Horses of Coast Islands, A Regional Symbol, Harm the Environment
By CORNELIA DEAN
Published: July 27, 1993
BEAUFORT, N.C.— MORE than any other creatures, wild island ponies personify the rugged beauty of the sandy barrier beaches that line much of the East Coast.
Motels are named for them. They are a recurring decorative motif in restaurants. And tourists by the boatload venture out to watch as mares and foals walk along the water's edge and bend gracefully to crop the marsh grass, while stallions watch alertly from nearby dunes.
But a growing number of scientists say these scenes are not as benign as they seem. The horses are not existing with nature, the scientists say, but destroying it with every mouthful of the tender shoots they favor.
New research on barrier islands near here shows that grazing horses greatly reduce the amount and variety of island plants. And when the islands lose the plants, they can lose much of their ability to trap sand and defend themselves against erosion. The horses also cause trouble by trampling the soil, destabilizing the dunes, grazing on rare plants and by leaving droppings that alter the nutrient balance in the soil. By destroying the low-growing plants in the islands' maritime forests, they leave trees open to destruction through salt spray and wind.
The National Park Service has begun a three-year study to develop a management plan for horses on barrier islands in the Southeast. Initially, researchers will study horses on Cumberland Island National Seashore in Georgia, where earlier research showed that horses reduced above-ground vegetation by up to 98 percent, and Cape Lookout National Seashore and Cape Hatteras National Seashore, both in North Carolina.
Many researchers who have studied the issue have concluded that the several hundred horses on the islands do not belong there and say their numbers should be reduced by culling herds or other means, like sterilization. Scientists at the Assateague Island National Seashore in Maryland are testing drugs that make mares temporarily infertile. Another way of keeping the island's horse population down is the annual roundup and auction of ponies from Chincoteague, as the southern part of the island is known, to be held this week. Others call for ousting the horses altogether.
But, as a North Carolina report noted in 1990, "the horses of the barrier islands have a strong and emotional constituency." Biologists Debunk Lore
Horses have lived on many of the islands since the 19th century or even earlier, and many a restaurant place mat tells a romantic story of their arrival: noble Spanish steeds shipwrecked on treacherous shoals or bog ponies brought over in Elizabethan times.
Most biologists believe these stories are false; they say the ponies descended from horses left behind when settlers abandoned the islands or were dumped there when they had lost their usefulness on mainland farms.
In fact, until a few years ago ponies shared some of the islands in the Rachel Carson Estuarine Research Reserve here with pigs, goats and sheep. All the other animals were removed because of the damage they were doing to the islands. But the horses were allowed to remain.
They eat all sorts of plants but especially spartina, the cordgrass whose tall, graceful fronds are almost ubiquitous in East Coast marshes. Although the loss of other vegetation takes its toll, spartina is such a prodigious sand catcher that ecologists call it a "keystone species" whose disappearance can throw an entire ecosystem out of kilter.
That is what has happened on Carrot Island in the Carson reserve, Dr. Mark Hay and Dr. John Wells of the University of North Carolina found. The scientists, at the university's Institute of Marine Studies in Morehead City, began studying Carrot Island in the spring of 1988. They fenced off 32 areas 28 feet wide on each side. Then, for the next two and a half years, they watched what happened. Damage by the Horses
"All over those areas there was a huge change in the amount of spartina that was there," Dr. Hay said. "When the horses had access to it, it was real short."
In the enclosed areas, he said, "it was increasing in density like a shag carpet rather than a few little feathers sticking up here and there," adding, "Then you got a lot of other things as well -- gastropods, clams and a lot of associated plants and animals that weren't there at all when the horses were there."
As the grass grew, he went on, it began trapping sand carried by wind or water "so the height of the island changed," adding that it was "pretty dramatic, really, in the area where we excluded horses."
Other parts of the island, meanwhile, were either unchanged or eroding, he said.
Duke University researchers are conducting similar studies on a nearby island, Shackleford Bank, with similar results. Dr. Orrin H. Pilkey Jr., a Duke geologist who supervises graduate students working on Shackleford, said there was more than enough evidence to justify removing the horses. "There's a time when you don't need statistics," he said, "when you're standing on a salt marsh and it looks like a lawn."
Dr. Pilkey, an ardent advocate of barrier island preservation, grouses that "if a developer damaged these islands the way the horses do, he would be put in jail." What to Do With Them?
If the horses are left alone, most scientists agree, the herds will grow until a food or water crisis causes the population to crash, as happened on Carrot Island in the winter of 1987, when dismayed townspeople looked across the creek to see starving horses dying on the far shore. Eventually, some of the horses were removed and feed was provided for the rest. But if that approach was continued, Dr. Hay said, it would ultimately turn the island into "a sandbox with horses."
But what to do with them?
The answer, said Dr. Daniel Rubenstein, a Princeton biologist who has been studying the social organization among horses on Shackleford Bank, depends on the goals of preserve management.
"If you're managing for historical reasons, the horses are part of the islands' history," he said. "If you're managing for cultural reasons, they're part of the culture. If you're managing for biological diversity, the horses are a problem."
Dr. Hay refused to be drawn into the controversy over whether horses should be removed from barrier islands. "We need to stay out of that," he said. "We provide information. What's done about it is a political decision. It's not a science decision."
He said that people who come to Beaufort to see the horses "learn in the process about the value of marshes and near-shore processes," adding: "You may build a constituency that will save more marsh than these horses could ever eat. In the long term maybe the horses are saving barrier island habitat."
Photo: Horses on barrier islands on the East Coast eat valuable plants, destabilize dunes and change nutrient balance, some scientists say. This wild horse wades in a salt marsh at Assateague Island National Seashore. (Fred Whitehead/Animals, Animals)