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]