The Collaborative International Dictionary of English v.0.48:

arboraceous \arboraceous\ adj.
   1. 1 abounding in trees. an arboraceous landscape

   Syn: arboreous, woodsy, woody.
        [WordNet 1.5]

   Arbor Day, a day appointed for planting trees and shrubs.
      [U.S.]
      [1913 Webster]

WordNet (r) 3.0 (2006):

Arbor Day
    n 1: a day designated for planting trees