The Secret Life of Trees. By Colin Tudge

Feats, shoots and leaves

Trees are the tallest, oldest and in many ways the most efficient of all living things. Powered by the sun, they are the planet's biochemical engines, drawing water and minerals from the soil and converting harmful carbon dioxide into life-giving oxygen. They live simultaneously in the earth and the sky. And each mature tree is an ecological city, home for thousands of interacting plants, animals and fungi.

Yet we take trees for granted. By planting them in rows like fence poles with leaves, we strip them of individuality and turn them into commodities. We tend to see them in economic terms as sources of timber or part of the scenery. The miracle of life that creates a hundred-foot, sky-grabbing monster that is also an object of beauty is easy to overlook.

Colin Tudge's aim is to explain why trees matter and to reveal their hidden lives in all their dynamism and diversity. It is, however, no simple matter to define what a tree is. They are not a natural group. There are trees related to flowers as different as daisies, spurges, asparagus and stinging nettles. There is even a tree version of grass: bamboo.

There are ancient trees whose fruits were probably once nibbled by dinosaurs and ultra-modern ones like the willows, evolving in front of our noses. What they all share is lignin, the simple chemical that makes wood as tough as concrete, and enables a tree to suspend a ton of leaves high above the ground. And there are a lot of trees: 60,000 species is a rough guess.

Unlike animals, which eat, breath, sense and even think, trees seem to do only one thing: they grow. Their secret, Tudge reveals, is that they are more like animals than they appear. Hormones provide a kind of chemical intelligence. Trees have a memory. They can analyse problems and find solutions. A tree shaken by a gale puts on a spurt of growth and becomes slightly fatter and more wind-proof. It reacts to an invasion of caterpillars by producing smaller, less caterpillar-friendly leaves.

Shedding leaves takes weeks of preparation. An oak tree knows autumn is coming by measuring day-length with meteorological accuracy. In truth, trees are fighting for survival every day of their long lives, competing for water, nutrients, light and space, coping with cold, heat and drought as well as armies of leaf-guzzling insects.

There is an evolutionary intelligence that makes trees to fit almost every circumstance. A mangrove can breathe in salty silt with the help of aerial roots. The baobab survives in near-waterless places by turning its trunk into a massive rain-water barrel. Pines can live on virtually bare rock by forming a mutually beneficial partnership with fungi.

One of Tudge's strengths as a science writer is that he can make complex matters intelligible without resort to jargon or telly-talk. However, he is careful not to oversimplify. For example, he spends a whole chapter trying to unravel one of the world's great mysteries: why most trees grow in the tropics while the vast forests of Canada consist of just nine species. The best explanation is that Ice Ages have wiped the slate clean in northern latitudes so that the forests have never had enough time to diversify.

This book could have been tightened. Tudge is apt to take off on hobby horses like DNA and the evolution of plants. And by attempting to cover the variety of the world's trees, he does less than justice to the personality of our native ones. He leaves us with a sense that the destiny of a tree is to be tree-shaped. Yet this isn't true of northern forests, where a combination of climate and nibbling herbivores produces cranky trees that are bent, bushy or even horizontal.

The Secret Life of Trees is a fascinating journey, full of scientific insights and never (or hardly ever) losing sight of the quirky, endlessly inventive nature of trees themselves. As Tudge notes, in a world which deals increasingly in abstractions, trees are refreshingly real and down-to-earth. By understanding how they live we are in a better position to appreciate why they matter.