Sunday, October 28, 2007

Virginia Creeper

What’s blooming in the area: Roses, white sweet clover, pink evening primrose, winterfat, chamisa, snakeweed, áñil del muerto, golden and purple asters.

What’s blooming in my garden: Pinks, snapdragon, petunia, chocolate flower, blanket flower, chrysanthemum.

Inside: Aptenia.

Animal sightings: Ants.

Weather: Frost on my windshield Monday morning; last rain, 29 September.

Weekly update: Virginia Creeper. The very name evokes the Blue Ridge or primeval forests that greeted the first settlers at Jamestown.

I shouldn’t be surprised it grows almost elsewhere in the country. After all, many plants are named when they’re first encountered, before more is known about them. Canadians call it Engelman ivy.

Still it’s a surprise to have it constantly volunteering in arid New Mexico. Most of the specimens in the university herbarium are from counties along the Continental Divide, east of the Sangre de Cristo, or along the roads and railroads west from Albuquerque. Nothing from Rio Arriba or its neighboring counties.

The Zhangs and Shi tested Parthenocissus quinquefolia as a potential restoration tool in the Hunshandak sand lands of northern China and discovered that when the woody vine has less soil moisture, it transfers its growth to its taproot and alters the breathing patterns of its leaf stomata.

Here many of the places it grows are shaded, but some are in sun all day. Many, including those under trees, may have access to preserved water. The vines growing along fences may also have found water conserved by nearby roads. The liana is apparently very adept at exploiting soil, water, and light conditions.

Since it seems unlikely it invaded the Española valley by itself, it probably was introduced: the local hardware often sells rooted cuttings. I suspect the plants covering two tall cottonwood stumps down the road were deliberately planted, and I think the vine in front of a large pine tree hitched when they dug the tree up and moved it here.

It has erupted in my yard in so many places I thought maybe the seed was in the soil, waiting for water. But Van Clef and Stiles says that’s not possible, that the seed is only good for a season. Indeed, most forest herbs don’t create seed banks.

The seeds are spread by birds. However, less than half the dozen places it’s growing along the main road are near utility lines. The only vines that aren’t on fences, are in trees. Normally I drive in heavy commuter traffic when the birds have retreated to a few sections of the overhead lines; pigeons prefer the metal roofs of two out buildings. Birds don’t perch everywhere Virginia creeper grows.

In my yard, birds occasionally land on one of the fences, but not the fences where Virginia creeper has attempted to grow. Various types of birds have nested in my porch, in my garage, and in my neighbor’s metal barn. A number of the seedlings have sprouted near the eaves or down wind or downhill from the undereave entry points.
Virginia creeper has been growing next to my neighbor’s barn since at least 1997, but didn’t start to put many vines through or under the border fence until after last summer’s wet season. It usually takes a few years to establish itself. So far, the tendrils haven’t used their adhesive pads to climb the wood, so they might safely be left to compete with the downy chess grass, wild lettuce, and horseweed that grow along that section of driveway.

The only problem with birds as the agent for diffusion is that before there can be seed to drop, there must be flowers. Like other members of the grape family, Virginia creeper’s green floral clusters are so small they wouldn’t be seen from the road and the purple berries are too dark. So it means nothing to say I’ve never seen them blooming. However, Iverson’s team says they don’t flower often, at least in Illinois, and Grey-Wilson warns his vines only fruit during hot summers in Britain.

That leaves a puzzlement. Along the main road, the places with dense colonies of vines are too far apart to be spreading from a single plant, and neither far enough nor close enough for birds. The only alternative is that once a plant is established it roots its own branches, which may grow twenty feet a year, and expands on its own momentum. Then, when it does produce fruit, a bird can move it another thousand feet down the fence or across the road.

It’s persistence and spread may be a bit of a riddle, but nature is unfaed. Most of the year, Virginia creeper blends with other vegetation, dark green leaves in summer, dead leaves in fall, bare branches in winter. For just a brief spell, ended this year by last Monday’s cold, nature shows off when the five-part leaves turn burgundy and reveal their profligacy.

Grey-Wilson, Christopher. Gardening on Walls, 1982, cited by Ken Fern, Plants for a Future Database, available on-line.

Iverson, Louis. Illinois Plaint Information Network, with data compiled by David Ketzner and Jeanne Karnes; available on-line.

University of New Mexico herbarium. Institute of Natural Resource Analysis and Management on-line database.

Van Clef, Michael and Edmund W. Stiles. "Seed Longevity in Three Pairs of Native and Non-native Congeners: Assessing Invasive Potential," Northeastern Naturalist, 8:301-310:2001.

Zhang, Z.J., L. Shi, J.Z. Zhang and C.Y. Zhang. "Photosynthesis and Growth Responses of Parthenocissus quinquefolia (L.) Planch to Soil Water Availability," Photosynthetica 42:87-92:2004.

Photograph: Virginia creeper growing over a stone wall near the orchards and climbing into the apple trees behind; dried pigweed in front; 20 October 2006.

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