State News

March 2, 2014

Coastal Georgia tree ’ecologically extinct’

Not long ago, healthy redbay trees were easy to find in coastal Georgia. Related to the avocado, these evergreens grew 45 feet tall, with black berries that fed songbirds and aromatic leaves that lent their flavor to traditional gumbo.

Then around 2000, a beetle no bigger than a poppy seed snuck into Georgia, probably through packing material unloaded at the Savannah port. The Asian ambrosia beetle spread rapidly, carrying with it a fungus that it farms within redbays to feed its young. That fungus clogs the flow of water in redbays, turning them brown and killing them. Since 2002, researchers have mapped the spread of the resulting disease, laurel wilt, from North Carolina to Florida and west to Alabama.

Now, at least one group of researchers is writing an obituary for redbays in Georgia. Writing in the journal Biological Invasions, they documented the steep decline of the trees on St. Catherines Island.

“You never say it’s completely hopeless,” said lead author Jonathan Evans, professor of biology and provost for environmental stewardship and sustainability at Sewanee: The University of the South. “But ecologically, the species is extinct. It will not play the role it played before.”

Evans was teaching a field course on the island when he noticed the dying trees, which were hard to miss.

“It looked like somebody had gone in and burned individual redbays,” Evans said. “They went from green to brown.”

He and his co-authors then studied the redbays from 2004 until 2009, setting out research plots and documenting the demise of trees within them.

“It’s rare to be able to catch something early and track it completely,” he said. “It was depressing.”

They found that 98 percent of the main stems in their study plots died. At first, new growth that sprouted from the base of died-back trees offered Evans some hope for the trees’ survival. But then the island’s deer found that new growth, too.

“Some trees looked like they might make it, but the deer are so pervasive it was preventing that from happening,” he said. “It was like the first food at that browse level.”

Other biologists are similarly pessimistic about redbays.

“I mean, it’s kind of toast as far as the Georgia coast,” said Eamonn Leonard, natural resources biologist with the Georgia Department of Natural Resources. “We keep hoping that we’re going to find one or two that are resistant.”

Redbays served as the primary host for some native insects, including the palamedes swallowtail butterfly.

But Leonard isn’t too worried about the swallowtail, which he said is able to feed on the growth that sprouts from the base of the trees.

“That’s one species that’s not going to blink out,” he said.

But redbays play other roles, too. With their evergreen leaves, they helped form a year-round protective blanket moderating temperature, light and the intrusion of salt spray in maritime forests, Evans said.

“Much of that understory was dominated by redbay and in some places so was the canopy,” he said. “If you punch holes in the roof it changes the dynamic.”

With intensive pressure from deer, other trees aren’t likely to take over that niche, Evans said.

“The forest is becoming less forest and more savanna,” he said.

For Evans, it’s clear that redbay is joining the ranks of chestnut, hemlock and American elm as a tree whose populations have been decimated by an exotic disease.

But Chip Bates of the Georgia Forestry Commission isn’t willing to put it in that category yet.

“It is a true disease,” said Bates, forest health coordinator. “It has decreased the population of redbay and sassafras in the eastern part of the state. But I don’t see it as something that will totally eliminate redbay and sassafras. Remember where the survey was done. It was an isolated island that does have an overpopulation of deer.”

Georgia Forestry surveys elsewhere on the coast have shown regrowth of trees 2-3 inches in diameter, Bates said.

“Are we going to lose all red bay? We don’t think so,” he said. “The population is going be severely diminished.”

Still, efforts to curtail the spread of laurel wilt have failed, said Bates, citing one Georgia Forestry study on Jekyll Island.

“We cut down everything with signs of laurel wilt and skidded it out to the landfill and burned it,” Bates said. “The idea was to cut it down and stop it. Three months later it didn’t look like we had even been there.”

One fungicide has shown some results but it must be injected into individual trees, making it too costly and time consuming a remedy for whole landscapes.

The upside of laurel wilt, if there is one, is that the disease served as a notice about invasive species coming into the port.

“This is a wakeup call to be more vigilant about how we work with partners at the port,” Bates said.

Representatives from Georgia Forestry now conduct a pest risk management meeting every other month with other state and federal agencies including USDA Forestry, Georgia Department of Agriculture, U.S. Customs and Border Protection Operations, and USDA’s Animal and Plant Health Inspection Service.

The forestry commission identified the Asian ambrosia beetle in 2002 in Port Wentworth, Bates said.

“We were somewhat told it wasn’t going to be an issue,” he said.

That won’t happen again, he promised.

“Now when we find something new we don’t ignore it,” Bates said.

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