Posted by Kelly McGlothlin, M.S., Associate Arborist

Figure 1
This acacia tree broke at the trunk during a storm, damaging a house in San Jose, California. Had an Arborist examined the tree prior to the failure, they would have seen fruiting bodies (conks) of a decay fungus on the trunk and likely recommended a more detailed inspection to determine the extent of decay and ultimately recommended that the tree be removed.

The structural development of trees in unpopulated areas is not a problem since there are usually not any targets of concern when a tree falls or loses a limb. But in urban settings, trees left to develop on their own often develop structural defects, which make the tree more susceptible to failing (breaking or falling). Tree Risk Assessment involves a systematic identification of structural defects within the canopy, trunk and/or roots of trees; assessment of the likelihood of tree failure (loss of tree part or toppling); and identification of the likely target for the failure. In addition to the above, we at Tree Associates Inc., also assess the probability of costly tree root damage to structures such as foundations, patios, walk and roadways.

Over the years of conducting Tree Risk Assessments, I have noticed that many defects could have been eliminated in the trees’ early development. Trees that were not trained during their early developmental stages are more likely to have structural defects that increase the probability that part or the whole tree will fail. Therefore, I encourage all to invest a little time to select trees for planting that have a good beginning structure, as well as time to train them in the first few years of their development. This time investment will ensure a safe, structurally sound tree and decrease future maintenance costs by hundreds or thousands of dollars.

Figure 2
A large limb on this Monterey pine in Menlo Park, California broke during a windstorm as a result of the limb's large size and windsail. The failure could have been prevented if the defect had been identified and the limb shortened.

• TreeQualityNurserySelectionBrian Kempf, with the Urban Tree Foundation, and Edward F. Gilman, Professor of Environmental Horticulture at University of Florida, put together some valuable resources related to tree selection and training:

• YoungTreeTraining

Tree Associates Inc., Arborist-experts in Davis, California can help you by objectively identifying potential defects and specifying mitigation alternatives. For clients who have large numbers of trees, such as Homeowners Associations, School or Park Districts or Municipalities, we can provide Tree Risk Assessments with risk-prioritized hazard abatement recommendations. These recommendations can be used to obtain and compare tree work bids for the same scope of services. Please contact us if you have any questions about this article or would like to schedule a Tree Risk Assessment for your home, business, or government entity.

Figure 3
A large scaffold limb split away from the main trunk of this valley oak tree in Citrus Heights, California. The blackened area (oxidation) on the bark indicates that a crack had existed previous to the failure. While the crack may not have been visible to a lay person, an arborist would have identified it during a Tree Risk Assessment and recommended mitigation measures (e.g. limb removal) to avoid the failure.

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