Immediate medical assistance from volunteers I had found after trees (5,3)
I believe the answer is:
first aid
'immediate medical assistance' is the definition.
(I've seen this before)
'volunteers i had found after trees' is the wordplay.
'volunteers' becomes 'TA' (abbreviation for Territorial Army).
'i had' becomes 'I'd' (contraction).
'found after' is a charade indicator (letters next to each other).
'trees' becomes 'firs' (fir is a kind of tree).
'ta'+'id'='taid'
'taid' put after 'firs' is 'FIRST-AID'.
'from' is the link.
(Other definitions for first aid that I've seen before include "Immediate medical assistance" , "Initial treatment for injured person before doctor arrives" , "Preliminary treatment before doctor comes" , "'Immediate emergency care (5,3)'" , "Instant help for the sick" .)