Tree obstructions can take on many forms, including well intended structures installed under the guise of helping trees.
Tree grates if not managed can result in stem girdling and trunk failure. The concrete walled tree vaults have also been known to produce dense girdling roots, which can expose the tree to the risk of failure as it matures.
Click on the link to read further on tree guard girdling:
Stems & Object Consumption
Trees have the ability to consume objects as they expand their trunk diameters. Some species are more capable of this skill than others. Manitoba maple trees have been known to consume entire chain link fences into their stems, and show no signs of damage to the exterior bark in future years. The white spruce tree shown in the image above, self seeded underneath some decking and was allowed to grow to maturity. This tree could have been easily removed when it was a sapling. Now its compromised structure is at an increasing risk of failure, and it is difficult to remove the tree without putting an arborist at risk. The deck board has effectively created a back cut as a chainsaw would, and with the right frequency of wind gusts the stem will ultimately fail.
Girdling Wires
Stem girdling can often occur from abandoned staking wires installed during the trees installation. Over time the stem expands and once the wire loop cannot expand further, the stem begins to consume the wire. Many of these defects result in failure when the tree reaches a size that the inner girdled stem can no longer support. In some cases wind gusts occur at an ideal destructive frequency, and entire rows of trees with abandoned wires can fail at the same time. Typically when the failure occurs it is revealed that bark exists on the interior of the tree surrounding the wire in a “u” shape. The internal core of the tree trunk inside the wire, is limited in size to the wire loop’s diameter. Even though a trunk may increase in size and grow around the wire, the inner confined stem is unable to support the larger tree which eventually can result in failure.
Landscape Obstructions
Trees planted too close to permanent landscape structures can develop abnormally, or decline from limited space. Trunk defects, declining health, and girdling roots can all develop from structures not appropriately designed. Some trees are designed to fail such as the image in the above slide show labeled “Planning to girdle if successful”. The size of the mature trunk would exceed the size of the hole provided in the concrete for it to grow. If the tree were to successfully grow to maturity, the ring would be obscured under the trunk hiding the defect. This could lead to failure as the forces of the tree’s movements tansend down the trunk, and accumulate at the defective base.
High Voltage
High voltage lines often find themselves competing for the same air space as trees. This can create a significant hazards on the ground with step voltage. It can also cause trees to catch fire or arc dangerously. Trees must be pruned to maintain appropriate clearances to ensure that they do not induce a current from the high voltage lines, which could endanger anyone in the vicinity of the tree. Trees with electrical contact must be removed in conjunction with professional linesman from the local power company that owns the lines. There are no safety systems on high voltage lines that protect people, all the recloser switches are designed to do is protect the electrical hardware. In the link below you can see the recloser trip briefly as the power goes out before the power comes back on and the tree explodes. A person in contact with that kind of power would definitely not fair very well.
To witness the power of tree electrical contacts click on the link below:
Safe distance clearances from power lines:
Sewer Conflicts
Below ground there are many hazards that are not front of mind until they become an issue. The tree pictured above had aggressive root growth, that repeatedly plugged the sewer lines from the adjacent homes. The tree destroyed the sewer line which required replacement, and the homes were impacted with a significant health hazard from the sewer back up. While not a typical defect, this is a health hazard and can negatively impact infrastructure.
For more information on trees & sewer line management:
Western Canadian Tree Defects 