Thin on the ground (6)
(Other definitions for meagre that I've seen before include "Poor in quality" , "Small, insufficient" , "Miserable" , "Slight" , "Insufficient; scanty" .)
'thin on the ground' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for sparse that I've seen before include "Meagre, scanty" , "Thinly dotted about" , "Meagre; scarce" , "Thinly populated" , "Thin on the ground, scarce" .)
(Other definitions for scarce that I've seen before include "Wanting" , "Uncommon" , "exceptional" , "Not plentiful, in short supply" , "Hard to obtain" .)