How old are our trees?

An ideal urban forest is made up of one-third young trees, a third maturing trees and a third large trees. Charleston's is a little out of balance, possibly because of Hurricane Hugo's toll in 1989.Age/Size | In Charleston | IdealYoung (less than 10 inches in diameter) | 56.1% | 33.3%Maturing (11-36 inches) | 42.5% | 33.3%Mature (more than 36 inches) | 1.4% | 33.3%

The homeowners at Congress and Hagood streets didn't like the oak blocking their view of The Citadel's football stadium just down the street, so they had it cut down.

Now Tobin Stewart and Daniel Tollens have been ordered by a city court to pay $3,200 in restitution.

They're the latest to learn just how seriously the city of Charleston takes its street trees. And why not?

A study by the U.S. Forest Service found that for every dollar the city spends maintaining its approximately 16,000 street trees -- trees along streets, in city parks and on other city lands -- it receives about $1.37 worth of benefits.

Trees cool buildings and sidewalks, reducing summer energy costs. They soak up stormwater, helping the city's occasionally inadequate drainage system. They remove carbon dioxide from the air. That's why no fewer than nine city employees have full-time jobs pruning, irrigating and monitoring these trees.

And while the city's urban forest is relatively young and healthy, its chief forester wants to see more diversity among its species. Live oaks, crape myrtles and controversial Sabal palms make up more than 70 percent of its trees.

Tending the urban forest

The city of Charleston spends almost $1 million a year to tend its trees, which number about 45,000.

About a third line the city's streets; the rest are found in public parks (West Ashley Park alone has about 2,000, while Hampton Park has about 1,000) and in city drainage easements and public buffer zones.

Danny Burbage started as the city's first "urban forester" in 1983, not long after local governments began responding to the Dutch elm disease, which decimated so many urban trees in the northeast.

Before Burbage was hired, someone else ran the city's "tree gang," but his job description was to plant and maintain trees.

Burbage's eight-member staff spends most of its time pruning. While trees in the woods can shed dead or dying limbs with no incident, this poses a danger when people or cars regularly pass underneath. Also, Burbage notes the pruning helps the trees stay healthier by ridding them of their struggling branches.

Unlike contractors working to prune trees for power companies, whose work often leaves unsightly notches, Burbage says when a city crew prunes a tree, it aims to do everything necessary for the health of the tree "and when they leave, it should look like they've never been there."

Of course, the tree that Burbage's department fusses over the most is the Angel Oak, the massive tree with its own park on Johns Island. Burbage inspects it monthly, and its network of lightning rods and support cables are adjusted once a year. Also, it gets an annual treatment of ground drenched insecticide to ward off pests, as well as an aerating treatment and a fresh 3-inch layer of mulch below its drip line to protect its roots from the thousands of visitors that frolic under its canopy.

Wayward cars claim about four or five street trees a year, while lightening and strong winds can take others. "Humans are perhaps the biggest problem," Burbage says, mostly because construction activity often damages their roots or trunks.

There's also a problem with Formosan termites, too.

"It's difficult to say how many have died because of Formosan termites because those termites will migrate toward a tree that's in stress first," Burbage says. "You can't always tell they're there." Unlike native termites, Formosans will eat live - not just dead - wood.

Paying their own way

The city's street trees have been the focus of two studies, paid in part with federal dollars.

One, done in 2000, actually inventoried the number, size and type of city street trees. The second, done about five years ago, built on the first by calculating the costs and benefits of the city's known street trees.

The 2000 study found that 84 percent of Charleston's possible street sites have trees, but Burbage says the city still is a long way from completing its urban forest. It currently is negotiating with state highway officials to continue planting trees down Calhoun Street.

The 2006 analysis -- done by the U.S. Department of Agriculture's Center for Urban Forest Research -- puts a price on how much trees give back by providing shade (and lowering cooling bills), absorbing stormwater runoff and offering aesthetic benefits.

Dr. Greg McPherson, who was the center's director at the time, says, "Our research in Charleston has shown that the municipal street trees provide $717,000 in annual benefits, about $47 per tree, and only cost the city $530,000 per year to maintain. That is a huge return on your investment."

The city's trees provide intangible benefits, such as better-looking neighborhoods, stress reduction, reduced crime, and recreational opportunities, McPherson says. "If we could put a dollar value on these kinds of tree benefits, Charleston's return on investment would be a lot higher. Right now we can't, but we are working on it," he adds.

Seeking diversity

James Ward, a landscape architect and assistant professor at the College of Charleston, says the city has more street trees today than it has historically -- at least judging from old photos.

"Street trees have been around for a while, but we're completely dependent on narrow confines for street trees at this point," he says. "Nature was a lot closer then than it is now. Street trees have become necessary because we paved it all."

Ironically, Burbage's greatest worry these days is the same sort of concern that led to his job's creation a generation ago: that a Dutch elm-like disease will emerge and claim a huge number of trees here.

"We need to diversify," he says, "but because they're so iconic, it's hard to convince Charlestonians not to plant live oak trees."

But Burbage says too many live oaks will leave the city vulnerable to some future disease that attacks a single species.

"We could lose 35 percent of our tree population, so it's good to have a diversity," he says. "There used to be a lot more elms in Charleston."

Choosing the right trees for a street is a balance between what the residents want and whether the city is aiming for a uniform look or a mix of shade and color.

Burbage won't plant a few trees, such as laurel oaks and water oaks, whose root systems are too shallow to hold the tree up in tropical winds. Also, Bradford pears are off the list because their limbs are too brittle. He also won't plant Chinese tallow in parks because it's so invasive.

The city has help: Charleston Trees, a committee of the Charleston Horticultural Society, raises money to plant more street trees.

The city plants about 250 more trees than it removes in a given year, and it prunes more than 1,700.

Still, Burbage estimates there's still room for about 10,000 more street trees. "If you drive down any street in Charleston, including the peninsula, you'll see gaps."

The city only plants from October to late March, when trees are dormant. Newly planted trees need more water during their first year, as their roots are getting established. Of all the trees planted, only 3 to 5 percent don't make it, a survival rate that pleases Burbage.

His department ultimately will use the $3,200 settlement from the illegally cut tree near the Citadel to plant more trees in that neighborhood.

Asked whether he plans to replant a tree precisely where the first was removed, Burbage smiles and says, "I'm giving some thought to that. I don't know how much insult I want to add to injury."

Cost-benefit analysis

What it takes to maintain Charleston's street trees:

$35 Approximate cost to maintain a street tree per year (pruning, planting, stump grinding, irrigation, administration, sidewalk and other infrastructure repairs, etc.)

$47

Approximate value of a street tree, including:

$11 value of its intercepting stormwater, helping the city comply with federal stormwater rules.

$8 Value of energy saving (both electricity and natural gas) saved because of its shade.

$0.50 Value of carbon dioxide and other pollutants removed, released or avoided by trees.

$26 Value of aesthetics, property value increase and other less tangible improvements.

$1.50 Value of carbon dioxide sequestration and emission reductions, minus carbon dioxide released during decomposition.

Tending the urban forest

Trees planted in the city last year: 354

Trees removed: 95

Trees pruned: 1,763

Source: Charleston's Urban Forester

What they're worth

$42.5 million Approximate cost of replacing Charleston's street trees (About $2,800 per tree)

Source: City of Charleston, S.C. Municipal Forest Resource Analysis by the Center for Urban Forestry Research

Tree contacts

To request pruning, report a sick tree or inquire about having one planted, call the city of Charleston's Urban Forestry Department at 724-7416.

Reach Robert Behre at 937-5771.