Relates to The Joshua Tree identifying with The Big Tree (8)
I believe the answer is:
arboreal
'identifying with the big tree' is the definition.
I can't tell whether this definition defines the answer.
'relates to the joshua tree' is the wordplay.
I cannot really see how this works, but
'tree' could be 'bo' (bo tree is a kind of tree) and 'bo' is present in the answer.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for arboreal that I've seen before include "high living" , "Like the sloth" , "found in 20 [TREETOP] ?" , "Inhabiting trees" , "Wooded" .)