tree. But it's just a guess. There can be 300 different species in any one hectare, and all you can see of them is their bark because the leaves and fruits are way up in the gloom, and there are different species in different regions. We just don't know how many there are in all. But what really matters is how all these myriad creatures live their lives, and how they interact with each other, and with the physical world: not the cast list, but the plot. And although the modern science of ecology is wonderful, all we have so far is glimpses; yet each glimpse is a revelation. What is becoming clear -- one of the most important of those revelations -- is that although biologists have stressed the significance of competition in nature -- "nature red in tooth and claw" as Tennyson put the matter -- and of course the entire modern economy is built on competition -- life is at least as cooperative as it is competitive. Some of the creatures that live in and around any one tree are indeed competing with that tree -- they are there to eat it -- but many others are vital to its own survival. Pines grow well on very poor soils -- but only because they have fungi in their roots, known as mycorrhizae, that help to draw nourishment from the soil. Actually, most trees have mycorrhizae. In fact it's very likely that plants could not have ventured on