Much of hole is concealed by skill shown by tree expert (8)
I believe the answer is:
arborist
'tree expert' is the definition.
(I've seen this before)
'much of hole is concealed by skill' is the wordplay.
'much of hole' becomes 'boris' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'is concealed by' means one lot of letters goes inside another.
'skill' becomes 'art' (I've seen this before).
'boris' going into 'art' is 'ARBORIST'.
'shown by' acts as a link.
(Other definitions for arborist that I've seen before include "tree surgeon" , "Tree expert" .)