Dense mass of trees or shrubs (7)
I believe the answer is:
thicket
I believe this clue is a double definition.
'dense mass of trees' is the first definition.
(I've seen this before)
'shrubs' is the second definition.
(I have seen 'dense shrubs' mean 'thicket' so perhaps 'shrubs' could also mean 'thicket')
(Other definitions for thicket that I've seen before include "Mass of shrubs and small trees growing close together" , "Dense bushy area" , "Copse" , "Dense group of trees or bushes" , "dense vegetation" .)