Yes, fallow areas can also be converted to forest uses when not used for agriculture. In fact, if unused for agriculture after 20 years, fallow areas are converted into forests. By default, the Land-use Planner will convert these into the forest category available in your project. If there are several forest categories available in your project, the one with the lowest carbon storage will be used. This is because the LUP operates under the assumption fallow areas do not convert immediately to the densest types of forests.