The Green Planet

(gentle music) Mushrooms are the familiar face of fungi, but they're merely the fruiting bodies. Some of them only last for a few days. They are however, evidence of the giant organism that lies in the soil beneath. Just a single handful of soil may contain several thousand meters of their microscopic filaments. It's only recently that we have discovered the extraordinary role that these fungi play, in a forest like this. Their filaments plug into the tips of the trees roots, and nutrients pass between tree and fungus throughout the year. Some fungi have the ability to link with not just a single tree, but with a whole group of trees. So that the entire forest may be linked together by these microscopic threads, form what you might call a wood wide web. (orchestral music) Hundreds of trees can be interconnected by these webs. Scientists call it, the microrisal network. And it might look something like this. (music crescendo) (bright music) They've discovered that trees not only send nutrients along it, but chemical and electrical signals, allowing them to communicate with one another. But some trees can also be selfish and steal from their rivals, or even wage war by sending out toxins that will harm competitors. It seems however that most trees do try to help each other. They raise the alarm when attacked by leaf eaters, giving other trees time to produce defensive chemicals. Those that are dying may send their food reserves to their neighbors. And some individuals known as Mother Trees recognize their own offspring, and will channel resources to them. (gentle music fades)