The Secret Life of Trees

"This is basically a tree-lovers’ book and it’s a bit of a catalogue in a way. He talks about what makes a tree a tree. A tree is a woody plant with a trunk, which is a pretty obvious definition, but that way of being a plant has evolved many times. So trees are not, evolutionarily speaking, one thing. They are a group of things with different evolutionary origins. For example, pine trees and oak trees have quite different origins. They are seed plants, but they acquired the habit of standing up on a long tall trunk independently of each other. Their ‘treeness’ evolved independently. Palms are a good example – they evolved the habit of standing as they do quite separately from oak and pine trees. It’s a different way of being a tree. The interesting thing about palms is that if you plant an oak seedling after five years it is five centimetres in diameter, after ten years 20 centimetres and so on, but that isn’t the way palms grow. Palms don’t get fatter as they get older. A baby palm sits on the ground accumulating leaves until it’s fat enough to grow upwards. Once it begins to do that, you’ll see that a baby palm of a metre high has a trunk that will ultimately support something that is ten metres high. The reason for this is that they’re not built in a way that allows them to get fatter, because the trunk is made of the bases of old leaves. The coconut germinates and lots of leaves accumulate like a huge rosette and only when it’s got enough of those can it start to grow upwards. But, an oak tree starts off slender and gets fatter. These are completely different evolutionary tracks. So, this book is about different ways of being a tree, all the trees in the world in their different groups – trees without flowers, conifers, magnolia (which is a relatively primitive early tree), and so on. So, if you like trees, and lots of people do, this book is for you. It has done very well. We can’t really know because it happened a long time ago, but it happened after colonisation of land by plants. Life evolved in the sea and the earliest photosynthetic fossils are of things that lived in shallow water. Eventually, plants colonised the land and there is a little tiny fossil, about the size of a moss, that is the first land plant. But as competition among plants grew, trees evolved, almost certainly driven by the simple fact that the highest plant gets most of the light."