  We perform a dimensional reduction of the $U(1)\times SU(2)$ Chern--Simons
bosonization and apply it to the $t-J$ model, relevant for high $T_c$
superconductors. This procedure yields a decomposition of the electron field
into a product of two ``semionic" fields, i.e. fields obeying abelian braid
statistics with statistics parameter $\theta={1\over 4}$, one carrying the
charge and the other the spin degrees of freedom. A mean field theory is then
shown to reproduce correctly the large distance behaviour of the correlation
functions of the 1D $t-J$ model at $t>>J$. This result shows that to capture
the essential physical properties of the model one needs a specific ``semionic"
form of spin--charge separation.
