Skilled arboriculturist initially shortened branch (5)
I believe the answer is:
adept
'skilled' is the definition.
(similar in meaning)
'arboriculturist initially shortened branch' is the wordplay.
'initially' suggests taking the first letters.
'shortened branch' becomes 'dept' (abbreviation for department).
The initial letter of 'arboriculturist' is 'a'.
'a'+'dept'='ADEPT'
(Other definitions for adept that I've seen before include "Skilful, expert" , "Dexterous" , "capable" , "Proficient - expert" , "Having the required skills" .)