Growing or burnt timber (3)

I believe the answer is:

ash

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'timber' is the definition.
(I've seen this before)

I don't understand the remainder of the clue.

(Other definitions for ash that I've seen before include "remains after forest fire?" , "Common tree" , "Remains from the yule-log?" , "deposit" , "One [TYPE OF TREE]" .)

I've seen this clue in The Guardian and The Globe and Mail.

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