The man under this tree is a civic dignitary (5)
I believe the answer is:
alder
'the man under this tree is a civic dignitary' is the definition.
'alder' can be an answer for 'tree' (alder is a kind of tree). I'm unsure of the remainder of the definition.
'the man under this tree' is the wordplay.
'the man' becomes 'Al' (man's name).
'under' is a charade indicator (letters next to each other).
'this tree' becomes 'der' (I am not sure about this - if you are sure you should believe this answer much more).
'al'+'der'='ALDER'
Can you help me to learn more?
(Other definitions for alder that I've seen before include "Type of birch tree" , "Shrub or tree with cone-like fruits" , "North temperate tree with cone-like fruit" , "Tree or shrub of the birch family" , "Tree or shrub whose wood is resistant to underwater rot" .)