National park replaced green site (9)
I believe the answer is:
serengeti
'national park' is the definition.
(I've seen this before)
'replaced green site' is the wordplay.
'replaced' indicates anagramming the letters.
'green'+'site'='greensite'
'greensite' anagrammed gives 'SERENGETI'.
(Other definitions for serengeti that I've seen before include "Afr. plain; green site (anag.)" , "Wildlife-rich region of Africa" , "Huge plain in Tanzania" , "Tanzanian wildlife area" , "Wildlife preserve (and National Park) in Tanzania" .)