Succession is an orderly process of community change. It involves replacement, over time, of the dominant species within a given area by other species. Primary succession occurs in newly formed habitats.
Stratification is the separation of components of an ecosystem into layers/strata/storeys e.g in a forest three layers are seen; the upper storey/emergents, middle storey and under storey. Can also be seen in deep water bodies which may differ in light Penetration, salinity or temperature. It helps to reduce competition between organisms.