Friday, May 25, 2007

Climate Change in Chapel Hill

Much media attention has been paid in the last year to climate change and some of the more dramatic possible global consequences--sea level rise, drought, and disrupted water supplies, with poor nations bearing much of the burden. But, as a Chapel Hill gardener and frequenter of nature trails, I began to wonder what may happen in my own backyard.

The last 100 years have seen a warming and drying out in piedmont and coastal North Carolina. Temperatures rose significantly in the piedmont and coastal regions, with an increase of 3 degrees F in coastal Carolina between 1911 and 2002, according to a 2006 report by the State Climate Office of North Carolina. Although maximum summer temperatures did not increase significantly in the state in the last century, minimum temperatures rose, particularly in urban areas. As for rainfall, the greatest decrease occurred in Chapel Hill, which saw a decline of 4.1 inches between 1893 and 2002.

Although the International Panel on Climate Change has little to say about global warming’s likely consequences in the Southeastern United States, climate scientists do predict that an increase in temperatures will be accompanied by more frequent storms, more heavy rainfalls, and more frequent droughts.

Flora at the southern end of their distribution range, such as those found in the Appalachian Mountains, will be particularly affected by warming, according to a study by the National Biological Service. Spruces, firs and the rare endemic herbaceous plant, Geum radiatum, are highly vulnerable, says Johnny Randall, assistant director for conservation at the North Carolina Botanical Garden.

Closer to home, Randall says he worries most about Catawba rhododendrons growing on north-facing slopes of Morgan Creek. These rhodies are not particularly well adapted to warmer temperatures and unpredictable rainfall. “I think we’ll see them drop out relatively quickly,” he says.

If plants that like cool conditions may be losers, vines may well be winners in a warming climate. This includes the backyard scourge (and native) poison ivy, Toxicodendron radicans, as well as exotics like Japanese honeysuckle, Lonicera japonica. A study by Duke University found that poison ivy grew 2 ½ times faster with increased carbon dioxide.

A changing climate also favors weedy exotics such as Microstegium vimineum, says Randall. Weeds tend to take over disturbed sites because they are highly adaptable and have a lot of genetic diversity, traits that may give them even more of an edge when some native plants begin to struggle.

Some early shifts in vegetation are already detectable in the Piedmont, as wax myrtle (Myrica cerifera) and Baccharis halimifolia have begun moving inland from the coast, Randall says. It is unclear, however, whether this is related to global warming or to land disturbance created by development, he says.

What’s a gardener to do in these uncertain times? I began to wonder if my neighbor who created a garden entirely of tropicals had the right idea. But Randall helped abolish these heretical thoughts. “Planting native plants is more important than it ever has been if we want to maintain some biodiversity,” Randall says. Biodiversity is an important component of ecosystems’ resilience to change. Another reason to continue using Southeastern native plants in our gardens is that most of them are already are adapted to extremes of weather—heat, periods of drought, and heavy rainfalls.

So, I’m planting a variety of natives, most of them somewhat drought tolerant. I study the heat zone maps and avoid buying plants that are already at the southern end of their comfort zone. I installed a rain barrel to catch runoff from heavy rains and keep my new plants alive during droughts. And, most important, I’m doing what I can to reduce my carbon footprint.