Deep in the sleepy heart of New Jersey's million-acre Pinelands, the quiet of the forest is pierced by a series of otherworldly electronic chirps.

The noise comes from atop a 55-foot metal tower, home to a sophisticated sonarlike device that bounces sound waves off the wind and captures the resulting data on a computer.

The goal: to prevent the forest from going up in flames.

Researchers at the U.S. Forest Service are in the midst of a $2 million, five-year study of the potential for fire in the vast, sandy treescape that spans South Jersey, an area that's flammability is said to rank second only to Southern California's.

It has been 41 years since the last big one, a series of fires that consumed 193,000 acres and killed seven people. Experts say the ensuing buildup of "fuel" — underbrush, trees, fallen limbs and twigs — coupled with the growing number of houses in and around the forest, puts much of the area at high risk.

"Not being alarmist, I would say it's about time," said John Hom, a deputy program manager at the Forest Service's Northeast Research Station.

At stake is the delicate balance between the needs of people and the forest, a swath of scrubby pines that is home to a unique population of animals. While fire spells trouble for houses, the trees that surround them have evolved so that their very health relies on periodic scorching.

State firefighters set smaller, intentional fires each winter to clear out underbrush and maintain the ecosystem, but say they are limited by the number of homes in the forest and by pollution concerns.

The reason for the Forest Service study is that the national "fire danger" rating system, a five-tier scale ranging from low to extreme, just doesn't work well for the Pinelands. The unusual soil consists largely of sand — originally deposited as gravel by the ocean eons ago — so it dries out quickly.

"It's like trying to grow stuff on a beach," Hom said. "A very old beach."

Fire experts like to say the Pinelands, also known as the Pine Barrens, can get rain in the morning followed by fire the same afternoon.

And so weather conditions that would merit a fire-danger rating of "moderate" in most of the United States might instead be worth a "high" ranking in the Pinelands, said Maris Gabliks, chief of the state Forest Fire Service.

The Forest Service hopes the research, carried out in cooperation with state officials and Rutgers University, will help in tweaking the rating system to fit the piney forest that covers 22 percent of New Jersey.

The idea also is to make fire prediction updates available on the Internet every half hour. That is needed here because moisture conditions change so quickly; most of the rest of the country relies on predictions based on data from the day before.

The electronic chirps from the tower are used to measure wind speed and direction up to 2,000 feet in the air, said Ken Clark, a research forester for the Forest Service.

The device, a sonic detection and ranging system, does this by measuring how much the sound waves have been deformed upon their return. Keeping tabs on the wind is critical to determining if, where and how fast a fire will spread.

Researchers also have used lasers to measure the height and type of vegetation while flying over the forest in a helicopter. Another device records changing levels of carbon dioxide, a measure of how fast the forest is growing.

Still other tasks are more mundane. Clark and his partner, research technician Nick Skowronski, have placed wire baskets throughout Brendan T. Byrne State Forest in the Pinelands, and they periodically collect and weigh the amount of twigs, needles and other litter fallen from the trees.

Though the last epic fire was in 1963, a handful of more recent blazes have been large enough to give homeowners a scare.

In June 2002, when the region was in the grip of a drought, an illegal campfire in Double Trouble State Park sparked a blaze that swept through 1,300 acres.

The flames burned one house and damaged several others. Officials evacuated 500 homes and shut down part of the Garden State Parkway for 12 hours.

"When I left, the embers were floating in the air and into my car," said Larry Hoff, whose house suffered smoke damage. "I was never so scared in my life."

Melody Ferguson had to return home during the evacuation in order to pick up some medicine and found her house shrouded in smoke. She was just able to make out the American flag she had raised in honor of her two children who are in the Marines.

"That was the only way I could tell it was my yard," Ferguson said.

But not all fire is bad.

The Pinelands' unique ecosystem adapted as the result of fire, and ecologists say periodic blazes are vital to the forest's health.

For example, some of the pine trees pop open their cones to distribute seed in response to high heat. In addition, pitch pines and shortleaf pines can survive even if all the branches have burned off, as needles can grow straight from the trunk.

Without fire, oak trees and other hardwoods would take over the forest and crowd out the pines, destroying a habitat for threatened and endangered species such as the tree frog and the timber rattlesnake.

"The ecosystem is a creation of fire," said Carleton Montgomery, executive director of the nonprofit Pinelands Preservation Alliance. "If you allow the Pine Barrens to change into something else, we're going to lose those unique communities."

State firefighters are very good at snuffing out the hundreds of smaller wildfires that occur each year in the Pinelands, most of them caused by human carelessness or arson.

In order to keep the forest in check, every winter they set larger "prescribed burns" on more than 15,000 acres of the Pinelands — a practice once used here by Natives to improve hunting prospects.

But critics say the state is too cautious in the interior, uninhabited sections of the forest, as the prescribed burns are so carefully controlled that they don't mimic the hot, natural blazes that renew the ecosystem.

One problem: more and more people are in the way. The Pinelands Commission, a state agency that regulates development in most of the Pinelands, has permitted 39,000 new residential units there since 1980.

Most are in places designated as "growth areas" decades ago by state law. But some of these areas were poorly chosen, Montgomery said.

A partial solution may lie in a bill pending in the Legislature, which would allow the state to conduct prescribed burns on private land, even against the owner's wishes if needed for safety reasons.

Bob Williams, a private forester with Land Dimensions Engineering, advocates a combination of burning and cutting selected trees.

"I don't think you can ever be Mother Nature, but you try to mimic some of those impacts" from natural fires, he said.

For many homeowners, the potential for danger clearly is outweighed by the chance to live in a tranquil setting between Philadelphia and the Jersey Shore.

Even those who have been evacuated, such as Larry Hoff, say they are here to stay.

"I wanted privacy," he said. "You're out here in the woods."