Although long used as a groundcover, ivy is harmful for trees. It is not indigenous, and many species are aggressively invasive and displace native species. In North America, the most common culprits are English ivy (Hedera helix) and Irish, or Atlantic, ivy (Hedera hibernica). Tree health and safety are the major concerns regarding ivy for arborists.
Ivy can reduce tree stability and lead to failure for a number of reasons. Structural or flare roots are one of the most important areas of a tree to inspect. If this area is obscured by ivy, the arborist cannot conduct a proper risk assessment of the tree, and critical information about tree stability cannot be determined. Another concern is that ivy adds considerable weight and wind resistance in a tree canopy. Because ivy is evergreen, trees that would normally be bare during winter suffer extra stress from rain and wind.
Eradicating ivy is the best scenario for trees and the native environment. However, if complete removal is not desired, there are practices that can limit the negative effect of ivy on trees and the environment. First, remove ivy from tree trunks, and pull it back at least three feet from the base of a tree. This will mitigate the weight, moisture, and wind resistance issues associated with ivy, and will leave the structural roots visible for inspection. In addition to attending to ivy on tree trunks, whenever possible, ivy should be prevented from climbing on any vertical surfaces. Ivy produces seed only when it is growing vertically, so a well-maintained groundcover is far less likely to provide seed for invasion of natural areas than ivy that is climbing walls or trees.