The urban jungle

Cities are gaining new respect for trees. Here’s how contractors are working with the City of Milwaukee to protect mature trees and make room for more on construction projects.

by Clair Urbain

Whether your work takes you to an established neighborhood or to a newly zoned industrial park, there is a good chance that trees stand in the way of fast, efficient progress.

Trees are sitting targets for removal in the name of progress. They suffer unintentional, but every bit as lethal, hits because no one on the jobsite – or the design room, for that matter — truly understands how trees live in the urban jungle.

Even when designers work mature trees into their site plans, many die within a few years because of the damage contractors commit during construction.

A generation — maybe two — passes before many trees in urban areas reach the size and grandeur that makes neighborhoods and business parks distinctive. The trees stand as sentinels, offering shade, protection and a welcome visual break from the otherwise gray canyons of the urban landscape.

They also provide benefits that save the community money in water runoff costs, cooling and air quality.

Fallen trees raise awareness
The City of Milwaukee learned how construction affects the health of its cityscape in a big way in 1978  when the contractors it hired finished a sidewalk replacement project in a section of a long-established residential area. It had hundreds of mature trees.

“When a storm came through in August of 1978, the city lost 90 trees in that area. The aldermen demanded that changes take place,” says Jim Kringer, forestry inspector for Wisconsin’s largest city.

To that point, the city’s forestry program didn’t deal much with construction issues. But when city officials learned the sidewalk reconstruction projects cut the support roots of the 50- to 150-year old trees and made them susceptible to blowing over, they implemented a program to help Milwaukee rebuild its aging infrastructure without sacrificing its mature trees.

It was the beginning of a career for Kringer as a “professional tree hugger,” as he puts it. Contractors who worked with him over the past two decades refer to him as “Mr. Woody”.

“When this program started, the City of Milwaukee was losing up to 400 trees annually to uprooting. Now, we see as few as two lost annually,” he says. “We save 99 percent of the trees involved with city construction.”

Understanding the urban jungle
In 1981, the City of Milwaukee  hired Kringer to learn the ropes of forestry management. he was charged with finding a way to prevent tree damage. “It took two years of talking with engineers, designers and contractors to understand the problem.

“Many had the attitude that trees were an obstacle; they could be hacked on, bumped into and chopped away or easily replaced in the name of getting the job done. We had to change that perception,” Kringer says. That was not easy.

Mike LaLonde, one of the owners of LaLonde Contractors Inc. a long-time street, sidewalk and local highway contractor for the city, says he and other contractors now have a whole different attitude about trees.

“When I started as a setup foreman, protecting trees wasn’t much of a priority for us. We did many things that caused additional expense because we didn’t watch out for trees,” he says.

For example, the slipform curb machine the company used to pour curb and gutter needed at least 1' of curb clearance to operate, which is typical for road reconstruction. That meant workers had to cut 1' back into the terrace to give the machine enough access to form the curb, but it tore up the brace roots of many otherwise healthy, mature trees.

“We worked on the equipment to move the rear track over and we relocated the curb mule so we could have zero clearance. Now, we can pour the curb without causing extensive tree damage,” he says.

Where the tree roots have grown right up to or even over the old curb, crews first tear out the street, then pull away the section of the curb next to the tree. From there, Kringer prescribes surgical-like cuts that minimize tree damage.

“Any cuts to tree roots are done with an axe. We do not allow mechanical root cutting because they can tear roots apart. Mature softwood trees like maples do not regrow support roots which are most likely to be cut when sidewalks and curbs are replaced. We closely monitor where roots are throughout construction. Our goal is not to disturb roots,” Kringer says.

How to save trees
Saving trees starts at the design phase of the project. Kringer analyzes the site, then works with designers and engineers to develop plans that protect the trees.

“If a sidewalk is raised because a tree root grew underneath it, we will change the summit of the walk so it gradually raises and falls over the root instead of cutting it out. We may replace the sidewalk with an arc around the base of the tree, or we may narrow the sidewalk – or even the road – by as much as 1' to protect the trees,” he says.

In some cases, a narrower curb head can save a tree. “A 7" curb head takes an additional 1" of root space from trees. We have gone to as narrow as a 4.5" curb head reinforced with rebar. We have even poured the curb as close as we can to the tree, then came back with a 10' straight edge that was pushed up against the curb by hand before it’s fully cured to move it next to the tree,” Kringer says.

Few contractors realize their actions affect tree roots. For example, vehicles parked in the shade of a tree compacts the soil, compromising the tree’s ability to soak up water and nutrients. Staging building materials under trees can suffocate roots, and in turn, the tree.

Roots are not the only part of the tree in danger during construction. Leaves and branches can be seared by the intense exhaust heat.

“We spent $15 on a 45-degree elbow to put on our concrete paver to prevent the hot exhaust from torching tree leaves,” says LaLonde. “Otherwise, we would have been fined thousands for leaf damage.”

Excavators, wheel loaders and dump trucks can severely damage the tree canopy that reaches across city streets. “In our contracts, we suggest contractors use asphalt trucks with conveyors instead of dump boxes. They need less clearance, which cuts the chance of branch damage,” Kringer says.

City crews also come in ahead of contractors and trim branches to a height of 14' above grade for clearance.

Underground utilities present ongoing challenges to tree health. In the past, tree vs. utility placement wasn’t always carefully considered, so gas, water and sewer lines and roots run together.

“In an emergency, sometimes the tree is sacrificed to make the repair, but we relocate utilities to prevent problems in the future,” says Kringer, “Any new tree must be planted 5' from gas and water shutoffs and 20' away from streetlights. We plant a tree only when we understand the site’s big picture.”

As curbs are replaced, cables that run along the street and near trees are installed inside a 1"- or 3"-diameter PVC conduit and placed behind the curb for easy access in the future.

City engineers are also incorporating green spaces in areas where there is none. As a street comes up for renovation, they add 6'x12' green spaces for tree planting.

It’s all in the spec
To protect trees, Kringer outlines the tree challenges on the job in the Special Provisions section of the spec and offers contractors ways to address them. “The methods outlined in the Special Provisions are based on what has been developed by the successes we’ve had through work with designers, engineers and contractors. Contractors must consider those provisions as they prepare their bids,” he says.

The Special Provisions section can run as long as six pages; it also outlines hefty fines if the contractor damages any trees during the job.

The penalties reflect the lost value and the cost for tree repair or replacement and are deducted from the contractor payment.

“We estimate the insured value of a 30" diameter elm tree in a good neighborhood at $40,000. The Common Council authorizes a charge of $100 per diameter inch be assessed to the contractor if the tree needs to be removed. In addition, the removal process requires two men and a boom truck, two men and a chipper, a ladder operator and a backfill crew just to remove the tree. Even though a new tree planting may only cost $400, the total replacement cost charged to the contractor can be as high as $10,000,” he says.

“Contractors often view the value of the tree as what it would cost to replace it. But if you can work around trees, they accentuate the value of your work. If all of the beautiful trees stay, they add value to the project.

“The Milwaukee Municipal Sewer District (MMSD) wants to double the number of trees in the city. The MMSD estimates that trees save $21 million a year in runoff management by absorbing 15.5 million gallons of rainwater that would have to be processed through the storm sewer system.

“It also estimates that the trees provide $4.4 million in pollution abatement and the equivalent of $2.1 million in cooling cost savings. That’s why trees are so important to the city. Besides, they help property values tremendously,” Kringer says.

Also check out "Minimize construction's impact on trees." 

Published in the September/October 2003 issue of Contractor Tools and Supplies magazine.

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