How to write a tree decay report your client will understand

By Alex Shy, ISA Board Certified Master Arborist (MA-5832B)October 16, 2026

Your client didn't hire you for a decay map. They hired you to tell them whether their tree is safe to keep and what to do about it. A good report gets them there quickly, in words they understand, and holds up if anyone looks at it again later.

Here's a structure that works for most decay assessments, whether the reader is a homeowner, a property manager or a city forester.

1. Start with the answer

Put the conclusion at the top in two or three sentences. Many readers will stop there.

Then use the rest of the report to support it.

2. Say what you tested

Keep it short and factual. It tells the reader the scope of your assessment, and it lets you or someone else repeat the test later.

• Tree: species, size (diameter or circumference), location on the property.
• Date of the visit and who assessed it, with credentials.
• Method: sonic decay testing, the device, how many sensor positions, the test height, and which way the first position faced.
• Anything else you used: resistance drilling, sounding, root collar excavation.

3. Describe what you saw

Observations from the outside of the tree come before the test results, because they're why you tested. Cavities, fungi, cracks, old wounds, dead bark, lean, crown condition, root damage, site changes. Photos help a lot here; a picture of the conk at the base explains more than a paragraph.

4. Report the test result honestly

Include the decay map and give the result as a range, not a single number:

• Confirmed decay: about X% of the cross-section.
• Possible decay: up to Y%, if the uncertain areas turn out to be decay.
• Where it is: "centered toward the street side, reaching the bark at the old pruning wound."

Say briefly what the colors mean if the map is in the report. Something like "red is decay confirmed by readings from more than one direction; yellow is possible decay" is enough.

Be clear about the limits: the test shows one height, slow wood can be decay, a cavity or a crack, and the map is an estimate based on the readings. That isn't hedging. It's what makes the report trustworthy.

5. Explain what it means

This is where your expertise goes, and it's the part a client values most. Connect the result to the tree's situation:

• How much sound wood is left, and where (a sound shell all round is different from decay open on one side).
• The species and how it tends to respond to this kind of decay.
• The loads on the tree: crown size, lean, exposure.
• The target: what's underneath and how often it's occupied.

Use plain words. "The trunk is hollow on the house side, and the remaining wood on that side is thin" lands better than technical shorthand.

6. Recommend clear next steps

Every recommendation should be something the client can act on:

• What to do (reduce, cable, remove, monitor, nothing).
• When (this winter, within 30 days, before the next storm season).
• When to re-test or re-inspect, if you're monitoring.

If there are options, list them with the trade-offs in one line each, and say which one you recommend.

7. Keep it short

One to two pages covers most single-tree decay assessments. Put the map and the key numbers on the first page, and move detailed tables (path-by-path readings) to an appendix for anyone who wants them.

Words that help and words that hurt

• Helps: "confirmed," "possible," "about," "on the street side," "I recommend."
• Hurts: "the tree is safe" (no tree is risk-free), "there is no decay" (only "no decay was detected at the height tested"), unexplained percentages, jargon without a plain-language line after it.

Where Sound Wood helps

Sound Wood's field report puts the tree details, the decay map, the decay range, your photos and your notes on one page, with your name, credentials and business details. The PDF is ready to email before you leave the site. Write it up drafts the observations and recommendations from your readings, results and notes, and you edit it before it goes into the report. It never changes your readings, the decay figures or the verdict.

The judgment in the "what it means" and "what to do" sections is still yours. The goal is to spend your time on that part, not on formatting.