’t – already some centuries old at the time of Christ.
There’s a kauri tree in New Zealand called Tane Muhuta (the oldest and biggest kauris are given personal names), with a trunk like a lighthouse, that was 400 years old when the Maoris first arrived from Polynesia. For the first 900 years or so of Tane Mahuta’s life the moas, related to ostriches but some of them half as tall again, would have strutted their stuff around its buttressed base, threatened only by the commensurately huge but short-winged eagles that threaded their way through the canopy to prey upon them. Now the moas and their attendant eagles are long gone but Tane Muhuta lives on. Many a redwood still standing tall in California was ancient by the time Columbus first made Europe aware that the Americas existed. Yet the redwoods are striplings compared to some of California’s pines, which germinated at about the time that human beings invented writing and so are as old as all of written history. These trees out on their parched hills were already impressively old when Moses led the Israelites out of Egypt, or indeed when Abraham was born. So it is that some living trees have seen the rise and fall of entire civilizations.
Some redwoods, Douglas firs and eucalypts are as tall as a perfectly respectable skyscraper, and there’s an extraordinary banyan in Calcutta that would cover a football field. Many are host to so many other creatures that each is a city: as cosmopolitan as Delhi or New York and far more populous than either. Creatures of all kinds may feed on trees, or maraud among their branches. At least, I know of no arboreal octopuses – but there could be, out in the mangroves. There’s many a tree-happy crab in the mangroves, as I have seen for myself, and the robbers of the Pacific islands, giant hermit crabs, come on land (as many crabs do) to feed on coconuts. When the Amazon is in flood – deep enough to submerge well-grown trees entirely, over an area not far short of England – the fish feed on fruit and river dolphins race through the upper branches of what should be the canopy, while monkeys hop and swim from crown to crown like ducks. In New Zealand little blue penguins nest in the forest at night with ground parrots (or at least they do on the sanctuary of Maud Island). In the 1970s in the crown of one fairly modest tree in Panama a scientist from the Smithsonian Institution counted 1,100 different species of beetle – yet he didn’t bother with the weevils, although they are beetles too, or look closely at the host of creatures that are not beetles, or those that were living in the roots. I once found myself in an old kapok tree in Costa Rica in which biologists had thus far listed more than 4,000 different species of creatures.
Yet a tree cannot afford simply to serve as someone else’s monument and feeding ground. From the moment the seed falls on to the forest floor (or the sand of the savannah, or a fissure in some mountain crag, or a glacier’s edge, or a lakeside, or a tropical seashore) to the moment of its final demise, perhaps a thousand years later, the tree must compete
through every second – for water, nutrients, light and space; and to fend off cold, heat, drought, flood, toxicity, and the host of parasites and predators of all conceivable kinds (from a tree’s point of view, squirrels or giraffes are ‘predators’). A village or a civilization may choose to make a tree their symbol. The entire nation of Brazil is named after a tree – for brazil wood was known to Europeans before the country was. But however we may choose to ennoble it, the tree must fight its corner, a creature like all the rest. If it did not fight it would be dead. Even when it sheds its leaves to ride out frost or drought its cells are still busy beneath its armoured bark. Were it not so the leaves could not burst out as they so spectacularly do when the temperate spring or the tropical rains return – or sometimes in advance of the rains, to the delight of camels and goats, which thus may find green fodder in the depths of drought. In many trees, too, tropical and temperate, the flowers emerge before the leaves – which keeps the path clear for pollinating winds, bees or bats. Since there are no leaves to provide nourishment, the flowers must be fed from the tree’s reserves in its trunk and roots. The living timber is multipurpose: a prop, a conduit, a larder.
Flowers, of course – and the cones of conifers – meet life’s other demand: not simply to survive and grow, but to reproduce. Here, the trees’ immobility is a particular drawback. Many trees reproduce without sex, commonly though not exclusively by root suckers, but all trees (to my knowledge) practise sex as well. For sex, gamete must meet gamete: sperm and egg in the case of animals and primitive plants; pollen and ovule in the case of conifers and flowering plants. Since many flowers of many trees are hermaphrodite (male stamens and female carpels on the same flower), and many trees (like oaks and many conifers) are monoecious (the individual flowers are exclusively male or female, but both kinds occur on the same tree), it may seem easy enough for trees to pollinate themselves. But on the whole they don’t. One of the botanical surprises of recent decades (finally proven by genetic studies) is the length to which most trees go to avoid self-fertilization. ‘Out-crossing’ is the norm: pollination of, and by, other individuals who of course are of the same species but preferably are not too similar genetically. To achieve out-crossing, trees must elicit the help of the wind – or bribe or otherwise coerce a variety of animals, from flies and beetles and bees to birds and bats – to carry their pollen for them. Some temperate trees (like apples and horse chestnuts) are pollinated by animals but most (like oaks and birches and beeches) are content to use the wind. But in tropical forests, where most kinds of trees live, animal pollination is the norm; and because life is competitive, the mechanisms that have evolved for this have become more and more elaborate. Thus for every one of the 750 different species of fig there is a corresponding species of specialist wasp to pollinate it; and each wasp knows its own fig (although, as recent studies have shown, the relationship between figs and their wasps is not quite so cosy as had been supposed). When the ovules are fertilized and become seeds, encased in fruits (or some other kind of fruiting body) they must then be dispersed – sometimes again by wind but often by another, entirely separate, suite of animal accomplices – birds and fruit bats and rodents and orang-utans – whose help must again be actively co-opted.
