NORTH WATERBORO -- Dale Tarbox says he's glad to share his small corner of Maine, a picturesque pond with clear water and plenty of bass.

So he allows anyone to use a dirt road and trail across his land for launching kayaks, canoes and small motorboats on Isinglass Pond. "It doesn't bother me, as long as they respect it," he said.

But he's had to think twice this summer, Tarbox said, as he stood on the road near a pile of discarded roofing shingles, a half dozen empty beer cans and the carcass of a dead skunk. Posted on a tree above the shingles is a yellow "No Dumping" sign, with a clear warning that abuse could result in loss of access.

"We put those up (in May) after they brought the hot tub in," Tarbox said.

Landowners like Tarbox are the keepers of a distinctive Maine tradition -- open recreational access to privately owned woodlands and waterfronts. But it's a tradition that may be in jeopardy, as lands are subdivided, populations spread out and abuses test the limits of landowner hospitality.

"There is absolutely no question that what makes recreational opportunities accessible in the state of Maine are the private landowners," said Dan Scott, a captain in the Maine Warden Service who works with property owners. And, he said, "there definitely is an increase in interest about how to post lands or keep people from recreating on their property."

An estimated 18,000 family forest owners posted restrictions on the use of their land in 2006, three times as many as in 2003, according to a report prepared earlier this year for the Governor's Council on Maine's Quality of Place. An estimated 36 percent of small woodlot owners had posted their land as of 2005, up from 15 percent in 1991, it said.

Eroding access can affect everyone from hunters to birdwatchers, and snowmobilers to kayakers. It also carries potentially large costs for rural economies that rely on opportunities for outdoor recreation.

Unlike other rural states with vast swaths of federal lands, Maine is 94 percent privately owned. The state instead has relied on an old, unwritten social contract that goes back to a time when the state's forests were owned by a small number of timber barons: Recreational access is allowed on any open lands that are not specifically posted as off-limits. Landowners, meanwhile, have strong legal protection from any liability should a visitor get injured on their unposted property.

Maine's cultural tradition of permissive use is at the core of Maine's character and quality of place, said Richard Barringer, chairman of the Quality of Place council. "To our knowledge, it's unique, not only in this part of the world, but in the world. There is nothing like it."

Tarbox, a Maine native, had never really questioned the tradition.

"That's the way I grew up," he said. So he understands that none of the people who use his land to visit the pond ever thank him. "They've used it so many years, they think it's there for them."

He said, he's sure those are not the same people who dumped the shingles, or the old hot tub and other trash that has shown up this year.

Tarbox said he would still hate to shut off the road. But, he added, "I just can't keep lugging stuff off all the time."

Illegal dumping, while somewhat of a rural tradition in its own right, is one of the primary reasons landowners post no trespassing signs or block roads, according to the state report. Vandalism, damage from ATVs and hunters coming too close to houses are other frequently cited reasons, it said.

Contrary to popular belief, according to the report, research by the University of Maine found that landowners from other states were no more likely to post land than Maine residents.

In the Greater Portland area, development of open spaces is a major factor.

"It's pretty difficult to do an off-road ride in Portland today," said Tim Corcoran, a rider and an owner of Gorham Bike & Ski in Portland. While you can get around the new houses and no trespassing signs, he said, "it's not easy to put a loop together."

Population growth and declining access in the Portland area seems to be putting more pressure on lands in nearby rural communities, said Standish Town Planner Bud Benson.

A privately owned trail to the Saco River where locals had launched canoes for years is one of the special places recently closed off because of overuse and abuse, he said. Many see the loss of access across private lands to publicly owned rivers, lakes and coastal waters as one of the biggest threats.

"Down the road, it's going to become a bigger and bigger issue," Benson said.

Recreational users are organizing to reverse the trend.

In South Portland, for example, mountain bikers have been repairing and cleaning trails to help persuade landowners not to shut off access, said Calvin Weeks, who heads a local chapter of the New England Mountain Bike Association. "Nine times out of 10, it irons it out enough so that we are able to continue access," he said.

ATV riders have organized to police trail use and prevent damage in the wake of a 2003 law requiring them to get permission to use private land.

And snowmobiler and hunter organizations strongly promote respect for landowners.

Josiah Pierce, a woodlot owner in Baldwin, said despite the abuse by a few, recreational users overall are more educated about the state's permissive use tradition than they used to be.

"I have more people come and ask me permission to hunt on my land than I ever did before," he said. And Pierce regularly gets thank-you notes, and sometimes even deer meat, after each hunting season, he said.

Land conservation funds are increasingly steered toward recreational opportunities, including waterfront access for fishing and launching boats. And last fall, the Baldacci administration hired Maine's first full-time director of landowner relations.

Funding for the position is due to run out in 2009, although the Quality of Place report recommends continuing and expanding the program.

Robert Duplessie, a former lawmaker from Westbrook, holds the job and tries to resolve a steady flow of conflicts before angry landowners cut off access. He often helps post signs that say "No Dumping," "Foot Traffic Only" or "Access by Permission Only," a preferred alternative to the "No Trespassing" signs available in hardware stores.

"There's been some tension in some areas." But, Duplessie said, "I think there's been some improvement."

Duplessie has been trying to help Tarbox, and he arranged for a local ATV club to haul away the hot tub. "I want to keep this access point open to the pond so people can use it," Duplessie said.

Luckily for the state, he said, Tarbox does, too.