by Whit Gibbons

September 11, 2011

As we went through the jungle at midday, all was dark. A canopy of green leaves, gnarled limbs, and twisted vines let only patchy yellow shafts of sunlight reach the ground. Last year's fallen leaves and brown twigs made a dark flooring for an already gloomy setting. The "jungle" is what the locals call this natural, inland habitat on the northernmost undeveloped part of Kiawah Island, S.C. Botanists recognize this type of coastal habitat as a distinctive early successional stage known as the thicket, which thrives between sand dunes and inland forest of barrier islands from North Carolina to Florida. We were moving through the habitat in search of lizards, snakes, and frogs. Had we been looking for mosquitoes or spiders and their webs, our quest would have been quite successful.

But aside from not finding reptiles and amphibians, and its being way too hot and humid for comfort, something was not right with the habitat. We had noticed that leaves on some of the standing trees were already dark brown. The scene was wrong because it was late summer, long before autumn would place its claim on the chlorophyll that makes a leaf green. The frequent brown-leafed trees made an odd addition to the forest mosaic. But not just the leaves were lifeless. The trees themselves were dead, from stems to roots. Some of the trees were more than a foot in diameter and 30 feet high. Similar dead and dying trees can be seen throughout the coastal forests of the Carolinas, Georgia, and Florida, their dark brown a stark contrast to the evergreen trees and shrubs. The afflicted tree is red bay laurel, a species in the plant family that includes sassafras, avocados, and bay laurel, known by any good cook for its aromatic leaves.

Red bay laurels have become infected by two foreign invaders, ambrosia beetles and an associated fungus, both from somewhere in Asia, possibly India or Japan. The beetle bores into a tree stem to lay its eggs and introduces the fungus, which eventually clogs up the water transport system throughout the tree. The dying process can take several months, but once a tree is infested with the beetle and fungus, the death knell has sounded. The disease is called laurel wilt.

The historical range of red bay laurel is in the Coastal Plain from southern Virginia to Texas. Laurel wilt was first reported in 2002, near Savannah, Ga. The developing threat became apparent in 2003 with dying red bay trees on Hilton Head, and the cause of the disease was determined in 2004. Today, the hardest hit areas are in the eastern part of the tree's geographic range, and the impact is now noticeable in many areas along the Atlantic coast. Someone visiting an area where laurel wilt is prevalent will quickly become aware of how abundant laurel bay trees are in a coastal plant community, an otherwise lush habitat of perpetual green.

Unfortunately, the killer of red bay laurels could be moving slowly but steadily west, through Alabama and Mississippi, toward Louisiana and Texas. Agriculturists have not discovered a way to stop the spread. The fate of the red bay laurel could soon be that of American chestnut trees, once the largest trees native to the eastern United States. Chestnuts disappeared as a dominant forest tree when infected by chestnut blight, a fungus introduced from Asia.

Although the spread of laurel wilt won't have the economic impact that the disappearance of chestnut forests had, the extinction of red bay laurel will leave an ecovoid in some coastal ecosystems for many years to come. And the disease raises the specter that related species might also become susceptible. Such invaders from foreign lands can have devastating impacts on native plants and animals that have no natural defenses against them. We should be more aware of such invasive threats and try to prevent their appearance here because little can be done to stop such invasions once they have taken hold.

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