Russian plain (6)
I believe the answer is:
steppe
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">russian plain</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 steppe that I've seen before include "Large treeless area of Siberia" , "Dry area of grassland in southeast Europe and Siberia" , "Large area of unforested grassland" , "Large area of flat grassland in Europe or Siberia" , "Dry plain of Eurasia" .)