Renew section of forest or ecosystem (7)
I believe the answer is:
restore
'renew' is the definition.
(I know that restore is a type of renew)
'section of forest or ecosystem' is the wordplay.
'section of' indicates the answer is hidden within the clue.
'RESTORE' is hidden in the letters of 'forest or ecosystem'.
(Other definitions for restore that I've seen before include "Repair, put back" , "Build up again" , "Make good, reinstate" , "Give or put back" , "Bring back, reinstate" .)