Josh repulsed by 50 percent of chestnut trees (7)
I believe the answer is:
birches
'trees' is the definition.
(birch is a kind of tree)
'josh repulsed by 50 percent of chestnut' is the wordplay.
'josh' becomes 'rib' (I've seen this in another clue).
'repulsed' shows that the letters should be reversed in order.
'by' means one lot of letters go next to another.
'50 percent of' becomes 'es' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'chestnut' becomes 'ch' (I've seen this in other clues).
'rib' in reverse letter order is 'bir'.
'es' put after 'ch' is 'ches'.
'bir'+'ches'='BIRCHES'
Can you help me to learn more?
(Other definitions for birches that I've seen before include "Flogs" , "silver in some cases" , "what might be silver" .)