Small pears turn out to be rare (6)
I believe the answer is:
sparse
'to be rare' is the definition.
(I've seen this before)
'small pears turn' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'turn' is an anagram indicator.
'pears' anagrammed gives 'parse'.
's'+'parse'='SPARSE'
'out' acts as a link.
(Other definitions for sparse that I've seen before include "Thin on the ground, scarce" , "Thinly-spread" , "Infrequent" , "Scarce like thinning hair" , "Thinly distributed" .)