A: The answer from the American Ivy Society is NO.
When people look at deciduous trees in winter and see evergreen ivy growing up the tree trunks, they incorrectly assume that the ivy (Hedera) is taking over the tree, or damaging or even killing the tree. Ivy is not a parasite but simply attaches to the trunk by means of adventitious roots that cling to the surface of the tree’s bark. The roots do not penetrate the bark which is a non-living, outer protective layer of a tree. Nor does ivy grow into the leafy outermost layer of a tree (the canopy) and smother a tree or prevent photosynthesis. Ivy grows on the trunk of a tree and, when the tree declines because of disease or old age, the ivy may develop at the uppermost tips of the vines into a bushy, mop head that is confined to the interior of a tree.
Vines, particularly ivy that is confined to the interior of a tree, do not damage healthy trees. However, trees that are weak-wooded or in decline and have any kind of vines on them may be damaged in wind and ice storms as has been documented for grapevine (Siccama et al, 1976). When dead tree limbs fall to the ground and decompose into nutrients, these nutrients are taken up by other surrounding plants. This phenomenon is part of the recycling of nutrients that takes place in a forest ecosystem. Even nutrients taken up by ivy are returned to the soil as the ivy leaves are shed and decompose thus adding nitrogen to the soil to be used by the neighboring trees. Although ivy is an evergreen, it does shed its leaves but not all at once. Only ivy leaves that are 2-4 years are shed annually but, since the new leaves remain, ivy is evergreen..In Europe, where ivy is native, ivy researchers have been observing ivies on trees for years. Respected ivy expert Br. Ingobert Heieck in Heidelberg, Germany pointed out (1990) that ivies, which are confined to the trunks of trees, flourish when the trees decline (often from disease, or old age) and the ivy takes advantage of the thinned or now-opened canopy to become adult. That ivy does not damage healthy trees has also recently been pointed out by British ivy authorities Peter Rose (1996), Stephen Taffler (1990) and author Fearnley-Whittingstall (1992).
Fearnley-Whittingstall, Jane. 1992. “False Accusations.” pp. 7-10.
Ivies. Random House. New York. 160 pp.
Heieck, Ingobert. 1990. Was man vom Efeu noch wissen sollte. pp. 31-33. IN: Der Efeu auf unseren Friedhöfen. Gärtnerei Abtei Neuburg. Heidelberg, Germany. 34 pp.
Rose, Peter Q. 1996. [Ivy in…Architecture}. p. 21. IN: The Gardener’s Guide to Growing Ivies. Timber Press. Portland, Oregon. 160 pp.
Siccama, T.G; Weir, G.; and K. Wallace. 1976. Ice damage in a mixed hardwood forest in Connecticut in relation to Vitis infestations. Bulletin of the Torrey
Botanical Club 103: 180-183.
Taffler, Stephen. 1990. In Defence of Ivy. p. 97. IN: Climbing Plants and Wall Shrubs. Crowood Press. Swindon, Wiltshire, England.
Sabina M. Sulgrove, PhD
Taxonomist, American Ivy Society