Thursday, May 3, 2007

Go North, Young Plant!

The New York Times reports that as the climate warms, growing zones are shifting.
Forget the jokes about beachfront property. If global warming has any upside, it would seem to be for gardeners, who make up three-quarters of the population and spend $34 billion a year, according to the National Gardening Association. Many experts agree that climate change, which by some estimates has already nudged up large swaths of the country by one or more plant-hardiness zones, has meant a longer growing season and a more robust selection. There are palm trees in Knoxville and subtropical camellias in Pennsylvania.
But horticulturists warn that it is shortsighted to view this as good news. Warmer temperatures help pests as well as plants, and studies have shown that weeds and invasive species receive a greater boost from higher levels of carbon dioxide, a heat-trapping gas, than desirable plants do. Poison ivy becomes more toxic, ragweed dumps more pollen, and kudzu, the fast-growing vine that has swallowed whole woodlands in the South, is creeping northward.
Already, some states are facing the possibility that the cherished local flora that has helped define their identities — the Ohio buckeye, the Kansas sunflower or the Mississippi magnolia — may begin to disappear within their borders and move north.
By the end of the century, the climate will no longer be favorable for the official state tree or flower in 28 states, according to “The Gardener’s Guide to Global Warming,” a report released last month by the National Wildlife Federation.
By the time of the annual Atlanta Dogwood Festival last month, the pale dogwood blooms had come and gone. Tara Dillard, a landscape designer and garden writer, said she now steers clients away from longtime favorites. “I’m writing a column about rhododendrons right now,” Ms. Dillard said. “And I think my conclusion is going to have to be not to plant rhododendrons. We have heated out of the rhododendron zone.”
In this warmer age, she said, “You might be planting some stuff you don’t like, like hollies.” But she brooks no objections from her clients. “I don’t care if you don’t like them,” she tells them. “I used to not like them either.”
David W. Wolfe, a professor of plant ecology at
Cornell University, who spoke at a recent symposium at the Brooklyn Botanic Garden called “Gardening in a Changing Climate,” confirmed that in many places bellwether plants and animals were beginning to disappear. “There is clear evidence that the living world is responding to this change already,” Dr. Wolfe said.

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