The Perils Facing Our Urban Trees

Arlington is a very urbanized County and is becoming denser every year. The residents care a lot about maintaining our environmental and natural health, so trees play a big part in design. While managing a traditional forest comes with significant management obstacles, the addition of people and hardscape complicate the care for our trees further. Here’s how we’re addressing some of the major issues facing urban trees in our County.

Tree Damaging Sidewalk

Trees will find a way when soil space is restricted, damaging sidewalks and roots simultaneously. Photo courtesy of Vincent Verweij.

Soil Space and Quality

Problem: Urban soil tends to be restricted by surrounding sidewalks, buildings and compacted soil. Trees need uncompacted, healthy soil to expand their roots if we want them to grow to a size where they provide the full benefit trees give us.

Potential solutions:

  • Expand soil space through larger tree pits and innovative techniques, such as continuous soil panels and structural cells.
  • Remove and replace poor soil.
  • Prevent degradation of soil by protecting tree soil areas from further compaction and pollution.
  • Plant smaller trees.
Soil volumes diagram.

Soil volumes should be optimized to get the greatest benefit from our trees. Photo courtesy of Casey Trees.

Utility Tree Pruning

Typical utility pruning. Photo courtesy of Vincent Verweij.


Problem: Overhead and underground utilities pose major obstacles to trees. Both branches and roots can interfere with utilities, and most of the time, the tree loses the battle when a power line is struck by a branch. What is important to know is that, particularly electrified lines, sag under high demand loads, and can touch branches that seemed otherwise out of the way. This is why Virginia Dominion Power often clears trees beyond the immediate reach of the power line.

Underground utilities suffer from different conflicts, and most of them occur when the lines are buried shallowly and a tree is planted, or a stump is ground, without checking whether a line runs through the ground.

Potential solutions:

  • Plant small trees under power lines only. Where little space is available, it may be more prudent to look for better planting sites.
  • Bury lines underground. While this is an expensive solution, it’s being performed in many communities.
  • Always call Miss Utility to locate underground lines before planting or removing a tree.
Fallen tree on a car.

Cars are a common victim of tree failure. Photo courtesy of Wikipedia.

Lower Threshold for Risk

Problem: When assessing risk, certified arborists always assess what the potential target (such as a car, pedestrian or building) may be. In an urban environment, the amount of targets is significantly higher, and this creates a lower threshold for accepting risk. This can result in the removal of trees in urban areas that may not have been necessary in less dense settings.

Potential solutions:

  • Provide the right environment for trees to develop in a healthy fashion, reducing defects from decay.
  • Respect the space of the tree. Enough aerial space should be given to our trees to reduce the potential conflict with surrounding targets.
  • Where necessary, prune hazardous limbs and address defects before it’s too late.
  • Always assess risk realistically. For example, where a leaning tree may appear hazardous, strong root systems compensating for lean can help alleviate risk. On the other hand, a species known for failure can look perfect, but drop a limb without warning.
Bulldozer cutting down trees.

Photo courtesy of Vincent Verweij.

Development Pressure

Problem: Whether or not residents view development in itself as a problem, large developments can be harmful to trees. Disregard for the ecology of trees and how to work with them can cause major damage to our tree canopy.

Arlington works closely with developers to ensure survival of trees are retained after development, but disturbance can cause unexpected negative effects on our tree canopy.

Potential solutions:

  • Education of developers and construction companies can help them understand the value of trees and their needs.
  • Health assessment of trees by certified arborists to determine the potential for survival of the trees through development can help paint a realistic picture of what’s feasible, and what isn’t.
  • Continued enforcement of tree protection policies and respecting the critical root zones of trees can help retain the soil and space for trees to be protected.
Determining critical root zones diagram.

Determining critical root zones.