Ivy has been the subject of considerable debate in the press recently so I would like to publish our position and advice on it’s presence on trees.
Conrad Evans – Arboricultural Officer, Jersey Trees for Life
Many people believe that ivy is extremely detrimental to the healthy growth of trees. This is rarely the case. In fact ivy is not parasitic, but uses the tree (or wall, building or other structure) purely as a means of support to climb up in order that it can manufacture its own food through the process of photosynthesis. Its root-like structures are used purely to grip the bark, resulting in no harm to the tree.
It is right to say however, that ivy may become a problem when it is left to grow and accumulate into a top-heavy weight on dead or weakened trees, when a gale may bring both tree and ivy crashing down due to a greater surface area for the wind to catch. In a few cases, extremely vigorous ivy growth in the upper crown of a tree, may reduce its ability to photosynthesis due to excessive shading and competition for light, at which point it could become a threat to the health of the tree.
It is the policy of Jersey Trees for Life to recommend that ivy is left alone, unless it is becoming too vigorous on a particularly fine ‘specimen tree’, or is encroaching on the crown of an established tree where it may hinder its development or contribute to the risk of the tree falling in gales under the additional weight.
The Forestry Commission states that: “Ivy rarely harms vigorously growing trees. Ivy neither strangles nor smothers young trees although it may compete with them for water and nutrients, whereas Clematis and Honeysuckle, which unlike ivy, climb by twining around a tree, can do much damage.”
In the booklet “Wildlife Conservation in Woodlands”, also by the Forestry Commission, the important point is made that: “Climbing ivy provides nesting sites and cover for birds, and also cover and hibernation sites for various insects (and some small mammals). Its flowers, which appear late in the year when little else is in bloom, attract a variety of insects. The berries are taken by birds which are also partial to the numerous insects”.
In fact it is true to say that ivy is an extremely important part of the food chain and is of enormous benefit to a wide variety of our native wildlife species. The stems on trees provide nesting sites for wrens and spotted flycatchers, as well as the short-toed tree creeper (which is only found in the Channel Islands and lowland parts of the continent). The dense growth of fertile shoots from the climbing stems provides nesting places for blackbirds, robins and song thrushes. It also provides warm cover on winter nights for roosting sparrows and other woodland birds. The dense growth high in trees provides owls with day roosts, as well as nesting places for them and kestrels. Squirrels will form the basis of their drays in trees that are heavily clad in ivy. The flowers provide abundant nectar when hardly any other source is available, and is the sole food of the late summer brood of the holly blue caterpillar. The berries ripen gradually throughout the winter and are eaten by most species of the large thrush family, and by many other birds.
Removing a ring of bark around will kill the tree it so it is vital that damage to the tree’s bark is avoided if ivy should need to be removed.
Rather than severing all ivy stems on all trees in a garden, woodland or along a field boundary it is better to manage its presence by being selective and say only stop it from colonising certain specimen trees. Trees of little value or significance can be “sacrificed” as they will probably not grow into good quality trees. If over-keen ivy in woodland needs to be controlled generally, focusing on cutting the ivy on perhaps one five trees still leaves cover for the birds, insects and mammals mentioned previously.
When cutting ivy on tree trunks care must be taken not to cause damage to the bark of the tree itself. Rather than using a blunt axe or a billhook that can be rather dangerous to use anyway, a sharp pruning or bow saw is the best tool to use but remember – removing a ring of bark around will kill the tree it so it is vital that damage to the tree’s bark is avoided.
Cutting and peeling off an entire ring or band of ivy of some 4 inches or 10 cm wide is usually enough. The tendrils if ivy, especially when mature, can be hard to pull off. A crowbar, claw hammer, strong trowel or even garden spade can make a useful lever.
Managing ivy if it reaches or approaches the upper crown of a tree where it possibly could cause damage requires careful work off an extension ladder or from rope and harness. In the case of professional tree surgeons, ivy can be severed up in the tree, around or above the first major branch break. This retains the ivy on the main trunk and allows it into the lower crown but only as far as the major limbs. This is more specialist work but is a good alternative to the ivy’s complete removal which can be drastic for wildlife as well as risking harm to the tree.
As an essential component of the best local woodland habitats, ivy often provides the only evergreen shelter in winter. Many of the trees that appear to be completely smothered by it, prove to be on closer inspection, dead or dying elm trees, which have fallen victim to the ravages of Dutch Elm Disease. Ivy has a generally undeserved reputation as a rogue and in the majority of cases lives an harmonious existence with trees and the woodland habitat.