  Let $T$ be an $\R$-tree in the boundary of Outer space with dense orbits.
When the free group $\FN$ acts freely on $T$, we prove that the number of
projective classes of ergodic currents dual to $T$ is bounded above by $3N-5$.
  We combine Rips induction and splitting induction to define unfolding
induction for such an $\R$-tree $T$. Given a current $\mu$ dual to $T$, the
unfolding induction produces a sequence of approximations converging towards
$\mu$.
  We also give a unique ergodicity criterion.
