Stratification

stratification

[‚strad·ə·fə′kā·shən]

(geology)

An arrangement or deposition of sedimentary material in layers, or of sedimentary rock in strata.

(hydrology)

The arrangement of a body of water, as a lake, into two or more horizontal layers of differing characteristics, especially densities.

The formation of layers in a mass of snow, ice, or firn.

McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

stratification

see SOCIAL STRATIFICATION.

Collins Dictionary of Sociology, 3rd ed. © HarperCollins Publishers 2000

stratification

1. The separation of overwet or overvibrated concrete into horizontal layers with increasingly lighter material toward the top; water, laitance, mortar, and coarse aggregate tend to occupy successively lower positions in that order.

2. A layered structure in concrete resulting from the placement of successive batches that differ in appearance.

McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.

The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Stratification

 

the disposal of sedimentary rocks in the earth’s crust in strata or layers. Initial stratification is ordinarily almost horizontal. As a result of tectonic movements of the earth’s crust, stratification may become inclined, folded, or broken by faults.

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Stratification

 

in agriculture, a presowing method of accelerating the germination of seeds. Stratification is used mainly for difficult-to-sprout seeds of woody species (fruit, forest, and ornamental species) and certain medicinal plants. The seeds are stored in layers in a moist well-aerated medium (sand, sawdust, crumbled peat, moss) and kept at low temperatures (I° to 5°C). Three to four parts substrate are used to one part seeds. The seeds are stratified for one to several months.

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Stratification

 

(also layering), the vertical division of plant communities, or phytocoenoses, into strata, that is, into rather precisely delimited levels of concentration of the active organs of the plants.

Aboveground stratification is the result of the selection of species capable of growing compatibly by using different levels of the aboveground environment. For example, some plants prosper under conditions of decreased light intensity caused by shading from taller plants. Thus, stratification ensures more complete use of the aboveground environment by components of phytocoenoses.

Stratification is most marked in forests of the temperate zone, where the following strata are distinguished: arboreal (sometimes two arboreal strata), shrub, herbaceous (or herbaceous-shrub), and moss (or lichen). Strata may be formed by one or two or more species, including those belonging to different ecobiomorphs, for example, the arboreal stratum of coniferous and deciduous trees in mixed forests. A stratum is defined when the composition of plants within it is quite closed. Each stratum is characterized by special conditions of the environment, for example, specific light and temperature conditions. Epiphytes and lianas do not belong to any stratum. Young and stunted individuals of tall plant species are usually assigned to the stratum in which their active organs are located.

In some types of phytocoenoses (most herbaceous ones, certain types of tropical rain forests and broad-leaved forests) stratification is absent or weakly expressed; absent or weak stratification has strong implications for the structure of phytocoenoses. Strata are formed early in the establishment of phytocoenoses. They subsequently represent a relatively stable formation (for example, the spruce stratum in spruce forests), or they are subject to changes in the course of the vegetative season (for example, strata formed of herbs or deciduous trees) or sometimes even from year to year (herbaceous polydominant strata).

Depending on the depth of rooting, subterranean stratification is sometimes discerned in phytocoenoses. One stratum is readily distinguishable. Only rarely can a second stratum be discerned, for example, on solonetzes, in arid regions, or in places where groundwaters are close to the surface. The second stratum is an aggregation of absorptive roots in a soil moistened by groundwater.

T. A. RABOTNOV

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.