CHAPEL HILL - JoAnna Barnes noticed something odd while running errands last winter: a stand of dying evergreen trees along Willow Drive next to University Mall. She saw other trees turning brown around Chapel Hill and wondered what was killing them.

"I didn't know if this was something we should all be worried about," she said.

Curtis Brooks, a landscape architect and urban forester at the Chapel Hill Public Works Department, offered an answer to the mystery.

He said the drought killed dozens of Leyland cypress trees around town, including those in front of the mall.

The Christmas tree-shaped evergreens are popular because they grow rapidly and can serve as privacy screens.

But Brooks said the trees are drought-sensitive, especially in narrow areas like the strip next to University Mall where roots are squeezed into a tight space.

Robert Jackson, a professor of global environmental change and biology at Duke University's Nicholas School of the Environment, speculated that a fungal disease may have contributed to the death of the trees. He said extreme temperatures and drought can weaken trees, making them more susceptible to pathogens.

Jackson warned that global warming may amplify the effects of insects and disease on trees.

"Many of those pathogens and pests do better in warm weather," he said.

But climate scientists are still not sure whether global warming will cause more frequent tree-slaying droughts in this region.

"It's pretty clear that the Southeast will be hotter in the future," Jackson said. "It's not yet clear whether it will be drier."

Data released by the U.S. Drought Monitor on May 6 indicate that despite recent rains, Orange County is still in the midst of a moderate drought. Scientists expect the drought to continue easing over the next three months.

Meanwhile, University Mall has removed the 85 dead trees on Willow Drive, said Susan Nininger, the mall's assistant general manager.

"We were hoping not to have to cut them down," she said. "It was a sad thing."

She added that the mall will replant with a drought-tolerant species in the fall.

Brooks likewise advised landowners to avoid planting Leyland cypress trees.

He recommended that landowners instead plant the Eastern red cedar, a native tree that looks like the Leyland cyprus but is hardier.

"People should pay attention to the fact that the Leyland cypress is drought-prone," he said. "If we have another drought like last year, we should see a repeat performance."