English Ivy, Hedera helix.
Introduced as an ornamental to America from Europe during colonial times.
Miller (2003) describes this plant as an evergreen woody vine that can climb up trees to heights of about 90’ (28m). The plants cling to the trees by aerial roots and can also form a dense ground cover. The plant has thick dark-green leaves with whitish veins and three to five pointed lobes when jeuvenile. The ivy matures in about 10 years and produces branches with unlobed leaves and terminal flower clusters that yield purplish berries. These plants thrive in moist open forests, but are adaptable to a range of moisture and soil conditions. Their tolerance for shade allows early growth under dense stands of trees, but they become adapted to higher light levels with maturity. These plants amass on infested trees, decrease the trees vigor, increase the chance of the tree being downed by windthrow and serve as a reservoir for bacterial leaf scorch that infects oaks (Quercus spp), elms (Ulmus spp.) and maples (Acer spp.). The plant is spread by its bird-dispersed seeds and colonizes by trailing and climbing vines that root at nodes (Miller, 2003, p.37).
Dr. Dahl’s experience of this invasive and damaging plant include observation of how it can completely encapsulate a tree trunk with a woody, intermeshing mass that can reach a thickness of several inches. It can spread throughout an entire wooded area and is not restricted to the relatively highlight of the forest edge.
Moreover, the weight of the plant tends to cause its supporting tree to lean and bend over, particularly when a tree is still young (about 20-40’ tall). The vine then trails downward toward the ground where it can re-root; a cascade.
This appears to be the final death-nell for the tree. In one area of woodland in the Fernbank area, about 50% of the smaller, young trees (DBH 6-9”; height 25-45’), had died consequent to being overwhelmed by English Ivy.
Treatment.
Even the most massive infestations can be cut away from the tree by the skillful use of a machete to a height of about 9’ and without seriously damaging the bark. The bottom 9’ of the tree trunk is completely stripped of the ivy, and its root systems are pulled and cutaway to a distance of about 2’ from the tree. This reveals the natural beauty of the tree’s trunk. Judicious use of mulch and relatively minor maintenance activity can effectively and completely control the re-growth of this vine back into the tree. No herbicides need be used to control and eradicate this vine albeit some roots systems have grown so intimately and so long with the tree that completely cutting them out might damage the tree. Cut and Treat is then found to be a most useful control agent. The School views the spraying of herbicides as potentially harmful to the tree, but particularly harmful to nearby tree seedlings and saplings that have managed to grow up through the infestations and constitute the forest of the future.
CHINESE WISTERIA, Wisteria sinensis.
Introduced from Asia in the early 100s, and used to adorn the porches of southern homes, this invasive does well on both wet and dry sites.
Miller (2003) describes this plant as a deciduous, high climbing, twining, or trailing leguminous woody vine. The woody vine can grow to 10” in diameter with alternate pinnately compound leaves from 4 - `16 inches long. The flowers are produced from March to May as the leaves are emerging. The stalked flower clusters (racemes) appear lavender to violet, with each flower pea-like but with a strong fragrance. Seeds are produced from July to November in a flattened legume pod.
This species of Wisteria (and the very similar W. floribunda, Japanese Wisteria) can form dense infestations at ground level and can climb up and over shrubs and small trees so as to completely inundate them. Long-term infestations in large trees can twine around trunks and act to strangle them, and climb up to 70’ and above. Like English Ivy, they can cascade down and re-establish a root contact with the ground quite some distance from the main bole of the tree. Similarly, they can use other plants as stepping-stones to climb into the branches of tall trees and then continue to take over the entire plant. What makes this invasive such an on-going threat to trees and woodlands is its ability to colonize by runners rooting at nodes; this also poses problems for control and eradication (see below).
Treatment.
The vines of the Wisteria do not become tightly oppressed to tree trunks in the same way as English Ivy (except when twining round trunks in a strangle hold), and are comparatively soft, so that they are easy to cut through. This means that cutting these vines away from vegetation is relatively straightforward. They can get a strong hold on the upper branches of trees, however, and can not be pulled down in their entirety without the risk of breaking the native tree’s branches. The roots of Wisteria become deeply established within the soil, and cannot be pulled or cut out with anywhere near the same effectiveness as the roots of English Ivy. The “Cut and Treat” approach has been found to be highly successful is this context.
“Cut and Treat” also has to be applied along runners before and after each node if eradication is to be achieved. This requires meticulous, time-consuming patience. As Wisteria is a legume, however, it can be treated with a legume-specific herbicide that can be used as a spray. The School has not used these expensive sprays because, in principal, they can also kill native legumes such as Red Bud (Cercis canadensis), but clearly this approach is an option that should be considered when large open areas dominated by Wisteria have to be dealt with.
Infestation of Wisteria before
and after treatment by Machete Man