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Trees in Urban Design

Pittsburgh needs a green roof

Pittsburgh Post-Gazette
Wednesday, Nov. 9, 2005

By Thomas Hylton

Recently, city forester David Jahn asked City Council for $1.8 million in 2006 to remove dead street trees, trim existing trees, and plant new ones. That’s nearly three times his current budget.

In a city whose credit rating only recently emerged from junk bond status, Jahn’s request might seem frivolous. But if the issue is Pittsburgh’s long-term viability, few investments are as worthy and cost-effective as street trees.

Take energy savings alone. Cities are heat sinks. Urban temperatures are often five degrees above surrounding suburbs and rural areas. That’s because jam-packed rooftops along miles of black asphalt streets, interspersed with acres of parking lots, all absorb a tremendous amount of heat from the sun. Air conditioning buildings, which consumes one-sixth of the electricity generated in the United States, becomes far more expensive than it needs to be.

A study by four energy experts, reported in the Massachusetts Institute of Technology publication “Technology Review,” concluded that the two most effective ways to reduce urban temperatures in the summer are to use light colors for roofs and pavement and to plant millions of shade trees. Light colored surfaces reflect rather than absorb the sun’s rays, and shade trees reduce ambient temperatures: One mature tree can provide the equivalent of five 10,000 BTU air conditioners running 20 hours a day.

Computer modeling shows that the use of light-colored surfaces and shade trees in cities nationwide could reduce peak air conditioning use by 10 percent, saving hundreds of millions of dollars.

Of course, we’re talking about rows and rows of shade trees, carefully nurtured, 50 feet and more high. Pittsburgh is a long way from meeting that standard. A recently completed inventory shows the city has just 31,500 street trees, and most of them are only in fair condition. More than 1,000 trees are dead or soon will be. Minneapolis, a city with the same population and land area as Pittsburgh, has 250,000 street trees. Minneapolis spends about $8 million annually on urban forestry. This year, Pittsburgh is spending just $650,000 – and that doesn’t include planting any trees.

Politicians like to lavish money on glamour projects like the stadiums and the convention center. But if Pittsburgh aims to be a place where people live, not just visit, it’s vitally important to pay attention to the appearance of its neighborhoods. That’s why Chicago Mayor Richard Dailey has planted more than 300,000 trees since 1989.

Street trees are the perfect way to make neighborhoods green and inviting. Trees take up very little ground space, while their canopies stretch out over streets, sidewalks, and buildings. An oak or sycamore with a 2-foot diameter trunk can support a canopy five stories high, spreading over an area the size of a house.

Consider the Gothic cathedral. The nave is a huge indoor room framed by giant stone pillars, imitating tree trunks. The stone tracery forming the ceiling mimics the tree branches emerging from the trunks. By using the real thing—trees—Pittsburgh’s grid of streets could be turned into magnificent living cathedrals that change in beauty with the seasons.

With a clear vision and effort sustained over several decades, it is possible to give an entire town a green roof that will only improve with time. Viewed from top of Princeton University's Cleveland Tower, for example, the town of Princeton disappears under a green blanket every spring.

In European cities such as Amsterdam, Vienna, and Rome, shade trees are actually planted in the streets. Cars park in between them. Putting trees in the street forces cars to slow down, and it allows an even canopy to form over outdoor spaces.

Even utility wires shouldn’t be a problem, if they are insulated and bundled to reduce the clearance needed from tree branches.

In my small town of Pottstown, a group of us raised a half million dollars in the mid 1980s to plant and help maintain more than 1,500 new shade trees. For that relatively small sum, we have transformed the appearance of our downtown and surrounding neighborhoods. Some of the first trees we planted now have canopies that soar over two story houses and shade entire blocks. Our new land development ordinance requires one tree for every 30 feet of street frontage, and in parking lots, one tree for every two spaces.

On Monday, Pittsburgh Council voted to spend $109,000 in community development block grant money to plant new trees in low-income neighborhoods. That’s not enough. Trees should be an integral part of the city's infrastructure – as obligatory as water and sewer, and just as ubiquitous. If the city wants to enhance its future, Pittsburgh needs a comprehensive tree planting and maintenance program.



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