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

Country Living (UK) - - Contents - Il­lus­tra­tions by mar­i­ana ro­drigues

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?

BRANCH LINES

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.

GROW TO­GETHER

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.

COM­MU­NITY SER­VICE

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.

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