Five large tracts of land valued at about $72 million, which includes nearly 20 miles of Potomac River and Bay waterfront, is being acquired by Maryland as part of what Gov. Martin O'Malley called a "once in a lifetime opportunity."

In announcing the acquisition of the 9,242 acres, the governor also unveiled a new Internet-based mapping system called GreenPrint, which will direct future land protection efforts toward areas that are most ecologically valuable.

The five new tracts, which contain forested habitat for rare species and waterfront property for public access, were recently secured by The Nature Conservancy and the Conservation Fund. The state plans to purchase them with Project Open Space and federal money.

Four of the tracts, totaling 4,473 acres and known as the Province properties, are located in St. Mary's, Charles and Cecil counties, and include more than 19 miles of Potomac River and Bay shoreline.

The properties had been owned since the 1600s by the Maryland Province of the Society of Jesus. The Jesuits wanted to sell the valuable properties, but did not want it developed, so they negotiated a deal with the Conservation Fund.

The organization was interested in the properties for both their ecological values, and because they provide access for the new Capt. John Smith National Historic Trail, for which it has been a major advocate.

"These are important legacies," said Pat Noonan, chairman emeritus of the fund. "History reaches back to the Native Americans who lived here, to Captain John Smith's explorations, and the very founding of Maryland."

Also being protected is a 4,769-acre tract in Worcester County, which includes 90 rare, threatened or endangered wildlife and plant species. Known as the Foster tract-named for the family that has owned it for the last century -it is the state's largest privately owned forest parcel.

The deal was brokered by The Nature Conservancy, which has been working to protect land in the Nassawango Creek and Pocomoke River watersheds.

"It is vital that we do everything we can today to preserve our natural heritage for tomorrow," said Nat Williams, director of the Nature Conservancy of Maryland/DC. "Our natural capital is every bit as important as our economic capital, and it is crucial that we take the long-term view when it comes to our ecological heritage."

Taken together, the two separate acquisitions will more than double the amount of open space purchased since O'Malley took office nearly two years ago. So far, his administration has purchased about 8,175 acres.

To guide future land protection efforts, the state has developed GreenPrint, a mapping program that uses data about land cover; important habitats for birds and animals; areas important for water quality; and other factors to identify high- value areas for conservation. The GreenPrint website, www.greenprint.maryland.gov, makes the information available to everyone.

O'Malley said 21 percent of Maryland is already developed, and another 21 percent is already protected. "Our future will be defined by the choices we make on the remaining 58 percent of the land mass in our state," he said.

GreenPrint is designed to help make the best decisions on that land. Priority areas, such as most of five tracts the state plans to purchase, show up in light green. The GreenPrint criteria rated the Foster property highly because it was a forested tract adjacent to the Pocomoke and Chesapeake state forests, and therefore helped to secure a large, unfragmented forest tract.

Protecting large forest tracts and wetlands are some of GreenPrint's most important criteria. But the property is also highly rated because it is the home for numerous rare species, and because two-thirds of the state's forest interior-dwelling birds inhabit that watershed.

Once purchased, tracts become dark green on the map-indicating they are permanently protected.

O'Malley said the state may still purchase some properties not identified on the GreenPrint map because of they are historically valuable, contain high-value farmland, offer recreational opportunities or provide public access.

A portion of the Province properties were not identified as critical using GreenPrint, but were considered valuable because of their potential for recreational water access.

The website allows visitors to see the amount of high-priority areas in each county, and how much of it is protected. Conservation groups can also use the information to prioritize their land programs.

"GreenPrint is a national model," Noonan said. "It is important that it succeeds, and it is important that it be replicated across the nation and become an international success. I have a philosophy that haphazard conservation is worse than haphazard development."