Since 1882, it marks success in tests for trees (5)
I believe the answer is:
ashes
'for trees' is the definition.
(ash is a kind of tree)
'since 1882' is the wordplay.
'since' becomes 'as' (I've seen this in other clues).
'h88e' becomes 'hes' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'as'+'hes'='ASHES'
'it marks success in tests' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for ashes that I've seen before include "Test cricket series" , "Former Wimbledon champion's" , "Residue from fire" , "Remains of anything burnt" , "sports contest" .)