A southern hard wood (3)
I believe the answer is:
ash
'wood' is the definition.
(I've seen this before)
'a southern hard' is the wordplay.
'southern' becomes 's' (abbreviation).
'hard' becomes 'h'.
'a'+'s'+'h'='ASH'
(Other definitions for ash that I've seen before include "Tree with silver-grey bark" , "Tree - effect of burning" , "Oleaceous tree" , "It comes from volcano" , "Hardwood" .)