A positive word for Ivy

Ivy undeservedly has a bad name for killing trees - here are some surprising observations and facts on it's benefits.

Ivy and birdbox

Extract form Route and Branch by Bill Clark, podcasts - full podcast here:

https://archive.org/download/a-good-word-for-ivy/Ch11b-A-good-word-for-ivy.mp3

From time to time I go into print to help the ivy – usually in answer to published letters and articles wanting a purge on it. Despite the popular conviction, I have never seen a mature tree killed by ivy! Of the 250 huge Beeches that died on this estate during the 1976 drought – when I reckoned that the ivy must be competing with the trees for water – no dead trees were ivy covered: but among the 1,700 that remained, many of the healthiest had ivy covered trunks. I decided that the ivy had protected these thin barked trees from sun scorch. Of a further 3,000 mixed species lost in various gales, only four were heavily ivy covered – even I had thought that an ivy covered tree would be more vulnerable in a gale! 

Of our 600 Elms that were lost to ‘Dutch Elm Disease’ I noticed that the ivy covered ones were the last to go – I believe the ivy camouflaged the trees from the causative beetles (mainly Scolytesscolytes) which seek out the living trees by scent in order to feed on the young shoots, thereby introducing the fungus. In really hard winters, ivy covered trees did not suffer from frost crack – which spoils the timber for future marketing. (Ash trees are still being cut down with ancient frost crack present.) Continuous observation shows that ivy spreads vigorously over dead and dying trees after leaf loss lets in more light – the casual observer then believing the ivy caused the tree’s demise. On many dead trees, branches that could be dangerous, are held in place by the ivy, so gradually disintegrating rather than crashing down – which is good for the 60% of woodland wildlife that depends on rotting wood in part, or all, of its life-cycle!

Ivy provides nest sites in one way or another, to a greater variety and number of birds than any other shrub; helping to make up for some of the thousands of miles of lost hedgerows. Similarly, because of the loss of hollow elms to disease, many of the larger birds that nested in them, now frequently use the thickly ivy covered crutches of trees. It is also our last shrub to flower, providing heavy yields of nectar and pollen – a final and often only food source – for a variety of insects, including bees, beetles, hoverflies and butterflies. 

In fact, butterfly species such as Comma, Small Tortoiseshell, Large Tortoiseshell, Peacock and Camberwell Beauty – many of whose last broods go into winter as butterflies – search for ivy flowers because they need to build up body-fat before they go into their winter torpor: interestingly, you can look at ten ivy covered trees in the shade and not see a butterfly, look at the next in full sun – when it smells most honey-like – and count them by the dozen! I believe some of the visiting Red Admiral and Painted Lady butterflies – two more ivy nectar imbibers – are now managing to hibernate here because of our milder winters. After feeding up on the nectar and pollen, many of these insects then snuggle under the ivy mat on tree trunks and walls – especially lacewings and ladybirds which devastate the hated aphids the following year. Ivy is also the last of our berries to ripen, and coupled with the insect life hiding in its depths, feeds many birds just when food is most scarce – at winter’s end.

It can also be linked with the Holly – besides in the much loved Christmas carol – through the Holly Blue butterflies, Celastrina argiolus, which emerge in April/May from chrysalids attached under the ivy leaves: they mate and then the females search for a holly tree, and lay their eggs on the flower buds. Once hatched, the tiny caterpillars start by devouring the opening flowers, later eating the developing berries – those that get laid on the male flowering trees, have to move onto tender young leaves – eventually pupating in chrysalides attached under the holly leaves. This brood emerges in July/August, when after mating, the females go looking for ivy flower buds on which to lay their eggs – so giving rise to the caterpillars, which after finishing on young ivy berries, will go into pupation and start the cycle once again the following May. 

I have also seen them laying eggs on Spindle and Dogwood flowers, and others mention Snowberry, Buckthorn, Furze and Bramble. In some areas, it is known only as a single spring brood, which makes me wonder if there are two distinct families, with only the single brood one managing to survive where there is no ivy! There are times when their numbers crash. Ted Ellis was overjoyed in June 1974, when, just as he had decided that this time they could be extinct, I phoned him, to say I had just seen two flying around our holly trees.