Contributor: Bud Reaves
Invasive vines are colorful and decorative plants that are often used for ornamental purposes for their showy flowers and colorful, sometimes uniquely shaped fruit. They have a downside however, as many invade forested habitats where they can severely limit the growth of, or even kill, trees and shrubs. Fall is a great time to control invasive vines. For this reason, invasive vines are the October Invader of the Month.
Vines are fascinating plants that have evolved a unique strategy that allows them to compete with larger woody plants. Vines use other plants for support to reach sunlight and further their growth, foregoing the need for large root systems and sturdy stems to keep them upright. This ability to climb allows them to grow rapidly and maintain a narrow and flexible stem. The stem of a typical vine has larger vessel elements or water conducting tissue that allows it to bring water to the upper reaches of the plants. It most importantly allows the plant to support more leaves than a tree with a similar sized stem. Vines have been observed to comprise 40% of the total leaf surface area of a forest while accounting for only 5% of the above ground biomass.
Vines are for the most part light loving plants. They grow in the open or on the edges of forests where light is more abundant and where they can find trees for support. They usually start by themselves and will grow toward any objects that can climb. Vine climb by several methods. Some use tendrils or rootlets to latch onto the tree or shrub to hold it as it grows. Others use phototropism to climb by winding around the stem it is climbing. This is called circumnutation. Once they reach the top they will often send out growth looking for adjacent tree to expand to.
There are native vines in the eastern forest. Wild grape(s), poison ivy, and Virginia creeper are the most common ones encountered. All are valuable as providers of grapes or berries for wildlife such as birds and many mammals including foxes, raccoons, and opossums. These vines do climb trees and shrubs to reach light, like invasive vine species but differ in one key characteristic. These vines do not use circumnutation as they climb the tree; instead they use tendrils or modified roots to attach to the tree. Non-native vines like Asiatic bittersweet, Japanese honeysuckle and Japanese and Chinese wisteria do twine around the tree and eventually strangle the stem and kill the tree. This is a serious problem with young and regenerating forests as the seedlings and sapling are killed before they can become established as the replacement for the next stand of trees.
Another way vines can be damaging is by smothering a tree. Once reaching the top of the tree, vines continue to grow covering the crown of the tree and blocking light from reaching the leaves. They often grow across gaps in the canopy and latch onto the adjacent tree. The vine also adds considerable weight to the crown and will often cause trees to collapse under the extra weight. No vine is more capable of this than the legendary Kudzu vine, often called the vine that ate the south. Kudzu will continue to grow until it covers any stationary object including buildings and abandoned vehicles. Kudzu transforms the habitat of an area by creating a blanket of leaves and vines that doesn’t allow other plants to grow. Kudzu, once planted to control erosion has been found to not have a controlling effect on erosion as the stems and leaves are perched above the ground and aren’t in contact with the soil.
Invasive vines also have negative effects on wildlife habitat. Asiatic bittersweet berries are only half as nutritious as those from the native American bittersweet. This has implications for migratory birds that also depend on this food when migrating south in the winter. There is also concern that rising CO² levels associated with climate change will stimulate greater growth of these invasive plants.
Getting control of vines can be difficult. Some vines like Kudzu usually require herbicides to kill. Most produce abundant amounts of seed and develop a seed bank from which seedling will sprout for many years. Mechanical control can work if persistent effort is made to repeatedly cut them until the roots are exhausted of food reserves. The most common method is to cut a “window” in the vine, severing it at the base of the tree, and then again several feet up, to prevent re-attachment. English ivy, one of the most notorious invasive vines in the mid-Atlantic, area can be dealt with mechanically by cutting the vines at the base of the tree and allowing the growth on the tree to wither and die. Pulling English ivy from the trunk can damage the tree or cause dead branches to fall so it’s best to leave it on the tree. The vines on the ground can often be easily pulled up. Again, persistence is required. It’s also important to not let the cut stems lie in contact with the ground. They can root themselves and become reestablished. Instead bag them, and either take them to the landfill, or store them for several months until you are certain they are dead before composting. Beware of the seeds too. They can persist for years.
An important thing to remember is to not plant invasive vines. Many are available for sale in local nurseries. Instead look for native alternatives. Be aware of things like Christmas wreaths made of bittersweet vines. They often have berries on them that can germinate if disposed of carelessly. The good news in the fight against invasive vines is that persistence will lead to success. The challenge is there and real, but it is not hopeless with dedication and application of sustained effort.