BMP - Tree Risk Assessment - 5

1. Introduction
Trees provide numerous benefits to those living and working in the urban
environment. These benefits increase as the age and size of the trees increase.
However, as a tree gets older and larger, it is also more likely to shed branches
or develop decay or other conditions that can predispose it to failure. In assessing and managing trees, we should strive to strike a balance between
the risk that a tree poses and the benefits that individuals and communities
derive from trees.
Many trees are located where the consequences of failure are minor
or negligible. In urban and developed areas where people, property, and
activities could be injured, damaged, or disrupted, the consequences
of tree conflict or failure may be significant or severe. Decisions on
whether a tree inspection is required or what level of assessment is appropriate should be made with consideration for what is reasonable and
proportionate to the specific conditions and situations. These are tree
risk management issues.
It is impossible to maintain trees free of risk. Some level of risk must
be accepted to experience the benefits that trees provide. Fortunately, tree
failure that results in serious damage, injury, or death is rare. Tree failures
during " normal " weather conditions are often predictable and preventable.
However, any tree, whether it has visible weaknesses or not, will fail if
the forces applied exceed the strength of the tree or its parts. For example,
hurricane-force winds, heavy snow, or freezing rain can break solid, defectfree trees.
Tree risk assessors often must perform risk assessments with limited
information about the structural condition of the tree and the environment
that affects it. Tree risk assessors form opinions about what is likely to occur in the future based upon their experience and what is observed. These
assessments are then provided to a tree owner or manager to make decisions
about tree management.
Arborists serving as tree risk assessors should have specialized education, training, skills, and experience, and they should be properly insured to
provide this service. Familiarity with basic tools and equipment is needed for
many assessments. Specialized tools or equipment may be required for some
assessments. In some jurisdictions certification, qualifications, or licenses are
required to conduct tree risk assessments.
The purpose of this document is to guide arborists to assess tree risk as
accurately and consistently as possible, to evaluate that risk, and to understand
which treatments can achieve an acceptable level of risk. In determining treat5

BMP - Tree Risk Assessment

Table of Contents for the Digital Edition of BMP - Tree Risk Assessment