Like author in Poplar (5)
I believe the answer is:
aspen
'poplar' is the definition.
(aspen is a kind of poplar)
'like author' is the wordplay.
'like' becomes 'as'.
'author' becomes 'pen' (to pen something is to author it).
'as'+'pen'='ASPEN'
'in' acts as a link.
(Other definitions for aspen that I've seen before include "city in Colorado" , "Trembling poplar tree" , "Tree that quivers" , "somewhere in Colorado" , "Growth" .)