Explore The Ivy Files and expand your knowledge of Hedera hibernica and Hedera helix

From Portland, OR, Rec and Parks--see https://www.portlandoregon.gov/parks/article/201781 for links.

• Learn the basics of ivy, and its interaction with our natural areas.

• Ivy Removal Methods

  Review the techniques of ivy removal. Familiarize yourself with the field-tested techniques developed by the No Ivy League.

• No Ivy League Project Statistics

   See the mind-boggling totals of ivy removed by the No Ivy League and dedicated volunteers.

• No Ivy League Chapters and Other Ivy Removal Groups

  Get in contact with a removal group near you or suggest others to be added to the list.

• Knowledge is Power!

  Still hungry for more ivy info? Here you'll find important literature regarding ivy removal, other invasive species, and the No Ivy League.

• Ivy Removal Instructional Video

  A handy visual guide to our field-tested techniques, perfect for preparing to remove ivy on your own.

• Community ResourcesLearn how you can make a difference, view resources available to citizens who want to remove invasive species from their property or community.

An Ivy Overview and Why We Remove Ivy from Natural Areas

Forest Park is one of America's largest urban forests. Set aside as a natural area within Portland's city limits, its 5,000+ acres are host to over 70 miles of hiking trails and bicycle paths. This natural area provides an unsurpassed opportunities to connect with the forest environment. However, our treasured resource faces a challenge experienced by many natural areas around the globe. Not only are humans changing the physical, chemical, and climactic structure of these ecosystems but we are responsible for the introduction of organisms previously not present. In the Pacific Northwest (PNW) one such organisms is the plant English ivy (Hedera spp.) 
Members of the Hedera genus have long been admired by humans in their historic range throughout Eurasia, Northern Africa, and Macaronesia. The hardiness of these evergreen plants, their tightly weaved vines and intimate relationship with trees led them to become a symbol of vitality and fidelity in Western culture. It is because of this rich cultural significance that we humans have taken ivy, and many other organisms,  with us to new lands. The prevalence of Hedera spp. in the PNW is thought to be primarily due to escape from horticultural uses.
Evidence suggests that modern ivy's relatives have been present throughout regions of Western Eurasia and Northern Africa for more than 1 million years [1]. In this time ivy evolved to fill the unique ecological niche of a liana, a climbing plant dependent on a host for support. Important to these ecosystems, ivy plays an role in nutrient cycling, soil erosion reduction, and animal forage [^2]. Ivy is highly plastic plant that can grow in a variety of light conditions, soil types and water levels - allowing it to rapidly recolonize disturbed areas as well as succeed in dense forests. The characteristics that make ivy a successful part of its native ecosystems have also made it a successful transplant in the PNW, though its success may be at the cost of our own native species.
English ivy has been observed to dominate the understory of PNW forests, especially in disturbed areas and edge habitat. In these areas the juvenile phase of ivy forms a thick mat of vines and climbs any available surface. This thick mat of vines may prevent significant amounts of light from reaching the forest floor and thus alter the species composition in these areas[3]. As the liana climbs it can reach below the crown of its host tree. A physiological change occurs when the juvenile form receives enough light and resources, transitioning to a mature form that spirals outward from the trunk of its host tree. Through this process ivy may further alter the composition of light reaching the forest below and in extreme cases from the host tree itself. The mature form of ivy is able to produce berries and distribute seeds, with the help of birds, expanding across a greater range than by vegetative growth alone.
Recent studies of ivy populations in the PNW have determined that the most prevalent species is Hedera hibernica (83% of 119 populations sampled) and not Hedera helix as was previously thought [4]. These species are closely related but differ in their ploidy, the number of duplicate sets of chromosomes, H. helix containing 2 sets (diploid) and H. hibernica containing 4 sets (tetraploid) [5] This distinction could be important for understanding why H. hibernica has been more successful in the PNW, but has not yet been explored in depth. H. helix includes over 400 cultivars with only a few identified as species of concern in the PNW including H. helix "Star", "Pittsburgh", and "California."
The efforts of the No Ivy League focus primarily on removing mature English ivy from trees in Portland's natural areas to reduce seed distribution and prevent possible damage to mature trees. In a number of areas the No Ivy League also removes substantial amounts of ground ivy in conjunction with non-native shrub removal and native plantings. This work aims to restore the plant community present before the introduction of species such as Hedera L. The No Ivy League uses hand removal exclusively throughout Forest Park and other natural areas. Though chemical and mechanical removal can be effective in the appropriate situation the No Ivy League uses hand removal techniques to provide the experience of stewardship to a wider audience than other methods would allow.

Footnotes and Further Readings
- 1:  Grivet D, Petit RJ (2002) Phylogeography of the common ivy (Hedera sp.) in Europe: genetic differentiation through space and time. Molecular Ecology (2002) 11, 1351 – 1362
- 2: Schnitzler A (1995) Community ecology of arboreal lianas in gallery forests of the Rhine valley, France. Acta Oecologica, 16, 219 – 236.
-3: This idea has not been the focus of specific research yet but could be reasonable. Seeds sense the ratio of red and far-red light to determine if they are shaded or not and thus whether they will face competition if they germinate. Notoriously shade tolerant, ivy could be altering the red/far red light ratio found beneath the mat and influencing the germination of the local seed bank. If you are interested in exploring this idea please contact us.
-4: Metcalfe, D.J. (2005) Hedera helix L. Journal of Ecology 93, 632–648.
-5: Clarke, M.M. Reichard, S.H. & Hamilton, C.W. (2006) Prevalence of different horticultural taxa of ivy (Hedera spp. Araliaceae) in invading populations. Biological Invasions 8, 149-157.