Clean area with dense vegetation (5)
I believe the answer is:
scrub
This clue is a double definition.
'clean' is the first definition.
(scrub can mean to clean)
'area with dense vegetation' is the second definition.
(scrubland)
(Other definitions for scrub that I've seen before include "Vegetation consisting of stunted trees or bushes" , "Rub hard with a brush" , "plants" , "Drop" , "Rub hard; brushwood" .)