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If the Southeast's cities and suburbs grow much like they have in the past, the region will be in trouble in 50 years.

That's the conclusion of a new study by North Carolina State University and U.S. Geological Survey that forecasts the extent of urban growth here based on historical patterns.

Asked to summarize the study's findings, researcher Jennifer Costanza said, "The current pace of urban sprawl in the South, if it continues, will lead to massive, unsustainable cities that are unpleasant to live in."

While large older Northern cities, such as Boston, New York and Philadelphia, have dense, tall buildings in their centers, the Southeast has grown the fringes of its suburbs.

"The South is also unique because almost all of the growth has occurred in the past few decades during a time when most people have had cars," Costanza said, "while the large cities in the North saw most of their development occur before World War II, when cars were not such a necessary part of how we get around."

The study was launched to find which places in the Southeast could be most impacted by urban growth so that conservation managers could factor that into their plans to adapt to climate change.

"We knew that urbanization could make it a lot more difficult to implement conservation plans that allow wildlife to have the space they need to deal with a warmer climate in the future," she said. "It was also important to us to produce data and maps of future urbanization that could be used by people in a variety of fields."

The forecast was based on changes reflected on a series of earlier maps, sort of like an old cartoon flip book. The patterns in more than 300 individual regions then were mimicked for future growth and stitched together to get a complete picture of the South.

The study defines an urban area not by population density but by the density of roads, so downtowns, suburbs and exurbs are all included, she said.

Currently, about 3,000 square miles - or 3 percent - of the Southeast is urbanized, but that could double or almost triple by 2060 if growth continues as usual.

Much of that is expected to be centered along the Interstate 85 corridor, which has fewer geographic constraints, such as coastlines, wetlands, steep slopes, or large protected areas like the Smoky Mountains National Park.

"In and around Charleston, our model suggests that the changes may happen fairly fast, too, and would follow the coast and move a little bit inland," Costanza said.

There's more at stake than humans' quality of life. Because urban growth will claim forests and fields near cities, species that need large blocks of natural land will be threatened, Costanza said. For instance, projections show that coastal pine forests that are home to the endangered red-cockaded woodpecker will be harmed by urban growth.

"Also, the Southeast has some of the most biologically diverse habitats in the world," she added. "If urban land encroaches on this habitat, any of the rare and unique species that live there will be negatively impacted."

Metro areas, such as Charleston, have created an urban growth boundary, and other cities have discussed so-called smart growth strategies.

The Charleston metro area even created its first regional plan two years ago - a plan that urges compact, mixed-use development in existing neighborhoods and conserving agricultural land and open space.

Harun Rashid, a senior planner with the Berkeley-Charleston-Dorchester Council of Governments, said the plan considers how to make communities where people can live, work and play without affecting the surrounding roads as much.

He noted that projections show the tri-county area grew by 21 percent between 2000 and 2010 and could add more than 200,000 more residents by 2040 - almost as many as currently reside in Charleston and Mount Pleasant. "The crux of this land-use exercise was to see how we could better allocate this growth," Rashid said.

But the plan is simply a vision for the future, not a regulatory document, and Costanza has her doubts about whether the South's future urbanization will differ much from its past.

"I think the change has to be fairly dramatic," she said. "For cities to be sustainable, I think that the way urban planning is done in the South needs to see substantial changes that encourage higher density development."

Reach Robert Behre at 937-5771.