In favour of mixed sets of woods (7)
I believe the answer is:
forests
'woods' is the definition.
('forest' can be a synonym of 'wood')
'in favour of mixed sets' is the wordplay.
'in favour' becomes 'for' (as in being for a particular cause).
'of mixed' indicates anagramming the letters (I've seen 'mixed' mean this).
'sets' anagrammed gives 'ests'.
'for'+'ests'='FORESTS'
'of' acts as a link.
(Other definitions for forests that I've seen before include "Large woods" , "Large, densely-wooded area" , "Woodlands" , "Densely wooded areas" .)