  In this paper we study random walks on a finitely generated group $G$ which
has a free action on a $\mathbb{Z}^n$-tree. We show that if $G$ is non-abelian
and acts minimally, freely and without inversions on a locally finite
$\mathbb{Z}^n$-tree $\Gamma$ with the set of open ends ${\rm Ends}(\Gamma)$,
then for every non-degenerate probability measure $\mu$ on $G$ there exists a
unique $\mu$-stationary probability measure $\nu_\mu$ on ${\rm Ends}(\Gamma)$,
and the space $({\rm Ends}(\Gamma), \nu_\mu)$ is a $\mu$-boundary. Moreover, if
$\mu$ has finite first moment with respect to the word metric on $G$ (induced
by a finite generating set), then the measure space $({\rm Ends}(\Gamma),
\nu_\mu)$ is isomorphic to the Poisson--Furstenberg boundary of $(G, \mu)$.
