Stratification refers to the vertical layering of habitats according to the different heights that plants grow. Habitats are divided into strata composed of distinct plant and animal communities. For example, a forest can be stratified into a subterranean layer, forest floor, herbaceous layer, shrub layer, and canopy layer. Organisms may move between layers on a daily basis. Stratification can also occur horizontally along environmental gradients or ecotones, which are transitional areas between biomes.