Root Layer Forest Design Plants covers all the plants that have large tubers and roots used as a crop. This type of plant includes carrots and Jerusalem artichoke. Note that almost all plants that have a root crop also fall into one of the other layers as well. The key to this layer is that we are actually using the root as a crop to harvest.
According to the Permaculture Research Institute, there are 7-Layers in a food forest. They are; canopy, understory, shrub, herbaceous, ground cover, vine/climbers, and root/tuber yield.