Each spring, small armies of volunteers fan out across the Jersey Shore's beaches armed with what may be the best defense against beach erosion, often caused by such ferocious foes as Hurricane Sandy and Nor'easters: tiny wisps of grass.

But the volunteers' immediate goal is more pastoral: to plant thousands of American beach grass plants in a matter of hours upon some of the miles of dunes that line the state's 127-mile coastline.

Like similar events planned up and down the shore in the coming weeks, which get the public involved in the work of digging a six- to eight-inch-deep hole in the sand and then inserting the rooted stems or "culms," more than 100 volunteers converged on Island Beach State Park in Berkeley Township, Ocean County, for three hours on Saturday to plant 30,000 of the American beach grass plants in specific dune areas of the coastal park.

"This kind of work is so critical to growing and preserving the dune system," said Bianca Charbonneau, a University of Pennsylvania doctoral candidate who has spent the five years since Hurricane Sandy studying dune grass and its effects helping preserve beaches - specifically, those at Island Beach State Park.

Dozens of beach towns that line New Jersey's Atlantic shoreline mostly have engineered dune systems that are only semi-contiguous and range in length from a few blocks to a couple of miles.

But Island Beach State Park provides one of the best examples of the contiguous natural dune system that once lined the state's entire Atlantic coast.  Stretching for more than  10 miles, the dunes are part of the largest reserve of undeveloped barrier island remaining in New Jersey, and one of the largest in the United States.  Nearly a million people a year visit the park to enjoy its bathing beaches, fishing areas and hiking trails.

For her study, which was published in January by the Journal of Applied Ecology, Charbonneau collaborated with four graduate students from universities in the region.  The thesis looks at how dunes respond to storms and the role of plants in stabilizing them. She wanted to know whether  dunes vary in resistance to erosion based on what plant species may be stabilizing the forefront area of the dune.

"In general we know that plant roots are integral for holding a dune together and that leaves of the plants provide surface drag when you have wash over from a storm. But what we didn't know is whether there were specific species differences in the amount of erosion control due to differences in morphology and density," Charbonneau said.

In the immediate aftermath of Sandy, Charbonneau found - to her surprise - that an invasive species of beach grass called Carex kobomugi, or Asiatic sand sedge, that park managers had been trying to eradicate at Island Beach for decades seemed to better hold the dunes together.  Across the park, approximately three meters more dune was lost in native grass stands compared with areas with the invasive species, Charbonneau said.

Though it's highly unlikely that the state Department of Environmental Protection, which oversees the environmental management of the park, would ever reverse its long-standing policy of not  introducing invasive nonindigenous species to Island Beach and other areas, Charbonneau's findings could help in determining future species management at the park, officials said.

And while removal of invasive species such as the Asiatic sand sedge was attempted in the past, the park isn't currently actively removing it,  said Caryn Shinske, a spokeswoman for the DEP.

In the meantime, Shinske said that the organizations Friends of Island Beach State Park and Barnegat Bay Partnership, which annually run the dune grass-planting event, purchased the plants for an undisclosed amount from a grower in Cape May and will stick with planting the American beach grass - or Ammophila breviligulata.  Grown in bunches, it is a long, narrow, leafy variety that grows two to three feet high.  It has a spike-like seed head that is about 10 inches long and appears in late July or August.

As the beach grass grows, its roots - called rhizomes - form a weave within the sand which in turn forms a core for the dune.  The blades of the grass on top of the surface also act to trap windblown sand, allowing the dune to retain the sand and grow naturally.

"Dune grasses are vital to protecting the island because they hold the dunes together with their web-like root systems," said Jen Clayton, the park's manager. "The park has been concentrating on fortifying vulnerable areas around the numerous paths to the beach, to keep public access open without compromising dune stability."

Farther south on the shore in Avalon, Cape May County, so necessary are the volunteers who show up to plant dune grass for that town's annual planting day on April 1 that they will get a free lunch, according to borough administrator Scott Wahl.

"The dune grass plantings are not only valuable from an ecology and resiliency standpoint, they are also important for education," said Wahl. "Each year, Avalon receives assistance from student organizations, scouting groups, and other volunteer organizations who have fun planting the dune grass but also learn about the fragile ecosystem in the dune and how dune grass benefits nature."

Avalon has one of the few maritime forests remaining on the East Coast in its dune system, which includes a freshwater pond and a high dune area that is taller than a five-story building.  Along with its beach access paths, the town has also created a dune and beach trail within the forest to allow for greater education opportunities and "appreciation" of the dunes, Wahl said.

"The dune grass planting events are not possible without the assistance of our volunteers. We plant thousands," Wahl said, "... which would be a monumental task for our public works department.  We hold these efforts twice annually and they result in pronounced environmental and resiliency impact on the borough."