Rooted Plant Sub-Model

In Rooted Plant Sub-Model (RPEM), how to set the specific region for plant growth. And plant can not grow except those areas.
In tab “Initial condition”, RPEM provides three options for IC, including constant, wqrpemrst.inp, and wqrpemsic.inp. While no matter how we set, the biomass of roots, shoots, or detritus show spatially value in whole study area rather than in specific region.