There's nothing like a walk in the woods to clear your mind. The chirping of birds, the wind rustling through the trees — far away from computers, microwave dinners, and traffic. It's peace, naturally.
But not all green is good. Most casual walkers on a stroll down a Lowcountry trail don't realize that in the calming shade of the vegetation around them, there's an ongoing war for survival between species native to Charleston and immigrants from abroad. These invaders arrive via bird droppings, through lawn ornamentals that naturalize, and in the ballast water of oceangoing tankers.
Since arriving at the port in Savannah in 2002, the ambrosia beetle is quickly spreading a fungus toward Charleston that literally annihilates every red bay and swamp bay tree in its path — each a principal species in maritime forests.
Chinese tallow, long used as a yard ornamental and fondly dubbed "the popcorn tree," has encroached into wetlands throughout the Lowcountry, drying up seasonal freshwater sloughs where many animals make their home.
In our marine waters, recent invaders like the Asian green mussel and the titan acorn barnacle can make quick work of an outboard motor once they become established; they also squeeze out native animals wherever they grow.
Plant and animal species migrate naturally, and competition is the crux of evolutionary theory. But the globalization of shipping and travel have thrown things off balance, dropping hardy species like the emerging threat of cogongrass into situations where they're able to out-compete everything else for resources. Just as kudzu overtakes plant ecosystems in the Carolina piedmont, a host of species are on the attack in the Lowcountry. Although some invasives can be fought back, many are so established in our environment that there's little we can do. But understanding how they get here in the first place is instrumental in protecting our remaining native species.
(Extra) Terrestrial Inhabitants
At the northern tip of Folly Beach, to the side of the roundabout where people park to walk out for a view of the Morris Island lighthouse, there's a waist-high Barbary fig cactus, adorned with yellow flowers and prickly spines. A closer look reveals that some of the spines aren't so spiny — they look more like soft, skinny yellow tubes protruding from the plant's fleshy "pads." Out of those tubes, in fact, will crawl 75-100 larvae of the South American cactus moth. They'll enter the plant and consume a pad, then bore through the joint into the next. Around the base of this particular cactus, itself a non-native plant imported as an ornamental from Central America, lies a pile of rotting brown pads, already devoured by the tiny larvae.
"When they get advanced, you can see the ooze coming out of the pads. Some of that gets really sloppy," says Billy McCord, a biologist with the S.C. Department of Natural Resources who has surveyed over 140 hammock islands in the state for native and invasive species. "They totally destroy the plant from the inside, and there's no control right now, other than people flicking the egg sticks off the cactus."
Although the substantially sized Barbary fig can withstand the moth's voracious appetite, smaller species like our native dune prickly pears cannot. McCord worries that the combination of a non-native host and pest invader will soon translate to danger for our endemic cacti. It's just the first of many invasive species that we discover in a short walk through the woods on Folly. Most appear harmless to the untrained eye.
"The definition of invasive is basically the same thing as naturalized — as soon as a plant (or animal) starts moving into natural communities of its own accord from self propagation, then it's invasive," explains McCord. A feral (and native-bird-eating) cat crosses our path up ahead. As we step off the worn trail, he quickly spots a clump of Russian olive, a non-native plant we'd seen lining the fences of more than a few homes on our drive out.
"Unfortunately, one of the things that makes invasives so successful is that many of them are very good wildlife plants, producing fruit in the fall that a lot of birds feed on, and in turn they spread the seeds," he says. Salt-tolerant plants like the Russian olive are popular at nurseries, and developers and utilities often use it to beautify electrical boxes and unsightly equipment. But the ability to grow in shade or sunlight that makes it attractive for municipal landscapers also allows it to proliferate easily in the wild.
"Anywhere a non-native species is taking up space, something that should be there isn't," says McCord. Before we leave the woods, he spots a tree wrapped in the familiar Japanese honeysuckle. It's a perfect example of a species most people are fond of, often planting it in their yards. But it has spread widely (it's a dominant plant on the West Ashley Greenway), choking out the honeysuckle varieties native to the Carolinas.
Walk the nature trail at Patriot's Point and you'll see a prime example of non-natives overtaking a forest. Sweet-smelling, evergreen privet trees make up the majority of the path's understory, shading out native plants that no longer receive enough sunlight to grow. Trying to eradicate them is futile since the plant produces large quantities of fruit, ensuring that enough seeds are spread . On the forest floor, English ivy creeps up the trunks of the occasional sugar berry or Carolina laurel cherry — native trees that would dominate the Mt. Pleasant understory were it not for privet.
Ironically, many of the terrestrial plants posing the largest threat to our forests are still widely available at area nurseries. Hyams Nursery on James Island confirmed that Russian olive, Japanese honeysuckle, English ivy, and both Chinese and Japanese privets are all currently in stock. Because Chinese tallow is "considered noxious in some parts of the state," the "popcorn tree" was not readily available. At Cross Seed in West Ashley, Chinese privets aren't for sale, but several other privets are.
Says one nursery manager who wished to remain unidentified, "It takes responsible citizens to maintain their property. Any plant in your garden could be a weed. A weed is any plant you don't want growing there."
After espousing the virtues of English ivy and referring to Chinese tallow as "a great old Charleston tree," the nursery manager was presented a USDA Forest Service pamphlet on S.C. invasives.
"Native plants are these peoples' god," he says. "But the government makes mistakes. They're sinners like the rest of us. And really, a lot of native plants just don't sell here. They don't sell."
Listing a plant as officially "noxious," and thus illegal to sell or transport, requires a new law approved by both the state House and Senate. Unless a species poses a threat to agriculture or the economy, that's a difficult road. Tallow is not on the list, but its ability to quickly infiltrate and dry up isolated wetlands have led DNR's McCord to spend weeks traveling to hammock islands with a machete to cut and spray herbicide on individual trees. Despite that labor-intensive effort, the dormant life of the seeds is unknown — they could literally germinate after a century of incubation in the ground.
"We're not proactive enough in the early stages of naturalization. Once something becomes established and classified as an invasive, it's hard to do anything about it," says McCord. Red imported fire ants are a good example — despite a statewide quarantine when the species first arrived, they're now prolific in almost every ecosystem in the Carolinas.
Fortunately, the terrestrial plant that could pose the biggest threat to South Carolina is already on a federal noxious weed list — cogongrass. First introduced almost a century ago as a packing material in a freight shipment at the port of Mobile, Ala., the fluffy white-tipped grass spreads through seeds and rhizomes (roots), with 65 percent of its biomass underground. Its pointy tipped roots so effectively spread that a three-foot diameter patch can grow to 50 feet in under two years. And because it's highly flammable and burns much hotter than native grass species, it can spread exponentially faster in pine forests by removing the canopy of trees and then popping back up.
"People who like the idea of grasslands and savannahs may think that what could happen will be very pretty," says George Kessler, a professor of forest resources at Clemson University. Kessler spearheaded a volunteer-driven survey last month that identified several cogongrass sites in S.C., from the Beaufort area up toward Aiken and in the Francis Marion National Forest.
"All of the sites have been treated, but we don't yet know how to effectively control it," says Kessler. Researchers often return to a site to find a band of new grass perfectly surrounding the treated area.
"If cogongrass spreads, it will prevent us from managing our land," says Matt Nespeca, a field representative for the Nature Conservancy. "It ruins property, ruins the ability to grow trees, and prevents us from managing for wildlife."
S.C. forests are currently facing a one-two punch from both cogongrass and laurel wilt disease, a fungus spread by ambrosia beetles. The beetle digs into the tree, carrying a fungus that then spreads to the tree's roots. At the Caw Caw Nature Center (just south of Charleston and the northernmost point the wilt has reached), the woods surrounding the entrance road are a dead zone of brown, decomposing red bay trees. By the time the trees are visibly infected, it's too late to act, so treatments are limited. Experimental solutions include using a pheromone trap that attracts the beetle away from the trees, but so far nothing has been successful.
"We don't want to be doom and gloom about it, but it's very dramatic," says Laurie Reid, an entomologist with the state Forestry Commission, pointing out that yellow swallowtail butterflies rely on red bays for pollination and could disappear with the tree. The wilt has been identified in eight S.C. counties. In places like Hunting Island State Park, just south of Edisto Island, red bays made up the majority of the understory just two years ago, but have suffered a 98 percent mortality rate. If the wilt reaches south Florida, it could devastate avocado crops, another member of the Lauraceae family. If it continues northwest to Appalachia, sassafras could be wiped out much in the same way the American chestnut was a century ago. Chestnut was once the East Coast's biggest tree, reaching ten feet in diameter and growing from Maine to Mississippi.
While eliminating invasive species on land is difficult, eradication in a marine environment is next to impossible. David Knott, a marine biologist with DNR, knows of only two instances of success — one involved hand-picking snails off a rocky beach in California, the other was a harbor in Australia that was blocked off and everything in it killed, all over an aquatic worm.
As climate change contributes to warmer average temperatures in Charleston's waterways, typically tropical species have begun to appear. In 2006, Asian green mussels were found blocking the water intake valves at DNR's Ft. Johnson facility on the harbor.
"They're the saltwater equivalent of the zebra mussel," says Knott; the zebra mussel is a notorious invader that has cost billions of dollars to treat in the Great Lakes. "They're prolific, growing to reproductive size in under three months."
Because Charleston's waters never dipped below 45 degrees Fahrenheit for longer than three days this winter, the populations easily survived, and likely built a genetic disposition toward strengthened thermal tolerance in the process. The shiny green bivalves are now abundant in the Folly River and can quickly cover a boat, engine, or pier. In the Gulf of Mexico, they've caused a power plant in Tampa Bay to shut down when its intake valves for cooling water were blocked by the creatures.
Similarly threatening to boats and ecosystems, the titan acorn barnacle made headlines two years ago when it was discovered at the Folly marina. The massive pink barnacle, which can grow several inches in diameter, is now peppered along docks and the pilings of the Folly Beach pier.
"After five months in the water, we found 30 growing on a boat propeller that had previously been dry-docked," says Knott. "The engine won't work with 30 of those things growing on it."
Whether the invaders will out-compete native fouling species (animals that attach themselves to hard surfaces in water) like oysters and clams is still unknown, but they certainly win the battle for space.
Although recreational boats, warmer waters, and the farming of non-native seafoods all contribute to invasive introduction, the most common mode of arrival is through the ballast water (used to add weight for safety) of shipping vessels entering the port of Charleston.
Federal regulations require ships to dump their ballast water 200 miles offshore, but loopholes about high waves, dangerous conditions, and the exemption of boats traveling between ports within the U.S. have meant the problem persists.
"If you have to go substantially out of the path of your intended voyage, than you're not required to dump ballast," explains Knott. "You can't discharge in a port unless it's necessary for the operation of the vessel, but every container ship that takes containers off then has to take ballast water." Even an "empty" ballast tank contains thousands of gallons of ocean water, and preventing the transfer of that residual material is virtually impossible if the tanks are opened.
"Ballast water is essential for ensuring the stability and safety of vessels, yet it's a pathway for the introduction and spread of nuisance species," says Byron Miller of the State Ports Authority, adding that the U.S. should sign on to an international treaty regulating ballast. "SPA supports an effective solution for managing ballast water to minimize the environmental risks they present."
The Coast Guard's reauthorization act earlier this year required ships to begin treating their ballast, and the EPA has until September to present their recommendations. Treatments may include chemicals, cooling, sonic disruption, or ozone, but nothing has yet proven 100 percent effective.
In many cases of invasive introduction, well-meaning citizens are as guilty as the shipping companies. Knott presents a jar of South American apple snails, collected from a pond in Myrtle Beach. The size of a child's fist, the voracious eaters literally consume all of the vegetation from a pond, destroying any ecological diversity.
"Somebody likely bought these snails for their aquarium, and then they got too big. They didn't want to kill them, so they dumped them in the closest fresh water," says Knott. He decries the lack of laws regulating the purchase and release of pet species into the wild, and cites aquarium dumping as a major threat to natural ecosystems. Put the unwanted animals in a ziplock bag and freeze them, he recommends. Even then, some animals like the hardy apple snails can survive days of subzero conditions.
Where S.C. has taken a proactive stance on invasives (and found some success) is in fighting aquatic plants. When 6,000 acres of Columbia's Lake Murray became overgrown with hydrilla in the early '90s, the state declared it a noxious weed and used a combination of chemicals and sterile, grass-eating carp to control it.
Hydrilla can grow inches in a day, and for that reason, it is often used by teachers to show live cell division under a microscope. It not only clogs intake valves on lakeside power plants, but makes waterways unnavigable to boats. Lakes Moultrie and Marion both suffered major blooms a decade ago, and the state still spends over half a million dollars a year controlling the weed. Because S.C.'s lakes are man-made, there's no "natural" vegetation in them, so it's difficult to determine what plants are invasive until the problem overtakes a large area. Hydrilla is under control, but at a significant cost that requires consistent maintenance.
Another major nuisance, phragmites (or "common reed") now covers 10,000 acres of the Winyah Bay area near Georgetown. Like cogongrass, most of its biomass is underground (80 percent). It spreads along the damp edges of waterways, and is prevalent on Drum Island and the old Navy Base.
"It grows densely, and crowds out natives to create a monoculture of just phragmites," says Chris Page of DNR's Aquatic Nuisance Species Program. "It can grow 12 feet tall, and choke out spartina (our common salt marsh grass). If we let it grow, all you'll see in the salt marsh is what looks like a cornfield without any rows." DNR is using helicopters to spray it, but its ability to spread through roots means the plant is likely here to stay.
A few years ago, a plant called beach vitex appeared to be the biggest threat to our beach ecosystems. It takes over sand dunes and creates a hazard for sea turtle hatchlings who become tangled in its vines. Largely because of that connection to the publicly-adored loggerhead, task forces successfully eradicated the plant from most of the state's beaches. Researchers hope that similar public interest will help to control infestations of other emerging invasives.
"Public outreach is our biggest avenue. Every nursery I go into, I ask where their natives are," says Colette DeGarady, president of the Lowcountry chapter of the S.C. Native Plant Society. "Some people look at me like they don't know what I'm talking about, but every time you ask it creates demand." Although she wishes that invasives like privet and English ivy weren't available at nurseries, DeGarady's approach is to educate the consumer.
"If a plant has the word Asian, Japanese, Chinese, South American, or Mexican in front of it, the chances are it's not native," she says. Her group hosts native plant sales and distributes lists of landscaping alternatives to invasives on their website, www.scnps.org. They also support local nurseries like Mepkin Abbey, Legare Farms, and Pon Pon Nursery in Adams Run that promote or specialize in native plants.
"My clientele is a good mix of regular customers and educated folks looking for particular plants," says Pon Pon owner Justin Pye, who cultivates dozens of native flowers, shrubs, and trees that naturally grow wild in the Lowcountry. "I'm often explaining why I don't carry plants like invasive wisterias or ivys."
In addition to public awareness, DNR's Knott and McCord both hope that the state will organize a central office or body to handle invasive issues, so that potentially dangerous new species can be addressed quickly. As more and more changes are made in the Lowcountry's biological make-up, problems like laurel wilt and cogongrass have a greater chance of proliferating and permanently altering our landscape.
"Invasives cause a gradual loss of biodiversity that's an additional blow to the problem of habitat loss," says McCord. "Everything shares a balance in nature. Bees gather nectar on a cactus for pollen, and they're food for other species. The food web is a three-dimensional jigsaw puzzle, and if we start taking pieces off, it has less integrity. Why the heck do we need mosquitoes and sand gnats? Because tons of stuff eats them. Everything has a part, and if we take enough small pieces from the puzzle, then the whole thing collapses."