In an old Bethlehem neighborhood, mature linden trees cast a cool shadow on the slate-roofed houses and frame the streets with a leafy canopy.

A picturesque image to be sure, but the foliage haunts Bethlehem's new urban forester, Cindy Smith.

Hidden by the leaves of the healthy linden trees, a tall leafless one stands dead -- probably strangled by its own roots. If left to nature, the tree could fall on nearby houses, parked cars or even one of the neighbors walking their dogs down Chestnut Street.

"This one has to come down," Smith said.

It's a decision that breaks Smith's heart, but she knows the tree will be replaced with a younger, healthier linden. And these are the types of decisions Smith, who started her job in March, wants to make before a tree becomes an immediate hazard or a neighbor complains.

Smith, with the help of the Montgomery County extension office, is launching a tree census that aims to count every single tree along Bethlehem's 300 miles of streets. She'll record the size, species, location and condition.

The information will give the city a better picture of the trees it has and what it needs to do to become a more environmentally sustainable community. At a time when global warming colors the political debate, communities across the nation have been turning to trees as a way to go green -- Los Angeles, for example, has launched a campaign to plant a million trees.

Trees absorb carbon dioxide, a main contributor to greenhouse gases that most scientists point to as a cause of global warming. Trees also absorb rainfall so that runoff doesn't clog storm water drains, and they reduce energy bills by providing shade.

But the first step is taking stock of what a city has. Communities like Allentown and Easton have done inventories, but Bethlehem is taking it a step further.

The tree information will be layered on top of computerized maps that the city is building in its Geographic Information System, or GIS. From there, Bethlehem can do anything from developing a tree care program to calculating the amount of carbon dioxide the trees are sucking out of the air.

While not widespread in Pennsylvania, tree counting programs are common in the Midwest, California and larger cities. New York City, for example, used its census in 2006 to show that it increased the number of trees by 19 percent over a decade to 592,130. Analyzing data, the U.S. Forest Service calculated a $122 million annual benefit for things such as energy savings, storm water absorption and increased property values in the Big Apple.

"Communities have been doing this for years, and it's become more advanced," said Julianne Schieffer, urban forester for the Montgomery County extension office. "More communities are realizing the importance of it."

The inventory will allow Bethlehem to develop a tree care plan that helps the forester decide if trees might need a bit of trimming to keep them healthy or need curb cuts to give roots more room, or if diseased trees might have to come down.

What's wanted is a tree that holds up to the pollution that vehicles emit and fits in an urban space. Fast-growing trees such as silver maples, for example, can cut into telephone wires if not properly placed; others will buckle the sidewalks.

But what Smith wants the most is diversity. Cities that rely heavily on one type of tree could be left treeless if a blight, like the Dutch elm disease, strikes.

That's not to say that the single species of lindens that line Chestnut Street should go. It's just that the next street should have other species. And it does -- a stone's throw from the lindens are sycamores.

"You don't want too many trees of the same kind, and you want trees of all different ages," Smith said. "The challenge we have in Bethlehem is that we don't know what we have."

An inventory can be expensive, with contractors charging $5 to $25 a tree. So Smith, along with city's Elm Street manager A.G. Pitsilos, are doing it alone for now. They're starting in west Bethlehem -- the inventory is mandatory for a state program aimed at sprucing up that neighborhood.

Pitsilos hopes to complete the inventory in the neighborhoods west and northwest of the historic downtown by the end of the summer.

"We're counting one tree at a time," Pitsilos said

How long it will take to complete an inventory of the entire city is still uncertain. They still must develop a budget for it and decide whether to use volunteers or interns to help with the work.

Allentown's head arborist, Randy Fey, understands such fiscal constraints. His city probably hasn't done a full inventory in 20 years. He's working on a plan to do another soon, using the GIS system if the budget allows it.

Over the years, Allentown has done smaller inventories. They recently counted 224 trees of 58 species in West Side Park, which will celebrate its 100th anniversary this year as the city's oldest park.

As she travels Bethlehem's streets, Smith argues passionately about the benefits of trees -- they suck up the rain and reduce the need to build bigger sewers, they reduce energy bills by cooling off homes with their shade.

But her most compelling argument could be the stunning view the lush lindens give Chestnut Street.

"I get goosebumps every time I go down this street," she said, pointing to the overhead canopy. "It's just simply gorgeous."

nicole.mertz@mcall.com

610-861-3614

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