  This paper is devoted to propagation phenomena for a
reaction-diffusion-advection equation in a heterogeneous environment with
KPP-bistable nonlinearities. A comprehensive analysis is presented on the
influence of advection and heterogeneous reactions, based on various values of
the advection rate $c$. When $c>-c_m$, it is demonstrated that propagation can
always occur with leftward spreading speed $c_m+c$ and righward spreading speed
$\min\big(\max(c_b-c,0),c_m-c\big)$, where $c_m$ and $c_b$ are respectively the
spreading speeds of KPP reaction and bistable reaction. Moreover, a logarithmic
delay of the level sets in the left direction is discovered. When $c\le -c_m$,
propagation phenomena are determined by the initial data and by the sign of
$c_b$. In particular, when $c_b>0$, the leftward propagation speed is $c_b+c$
if the initial population is ``large enough''; whereas extinction occurs if the
initial value is located in the bistable region and is ``relatively small''. In
addition, the attractiveness of the bistable traveling wave is obtained when
the leftward spreading speed is $c_b+c$ and/or when the rightward spreading
speed is $c_b-c$.
