The classical category Rep(S, Zp) of representations of a finite poset S over the field Zp is extended to two categories, Rep(S, Z p m ) and uRep(S, Z p m ), of representations of S over the ring Z p m . A list of values of S and m for which Rep(S, Z p m ) or uRep(S, Z p m ) has infinite representation type is given for the case that S is a forest. Applications include a computation of the representation type for certain classes of abelian groups, as the category of sincere representations in (uRep(S, Z p m )) Rep(S, Z p m ) has the same representation type as (homocyclic) (S, p m )-groups, a class of almost completely decomposable groups of finite rank. On the other hand, numerous known lists of examples of indecomposable (S, p m )-groups give rise to lists of indecomposable representations.