Hot cars & hardwoods: restoring forests in the Big Apple isn't your typical silvicultural exercise.

The morning begins with the smell of ashes, a scent familiar to the foresters in the New York City Parks Foundation's five-year, $6.2 million campaign to protect and restore 5,000 acres of hardwoods. Anthony Emmerich, project director, and Mark Busciano, his deputy project manager, pull over at the bottom of a City park hill in northern Manhattan to inspect a burned Mazda parked on its wheel rims on the sidewalk.

The headlights and windshield have melted. The wreck smells like last night's campfire.

The two foresters know stolen cars almost as well as they know trees. "They were only kids out joyriding, not professionals. They didn't strip anything," Busciano says. They even left the tires - steel radial wires lay like mats under the wheel rims, the rubber melted away.

Now he notices the natural damage. A cherry sapling that grows like a crooked flagpole out of the roadcut rocks overhead still wears its green leaves, but they are curled and singed - it's dead, he says. Flames from burning cars can reach 20 feet, frying the living cambium layer under the bark. On top of the roadcut, the trees all show gaps in their bark like opened shirts, scars from earlier fires.

At least the car burned on the sidewalk, rather than among the forest trees 40 feet down a nearby path. Several years ago, workers from the restoration project here planted a big wooden stake cut from a railroad tie in the middle of the path to block traffic. It has been rammed twice and burned once, but it still holds. One of the major goals of the restoration campaign is simply to force vandals to torch cars out on the streets instead of in the woods. The city will ultimately erect 20 miles of steel guardrails to protect the perimeters of its parks. For now, the crews plant wooden stakes or dig four-foot-deep "tank trap" trenches. These skills may not be taught in forestry school, but New York City doesn't offer the typical forest ecosystem.

From the Great Depression until the mid-1980s, New York City largely ignored the 5,000 acres of hardwoods growing in almost two dozen parks across the five boroughs, from large Pelham Bay and Van Cortland parks in the Bronx through the hills of northern Manhattan to the Staten Island Greenbelt.

"These are central hardwood forests like you would find in the rural areas of Pennsylvania, Missouri, and West Virginia," Emmerich says. These same species grew when the Indians lived here: oaks, hickories, maples, ashes, cherries, sweetgums, and tuliptrees. In places the towering trees date back 150 to 200 years, surpassing many of their country cousins that have grown up on former farmland in this century.

But the Indians didn't incinerate cars, introduce exotic trees and vines, or cause the other troubles that now beset the city's forests. In 1990, the Lila Wallace-Reader's Digest Foundation donated the money for a major restoration campaign. The City Parks Foundation, a nonprofit group created by the Parks Department and funded by philanthropies, now manages the campaign, employing 20 professional foresters and others with backgrounds as landscapers or park rangers. (In the past, the Parks Department employed only arborists, who planted and pruned the street trees.)

"We introduced silviculture to New York City," says Emmerich, who earned his master's degree at the Yale School of Forestry and relaxes by reading academic ecology journals. "What's conventional in other places is innovative here."

When the restoration work is completed next year, the Parks Foundation will have planted 130,000 tree seedlings, cleared choking vines from upwards of 600 acres, removed hundreds of rusty car hulks from the forests, and employed 30 high-school interns.

The educational branch of the campaign, run by Mary Leou, has published a beautiful coffee-table guidebook to the city's Woodlands, Wetlands, and Wildlife, built an Urban Forest Ecology Center in Van Cortland Park that draws 10,000 people a year, and sponsored school programs and teacher workshops. "Education is part of restoration," she says. After all, humans have caused 90 percent of the problems in these forests, so everyone from first-graders to adults can learn a lesson or two about stewardship.

To see some of the field work we join Timothy Wenskus, field manager for this area, for a tour of northern Manhattan's Inwood Hill Park, slowly navigating old asphalt pathways in a station wagon. The park boasts over 100 acres of forests, from a dell of giant tuliptrees to a broad ridge of mixed hardwoods and meadows. The dog walkers and joggers on the paths may see these woods as a happy riot of green, but the foresters see them as a mosaic of good and bad, natives and aliens.

Near the top of the ridge we see the stark aftermath of fire. A large patch of hillside below the pathway remains charred from a four-hour blaze in early May. A month later the site still smells burned. Some large trees wear a layer of soot on their trunks, the saplings are black skeletons, and the ground looks like burned toast.

"It was a very bad time of year for a fire," Wenskus says. "The trees did not have full-grown leaves, but they had leafed out. The roots were putting their energy into this spring flush of growth." Half the saplings are dead. The other half will resprout - like a nearby oak sporting a leafy-green stalk almost a foot tall, proof that the roots are still alive, even though the trunk is dead.

But fires discriminate among hardwoods, favoring oaks and cherries while discouraging maples and hickories. And many areas in the city's forests burn every year or two, a regimen that stunts the growth of any new trees and wounds the trunks of the giants until they rot at the base and topple over. It also exposes the mineral soil and floods the forest floor with sunlight, fertile conditions for alien weeds like the porcelainberry vine.

A low stone wall along the asphalt pathway provided the firebreak that held the May fire in check. On the uphill side of the path stands a forest that my guides envy. "This is what a rural forest looks like," Busciano says. "There are red oaks and ashes, tuliptrees and sugar maples. It has three layers of canopies - huge 180-year-old trees, 60-year-old trees in the understory, and native shrubs like spicebush and viburnum on the ground."

Blueberries, ferns, and moss grow here, away from the fires. Invading plants like mugwort and vines that depend on the sunlight aren't such a problem in these shady bucolic woods. But all too often the city's forests lack the younger generation of understory trees and the shrubs. They have towering elderly trees - and knee-high sprouts. Researchers are now studying several possible causes for this discrepancy between urban and rural forests, such as the different nutrient cycles in the soils created by exotic earthworms in the city's parks (see "As the Worm Turns" on page 34). But they know that New York's unusual fire regimen plays a role. As Wenskus explains, the burning season mirrors the school year, peaking at Easter break and at the end of the spring session.

During the 1980s, the Parks Department hardly noticed the exotic vines creeping over its forests, perhaps because they hadn't yet reached epic proportions in many places. Emmerich first saw them in 1984 on the wooded hillside overlooking the Hudson River that includes Riverdale Park and the Wave Hill estate. They had covered 11 acres, but still they seemed like a rarity. A year later, for example, the city's natural-resources inventory reported virtually no vines in one six-acre patch of woods in Pelham Bay Park.

"In 1990, though, it looked like kudzu had taken over," Emmerich says. "Everything under the vines was dead." Porcelainberry, an ornamental vine, had broken loose with a vengeance. With up to 15 or 20 shoots that grow 12 feet a year, it flourishes along sunny forest edges and in gaps created after trees have fallen. Another tenacious vine, Oriental bittersweet, can spread in shadier areas.

The foresters soon found big "vinelands" in other parks, including Inwood Hill, where we pass a ridgetop meadow of tall grass dotted by purple bull thistles. Several young red cedars poke up, easy to see, but the field also sports cherries, mulberries, ashes, oaks, and tuliptree saplings that the crews have planted.

Wenskus shows me a picture taken in 1991. The meadow looks as if a leafy circus tent has collapsed on it, the corners still caught in nearby trees. The taller shrubs look mummified with vines. In the summer of 1991, crews of three or four people each day would chainsaw paths into the nine-foot-high thicket of vines. Wenskus then donned a five-pound backpack of herbicides and sprayed all the vine leaves, returning in two weeks to hit the ones he missed. (The vines can grow four or five layers thick.) The following summer, the crew mowed the field and painted the vine stumps with herbicides to poison the roots.

Porcelainberry grows as ferociously underground as above. In a plot the size of a small room, Wenskus could find 30 vines, some with root systems 50 feet long. Even to-day, workers must return occasionally to weed the field of vines growing from seeds still left in the soil. The crews have cleared vines from 40 acres over the past four years, and they still have 10 more to go. But when they finish in 1996, Wenskus says, they should have beaten the vines back well enough to postpone the next massive pruning job for two or three decades.

Vines aren't the only villains. In the 1930s, the Parks Department planted sycamores and Norway maples to reclaim areas like Inwood Hill from villages and estates. "They chose cheap, fast-growing junk trees," Emmerich says. These maples look handsome enough with their lush canopies and big leaves, but the foresters and park managers now see them as detrimental species that monopolize their surroundings at the expense of native hardwoods, flowering plants, and wildlife. In the spring, Norway maples leaf out three weeks earlier than other species, and they hold their leaves three weeks longer in the fall. They cast a giant umbrella of shade that stops almost everything else from growing below them; the forest floor there now erodes in heavy rains. Prospect Park in Brooklyn, for instance, has forested hillsides of hard-packed dust under these trees. And the maples' high mono-canopy discourages many species of birds that nest out of the wind in understory trees or shrubs.

On the ridge we now stop at a stand of dead trees being replaced by sunlight and green plant stalks. The trees are quite stark, their tall trunks like twisted pitchfork blades stabbing overhead. Cracked bark hangs loose on many of them. Were they killed with herbicides, I ask. Suddenly the team grows quiet, as if I've discovered a carload of forestry hit men.

"I guess we can say it," Emmerich says. "Our commissioner, Henry Stern, told The New York Times several weeks ago that the department is killing Norway maples in Prospect Park in Brooklyn." Still, poisoning trees is a touchy subject for them. The department wants to promote the image of Emmerich's bumpersticker: "Warning: I Brake for Trees." They point out the many benefits of their deed. In the broad area of this former Norway maple kingdom, they've planted about 1,000 native saplings, although most are hard to see from the pathway, including red, white, and chestnut oaks, bitternut hickories, flowering dogwoods, and red and sugar maples. Not all the saplings will grow into mature trees, but the future forest will have more diversity and need less management work without the problem of soil erosion.

The work that Emmerich's crew has done in Prospect Park has grown into a major restoration campaign of its own. The Lila Wallace-Reader's Digest Foundation recently offered a matching grant of $1.3 million to the Prospect Park Alliance, a private group collaborating with the Parks Department on projects that could amount to $43 million over the next 25 years. In these woods, unlike the more remote forests in other parks, the hordes of people taking shortcuts through the trees add to the erosion. The restoration teams will build fences to block the unwanted paths, lay logs down on the eroding slopes as cribbing to catch the soil, add tons of additional fresh topsoil, and plant more than 130,000 new trees. The city's most famous woodland - Central Park - has had its own restoration campaign since 1989 under the Central Park Conservancy.

But these are New York's gold-plated parks, supported and enjoyed by the wealthy and the urban professionals. On weekends and vacations, they head to the rural forests of the Catskills or the Adirondacks, Emmerich says. The people who use the 21 parks that his crews have labored over are mostly immigrants and working-class residents of the surrounding neighborhoods. They may enjoy the greenery, but they probably don't worry about Norway maples as part of their daily lives. "Who cares?" Emmerich wonders. It's the great, nagging question of his work.

Yet Ann Early, president of the Inwood West Neighborhood Association, which covers the blocks at the base of the hill, sounds glad to hear about the program. "Any money put into the parks is money well spent," she says. "They are so overcrowded. And Inwood Hill is a wonderful natural resource. But I wish they could spend a little more on law enforcement. There are many brush fires in the park, and the Fire Department can't even get into them sometimes." She adds that some of her members have volunteered on the program's tree-planting days.

For our final stop we visit the Parks Department's nursery in the Bronx's Van Cortland Park. Emmerich shows me around the future forest: a plastic greenhouse of oak seedlings and outdoor cribs of oaks, hickories, white pines, red cedars, sweetgums, and tuliptrees. Even though oaks predominate in the history of the city's forests, his crews are planting a good mix of hardwoods because oak leaves last longer on the ground and fuel more fires.

Through hard experience, they've also learned to plant "containerized" seedlings that are raised in plastic pots and have grown 18 to 24 inches high and as thick as a person's finger. The height helps them compete against other plants, while the width seems to withstand predators, like mice and perhaps even crows, that have feasted on the small red oaks transplanted as "bare-root" seedlings from nursery fields.

This restoration campaign will finish by Halloween 1996. Emmerich likens it to other urban-renewal efforts in New York City. The South Bronx now echoes with hammers and cement mixers as private development agencies rehabilitate the bombed-out tenements of the 1980s. The subways have shed the graffiti that made them look like outlaw trains in the 1970s. And now, after 60 years of neglect, the hardwood forests have been weeded and replanted.

No doubt Emmerich would like to continue. Someone, perhaps volunteers or Parks Department crews, must continue to police the vines that can crawl back even after they've been chainsawed, poisoned, and cleared. It would be nice to return to the old Norway-maple stands once the new trees have grown and plant native spicebush and viburnum shrubs. But for the most part, these hardwood forests should grow and prosper on their own, just as their country cousins do. And future New Yorkers may wander through their lush native forests, thinking that nature has performed all this magic on its own.

WILL NIXON - is a freelance writer in New York City.