Like enclosure for tree (5)
I believe the answer is:
aspen
'tree' is the definition.
(aspen is a kind of tree)
'like enclosure' is the wordplay.
'like' becomes 'as'.
'enclosure' becomes 'pen' (pen is a kind of enclosure).
'as'+'pen'='ASPEN'
'for' is the link.
(Other definitions for aspen that I've seen before include "that's wooden" , "Trembling poplar tree" , "quill-like?" , "Type of poplar" , "Trembler" .)