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City Trees Can Get By With a Little Help From Their Friends

January 18, 2012

My dad kept a ficus tree for 27 years before it grew too tall and too wide to keep indoors during the winter months.

I was convinced that tree was his first child. My dad kept up on watering, cleaned out the sparse dead leaves when necessary and, in the summer, staked the tree container in our backyard to avoid damage from strong winds. Among the vegetables in his garden and the perennials we planted together each spring, it was quite obvious that ficus meant a lot to my dad.

When he decided to give his tree away for indoor space limitations, my dad posted ads in the classifieds for an appropriate and trusting new owner. Although he was giving away the tree at no cost, my dad screened the callers with questions to be sure his ficus tree ended up in the right hands.

Like my dad's ficus tree, all trees need proper maintenance, care and love. But some trees, like those planted in urban environments where they endure more challenging conditions, need a little extra TLC.

City trees, such as the frequently-planted honey locust, Bradford pear and red maple, encounter a variety of challenges in urban settings - concrete surfaces restrict the space in which trees can expand as they grow, construction debris and equipment decrease the quality of soil, exhaust pollution lingers in the air and heat builds up among crowded, highly populated areas.

Additional problems occur when high winds swoop through tall buildings, breaking branches off trees; when children and vandals tear off branches from park trees and when road salts leak through sidewalk cracks, disrupting nutrient absorption among the tree root systems below.

The main problem, however, is restricted root zones. In urban settings, trees' roots must compete within a small amount of space due to massive amounts of pavement and sidewalk surfaces.

"Tree roots disrupt sidewalks, trying to find nutrients and moisture," says Greg Mazur, The Davey Tree Expert Company's Tech Advisor. "The rule of thumb for the size of the root zone of field grown trees is 1½ to 2½ times the height of the tree," he says. "A small tree can have up to a 30- to 50-foot root zone, but in an urban setting, it generally only limited to 3 or 4 feet wide."

Unfortunately, the average tree in an urban/city area has a life expectancy of only eight years - a mere fraction of forest tree life spans. The poor growing conditions of many urban environments greatly reduce trees' life spans and sizes, limiting their ability to reach their full genetic potential. But since trees provide so many benefits, including cleaner air, shade, stormwater infiltration and carbon sequestration, they are important additions to urban environments. With proper care, city trees can potentially last as long as their cousins in wooded habitats, providing countless emotional, environmental and health benefits for many years.


One new piece of technology urban planners have used in the past three to five years that helps city trees by improving their root space is the Silva Cell Tree and Stormwater Management System. "It resembles interlocking milk crates, which prevent shifting," Mazur says. Artificial soil fills the interlocking, porous crates to avoid compaction. According to Mazur, this "fabricated chamber" might reach 20 by 20 by 3 feet.

"The system accomplishes two main things," he says. "The designed root space gives trees a much bigger expanse to grow and allows more oxygen to reach the tree roots."

Mazur says vertical drains and vertical mulching also help urban trees. In this process, professionals secure a well-perforated plastic sleeve in the soil near the base of a tree to allow air to better reach tree roots. Strategically placed holes (filled with non-decomposable material) around the base of the trunk may also improve the tree's ability to grow.

Another challenge city trees face is salt runoff. Air borne road salt residue can turn evergreens pale green and yellow the needles, which can remain an eyesore into the spring. The salts that trickle down to tree root systems can cause desiccation (drying), which alters trees' mineral nutrition balance and soil structure. Healthy, mature trees withstand road salt damage better than un-established or stressed trees, and species with thick bark suffer less severe air-borne salt damage. However, careful planning and placement can prevent all plants from encountering the problem.

Although calcium chloride is a more expensive type of salt than sodium chloride (a more common alternative), calcium is less harmful to plants. If sodium chloride must be used, mixing it with sand, sawdust or similar materials can reduce its negative effects. Supplemental watering, when appropriate, can also help wash away salts from tree leaves.

Healthy trees provide several benefits to people, their environment and their overall quality of life. My dad kept his ficus tree healthy for 27 years - more than half his lifespan at the time. As his careful attention to detail and proper maintenance resulted in a healthy, long-lasting ficus tree, more consideration to neighborhood and city trees can result in a long-lasting, flourishing community full of happy, healthy people.

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