  We identify the predual of the nonreflexive Bergman space of the upper half
plane, $L_a^1(\uP,\mu_{\al})$, with the little Bloch space of the upper half
plane consisting of functions vanishing at $i$. We then investigate both the
semigroup and spectral properties of the adjoint groups of composition
operators which are naturally obtained from the duality pairing and are
therefore defined on the identified predual.
