Birch kin (5)
I believe the answer is:
alder
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">birch kin</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for alder that I've seen before include "Tree akin to the birch" , "Birch relative" , "New Forest resident" , "Forward movement" , "A tree for Adler" .)