Dispute over a new tree (5)
I believe the answer is:
rowan
'tree' is the definition.
(rowan is a kind of tree)
'dispute over a new' is the wordplay.
'dispute' becomes 'row' (I've seen this before).
'over' says to put letters next to each other.
'a new' becomes 'an' (I've seen this in other clues).
'row'+'an'='ROWAN'
(Other definitions for rowan that I've seen before include "Man" , "Canterbury" , "The mountain ash tree" , "Tree - archbishop" , "Tree bearing bright red berries" .)