|Old Douglas-fir with English Ivy infestation|
"After habitat loss, biological invasion constitutes the greatest threat to biodiversity." - Jeffrey A. McNeely, Scientist
The first independent European to settle among the giant trees on Vancouver Island was probably also the first person to introduce an invasive species to the area. It was 1849 when Captain Walter Grant occupied land and planted the first Scotch Broom (Cytisus scoparius) to remind him of home. Less certain is the first individual to bring another nasty invader, English Ivy (Hedera helix).
The problem with invasive plants is that they show an inclination to spread and overtake native species. English Ivy is a shade-tolerant plant which alters the structure of a forest by strangling trees, and creating clearings in the forest when they fall. This disturbance can in turn create favorable conditions for other invasive plants such as Broom.
A study conducted in 2003 for the Department of National Defense found that English Ivy posed "the biggest threat to the defining ecology of the Royal Roads property." But it also found that the infestations generally were less than in other area forests of similar size, such as University of Victoria’s Mystic Vale, or Sannich’s Mt. Douglas Park.
English ivy reduces the amount of light that falls on the trees and the forest floor. It also affects soil properties, and interrupts normal forest succession processes. The vines, which can get as thick as your wrist, do not penetrate the bark of the tree. However, they do extend small hold-fasts which absorb water from the bark.
Often when I go for hikes I carry gloves and a small saw specifically to liberate trees from English Ivy. Stems should be cut close to the ground and again at breast height. The vines higher up the tree can be left to die, and may be removed after they become brittle.
Ivy is difficult to pull out of the ground, but if you do so, try not to disturb the soil. Make sure you get as much root out as possible or it may resprout from what is left.
Stem cuttings and roots left behind from pruning may resprout if contact with the soil is made. Take cuttings and roots away for disposal, or leave them in a dry, sunny location.
Contact with English Ivy may cause an allergic reaction. Wear gloves and full coverage clothing when doing the trees a favour and liberating them from invading, forest-altering English Ivy.