Trees occupy the top vertical strata or layer of a forest, shrubs the second and herbs and grasses occupy the bottom layers. This phenomenon is called:
Stratification represents the vertical zonation or layering in a community, typically the arrangement of vegetation in layers. Vertical stratification is easily evident in forests. The 5 main layers in a forest are the canopy, understory, shrubbery, herbaceous layer and forest floor.
Productivity refers to the total accumulation of organic matter or biomass in an ecosystem. Nutrient cycling is the movement of nutrients between the biotic and abiotic components of an ecosystem.