Tulip trees are known for their straight, tall trunks, but this young tulip tree has been encased in vines its entire life and they have pruned it, bent it, and shaded it. It looks like it doesn’t have long to live.
I may not try a grapevine swing anymore but I am conscious of vines when I walk in a Sourland forest, yet somehow I have failed to mention them when I write about the structure of the forest. I have pointed out that the forest is structured vertically—canopy at the top, then understory, shrub, and herbaceous layers. I usually give examples of plants that characteristically grow in each layer, but I never mention that a vine can occupy all of these layers. So now, to make amends for my previous negligence, I want to devote a separate essay to vines
Vines are wonderfully varied; some are short and insubstantial, while others are long and prominent; they can be herbaceous or woody. Most of them have at least one distinguishing characteristic. All parts of poison ivy—the leaves, stems, berries, and even the roots—carry a resin that, if touched by most humans, causes an outrageously itchy rash. Hog peanut vines are only about five feet long and their flower is easily missed but it has clusters of truly lovely leaves. Japanese honeysuckle has fragrant, orchid-like flowers, and it twines around its host and sometimes chokes it to death. Greenbrier has sharp thorns that are painful when they stab, and its new leaves are delicious—they are minty and thirst-quenching.
The subject of vines is too large to be confined to one essay, and I don’t know now if I will attempt more essays on vines, but for this essay, I want to focus on three of the woody vines that are prominent parts of a Sourlands forest landscape—wild grape, Virginia creeper, and poison ivy.
The several species of wild grape are all aggressive climbers; they grow to seventy feet in length, several inches in diameter, and their main stem can be covered with shaggy bark. They climb by producing tendrils that wrap around twigs and small branches. Virginia creepers (I am talking about a vine here—not sneaky residents of the Old Dominion) climb by having suction pads on the tips of its tendrils. Both wild grape and Virginia creeper loose their tendrils as they mature, causing the vines to hang loosely next to their host trees, often displaying fanciful loops or twists that resemble the patterns of circus acrobats. There is nothing fanciful-looking about poison ivy; it seems much more serious. It climbs by extending a dense network of modified, thin roots along its length, and the roots that are near the host tree hold the poison ivy vine to its host tree. All of its roots remain in place for most of the life of the vine, causing it to look like a hairy snake making its way up a tree. If any of these woody vines are growing in a place that does not have a host to climb they will crawl along the ground, or they will mound on themselves, or even grow like a small shrub.
Vines easily adapt to whatever kind of soil they encounter—well-drained or damp, clay or humus. They cannot, however, tolerate deep shade, so they are found on the edges or in the canopy gaps of forests or in hedgerows–seldom in forest interiors.
Vines make both positive and negative contributions to the ecology. On the negative side, their roots compete with other plant roots for water and nourishment, and their foliage competes with their host’s foliage for sunlight. Any vine that reaches the canopy of a tree makes the tree top-heavy (especially if the vine collects snow in the winter), and therefore the tree is more susceptible to wind throw. Further, since the vines often leap from the canopy of one tree to another, the vines on a falling host tree often pull down neighboring trees. The positive side of these vines is often equivocal. All three of these woody vines have fruit that is nourishing for birds and other wildlife, but the shade from their leaves sometimes diminishes the amount of fruit that the host can grow. The density of their foliage provides excellent nesting or roosting sites for birds, but this same density diminishes the host tree’s ability to have dense foliage. An unalloyed contribution to the ecosystem occurs when the vines grow at a forest edge because their density blocks sunlight and wind from getting into the forest, allowing the soil to remain moist. Vines at a forest edge also cause the edge to have a greater bulk of vegetation than the interior of a forest, which means more food for insects and animals, as well as more absorption of carbon dioxide to combat global warming.
Many species of birds enjoy eating the berries of grape, Virginia creeper, and poison ivy; the berries ripen in fall, ready to help refuel the migrating songbirds. But poison ivy berries are highly toxic to all mammals, and Virginia creeper berries—and leaves—will irritate the lips, mouth, tongue, and throat of anyone who tries to eat them. People can eat grapes without dire consequences, but Aesop’s fox was right—they are sour.
By Jim Amon.
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