A reader contacted me because she had become concerned about her spruce: It is 35 feet high, apparently healthy, growing on a bank near her driveway and power lines. Surface roots are visible. Could it blow down?
I walked her through an evaluation tailored to a spruce. Deciduous trees would be a different discussion.
All risk determinations involve two angles:
1. The situation.
2. The risk taker.
On the situation side, there is the likelihood of failure, the value of the target (what might get hit) and the frequency of the target (how often the potential victim is present).
In her case, the likelihood of failure is probably higher with an evergreen than most other trees. Blowdowns occur more frequently with evergreens, since they tend to be shallow-rooted. But blowdowns are also more common in wet soils, or in cases where companion trees have been removed. Since her tree is on a bank and presumably was not spared from a forest-cutting, it might be less likely to fail than one in wet soil or one that was adapted to depend upon its neighbors for wind resistance.
She should also consider which direction the wind would have to blow to get the tree to fall toward her driveway. In our area, east and northeast winds are rare. On the other hand, she may also examine if there might be existing and effective windscreens (for example, tall buildings, groves of tall trees, or sheltering hillsides) upwind from the driveway side of the tree.
Her driveway represents the more valuable target: It is designed to carry vehicle and pedestrian traffic regularly. So, for the people side of the target, it is priceless.
But perhaps her driveway is seldom used. The secondary target is the power lines. They are high-frequency, since they are always present. They represent the value of regular use, though perhaps for her home only. Though they can be repaired, the inconvenience has a price.
Now that we know the situation, we need to think about the risk taker. Perhaps the risk described in the situation brings constant worry. Removing the risk may provide peace of mind. (Of course, sometimes our minds immediately find new sources of unrest).
Peace of mind can be priceless.
On the other hand, perhaps peace of mind is not an issue. It was not an issue during the time it took for the tree to grow the last, risky 20 feet, and the beauty and function of the tree might outweigh risk concerns going forward. So perhaps counting the cost is possible, since failure would not seem to be imminent.
Finally, perhaps there is a middle ground. This tree can be removed and replaced with a beautiful, but much less sizeable specimen. Perhaps the replacement tree will provide both peace of mind and sufficient beauty and function.
Joshua Arp is an ISA-certified municipal specialist, Clarks Summit’s municipal arborist and an operator of an organic lawn and landscape maintenance business. Reach him at email@example.com.