Protected area (6,7)
(Other definitions for lee that I've seen before include "The sheltered side of something" , "Revolutionary general" , "Sheltered from the wind in Cork, perhaps" , "Protection" , "The sheltered side - of Cork's river?" .)
'protected area' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for nature reserve that I've seen before include "Area set apart for wildlife" , "rural environment" , "Protected area for plants and animals" , "Place set aside for flora and fauna" , "Say, animal sanctuary" .)