20 Dec What Tree? Ivy
Ivy (Hedera Spp)
This month, as Christmas approaches, we thought we would focus on one of the more festive species. Inspired by the Christmas carol ‘The Holly and the Ivy’ and already reviewed Common Holly, we decided this was a good opportunity to dispel a myth that plagues arboriculturists – that ivy is damaging to trees.
Ivy (Hedera spp.) tends to have a bad reputation. Commonly viewed as an aggressive and pathogenic threat, this evergreen climber is frequently blamed for strangling trees, stopping trees growing or causing trees to fail due to the additional weight. However, the reality is more nuanced and surprising – ivy, in many cases, is far more of a friend than a foe, and is a very important habitat.
The Myth
The belief that ivy damages or even kills trees is widespread, but it’s largely a misconception. In his book Flora Britannica, Richard Mabey explains that ivy “divides geographic regions and professions. In the gale-dashed West Country and the territories of commercial foresters it is regarded as a curse and a killer of trees. In less turbulent eastern regions and amongst more easy-going gardeners and naturalists it is looked on benignly, as an ornament to buildings and woods and a boon to birds and bees”. While ivy does climb and cover tree trunks and branches, it is not inherently parasitic. Unlike mistletoe, ivy doesn’t extract nutrients or water from its host tree. Instead, it uses the tree merely as a support structure to reach sunlight. Ivy has its own root system, drawing sustenance from the soil, not the tree.
The notion of ivy as a tree killer likely stems either from cases where ivy growth coincides with a tree’s decline or where the size of the ivy canopy is such that its structurally supporting tree can no longer bear the weight. In such instances, it’s important to recognize that the tree’s health was probably compromised by other factors, such as age, disease, or root damage, long before ivy became prominent. Ivy may exploit a weakened tree by expanding more aggressively, but it is rarely the underlying cause of the tree’s demise.
The Benefits
Far from being a villain, ivy provides a host of ecological and practical benefits. Its presence can actually enhance biodiversity and even protect trees under certain circumstances.
- Habitat for Wildlife
Ivy offers shelter and food for a wide variety of species. Birds, such as blackbirds and robins, nest among its dense foliage, while its berries provide an essential winter food source for thrushes and other wildlife. Insects, including bees and hoverflies, benefit from the late-season nectar of ivy flowers, making it an important resource during autumn when other flowers have faded.
- Climate Resilience
By covering tree trunks, ivy can provide a layer of protection against extreme temperature fluctuations. This insulation effect may help trees cope with frost in winter and scorching heat in summer, reducing stress on the bark.
- Erosion Control
Ivy’s dense ground cover stabilizes soil around tree roots, reducing the risk of erosion. This is especially valuable on slopes and in areas prone to heavy rainfall.
- Enhancing Urban Greenspaces
In urban settings, ivy-clad trees and walls can improve air quality by trapping particulate matter and absorbing carbon dioxide. Its greenery also softens hard landscapes, enhancing aesthetic appeal and providing a calming natural element for city dwellers.
Managing Ivy Responsibly
While ivy is not inherently harmful to trees, there are situations where its growth may need to be managed. Excessive ivy on a tree in poor health, for example, can add weight and increase wind resistance, potentially leading to structural failure. Similarly, when ivy climbs into the canopy, it can shade out a tree’s foliage, reducing photosynthesis in extreme cases. In addition, ivy can obscure tree defects (such as fungal fruiting bodies, cracks and cavities), however an affected tree will often display over symptoms that may indicates these defects.
Dense ivy cover obscuring stem of tree that has dead upper canopy
Large fungal fruiting bodies at base of tree with dense ivy cover
To balance ivy’s benefits with potential risks, follow these guidelines:
- Assess tree health: Focus management efforts on trees that show signs of decline or structural instability.
- Trim selectively: If ivy encroaches on a tree’s crown, carefully remove sections to allow light to reach the foliage.
- Preserve wildlife: Avoid clearing ivy during nesting season (typically March to August) to protect birds and other species.
Ivy’s role in the ecosystem is multifaceted and, when understood properly, overwhelmingly positive. While it’s natural to worry about the health of cherished trees, it is important to distinguish between correlation and causation. Ivy’s benefits – from providing critical habitats to stabilizing the environment – make it a valuable part of our natural and urban landscapes.
So next time you see ivy climbing a tree, think twice before reaching for the shears. It might just be a silent ally, working in harmony with the tree and the wider ecosystem to create a thriving, biodiverse habitat.
Source and Reference Materials
Information detailed in this post has been obtained from the author’s own knowledge and photographic library where possible. Additional source of information and photographs include:
Mabey, R. (1998) Flora Britannica – The concise edition. Chatto & Windus, London.