Burning forest's temperature (6)
I believe the answer is:
ardent
'burning' is the definition.
(thesaurus)
'forest's temperature' is the wordplay.
'forest' becomes 'arden' (I've seen this before).
'temperature' becomes 't' (abbreviation).
'arden'+'t'='ARDENT'
(Other definitions for ardent that I've seen before include "Burning with emotion" , "Having great warmth of feeling like a lover" , "Passionate, full of feeling" , "Intensely devoted" , "Ranted, being passionate" .)