Assessing Tree Health

Assessing Tree Health

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Kevin Zobrist, WSU Extension Forestry Educator, WSU Extension
Healthy trees are beneficial to our environment and our property values - but how do we determine if a tree is healthy? This publication briefly discusses common tree health problems and outlines a procedure for assessing tree conditions and getting diagnoses and recommendations from tree health professionals.
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When considering tree health, it is important to remember that tree health and forest health are not the same thing. Tree health refers to the health of an individual tree, whereas forest health refers to the health of an entire forest system, including trees, plants, soil, wildlife, and water. A certain amount of insect activity, disease, mortality, and decay is normal and healthy within a forest system, and damaged, deformed, dying, and dead trees provide critical habitat for wildlife.

I once spoke with someone who wanted to see diseases like root rot completely eradicated from forests. While I appreciate his passion for healthy trees, this goal is misguided. While there are some externally introduced exotic diseases of concern, most disease agents found in our forests, such as fungi and bacteria, are natural parts of the forest ecosystem.

Native trees have evolved together with native pathogens, and these pathogens, in turn, have a natural and important role to play in diversifying the physical structure of the forest, eliminating the weakest trees, and increasing the variety of tree species present. Consequently, removing all diseases or pests is not the answer and would result in negative ecological consequences.

Figure 1. Downed trees in a root rot pocket.
In some cases, however, the ecological role of disease may conflict with certain management objectives, such as when site-specific management actions are necessary to control or mitigate disease impacts. For example, dead and decaying wood, like the fallen trees in a root rot-infested site (Figure 1), provide diversity and wildlife habitat. However, this role might conflict with aesthetic and financial objectives.

Tree health is likely to be most problematic when a tree is in your yard or near your house. A dying tree in a forest of otherwise healthy specimens is typically not a problem.

However, if you only have a few trees in your yard, and one of them is sick, the impact is magnified.

So what should you do if you have a sick tree? The first thing is to determine whether the tree is actually ailing at all. Some trees, such as western redcedar, as seen in Figure 2, may temporarily appear sick due to normal seasonal dieback (see WSU Extension Fact Sheet FS056E: Seasonal Dieback in Conifer Trees for more information). If the tree is indeed showing symptoms of decline beyond normal seasonal changes, the next step is to determine whether it is a potential hazard (i.e., if it is likely to damage your house or barn, or injure children or animals in the area. Of course, a tree that poses a high risk of injury or property damage requires more immediate attention than a tree that does not carry this risk.

Figure 2. Dead inner foliage on western redcedar.
The next step is to determine the cause of the tree’s decline, especially if it is a potential hazard. For instance, if there is the potential of a falling tree damaging your property, you will want to know if it has a problem that weakens its roots or trunk. Your local WSU County Extension office has resources that can help you troubleshoot tree problems, including Master Gardeners and forestry agents. Note that a forestry agent is trained to deal with native trees in a forested setting, rather than ornamental trees in a landscape setting or fruit trees in an orchard setting. WSU also has a number of excellent publications, diagnostic tools, and other “self-help” resources located on its forestry website.

If you are going to meet with a tree expert about a potential problem, having the following information ready will improve your chances of getting an accurate diagnosis.

  • Which trees are affected? Just one tree or multiple trees? Which species are affected or unaffected? What is the size or age of the affected tree?



Copyright 2011 Washington State University

Published October, 2011

WSU Extension bulletins contain material written and produced for public distribution. Alternate formats of our educational materials are available upon request for persons with disabilities. Please contact Washington State University Extension for more information

Issued by Washington State University Extension and the U.S. Department of Agriculture in furtherance of the Acts of May 8 and June 30, 1914. Extension programs and policies are consistent with federal and state laws and regulations on nondiscrimination regarding race, sex, religion, age, color, creed, and national or ethnic origin; physical, mental, or sensory disability; marital status or sexual orientation; and status as a Vietnam-era or disabled veteran. Evidence of noncompliance may be reported through your local WSU Extension office. Trade names have been used to simplify information; no endorsement is intended.