Conifers affected by school science (9)
I believe the answer is:
forensics
'science' is the definition.
(I know that forensics is a type of science)
'conifers affected by school' is the wordplay.
'affected' is an anagram indicator.
'by' is a charade indicator (letters next to each other).
'school' becomes 'S'.
'conifers' anagrammed gives 'forensic'.
'forensic'+'s'='FORENSICS'
(Other definitions for forensics that I've seen before include "study of public debate" , "If censors combined in medical studies for legal purposes" .)