Author, really gutted, leaves say? (8)
I believe the answer is:
greenery
'leaves say?' is the definition.
(green leaves)
'author really gutted' is the wordplay.
'author' becomes 'greene' (Graham Greene, 1904-1991).
'gutted' means to remove the middle letters (to gut something is to remove its insides).
'really' with its centre taken out is 'ry'.
'greene'+'ry'='GREENERY'
(Other definitions for greenery that I've seen before include "something naturally colourful?" , "Leafy vegetation" , "Trees" , "Living foliage or vegetation" , "Foliage etc" .)