Tree area rising, becoming adequate (5)
I believe the answer is:
ample
'adequate' is the definition.
(I've seen this in another clue)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for ample that I've seen before include "Easily sufficient" , "Full-figured" , "Buxom" , "Fairly large" , "Large enough" .)