Chief is behind gathering wood (5)
I believe the answer is:
beech
'wood' is the definition.
(beech is a kind of wood)
'chief is behind gathering' is the wordplay.
'chief' becomes 'ch' (abbreviation).
'is behind' is a charade indicator (letters next to each other).
'gathering' becomes 'bee' (bee is a kind of gathering).
'ch' put after 'bee' is 'BEECH'.
(Other definitions for beech that I've seen before include "Tree variety" , "Deciduous tree with smooth grey bark" , "Tree (with green or copper leaves)" , "Tree of Fagus genus" , "Tree with bitter 'nuts'" .)