PITTSBURGH - The last undeveloped, privately owned island in Allegheny County has been purchased by a nonprofit group that plans to preserve it.

Sycamore Island, more than 14 acres in a bend in the Allegheny River near Pittsburgh, was acquired Friday by the Allegheny Land Trust, the group said.

The island has expanded through the years due to silt and sediment deposits. A 1959 bill of sale indicates it was just 6.7 acres.

It contains a floodplain hardwood forest - mostly silver maples, among the rarest plant communities in the world, said Roy Kraynyk, the trust's executive director. A statewide list of ecological sites, the Pennsylvania Natural Diversity index, shows all floodplain forest as imperiled.

"The conservation of Sycamore Island . . . ensures that this undeveloped island and its ecological, educational and recreational benefits will be forever protected," Kraynyk said.

He said the organization hoped to use the island as a demonstration site or to teach about the removal of invasive species and improvements in river water quality.

The group also said it planned to remove debris deposited by floods and the remnants of a restaurant that operated on the island before flooding caused by Hurricane Agnes destroyed it in 1972.

The trust bought the island from Mirric Realty Inc. for $250,000, using a grant from the Colcom Foundation in Pittsburgh.

Recreational boaters frequently visit Sycamore Island. Its conservation will offer the public the opportunity to visit a wild, natural island in an urban county, a news release said.

Since 1993, the Allegheny County Land Trust has bought and protected more than 1,350 acres in 18 municipalities.