TRENTON - Those columns of smoke rising Friday over hundreds of acres of forest and grassy areas of Burlington, Cumberland, Ocean, and Monmouth Counties weren't caused by wildfires.

They were set - part of the New Jersey Forest Fire Service's efforts to head off wildfires, state officials said Friday.

Blazes were set across South and Central New Jersey, including Washington Township in Burlington County; Manchester and Eagleswood Townships in Ocean County; Millville, Maurice, Commercial, and Downe Townships in Cumberland; and Monmouth Battlefield in Monmouth County.

"Prescribed burning is part of a planned strategy that the state uses to reduce accumulations of undergrowth, fallen branches, and downed trees that can act as tinder and increase the severity of wildfires, making them difficult to control," said State Forester Lynn Fleming.

The burns "help protect lives and property and, at the same time, improve the overall health of our forests," she said.

The Forest Fire Service, part of the state Department of Environmental Protection's Forestry Services, expects to burn about 10,000 acres of forests and grasslands this season.

Just how long the burns will continue is unknown, said DEP spokesman Larry Hajna. The end date "is a moving target because of the rain and snow," he said Friday. "We were trying for a few weeks to get this launched."

The burns will continue beyond the usual March 15 cutoff. "But we can't go too late into the season," Hajna said. "We go as long as we can safely do it."

The controlled fires are generally conducted during the winter months to minimize the amount of smoke produced, and when weather conditions tend to be safer for them.

They burn brush, leaves, needles, and debris, but do not reach the canopy of the forest or cause significant tree loss, as wildfires do, officials said. They improve forest health by removing thick undergrowth and competing nonnative trees that can harm the overall health of the forest.

"Prescribed burning is just one practice that State Forestry Services relies on to maintain overall forest health," Fleming said. "When combined with insect and disease treatments, habitat restoration, and carefully executed management plans, our forests will provide a greater diversity of habitats for wildlife, and create safe recreation opportunities for residents."

Prescribed burns, which are part of New Jersey's statewide forest resource assessment and strategies, are carried out by firefighters under optimum weather conditions and with the necessary support equipment.

"Firefighter and public safety are our top priorities as we implement these burns," said State Fire Warden Bill Edwards. "Roads in areas where burns are taking place are clearly marked."

These burns help reduce forest fire risks ahead of New Jersey's prime wildfire season, which generally begins in early spring, when leaves and debris are abundant, tree cover is sparse, and conditions tend to be windy.

The practice also has numerous secondary benefits. It improves the habitat for wildlife, recycles nutrients into the soil, enhances the appearance of the forest, and improves the overall health of woodlands by removing dense undergrowth.

Most of these burns will occur on state-owned property, such as state forests and wildlife-management areas, as well as other public lands, officials said.