Community stratification is the separation of communities (e.g tropical rainforest) into strata/layer/storey; usually three strata are readily recognised: upper strata, middle strata and lower strata.
Upper strata composed of emergent dominant/tall trees which form dense dense canopy, intercepts most of  sunlight; The middle strata is made up of small trees and shrubs and the lower strata made up of flower plants and herb.
-Stratification provides differentiation of micro habitats/niches
-Reduces competition, as organisms are found only in micro-environments to which they are best adapted.
-upper storey trees protect lower storey trees/organism from harsh effect of weather.
-Stratification could also occur in deep water bodies; caused by difference in temperature or salt concentration; it pose virtually similar ecological effects as above.