A quarter-mile into dark Pinelands woods, Terry Schmidt turned last week onto a sandy trail. A hundred yards later she pulled up to a wet, sunlit meadow in Wharton State Forest, and smiled.

Weeks ago anyone could have gunned a truck into its shallow bogs for a mud-spattered tour of its ruined beauty. But not today. Perhaps never again.

For years this two-acre site was an illegal playground for off-road vehicles whose drivers came to splash through its groundwater, cut ruts through its sphagnum-covered hummocks, and gaily spin their wheels until their "monster" trucks were coated in mud.

But today a new, 140-foot-long barricade stood between Schmidt's little hatchback and the rutted meadow beyond. Made of pressure-treated lumber, it is a series of 12 eight-foot-long planks, four inches thick, through-bolted to thick posts buried deep in the ground. Thirty-inch gaps between each plank allow for foot traffic.

"It's the most extensive barricade we've built," said Schmidt, a senior manager for the New Jersey Parks Department who in late February helped supervise dozens of volunteers in its installation. The five barricades here in Hammonton are the first in a Department of Environmental Protection pilot program, she said, that could turn into an extensive protection effort for dozens of ecologically sensitive bogs and ponds like this one.

Moments later a Subaru Outback pulled alongside, and out stepped John Bunnell, chief scientist with the New Jersey Pinelands Commission. "I call this O.R.V. pond," said Bunnell, "for 'off-road vehicle.' "  The wry nickname does not, however, make him smile.

For 23 years he has been making his way each spring to this and dozens of other ponds in the 125,000-acre Wharton Forest to check on the hatchings of the frogs, toads, and other amphibians that depend on their shallow waters to lay eggs. But much of what was once mud here, Bunnell explained, has in recent years been displaced by the white sand underneath, kicked up by wheels "like this one," he said, and pointed out a massive black tire with a rusted hub, leaning surreally against a tall pine.

"We pulled it out of the pond," Bunnell said. "We find all sorts of things here."

As Schmidt, Bunnell and his dog, Dexter — "a lab, a pointer, and maybe some Great Dane" —  stepped through a gap in the barricade, Bunnell observed that "we would normally be standing in water right here," but a near-drought has greatly depressed the water table in much of the forest.

Ironically, it was in some of the curving, parallel ruts scoured out by truck tires that Schmidt found a broad, gelatinous mass floating in about four inches of root beer-colored groundwater.

"Those are wood frog eggs," said Bunnell.  This bog, he said, is also the spawning habitat for the northern gray tree frog, spring peeper, green frog, southern leopard frog, New Jersey chorus frog, and Fowler's toad. About 3,000 such ponds, typically less than two feet deep, and ranging from 10 feet across to many acres, dot Wharton Forest.

Known as "intermittent" ponds because they often dry out, they are fed not by streams but by the fluctuating water table, and so are free of fish, which would otherwise feed on frog eggs. After turning into tadpoles and growing legs, some frogs make homes in the adjacent "upland" leaf litter where oaks and pines grow, explained Schmidt, while others will burrow underwater and into the mud.

About two miles away the two visited what Burrell calls "the soup bowl," a shallow, one-acre pond so damaged by off-roading — its scoured bottom and perimeter are now entirely sand, not mud — that it has ceased to be a spawning habitat.

"I don't see any eggs," he said as he waded ankle deep into its perimeter, "but this is the clearest I've seen it in a long time," perhaps, he surmised, because the new barricade is keeping trucks out. If that continues, he said, "we're going to study and collect data on the natural revegetation."

The problem of off-roading's damage in Wharton Forest "came to a head two years ago," said Schmidt.

Exasperated by the failure of its $250 and $500 fines — even the threat of vehicle confiscation — to deter the "sport," the Park Service had debated shutting down some of the dozens of trails through the forest. While conventional vehicles and motor bikes have long been permitted on them, the trails were serving as access roads for vehicles seeking out ponds and other off-road terrain.

A series of public meetings last year on the topic drew large, passionate crowds. "About 5 percent of people saw no problem tearing up natural resource for their own enjoyment," Schmidt recalled, "and another 5 percent wanted to play God and shut everything down."

But from the "90 percent in the middle" who drive the trails responsibly, she said, came the idea of barricades, and the pilot program that began last month. Helping to dig post holes and bolt the massive planks on Feb. 25 and 26 were members of groups as varied as the Pinelands Preservation Alliance, the riding groups Iron in the Pines and New Jersey Trail Ride Association, the Gossamer Hunting Club, and the South Jersey Botany Group.

The barricades are a welcome presence for Lee Jones of Burlington Township, co-owner of Mid-Atlantic Expeditions, whose notion of "off-roading" might seem tame to the "wildcatters" who spin wheelies in bogs and ponds.

Jones and his partner lead strictly legal guided weekend tours along Wharton Forest's paved roads, fire trails, and dirt paths, he said, pointing out its abandoned villages and the sites of former mills and taverns. "We just enjoy the peaceful quiet," said Jones, a machinist.

But his drives have brought him several times into the presence of drivers scouring out mud puddles "and trying to make them deeper."

"They act like fools," said Jones, "but if you say something they get all in your face and say, 'What are you, park police?' You want to tell them about 'treading lightly,' but they don't want to hear it."

The new barriers might serve not only as a deterrent to off-roaders who willfully break the law, Jones speculated, but also to motorists who don't know any better.  "They drive down a road, see tracks off to the side, and say, 'Let's go.' And they end up in places they shouldn't be."