EDISTO ISLAND -- Every time Henry Ohlandt sets foot on Raccoon Island, he gets that tingle.

The canopy of live oak and hickory folds over him, the palmettos sway, the smell of the ocean wraps around him in the wind. From the graze field near the old hunting lodge the mules come clopping over, those moon eyes watching like shepherd dogs.

"It's one of a kind," he said. "It's like going into another world."

So far, he's right. Raccoon Island is a one-mile-long slice of the verdant Lowcountry that the Ohlandt family put into conservation easement on the Edisto River, just behind the Pine and Otter barrier islands in the vast St. Helena Sound. In other words, right in the heart of the ACE Basin. The basin is a one-of-a-kind, public-private, ecological preserve of nearly a quarter-million acres of the deltas of the Ashepoo, Combahee and Edisto rivers -- the very nature of the place.

The preserve is considered one of the nation's "treasured landscapes." The public-private collaboration that created it is considered a groundbreaking achievement.

This year is the 20th anniversary of that creation.

Not so coincidentally, Raccoon Island sits just downstream from Prospect Hill, where in the late 1980s, a developer's plans to open a 120-slip marina in what was then remote tidelands ignited the conservation effort that led to the ACE Basin Task Force.

The island sits just upstream from Edisto island communities where similar, smaller-scale developments are being fought now by families who have lived there for years. The narrow dirt road to Raccoon Island used to be little more than a path, with three or four homes back in the trees on large lots. Now, there are runs of homes, "for sale" signs and a bulldozer clearing out trees to build another one.

That's the ACE Basin today. The vast delta that the Nature Conservancy lauded as one of the last great places on earth, the place often called South Carolina's Yellowstone, is coming of age facing a new era of threats. Rising sea level and salt water intruding into the groundwater are expected to slowly push the marshland deltas inland, toward more urban areas. Meanwhile, development expanding from those inland areas is inexorably chewing away at its edges.

Deep-rooted

The basin's unique quilt of conserved lands is about two-thirds of the land in the lower heart of the delta and looks more like a patchwork than an intact preserve. Most of those 200,000 or so acres are privately held lands donated into conservation easement by about 130 families like the Ohlandts.

They did it out of a deep- rooted love for their land and way of life. But over the next years, the families who agreed to those easements will change generations. Succeeding generations aren't always so closely tied to a piece of land.

Conservation easements are themselves a quilt of different contracts with different terms. Most have not yet faced serious lawsuit challenges. Every easement that could get overturned would set a precedent, making it more difficult to defend the rest. The groups that hold the easements are non-profits with limited funds.

"If they don't have the depth and capabilities to resist challenges it could unravel the whole quilt," said Mark Purcell, ACE Basin National Wildlife Refuge manager for the U.S. Fish and Wildlife Service. Meanwhile, property values in the basin have soared.

"The original property owners had that land ethic, that desire to protect the land, and it took a great effort (by them). But I think it's harder now to protect land than it was then," Purcell said.

'It never ends'

The threats to the marsh and its wildlife from sea rise and salt groundwater intrusion already are real to coastal people, who can point to shoals and small barrier islands that have disappeared under the sea in their lifetimes. The Ohlandts can no longer use the old freshwater well on Raccoon Island. Four miles inland, the well water at Purcell's office has begun to taste brackish.

From the other side, development continues to push at the headwaters of the three basin streams outside the conserved areas, increasing the threat of runoff pollution.

"We know in the upper ACE Basin things are going to happen that we have no control over," said Dean Harrigal, S.C. Natural Resources wildlife biologist who manages the state's Donnelly Wildlife Management Area in the basin.

The town of Yemassee has annexed a 1,300-acre plantation planned for development just south of the basin. A controversial construction debris landfill is in planning for Adam's Run in Charleston County, just north. The Edisto Island Land trust leaps from one preservation fight to another to stop waterfront development along the river. Every day more pleasure craft are "rooster-tailing" wakes up and down the waterway.

Plans are under way to complete the widening of U.S. Highway 17 from a two-lane country road to a four-lane parkway through the basin, a necessary safety move but one that could very well bring development on its heels. A recently deeded conservation easement left the commercial strip along the road out of the conserved area. Gated communities are under way in Beaufort County along the waterfront and watershed.

"It never ends. Every day you wake up with, 'Oh my God. Who would have come up with that ill-conceived plan?' " Charles Lane, one of the original organizers of the basin and a member of the ACE Basin Task Force, said.

'A working landscape'

What the basin's future has going for it is the same thing that created it. It's not a park; it's a way of life.

The waterways are open to commercial fishing, as well as recreation. The public lands are wildlife tracts open to hunting and other sports. The large plantations that make up most of the basin are farmed for timber and crops, hunted for deer, turkey and waterfowl. The place was created with the notion that keeping the land intact for those uses enhances its economic value, as well as its natural value.

"It's a working landscape, where people and nature co-exist. It was a different way of looking at conservation altogether," Lane said. "The basin has a culture, a history and a way of life, and the only tools we have to keep it is the willingness of the property owners. The people live in these areas because they want to live here."

The deed for Raccoon Island is in the name of the Ohlandt family. The family Thanksgiving is held there each year. The children each use it for occasions of their own. The grandchildren want their birthday parties out on the island with the mules, where the wind chimes on the old lodge are made out of oyster shells, the place where "when the wind's right and tide's high, we can hear the ocean," as Beth Ohlandt, Henry's wife, said.

"I don't know how much they realize what they have out here. But they all realize what they've got. They have no other place to go for this experience," she said. "And that's what I think we want for the ACE Basin, don't you think?"