The Collaborative International Dictionary of English v.0.48:

Silva \Sil"va\, n.; pl. E. Silvas, L. Silvae. [L., properly,
   a wood, forest.] [Written also sylva.] (Bot.)
   (a) The forest trees of a region or country, considered
       collectively.
   (b) A description or history of the forest trees of a
       country.
       [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Sylva \Syl"va\, n.; pl. Sylvae. [L. sylva, better silva, a
   wood. See Silva.] (Bot.)
   Same as Silva.
   [1913 Webster]

WordNet (r) 3.0 (2006):

sylva
    n 1: the forest trees growing in a country or region [syn:
         silva, sylva]