From The Collaborative International Dictionary of English v.0.48 [gcide]:
Afforest \Af*for"est\, v. t. [LL. afforestare; ad + forestare.
See Forest.]
To convert into a forest; as, to afforest a tract of country.
[1913 Webster]
From WordNet (r) 3.0 (2006) [wn]:
afforest
v 1: establish a forest on previously unforested land; "afforest
the mountains" [syn: afforest, forest]