Forest with walnut finally burning (6)
I believe the answer is:
ardent
'burning' is the definition.
(both can mean passionate)
'forest with walnut finally' is the wordplay.
'forest' becomes 'Arden' (forest in Shakespeare's As You Like It).
'with' is a charade indicator (letters next to each other).
'finally' indicates one should take the final letters.
The final letter of 'walnut' is 't'.
'arden'+'t'='ARDENT'
(Other definitions for ardent that I've seen before include "Ranted badly and became earnest in love" , "Intensely devoted" , "Fiery and passionate" , "very interested" , "Ranted, being passionate" .)