Perfected dam fashioned with trees (8)
I believe the answer is:
mastered
'perfected' is the definition.
(I've seen this in another clue)
'dam fashioned with trees' is the wordplay.
'fashioned with' is an anagram indicator.
'dam' anagrammed with 'trees' gives 'MASTERED'.
(Other definitions for mastered that I've seen before include "Brought under control, overcame" , "Streamed to be conquered" , "Overcame, difficulty or subject" , "Red meats (anag.)" .)