Something burning affected tree close to copse (8)
I believe the answer is:
campfire
'something burning' is the definition.
'affected tree close to copse' is the wordplay.
'affected' becomes 'camp' (I've seen this before).
'tree' becomes 'fir' (fir tree is a kind of tree).
'close to' suggests the final letters (the 'close' to the word).
The last letter of 'copse' is 'e'.
'camp'+'fir'+'e'='CAMPFIRE'
(Other definitions for campfire that I've seen before include "Scout location" , "Boy scouts sing around it in the evening" , "Social centre for scouts etc" , "Focal point of tented activity, singsongs etc" , "where singing is involved" .)