Growing or burnt timber (3)
I believe the answer is:
ash
'timber' is the definition.
(I've seen this before)
I don't understand the remainder of the clue.
Can you help me to learn more?
(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]" .)