Climber is wariest scrambling round island (8)
I believe the answer is:
wisteria
'climber' is the definition.
(the wisteria is a climbing plant)
'wariest scrambling round island' is the wordplay.
'scrambling' is an anagram indicator.
'round' means one lot of letters goes inside another.
'island' becomes 'i'.
'wariest' is an anagram of 'wsteria'.
'wsteria' enclosing 'i' is 'WISTERIA'.
'is' is the link.
(Other definitions for wisteria that I've seen before include "A flower, I swear it" , "Large climbing shrub, often attached to house" , "As I write badly about the flowering vine" , "Vine with pendulous clusters of flowers" , "Climber" .)