I have just finished reading the ‘Hidden Life of Trees’ by Peter Wohlleben. It’s a marvellous read and one of those books where you stop and read bits out loud to anyone who happens to be close. I had never heard or come across phytoncides before. These are volatile substances, wood essential oils, that are antimicrobial volatile organic compounds. They are responsible for the ‘pine fresh’ aroma in conifer forests. I mentioned the beneficial effects of trees a while ago but for some reason I had presumed that these were simply psychological rather than having specific chemical source. There is some peer reviewed research into this phenomenon that indicates an improvement in the immune system that can last for up to 30 days after a walk in the woods.
Obviously different trees produce different phytoncides. Walnut trees in particular are ideal for discouraging mosquitoes. So if you are going to have a bench or seat in the trees, put it under the walnut tree.
Trees are also good for each other. The author is a forester who currently cares for, rather than manages a beech forest in Hummel in Germany. He introduces the book with the concept of the ‘wood wide web’ explaining the interface between tree roots and mycorrhyzal fungi. This enables the exchange of nutrients and signals between trees. The idea that trees signal to each other was pretty astonishing to me, though once to read the book, it obviously works. The existence of mycorrhyzal networks is mainstream now and much of the gardening literature encourages the addition of dried mycorrhyza to any planting, though this is likely to have limited effect in a suburban garden.
An acacia tree produces unpleasant tasting chemicals when it is ‘attacked’ – or have its leaves eaten, by a giraffe. This prevents the tree being stripped of all of its foliage in one sitting. Other acacias close by also produce the anti-giraffe chemical, so there is some communication between them – via the wood wide web. The giraffes simply move a few trees down past the range of the alarm message.
He also follows an increasingly stated mantra about the preservation of the natural world – the best way to save nature is to do nothing. This means literally what it says, and not, leave the natural world for others to exploit. Just leave it to get on with what it has been doing for the last few billion years.