The Hidden Life of Trees: What They Feel, How They Communicate—Discoveries from a Secret World

by Peter Wohlleben

Sal is always labelled ‘gregarious’ because it grows in huge assemblies of its own kind, not quite in a monoculture but in massed stands in which it is, far and away, the predominant species. It has always been known that you can’t grow a sal tree on its own.

You won’t find a sal tree growing in a park, for instance, nor will you encounter an avenue of sal trees. Foresters tell us that sal trees die of ‘loneliness’ when they are planted singly.

Young trees are so keen on growing quickly that it would be no problem at all for them to grow about 18 inches taller per season. Unfortunately for them, their own mothers do not approve of rapid growth. They shade their offspring with their enormous crowns, and the crowns of all the mature trees close up to form a thick canopy over the forest floor. This canopy lets only 3 per cent of available sunlight reach the ground and, therefore, their children’s leaves. Three per cent—that’s practically nothing.

And so, in 2009, tree researcher Martin Gossner sprayed the oldest (600 years old) and mightiest (170 feet tall and 6 feet wide at chest height) tree in the Bavarian Forest National Park. The chemical he used,

pyrethrum, is an insecticide, which brought any number of spiders and insects tumbling down to the forest floor—dead. The lethal results show how species-rich life is way up high. The scientist counted 2041 animals belonging to 257 different species.48

There is a scientific observation that speaks to this: the blood pressure of forest visitors rises when they are under conifers, whereas it calms down and falls in stands of oaks.66