Source : Webster's Revised Unabridged Dictionary (1913)

Birken \Birk"en\, v. t. [From 1st {Birk}.]
   To whip with a birch or rod. [Obs.]

Birken \Birk"en\, a.
   Birchen; as, birken groves. --Burns.

Source : WordNet®

birken
     adj : consisting of or made of wood of the birch tree [syn: {birch},
            {birchen}]