I saw some trees with red A’s painted on the trunks, with vertical lines (or 1’s) painted on each side of the A.

Location: Crown land in eastern Ontario.

What do those markings mean?

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  • 1
    Noticed in Italy, too
    – mattia.b89
    Commented May 1 at 6:57
  • 3
    In UK marked trees are usually a sign from a tree surveyor or a botanist to tell the wrecking crew which trees need to be felled, perhaps from age, disease, or the weakest trees in an overcrowded area. That decision isn't left to the 'tree feller' because they love to cut them down. Commented May 1 at 19:04
  • 2
    Oh huh. That paint is the perfect hue to be invisible to my colourblind eyes. Needed a filter to see it at all.
    – Bob
    Commented May 3 at 12:34

3 Answers 3


Out of curiosity I spent some time Googling this, and it appears that Ontario has strict requirements for being a tree marker and the Canadian Institute of Forestry offers courses for you to become a certified tree marker. See for example the Tree Marking Courses page on the Ontario state web site.

Following links from that page I found a copy of the Ontario Tree Marking Guide here (this is a 4MB pdf).

Nothing I found explained the letter A, but red is used to indicate a boundary. Presumably trees surrounding an area would be marked in red to mark the edges of that area. For example in a blog post on the Canadian Institute of Forestry web site it is stated that red lines with CB inside them are used to mark a cut boundary. That symbol looks very like the ones you found but with CB instead of A, so I would guess that the A markings also indicate a boundary but for some reason other than felling.

If you go back to that area it would be interesting to see if the red markings do trace out some form of boundary.


Marks painted on trees are often (always?) indications whether to cut the tree down or not when they work in that part of the woods next.

The meaning of a particular mark is often not standard and can differ between crews and areas.

Different marks can be used for different grades of trees, they can indicate different stages of the felling process or different locations the trees are to be stored once down. Or something different again.


In addition to what Willeke wrote: I have heard from someone who works in forestry that forestry workers deliberately change their markings often, so that people opposed to logging have a harder time sabotaging their effort. For example, if they had a well-known marker for "this tree shall remain when others are logged", opponents might spread that mark on additional trees, making their work harder.

So, it's probably a forestry marker, and it might be that they don't want you to know what this marker means.

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