by James P. Engel, © 2013
Take a walk in any natural area throughout our region of New York State and you are almost certain to find at least one of three common vines growing. Virginia creeper (Parthenocissus quinquefolia), Poison ivy (Toxicodendron radicans) and Wild grape (Vitis species) are ubiquitous in the landscape. They are so common and relatively easy to identify that even when people learn to recognize them by leaf, fruit or vine they don’t give them a second glance. All three native plants provide important benefits for native wildlife, but at the same time they may have undesirable impacts for people and on the ecosystem they inhabit. For good or bad they are here to stay; they are widespread and if you spend any time in the outdoors you will certainly encounter them.
From our human perspective each of these vines has a good side and a dark side that invites a little more exploration of the role they play in our surroundings and how these plants impact us both positively and negatively. If a plant bestows positive benefits on us humans we bless it and say that it is good, if it has some traits that impact us negatively we say that it is bad. A plant we consider good, we will try to conserve or even encourage on our land, one we define as bad, will be condemn and banished from our property. For each of these vines, whether you classify it as good or bad will depend on you view the world, your personal interests in nature and what your management objectives are for your property. How do you reconcile a plant that has both good and bad qualities? That is the dilemma!
For all three of these species their benefits and their detractions are somewhat similar and for convenience can be lumped together. All three plants produce prodigious quantities of nutritious, high quality, bird sized fruits that many songbirds favor. The abundance of ripe fruit timed to coincide during peak bird migration makes these species invaluable to birds especially where most other native shrubs and trees are absent. Fruit that is not consumed during fall will remain and provide food during winter. All three plants provide important bird cover that makes for choice foraging, resting and nesting cover. Most birds that prefer thick cover, such as gray catbirds, northern cardinals and common yellowthroats will be found in dense tangles created by these vines. All three species grow, reproduce and spread very easily and are found growing in a range of habitats from the interior of forests to hedgerows, forest margins and old fields. For all of these reasons these three vine species are considered important wildlife plants and should be conserved if your objective is to promote birds and other wildlife.
The rapid growth habit and prolific fruit production that makes them such good wildlife plants also bestows upon them the characteristics of serious nuisance plants. On the forest edge, in young woodlands, hedgerows and shrubby fields where these vines can take full advantage of the available sunlight they will dominate and climb over all other plants, often to the detriment of those other equally valuable native species. The nature of vines is that they climb, they use other plants for support and they can climb faster than other plants can grow taller. That rapid growth enables the vines to reach the outer most canopy of foliage using the host plant for support. Once the vines have reached the outer canopy they will effectively cover the outer surface and outcompete the other plants for this crucial plant resource. As the vines intercept more and more of the sunlight and keep it from reaching the other plants underneath, those plants will declined in vigor, produce fewer seeds, struggle to stay alive and eventually die from being out competed. The intense competition for resources can over time create a monoculture of vines which when taken to extremes reduces plant diversity and therefore reduces the over all biological diversity of the area.
If forest stewardship and silviculture is your goal, the impact on forest health and timber production can be just as severe. In a mature forest with a closed canopy and dense shade these three vines have a low capacity to cause serious harm, but these conditions are seldom the norm in most forests. In dense shade the vines may be present but they will struggle to grow in the shade and their route to reach the forest canopy is slow and uncertain. In a young stand of trees, or a forest that has been recently cut or suffered a natural disaster such as wind throw or insect mortality the situation can be quite different. The difference between the two depends on the amount of available sunlight and the age of the vines in relation to the age of the trees. Large vines that are suddenly exposed to extra sunlight from an opening up of the canopy can quickly take advantage of this opening and fill the gap, effectively eliminating forest regeneration and potentially damaging the adjacent trees. Vines often take advantage of logging roads, trails, power lines or any opening that is created in a closed canopy forest, which allows the vines to harvest more of the sunlight and compete for resources with the established trees.
Where I see the greatest damage to forest trees from vines, is in forests where both the trees and vines became established when the forest was young. This commonly occurs after an agricultural field was abandoned and has undergone plant succession. If you went back in time to the early days of this young forest you would see an early successional forest with sapling size to pole size trees. There is plenty of available sunlight for both the trees and vines to grow fast and tall. As the trees grow taller the vines are able to keep pace. Not all of the trees will have an accompanying vine but many will. The number of vines will determine to a great extent the health and vigor of the future forest. The race for the sky is on. If the vine is able to win the race there may be a hole in the forest canopy where the vine out competed the young tree for sunlight, the tree subsequently died, the trunk decayed and eventually both fell to the ground. If the tree won, the battle for light would continue for many decades. An uneasy truce may have been struck with neither the trees nor vines having the upper hand. In these forests the vines can reach a massive size and be as old as the trees. Occasionally the vine will die from some unknown cause leaving the tree to reach old age intact, but more likely the vine will outlive the tree. The added weight from a heavy snow, an ice storm, or high winds on the added mass of the vine will throw a tree or snap the trunk or large branch. The vine suffers damage along with the tree but the vine can more easily recover and survive such a disaster.
There are a few differences between the species, in growth habit and their affects other plants, that bear mentioning. Each vine is unique in how it climbs and attaches itself to a tree. Wild grape climbs using slender tendrils that grow from young canes and twine around anything they touch. Grape vine require small branches that the tendrils can wrap around for support to enable the vine to climb. Poison ivy has numerous hair like roots along the length of the vine that attach to any hard surface, and Virginia creeper uses suction cups on the end of branched tendrils that adhere to the bark. Both Virginia creeper and poison ivy are able to grow straight up a tree trunk while wild grape tends to wrap around the trunk or drape over branches as it grows in its quest for the canopy. I have observed one impact on trees that is unique to poison ivy. Poison ivy seems to be able to kill or injure its host tree from its direct attachment to the tree bark. This appears to be unrelated to the direct competition with the host tree for sunlight. I have seen too many dead and dying trees to dismiss this phenomenon but I have never found an explanation for the cause. On living trees the bark will be dead only where the vine is directly attached to the trunk. The same phenomenon does not occur with the other two vines.
Poison ivy and Virginia creeper often carpet large areas of the ground and function like a ground cover as they spread horizontally from underground roots and from canes growing over the soil surface. Whenever a vine encounters a sold object such as a stem or trunk it can then use that object to grow vertically towards sunlight. All three species will grow just as readily in full sunlight in old fields as in the forest. The vines creep through the grasses and forbs until reaching a solid object like a shrub to climb on. This gives the vines a distinct head start as the old field moves through the stages of succession towards shrubland or woodland. The head start the vines have, may even prevent the shrubs and trees from getting established, creating a permanent jungle of vines.
After weighing all of the benefits and negatives of these vines, my personal recommendation for managing all three species is to cut and treat all of the vines I encounter. I recommend this strategy because I know there will always be plenty of vines around to provide for wildlife. Their rapid growth, explosive reproductive potential and available habitat ensures their future abundance. I cut the vines with the primary objective of encouraging other native plants like shrubs and trees that will be negatively impacted if the vines are left to grow unchecked.
I cut every vine that is climbing up a tree and those that have reached the upper canopy especially large ones. I may leave a few vines that are on the ground or in the shade as they pose little threat. I try to eliminate poison ivy wherever and whenever I can. My added incentive is that the dermal reaction that poison ivy causes in people will restrict human use and enjoyment of the out doors. In open fields, I try to eliminate all three species as they will impede the future succession of the old field and make walking through the field, or use for other purposes, all but impossible.
Simply cutting the vines will not kill the plant. Treating the cut with a systemic herbicide, typically glyphosate, is necessary to kill the root system and prevent new shoots from growing. When cutting the vine, cut as close to the root collar as is reasonable. Everything above the cut will die naturally; treating the cut surface with herbicide will prevent sprouting below the cut and hopefully kill the entire root system below the cut.The negative affect of all three vines on the natural world is really an indirect result of human activity. Humans have created an overabundance of edge and old-field habitat where these plants are able to proliferate. This wasn’t the case prior to widespread clearing of the forests for agriculture. Through our land use practices we have tipped the balance in favor of these native vines. On a property-by-property basis you have to decide how to reconcile both the positives and the negatives of these three vines. That! is the challenge.
this page updated Feb 25, 2013