Island with many a gnarled tree? (5)
I believe the answer is:
crete
'island' is the definition.
(Crete is an example)
'with many a gnarled tree?' is the wordplay.
'with' is a charade indicator (letters next to each other).
'many' becomes 'c' (C is the Roman numeral for 100**).
'a gnarled' indicates an anagram (I've seen this in other clues).
'tree' with letters rearranged gives 'rete'.
'c' put next to 'rete' is 'CRETE'.
(Other definitions for crete that I've seen before include "Greek island, capital Heraklion" , "Major island south of Greece" , "Large island south of Greece, once ruled by Minoans" , "Mediterranean island with Minoan remains" , "Herakleion its big port" .)