Hedera helix
(English Ivy)
Where it originates:
Hedera helix is a native of Europe, northern Africa and western Asia. It was first introduced to North America as an ornamental in 1727, and since has become a fixture in decorative landscaping; notably responsible for the "ivy league" moniker.
Identification:
Hedera helix is an evergreen, alternate-leaved climbing vine. On shady ground leaves are typically 3-lobed, but will lack these lobes once mature (un-lobed leaves are also characteristic just before flowering). Leaves can remain immature indefinitely while waiting to achieve proper light conditions; which are often realized once a vine climbs a tree, building or other structure. Flowers occur in small greenish-white terminal clusters that form black fleshy fruits in late summer. Fruits contain 1-3 stone-like seeds that may persist through the winter.
There are several cultivars and species within the Araliaceae family which may look slightly different (i.e. smaller or variegated leaves) but which pose the same threats as an noxious weed. Irish Ivy shares English Ivy's invasive characteristics, but is difficult to distinguish and is often classified similarly. Hedera helix vines can occur next to grape or poison ivy vines and it's important to differentiate it from these natives; look for the waxy evergreen leaves as an easy i.d. charactersitc.
Habitat:
Typically found in disturbed areas, and may be a sign of human inhabitation. Hedera helix grows wherever it can find a temperate to subtropical environment with sufficient moisture, typical of the East Coast and the Pacific Northwest. It prefers shady and moist forests, but is also drought tolerant and persistent once established.
Hedera helix occurs wild in 26 states, as well as in southern British Columbia, and southwestern Ontario.
Ecological Impacts:
Hedera helix impacts all levels of forested areas, from the ground up. As a groundcover, Hedera helix acts like a blanket blocking light and preventing germination of native plants. Climbing vines will loosen bark, block out light, and gradually kill branches as they move up the tree creating what's characterized as a "broccoli head." H. helix Rootlets will also increase moisture content on or below the tree's bark, which encourages fungus, bacteria, and decay. The plant pathogen known as Bacterial Leaf Scorch (Xylella fastidiosa) is frequently connected to Hedera helix and can harm elms, oaks, maples, and many native plants. As the tree slowly dies, the vines will continue to grow upwards putting an additional strain on the tree from the sheer weight of the invasive. Infested trees are much more vulnerable to wind-fall especially during heavy rains or snows, and can present a serious threat near roads or houses.
Although H. helix may serve as habitat for some wildlife (rats, mice), it greatly alters the natural landscape and disrupts the ecology of native plants, insects, and animals. Its leaves and berries contain a mild toxin making them generally inedible, and of little importance to wildlife. Rootlets of climbing vines will also dig into masonry, wooden siding, or joints in structures encouraging rot and destroying property.
Control:
Vines may be pulled or dug up, but will likely re-sprout without further attention. Covering with thick newspaper or other matting, and then mulching is usually effective in preventing re-growth. In a forest environment being tenacious is key in pulling and continuing to follow up on regrowth.
Herbicide may be necessary in some cases; however the waxy coating on H. helix leaves may inhibit success. Threats to other native plants must be considered and weighed before deciding to use herbicides.
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References:
Swearingen, Jil, and Sandra Diedrich. "PCA." Fact Sheet: English Ivy. 6 April 2006. Plant Conservation Alliance's Alien Plant Working Group.
Kaufman, Sylvan. Invasive Plants. 1st. Mechanicsburg, PA: Stackpole Books, 2007. 185-187. Print.
Photos and article by Jamie Brunkow