A climate for climbers

THE holly and the ivy/ When they are both full grown/ Of all the trees that are in the wood/ The holly bears the crown...

At carol-time, when holly and ivy hen? the only green leaves in the wood, it is actually the ivy that more often bears the crown - if the big, straggly mop it can make in the top of a tree actually deserves the term. How different from the "short, well-trimmed skirt of ivy", at the base of the trunk, which is how Dr Risteard Mulcahy would prefer to see this wayward Irish climber.

A year or so ago in this column I was provoked by an American visitor who complained of the "ugly, disfiguring, parasitic, ivy-like plant" that was running rampant in our trees, "causing once-lovely landscapes to appear grotesque and uncared for".

"Hederaphobia," as I wrote then, "has sustained a good many native Irish newspaper letter-writers well into their old age." Ivy-clad trees and ruins, I suggested, were not only wildlife-friendly, but distinctive of the Irish landscape - part, as it were, of what we are.

Now arrives a counterblast from a man who, as is bound to be said by someone, has a heartfelt interest in the matter. Dr Mulcahy, retired now from a career in cardiology, has had woodlands of his own in Co Wicklow since 1974, and in them, one feels sure, any "infestation" of ivy has promptly has its arteries nicked.

He has written a slim book, For Love Of Trees, most of it concerned with his deep conviction that trees and hedgerows are damaged by excessive ivy growth. He is scrupulously fair to differing views, as befits a man of science, and calls, ultimately, for research to resolve the matter.

"The notion that ivy kills the tree it grows on," says the Cambridge botanist Oliver Rackham, in his magisterial Trees And Woodland, "can be traced all the way back to Theophrastus in the fourth century BC, without anyone stopping to think whether it can be true!"

Dr Mulcahy certainly thinks it's true that ivy cripples and deforms trees grossly and leads to their "premature death". He offers photographs in evidence, in which ivy is presented as a funereal, leprous growth: "Note the paucity of lateral branches and of peripheral twigs, and the gross impairment of the tree's canopy.

Ivy may be important for bird life, he acknowledges, "but birds could be cared for at least as well by other means". A look at the pages on diet in Eric Simms's monograph on British Thrushes might disabuse him of the belief that "ivy berries do not occupy a favoured in the avian cuisine". All kinds of birds eat ivy berries when there's nothing around they like better, and the pine martens in the Burren do so too. The late-season nectar of ivy flowers is also valued by insects such as hoverflies, which might find fewer alternatives.

The Irish climate is clearly unusually favourable to the growth of ivy: indeed, the plant is unstoppable. Its ubiquity, so thoroughly documented by Dr Mulcahy, has laced it deeply, over many thousands of years, into the ecosystems of Ireland's cliffs and field-walls, hedgerows and woodlands. Its shade, shelter, evergreenness, water-shedding leaves, interior microclimate, its prolific nectar and berries, all figure in an ecological network of subtle benefit to many different kinds of organism, from spiders and snails to mites and moths.

Oliver Rackham, in his History Of The Countryside, tells of finding, on a lake island in Co Offaly, "an extraordinary wood of great ancient oaks, hung with ancient ivies (one ivy trunk is thicker than a fat man) ..." So some trees and ivy can flourish together for centuries.

Some other trees do not get on so well: they may, indeed, lose the perfect shape and symmetry all lovers of trees admire. Some may be blown down because the ivy in their high branches catches the winter storms. Others, including some hedgerow hawthorns, may become choked by the competing leaves, and may, indeed, "die prematurely".

But so what? That's what happens 0 this island at this particular point between Ice Ages. A fallen tree, covered with ivy, will rot down gradually, making a splendid habitat for ferns, mosses, liverworts and fungi, not to mention a whole army of insects that live in rotting trees and nowhere else (and the ivy, meanwhile, will live on).

OF course a great oak without ivy, its branches spreading nobly, the winter sun catching the texture of its bark, looks a lot more attractive than one muffled up in fuzzy evergreen - the pictures in Dr Mulcahy's book make the point very well. If it's your oak tree, by all means keep the ivy within bounds. But don't go worrying about all the other trees in Ireland, tormented by every shaggy shape across the land - it's bad for the heart.

May I wish Risteard Mulcahy - and all my readers - a very happy Christmas.