Short trees in need of treatment (5)
I believe the answer is:
terse
'short' is the definition.
('terse' can be a synonym of 'short')
'trees in need of treatment' is the wordplay.
'in need of treatment' indicates an anagram.
'trees' with letters rearranged gives 'TERSE'.
(Other definitions for terse that I've seen before include "Briefly expressed" , "Succinct about trees" , "Curt, laconic of speech" , "Brusque and curt" , "Concise about trees" .)