Vegetated areas are composed of a top canopy layer. However, they also have a vertical structure and different understory vegetated layers/strata can be encountered.

The understory is composed of a shrub layer, a field layer (ferns, herbaceous and graminoids) and a ground layer (mosses and lichens). However, vertical structure of vegetation differs from an area to another and all the previously mentioned layers do not necessarily exist in all vegetated areas.

Unit:  count