Subsidiary office of forestry service (6)
I believe the answer is:
branch
This clue could be a double definition.
'subsidiary office' is the first definition.
(I've seen this in another clue)
'forestry service' is the second definition.
'branch' can be an answer for 'service' (thesaurus). I'm unsure of the 'forestry' bit.
'of' is the link.
Can you help me to learn more?
(Other definitions for branch that I've seen before include "Divide (as a tree)" , "Part of tree/river" , "Offshoot or subdivision" , "division within large organisation" , "local office" .)