Essay: Lianas

One of the most prominent features of the Congaree that gives it such a distinct and unique character is the presence of numerous, large vines. Forest scientists call them lianas, a Spanish term that means, well, “vine.”  North American vines reach their greatest abundance in the humid, sunny South with its moderate temperatures and long growing season. At last count there were thirty species of vines found at Congaree, more than any other national park.

World-wide, lianas reach their greatest development in tropical rain forests and jungles (think Tarzan). And it is primarily Congaree’s lush liana growth that gives it such a special “rain forest feel.”

Reigning supreme among Congaree lianas is the wild grape or muscadine, Vitus rotundifolia. These vines attain enormous sizes, with one I found being nearly a foot in diameter at four-and-a half feet off the ground. They often form the most bizarre patterns of circular swirls, loops, and twists at some distance from their host tree before continuing their upward journey into the reaches of the canopy, seeking sunlight to continue their growth. In a wet growing season they produce abundant, reddish aerial rootlets that hang down in long, veil-like streamers. This could be the vine Edgar Rice Burroughs had in mind when he created his Tarzan character swinging through African jungles.

A champion-size grape vine.

Neal Polhemus is hiding behind these grape vine aerial rootlets.

Another large, impressive Congaree vine is trumpet vine, trumpet creeper, or cow itch, the last referring to a mild rash that a few people receive when handling it. The distinctive blond stem of Campsis radicans is easily told from the dark, blackish vines of grape. They don’t get as large as grape vines, but I have measured several that were seven to eight inches in diameter. The bright red tubular flowers produced in summer are a favorite hummingbird flower.

One vine that always draws attention is rattan or supplejack, Berchemia scandens. The jet-black, smooth vine doesn’t get nearly as large as the trumpet creeper or the grape, but its distinctive, corkscrew, “pigtail” growth pattern is eye-catching. The sap must suit yellow-bellied sapsuckers as I see a good number of rattan vines with sapsucker holes drilled in them.

Crossvine, Bignonia capreolata, is one of the few evergreen vines at Congaree. It could be even more abundant than poison ivy. I see it as a common, sometimes abundant, ground cover just about everywhere in the swamp, growing as an unvine-like sprig a few inches off the ground, awaiting an opportunity to climb onto something that will carry it up into the canopy and sunlight. Crossvine produces clumps of attractive, tubular red blooms with yellow throats in spring at a time when migrating hummingbirds are looking for nectar. Like trumpet vine, about the only way you know crossvine is blooming is when you find the spent flowers on the ground.

Perhaps the most abundant Congaree vine is the notorious poison ivy. In some areas it appears that one of every four trees has a “hairy” vine growing around it with the trademark three leaves. In some cases the ivy foliage is so thick, completely covering the trunk of the host tree, that it appears to be a “poison ivy tree.” The plant is easy to overlook in winter after the leaves fall, but the hairy, aerial rootlets are diagnostic, and there will often be clumps of small, yellowish-white berries at the end of the slender, horizontal branches that grow from the main stem wrapped around the tree. Poison ivy berries are relished by birds, and I’ve counted more than twenty-six species, everything from warblers to woodpeckers, feeding on them.

Often confused with poison ivy is Virginia creeper, Parthenocissus quinquefolia, but with leaflets of five rather than three. This member of the grape family has brilliant red foliage in the fall, and the small dark fruits are a quality food for both resident and migratory birds in late summer and fall.

A really attractive, but uncommon Congaree vine is climbing hydrangea, Decumaria barbara. It prefers organic, acid soils of the muck swamp, where it grows around the swamp tupelos and is easily seen near the boardwalk. The fragant, late spring-blooming corymbs of small white blooms are appealing but often overlooked. The vine has aerial rootlets like poison ivy, but they, and the vine itself, are light brown or blondish in color rather than dark like poison ivy.

Some of Congaree’s vines are unwanted, non-native exotics that don’t belong there. Foremost among these aliens is Japanese honeysuckle, Lonicera japonica. Despite their fragrant and attractive blooms, this aggressive honeysuckle will shade out native species and become so thick and lush as to smother and inhibit the growth of tree seedlings and saplings. Fortunately, Japanese honeysuckle has not become a widespread problem in the park. The really bad-news vine, the worst of them all, is of course kudzu, followed by Chinese wisteria. The good news is that both of these vines from hell prefer upland sites, and I have not seen either in the Congaree floodplain.

Researcher Bruce Allen, while at the Savannah River Ecology Lab and later at Ohio State University, has done extensive liana research at Congaree. His findings have shown an increase in the densities and sizes of Congaree vines, a finding corroborated by other studies. Hurricane Hugo may have been responsible for at least some of this increase, since the numerous canopy gaps and openings created by the storm allowed for more sunlight penetration, which in turn benefited liana growth.

It is not biologically correct to call vines parasites because they obtain their nutrients, moisture, and sunlight on their own, but they are in direct competition for these essentials with the tree or shrub that holds them up. The latter acts as a “trellis” for the vine, giving it support and enabling it to reach sunlight. Lianas can sometimes be detrimental to the support tree. Grape vines with their lush, abundant foliage can smother a tree canopy, reducing photosynthesis, and the sheer weight of a large vine can lead to limb breakage or deformed canopy limbs more susceptible to damage.

The vine “ecosystem” is just one of the many layers of the Congaree forest that makes it such a complex and fascinating place to study, contemplate, and enjoy.

John Torrence provides scale for this large trumpet creeper vine.

Rattan vine has a distinctive corkscrew growth form.