Week of 4/03/2005

Dear EarthTalk: Is the English Ivy covering the unattractive fence in my backyard really an environmental villain?

—Perry Pitcher, Seattle, WA

English Ivy is everywhere across the North American landscape, largely because it is an attractive, hearty and fast-growing groundcover that can hide other unsightly landscape and structural elements. But the ugly truth about this beautiful but non-native plant is that it aggressively invades new territory, often choking out native plants in the process.

According to the Seattle-based Ivy Off Urban Trees (IvyOUT) program, English Ivy is quite hazardous to trees it may colonize, weakening the bark by keeping it constantly damp, and blocking sunlight, inhibiting photosynthesis. Also, by reducing the airflow around the trunk, ivy makes trees more susceptible to wind stress and disease. As the vines grow higher and higher, they can eventually choke the life out of a tree.

Beyond trees, the plant tends to overwhelm other native flora, creating "ivy wastelands" devoid of biodiversity—except for the rats, slugs, mosquitoes and other pests it may harbor. It often spreads out of backyards and into parklands and other green spaces, both by climbing and through seed dispersal by birds.

Native to Europe, English Ivy was first introduced to North America as an ornamental garden vine in the 19th century. Like other invasive non-native species brought to the "New World," it had no natural predators or pests to keep it in check, and as a result quickly gobbled up habitat meant for native plants. While expensive government programs have helped halt the spread of a few well-known and intensely feared non-native species such as Zebra mussels and Purple Loosestrife, English Ivy continues to sprawl across the country, not only unabated, but often encouraged by unaware gardeners.

According to the Department of Environmental Services in Arlington, Virginia, ivy should be removed from any and all trees by cutting the vines at ground level and again several feet up any affected trunks. The remaining ivy should be peeled off, but with care so as not to strip off any bark. Beyond controlling English Ivy in your own backyard, you can be a good neighbor by also making sure it does not spill over onto adjacent land.

If you choose to remove your English Ivy completely and replace it with something more benign, the website eNature.com, run by the National Wildlife Federation, enables you to search a free database of native plants by simply entering your state and the type of plant (i.e. vine, wildflower, etc
) you seek. Local nurseries can also usually help you choose a good native replacement for English Ivy.

CONTACTS: Ivy Off Urban Trees, www.ivyout.org; Federal Invasive Species Website, www.invasivespecies.gov; eNature.com Database, www.enature.com/native_invasive/natives.asp.

Dear EarthTalk: I recently heard the term "Conservation Medicine." What does it mean?

—Steve Falbo, San Francisco, CA

Conservation medicine (sometimes called "conservation health") is a relatively new field of research that studies the links between human health, animals" health and the environment. One of its major fields of study is the emergence in recent decades of deadly diseases that have crossed over from animals to humans, including Mad Cow, AIDS, Lyme disease, SARS, avian flu and West Nile virus. Many of these plagues arose out of some form of human/animal contact in compromised ecosystems.

In 1998, for example, a previously unknown virus spread among some farm families in Malaysia, eventually killing more than 100 people. The outbreak was traced back to a pig farm where horses, cats, dogs and goats were also infected. The virus, named "Nipah" for one of its first human victims, eventually spread to Singapore, where nine slaughterhouse workers became ill after processing Malaysian pig meat.

Scientists deduced that the virus came from fruit bats that descended on Malaysia after their native habitat, forests in nearby Borneo and Sumatra, had been clearcut. The bats sought refuge in the fruit trees hanging over the animal pens at the pig farm, and then passed the virus to the pigs by dropping infected fruit into the pens, where the pigs eagerly ate it. How the virus jumped to humans is still a mystery, but scientists are quite sure that the clearing of forests in Borneo and Sumatra indirectly led to more than 100 human deaths.

"Diseases are moving from animals to humans and from one animal species to another at an alarming rate," says Lee Cera, a veterinarian at Loyola University"s Stritch School of Medicine. "When I went to school we were told, "This disease won"t go from a dog to a cat." Then all of a sudden a dog virus wiped out the lions of the Serengeti. How did it happen? When did it happen?" Conservation medicine is an attempt to answer these questions by bringing together professional fields that had previously worked in isolation: human medicine, veterinary medicine, infectious disease research, public health and environmental science.

Many factors are already understood. Increased human forays into wilderness areas (often spurred by population growth) have set up new points of human/animal contact. The international trade in exotic species also breaks down previously existing barriers. Climate change causes species to migrate to new areas, bringing with them new germs. Global travel plays a role: In 1950, three million people flew on commercial jets; in 1990, 300 million did. Two million people cross international borders daily, carrying with them huge amounts of agricultural products, live animals, soil—and disease-causing microbes.

The Wildlife Trust and the Consortium for Conservation Medicine are two organizations, both based in New York, at the forefront of this new field: "Conservation medicine demonstrates how healthy ecosystems are the basis for human well-being," says Mary Pearl, Wildlife Trust"s president, "and it can really engage people who didn’t see the relevance before."

CONTACTS: Wildlife Trust, www.wildlifetrust.org; Consortium for Conservation Medicine, www.conservationmedicine.org; Environmental Health Perspectives, ehp.niehs.nih.gov.