Hazard Evaluation of Community Trees
What does that mean?
Why should you bother?
- Hazard evaluation means a careful inspection of problems
and ranking of solutions for community trees that have 1)
a potential to fail, and 2) a significant target to hit.
- Such evaluation requires experience and knowledge to be done well,
though it is difficult to predict which trees will actually fail.
Who does that kind of work?
- To avoid hurting people and damaging property by
- identifying hazard trees and taking appropriate action, and
- managing trees in a reasonable and responsible manner.
- Communities are subject to liablility for trees on public land,
meaning that they are required by law to act in a prudent and reasonable
What do you look for?
- Professionals. Urban foresters, certified arborists,
or other knowledgeable and reputable tree professionals, can supply reliable
decisions on most common problems.
- Amateurs. Observant and responsible individuals
can be trained to work with municipal tree managers. They can 1) make annual
inspections, 2) note evident hazards, and 3) suggest a need for more expert
- You have to look for external defects, and guess about
internal problems, examining
- the crown for undersized, discolored, or missing leaves
that can point to problems above or below the ground you might not otherwise
- the branches and trunk for dead wood, breaks, holes, weak
attachments, decayed wounds, mushrooms, growing plants, cankers, fungal
conks, and bleeding, split, or included bark;
- the butt for lack of flare, cavities, loose bark, sawdust,
damaged buttress roots, soil mounding, or mushrooms.
Silver maple leader with diagonal crack
When should it be done?
- The main point is that you should be doing it, and any
time is better than none.
- Certain seasons are more productive than others:
- Winter is the easiest time to examine the branches and
trunk for defects, since all sides are visible (though you need binoculars)
when the leaves are absent;
- Late Summer is a good time to check the tree crown
for signs of a problem, since heat and drought will usually stress weak trees
before strong trees;
- Early Fall is the best time to look for decay in the
branches, trunk or base. Tree fungal infections are easiest to
spot and identify from the fruiting bodies they produce toward the end of
the growing season.
Where can I get more information?
USDA Forest Service. 1996. "How to Recognize Hazardous Defects
in Trees" Available from the Document Center (202-512-1800), or off
the web from the Hazard Tree Web Page at http://www.na.fs.fed.us/spfo/hazard/index.htm,
where there are many other useful documents. For other information,
advice and help on this topic, call offices of your State Urban Forestry
Coordinator or University Extension service, or visit urban forestry web