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March 17, 2012

South Carolina forest giants in peril

Giant oaks that have lorded over South Carolina forests from their high ridge perches for generations are dying at alarming rates.

Giant oaks that have lorded over South Carolina forests from their high ridge perches for generations are dying at alarming rates.

The killer is hypoxylon canker, a weak but deadly fungus. Hypoxylon won’t harm healthy oaks, but it gets under the bark of trees already under stress and strangles them by limiting the flow of nutrients. With annual rainfall below normal in 10 of the past 13 years, lots of trees in South Carolina are under stress these days.

It’s hard to quantify the number of oaks that have died in the past few years, but it’s enough that people who spend time in forests are concerned. They first notice thinning crowns in the trees, then bark begins to flake off. By that time, it’s too late. The tree is dead.

“We’ve been getting calls the last three or four years,” said Laurie Reid, an insect and disease specialist with the S.C. Forestry Commission. “It’s not across the landscape, but especially in the Upstate, it’s two or three here and two or three there.”

Visitors to Oconee and Table Rock state parks have noticed dead oaks on the trails and in the parking lots. While roots running under asphalt can add to the stress, the oaks now dying next to the Table Rock parking lots have been healthy for generations.

“Some of the trees we are losing are signature trees in use areas that once they are gone will leave a void, not only for the space they once occupied but for the character they brought to the site,” said state parks director Phil Gaines.

The dead trees are especially striking because they often are among the largest in an area – red oaks usually, but white oaks, too, Reid said.

Those high on ridges are among the hardest hit. When rain does fall, it runs off quicker on ridges, escaping before much moisture can sink into the soil. The water also takes nutrients in the soil with it on the tumble down the hill. Less water and fewer nutrients make for struggling trees, just the type the fungus loves.

Hypoxylon doesn’t compare to invasive Asian bugs such as the wooly adelgid, which has wiped out the vast majority of hemlocks in the mountains, or the ambrosia beetle, which is doing the same to red bay trees along the coast. Unlike those newcomers, hypoxylon has long been a factor in the tree version of survival of the fittest in Southern forests. Hypoxylon kills have been documented for more than a century.

Still, it’s sad to see the big oaks dying.

“It has its impact visually, aesthetically,” Reid said. But she noted that the understory will start growing better as it goes from shade to sunlight and the forest cycle begins again.

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