The Collaborative International Dictionary of English v.0.48:

Forester \For"est*er\, n. [F. forestier, LL. forestarius.]
   1. One who has charge of the growing timber on an estate; an
      officer appointed to watch a forest and preserve the game.
      [1913 Webster]

   2. An inhabitant of a forest. --Wordsworth.
      [1913 Webster]

   3. A forest tree. [R.] --Evelyn.
      [1913 Webster]

   4. (Zool.) A lepidopterous insect belonging to Alypia and
      allied genera; as, the eight-spotted forester (A.
      octomaculata), which in the larval state is injurious to
      the grapevine.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Forester
    n 1: English writer of adventure novels featuring Captain
         Horatio Hornblower (1899-1966) [syn: Forester, C. S.
         Forester, Cecil Scott Forester]
    2: someone trained in forestry [syn: forester, tree farmer,
       arboriculturist]

Moby Thesaurus II by Grady Ward, 1.0:

31 Moby Thesaurus words for "forester":
   arboriculturist, backwoodsman, briar-hopper, brush ape, bushman,
   clam digger, conservationist, cracker, desert rat, forest ranger,
   frontiersman, hillbilly, hinterlander, logger, lumberjack,
   lumberman, mountain man, mountaineer, piny, ranger, redneck,
   ridge runner, silviculturist, timberman, tree farmer, wood chopper,
   woodcraftsman, woodcutter, woodlander, woodman, woodsman