What is a Tree Health Assessment?


A Tree Health Assessment (THA) is a detailed, observational, analytic process used by professional arborists specializing in the diagnosis, treatment and prevention of woody plant decline. a THA is used to diagnose "sick trees" and recommend treatments to restore vigor and reduce the risk of mortality. Diagnostic arborists use various tools in their work; most common is use of a magnifying glass, binoculars and a field (optical) loupe. At times, samples may be taken for laboratory analysis. Observations and test results are recorded on a worksheet which is then used to determine a course of treatment. The final pages of a THA consist of a diagnosis sheet and a treatment recommendations.

To a diagnostic arborist, each property is considered a "micro-forest" and within the micro-forest may exist several "micro-climates". This means a THA is specific to each property and of considerable value to the property owner. Since woody plants in proximity interact with each other it is necessary to examine those also and this provides the opportunity for early detection of other problems.

Early detection and diagnosis often provides a much wider range of treatment options for trees then for those which have experienced several years of decline. Since the natural environment is in constant change with an influx of insects and diseases, annual Tree Health Assessments are recommended for high value and historic trees.

Treatment options can range from procedures and maintenance the average property owner can perform to procedures solely within the realm of a qualified professional. Often a range of treatment options can be provided to accommodate the financial resources available.

A diagnostic arborist may spend up to two hours on site, depending on size of the property, variety and number of woody plants. Rates start at $225 for an average residential property and there may be charges for laboratory and travel costs. Similar to other diagnostic professions, ISA Certified Arborists are bound by a code of ethics and cannot diagnose over the phone or through photos. A thorough physical examination of the woody plant is required for proper diagnosis.