Treeless Arctic region (6)
I believe the answer is:
tundra
'treeless arctic region' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for tundra that I've seen before include "Vast level Arctic regions with frozen subsoil" , "Sub-polar treeless zone" , "northern waste" , "Treeless frozen Arctic plain" , "where you might see caribou" .)