Forest burning? That's baseless (5)
I believe the answer is:
arden
'forest' is the definition.
(forest in Shakespeare's As You Like It)
'burning? that's baseless' is the wordplay.
'burning?' becomes 'ardent' (both can mean passionate).
'that's baseless' means to remove the last letter (the bottom or base of the word is removed).
'ardent' with its last letter taken away is 'ARDEN'.
(Other definitions for arden that I've seen before include "Shakespearean forest" , "The forest of --, setting for As You Like It" , "Playwright; Shakespeare's forest" , "Wood in play" , "Warwickshire forest" .)