De Vines or yet one more threat to your woodlot

Posted: May 16, 2014

Releasing your healthy, mature trees from vines, especially those non-native species, is one, low cost endeavor that will increase the health of your forest and ensure that your forest has a chance of regenerating naturally in the future.

De Vines – In this case we aren’t speaking of the hereafter, but many of the vines reaching the overstory of our woodlots certainly are trying to get to heaven. Here in the fragmented and often unmanaged forests of southeastern Pennsylvania, one should not overlook the impact competitive vegetation has on your woodlot. One need not travel far, but only travel the highway corridors in many of our metropolitan areas or look beyond a farmer’s field to the hedgerow to see the creeping and destructive effects of unmanaged vines. As our southeastern forests mature, the cumulative effects of competitive vegetation and other threats are taking a toll and leaving us questioning the health and regenerative capacity of the future forest.

Whether it is our native grape, the non-native bittersweet, or honeysuckle (let’s not even discuss kudzu), vines can be trouble to individual trees. When unmanaged, they can overtop and literally replace the canopy of a mature tree, killing it in time. If this doesn’t happen, the additional weight and leaf area can be a receiving area for wet and heavy snow or high winds, which leads to many more broken branches or even the loss of the entire crown of a mature tree. One needs look no further than the Halloween snow of October 2011 and Hurricane Sandy for evidence of this. Many mature trees were lost or damaged due to the additional weight or surface area of the vines found in their canopies.

The often overlooked, and arguably most insidious threat to our forests health, are cumulative stresses. Forests and individual trees can cope with a drought, insects, predation, and physical damage (storm or other) when they occur separately, but as more stresses are added to the forest system the greater the impact to the health of individual trees and certainly the forest’s ecology. In southeastern Pennsylvanian forests this is very pronounced as the loss of a canopy tree is not necessarily going to result in its replacement by another tree. In the most extreme, and unfortunately more and more frequent situation, the forest that was is now replaced, not with forest, but rather a sea of non-native (and non-preferred) shrub and plant species.

To understand what this looks like, one must first understand the forces at work. In many places in the Southeast the white-tailed deer population is well in excess of the landscape’s carrying capacity; deer consume nearly every seedling and stump sprout they can reach, along with what remains of our native shrub and herbaceous layer. There are places where they have even taken to consuming non-preferred species such as spicebush and multiflora rose, leaving behind the least preferred or inedible species that are often generally aggressive nonnative plants.

It’s a very natural occurrence when a large mature tree drops out of the canopy. This creates a hole where sunlight then can reach deeper into the understory, sometimes making its way to the forest floor. In a healthy forest, there should be several seedlings ready to take advantage of that light and start to grow in the space once occupied by the mature tree. In many of our degraded forests this is not the case. No seedlings are waiting for the sun’s rays, and any stump sprouts or root suckers that happen to start are quickly browsed. The shrub layer rapidly thickens with new growth fortified by the increased light; this quickly shades out the forest floor again and reduces the chance of any tree seedling that isn’t browsed to grow to maturity.

The deer and certain aggressive plants can literally short circuit forest regenerative processes. At the very least, these threats will dynamically change species composition and limit the diversity that may currently exist. Compounding this problem now are the vines that can and do threaten the overstory/canopy trees. If these are mature trees and just 60 or 70 years old, they were established in a time when deer numbers were not nearly as high and the presence of non-native plants nothing like it is today. These mature trees represent the last hope for regenerating a native forest naturally; as they are lost, from vines or other stresses, that seed source disappears. Releasing your healthy, mature trees from vines, especially those non-native species, is one, low cost endeavor that will increase the health of your forest and ensure that your forest has a chance of regenerating naturally in the future.

There are several methods for controlling vines, from simple mechanical removal to employing herbicides. When mechanical removal alone is employed, the optimum time to cut is in late summer. Cutting at this time causes the vine to re-sprout and expend energy it has stored for the winter. Not being able to recapture the energy in an abbreviated growing season, the weakened vine sometimes needs to be cut again the following spring after leaf-out. Cutting along with the application of an herbicide to the cut stump can be done at any time the vine is actively growing. The same applies for a basal bark application to those vines with thinner bark, such as bittersweet. Obviously special precaution should be taken when treating with basal bark application; herbicide should not be mistakenly applied to the host tree. For more information on the control of other competitive vegetation, including vines, visit the following websites:

Contact Information

Carl Martin
  • PA Forest Steward and Director of Property Stewardship, Wildlands Conservancy