THE HIDDEN LIFE OF TREES
Trees actively help and feed each other in times of need. Forester and author Peter Wohlleben uncovers a secret world that will make you look again at the woodland around you
Learn the secrets of an underground network that will make you look again at woodland around you
YEARS AGO, I STUMBLED ACROSS strange-looking mossy stones in one of the preserves of old beech trees that grow in the forest I manage. Casting my mind back, I realised I had passed by them many times before without paying them any heed. But that day I stopped and bent down to take a good look. The stones were an unusual shape – gently curved with hollowed-out areas. Carefully, I lifted the moss on one of them. What I found underneath was tree bark. So these were not stones, after all, but old wood. I was surprised at how hard the ‘stone’ was, because it usually takes only a few years for beechwood lying on damp ground to decompose, so it was obviously attached to the ground in some way.
I took out my pocket knife and carefully scraped away some of the bark until I got down to a greenish layer. Green? This colour is found only in chlorophyll, which makes new leaves green; reserves are also stored in the trunks of living trees. That could mean only one thing – this piece of wood was still alive! I suddenly noticed that the remaining ‘stones’ formed a distinct
pattern: they were arranged in a circle with a diameter of about five feet. What I had stumbled upon were the gnarled remains of an ancient tree stump, but all that was left were the vestiges of the outermost edge. The interior had completely rotted into humus long ago – a clear indication that the tree must have been felled at least four or five hundred years earlier. But how could the remains have clung on to life for so long?
Living cells must have food in the form of sugar, they must breathe and they must grow – at least a little. But without leaves, and therefore without photosynthesis, that’s impossible. No being on our planet can maintain a centuries-long fast, not even the remains of a tree, and certainly not a stump that has had to survive on its own. It was clear that something else was happening with this stump. It must be getting help from neighbouring trees, specifically from their roots. Scientists investigating similar situations have discovered that assistance may either be delivered remotely by fungal networks around the root tips – which facilitate nutrient exchange between trees – or the roots themselves may be interconnected. In the case of the old stump I had stumbled upon, I couldn’t find out what was going on because I didn’t want to injure it by digging around it. But one thing was clear – the surrounding beeches were pumping sugar to it to keep it alive.
If you look at roadside embankments, you might be able to see how trees connect with each other through their root
systems. On these slopes, rain often washes away the soil, leaving the underground networks exposed. This really is a case of interdependence, and most individual trees of the same species, growing in the same stand, are linked by their roots. It appears that nutrient exchange and helping neighbours in times of need is the rule, and this leads to the conclusion that forests are super organisms with interconnections much like ant colonies.
Of course, it makes sense to ask whether tree roots are simply wandering around aimlessly underground and connecting up when they happen to bump into roots of their own kind. Once linked, they have no choice but to exchange nutrients. But nature is more complicated than that. According to Massimo Maffei from the University of Turin, plants – and that includes trees – are perfectly capable of distinguishing their own roots from those of other species and even from the roots of related individuals.
Why are trees such social beings? Why do they share food with their own species and sometimes even nourish their competitors? The reasons are the same as for human communities: there are advantages to working together. A tree is not a forest.
On its own, a tree cannot establish a consistent local climate. It is at the mercy of wind and weather. But together, many trees create an ecosystem that moderates extremes of heat and cold, stores a great deal of water and generates humidity. And in this protected environment, a tree can live to be very old. To get to this point, the community must remain intact, no matter what. If every tree were looking out just for itself, then quite a few of them would never reach old age. Regular fatalities would result in many large gaps in the tree canopy, which would make it easier for storms to get inside the forest and uproot more. The heat of summer would reach the forest floor and dry it out. Every tree would suffer.
All individuals are valuable to the community and worth keeping around for as long as possible. And that is why even sick specimens are supported and nourished until they recover. Next time, perhaps, it will be the other way round, and the supporting tree might be the one in need of assistance. When
thick silver-grey beeches behave like this, they remind me of a herd of elephants. Like the herd, they, too, look after their own, and help their sick and weak back up onto their feet. They are even reluctant to abandon their dead.
Every tree is a member of this community, but there are different levels of membership. For example, most stumps rot away and disappear within a couple of hundred years (not long for a tree). Only a few individuals are kept alive over centuries. What’s the difference? Do tree societies have second-class citizens like human societies? It seems they do, though the idea of ‘class’ doesn’t fit. It is, rather, the degree of connection – or maybe even affection – that decides how helpful a tree’s colleagues will be. You can check this out by looking up into the forest canopy. The average tree grows its branches outwards until it encounters those of a neighbouring tree of the same height. It doesn’t grow wider because the air and light in this space are already taken. However, it reinforces the branches it has extended, giving the impression there’s a shoving match going on up there. But a pair of true friends is careful right from the outset not to grow overly thick branches in each other’s direction. The trees don’t want to take anything away from each other, so they develop sturdy branches only at the outer edges of their crowns – that is to say, in the direction of ‘non-friends’. Such partners are often so tightly connected at the roots that sometimes they even die together.
As a rule, friendships that extend to looking after stumps can only be established in undisturbed woods. Planted forests behave more like street kids. Because their roots are irreparably damaged when they’re put into the ground, they seem almost incapable of networking with each other. As a rule, trees in planted forests behave like loners and suffer from their isolation. Considered ready to harvest after only about a hundred years, most of them never have the opportunity to grow old anyway.