The Collaborative International Dictionary of English v.0.48:

Arboriculturist \Ar`bor*i*cul"tur*ist\, n.
   One who cultivates trees.
   [1913 Webster]

WordNet (r) 3.0 (2006):

arboriculturist
    n 1: someone trained in forestry [syn: forester, tree
         farmer, arboriculturist]