Treeless Arctic region (6)
I believe the answer is:
tundra
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">treeless arctic region</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(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" .)