Marshy pine forest (5)
I believe the answer is:
taiga
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">marshy pine forest</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for taiga that I've seen before include "northern forest" , "Boggy forest" , "Russian zone" , "Siberian subarctic forest(s)" , "Marshy pine forest" .)