Elena Bilheimer, EcoNews Journalist
Hedera helix, commonly known as English ivy, is an evergreen vine from the Araliaceae (ginseng) family. Native to Europe, Scandinavia, and parts of Russia, English ivy was introduced to North America by colonial settlers. It was first documented in the United States in Virginia in the 18th century. Despite this plant being invasive, it is still sold in plant nurseries as an ornamental that is advertised as fast-growing and shade-tolerant. In Humboldt, and across the United States, enormous effort and time is given to managing ivy infestations.
Why it’s invasive
Often planted in gardens to cover walls and large swaths of ground, English ivy refuses to stay contained to where it is planted. It will invade and persist in wild spaces, overwhelming native species and becoming a monoculture. Utilizing runners and vines that reroot as they move along, ivy can outcompete understory vegetation while also killing and dominating overstory trees. Due to its dense foliage, ivy blocks sunlight from reaching other plants, therefore restricting the process of photosynthesis and any new growth of native plants.
Additionally, the plant’s heavy vines can climb mature trees and cause death by loosening bark and holding moisture, creating a welcoming environment for fungal and bacterial infection. This extra weight can also make trees more susceptible to damage in winter storms and can increase the spread of wildfires. By displacing native plants and trees, ivy can negatively affect local wildlife. Joann Kerns, a member of the North Coast California Native Plant Society (CNPS), has worked extensively on local ivy removal efforts. “Ivy is a bit of a poster child for what havoc invasive species can wreak upon any given ecosystem,” said Kerns.
Physical Characteristics
English ivy leaves are dark green, glossy, palmate, and alternate along the stem. Although the shape is variable, leaves are usually three-lobed with a heart-shaped base; they often become un-lobed and spade-shaped throughout maturation. During its juvenile stage, ivy grows as a dense undercover, but becomes a vertical vine during its adult stage. As a ground cover, ivy is around 6 to 8 inches (10-20 cm) tall. When a vertical structure is available (including trees, buildings, and utility poles), ivy will climb using root-like structures that release an adhesive substance. Vertical vines can typically reach 90 feet (30 m) in height, although they can sometimes grow to the tops of 300-foot (90 m) conifers.
Habitat
According to the United States Department of Agriculture (USDA), English ivy can be found in the west in all Pacific Coast states and British Columbia, in addition to Idaho, Utah, and Arizona. In Pacific Northwest coastal areas below 3,000 feet (900 m), it is considered a threat to almost all forest types. Commonly associated with other non-native species, English ivy thrives in urban and disturbed forests near populated areas. Part of what makes this plant especially intractable is its ability to survive in full sun, partly-shaded and full shade areas.
In California, and specifically in Humboldt County, ivy can be found in redwood (Sequoia sempervirens) forests, as well as in riparian forests made up of Fremont cottonwood (Populus fremontii), white alder (Alnus rhombifolia), and willow (Salix spp.) trees. The USDA website states that sites in the Pacific Northwest dominated by English ivy have lower diversity compared to uninvaded sites, only appearing to provide a good habitat for rats. English ivy is common in climates with moderate to high annual precipitation, making Humboldt the perfect habitat.
Sexual Reproduction
Once adult ivy plants mature, they sexually reproduce by producing bisexual flowers that are cross-pollinated by a wide variety of insects. The flowers usually develop between late summer and early fall and are small, greenish-yellow, and have a globular starburst form. Once the flowers have been pollinated, black berries with fleshy outer layers and stone-like seeds develop. The seeds are then dispersed far and wide by birds who love to eat them, contributing to ivy’s expansion. The birds that spread the seeds include the European starling, cedar waxwing, American robin, Steller’s jay, mockingbird, and house sparrow.
How to Manage Ivy Infestations
In order to manage ivy infestations, there are a few options available. It is possible to deal with ground cover by pulling it out with thick gloves or with a trowel and making sure to remove all the roots. It is important to wear long-sleeved clothing as ivy may cause skin irritation. Mowing it can sometimes work as well, but it often needs to be done multiple times to have an impact. As an alternative to herbicides, white vinegar can sometimes be effective.
According to Kerns, tall trees that are being choked with ivy can be treated by cutting out a five foot band around the base of the tree, while also removing the ivy for six feet around it. This makes the ivy at the top of the tree die and eventually fall off. This allows the tree to regain the use of its foliage and bark for photosynthesis, increasing its ability to sequester carbon and mitigate climate change. Pulling ivy is “…a very concrete activity that anyone can do to help mitigate global warming,” said Kerns. “As you remove large patches of ivy from the ground or trees, you open up the area to repopulation by natives. Often there are still seed beds, or random patches of natives under the ivy, and they can thrive once the ivy is gone.”
Local Removal Efforts
Many local organizations and government entities are involved with ivy removal, including the State Park, Sequoia Park, Fortuna County Park. Once a month, The Sequoia Park Ivy League meets formally to remove ivy, however, it also hosts “pop up” ivy pulls during the month. The next formal volunteer work day is May 13. The North Coast CNPS is also working with the County on an ordinance that would prohibit the use of ivy (and other invasive non-natives) in any new building development.
In addition to benefiting local ecosystems, pulling ivy can be a tangible, measurable way to get outside and manage feelings of eco-grief. “Sometimes, after reading a Timber Harvest Plan (THP) or trying to wade through PG&E’s 1,000+ page ‘vegetation management’ protocol, I become daunted by the immensity of what we are working against,” said Kerns. “Heading out and pulling ivy with other people is one way that I keep from being swamped with eco despair. It seems like such a simple thing, but it can have far reaching consequences and make a real impact.”