The Collaborative International Dictionary of English v.0.48:

Sparsely \Sparse"ly\, adv.
   In a scattered or sparse manner.
   [1913 Webster]

WordNet (r) 3.0 (2006):

sparsely
    adv 1: in a sparse manner; "sparsely inhabited"

Moby Thesaurus II by Grady Ward, 1.0:

36 Moby Thesaurus words for "sparsely":
   at infrequent intervals, at large, diffusely, dispersedly,
   everywhere, exiguously, hardly, hardly ever, here and there,
   in all quarters, in places, in spots, infrequently, meagerly,
   not often, passim, piddlingly, rarely, scantily, scarcely,
   scarcely ever, scrimpily, seldom, skimpily, sparingly, sparsim,
   sporadically, spottily, stingily, thin, throughout, uncommonly,
   unfrequently, unoften, very seldom, wherever you look