Can be OK as a source of timber (4)

I believe the answer is:

oaks

I'm a little stuck... Click here to teach me more about this clue!

'a source of timber' is the definition.
I can't tell whether this defines the answer.

'can be ok as' is the wordplay.
'can be' indicates anagramming the letters.
'ok'+'as'='okas'
'okas' anagrammed gives 'OAKS'.

Can you help me to learn more?

(Other definitions for oaks that I've seen before include "Acorn producers" , "Epsom Classic race" , "material for shipbuilding" , "Acorn trees" , "Hardwood trees" .)

I've seen this clue in the Evening Standard.

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