From Portland, OR, Rec and Parks--see https://www.portlandoregon.gov/parks/article/201781 for links.
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Learn the basics of ivy, and its interaction with our natural areas.
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Review the techniques of ivy removal. Familiarize yourself with the field-tested techniques developed by the No Ivy League.
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See the mind-boggling totals of ivy removed by the No Ivy League and dedicated volunteers.
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Get in contact with a removal group near you or suggest others to be added to the list.
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Still hungry for more ivy info? Here you'll find important
literature regarding ivy removal, other invasive species, and the No Ivy
League.
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A handy visual guide to our field-tested techniques, perfect for preparing to remove ivy on your own.
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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.