In ecology, stratification refers to the vertical stratification of a living space (“multi-storey building”). It describes the layers (sing. Stratum , pl. Straten ) of the vegetation , which is essentially determined by the different heights of growth of the individual plants. The individual layers are populated by various animal and plant communities (stratocenoses).
Vertical structure in terrestrial plant populations
A distinction is made between root , soil , herb , shrub and tree layers . The vegetation stratification is mainly determined by the height of the individual plants, whereby the different elements can form sliding height sequences. The actual layer is characterized by the height area in which the majority of the photosynthetic organs (mainly leaves ) are located. High-growing species have part of their shoot system in the layers below. After the above-ground stratification, there is also one in the root space. In the broadest sense, the stratification of the diaspores in the soil can be added to the vertical structure. The plants in one layer, particularly of the same life form and similar root distribution, interact closely and are usually strong competitors for space, light, water and nutrients. The stratification of a plant community is the result of long selection and adaptation processes . By creating different layers, a given habitat is better used. Habitats that are heavily layered vertically are considered to be quite stable ecosystems . The reverse is not true, because some less layered types of vegetation, such as reeds , can be very stable. The layers of a stand are closely interrelated and partially mutually dependent. This often happens through the change in the microclimate caused by the higher layers, whereby the light factor is of particular importance.
In addition to the superimposition of different plants growing on the same soil surface, there is also a lateral extension of higher layers into neighboring plant stands, for example at the edges of forests and bushes. The special vegetation structure causes the development of certain types of vegetation such as mantle and fringe communities .
This vegetation layer begins at around five meters and includes the uppermost part of a stand consisting of phanerophytes . They can be about 45 m high. The trees (partly also bushes) have different heights. One tree already has its crown at a height where the other still has the trunk. At the top, the crowns of the various tree species form a more or less closed canopy. In tropical rainforests, individual reservoirs , which can be up to 60 m high, protrude over the main canopy.
In forests, this layer creates special ecological conditions in the layers below. The radiation inside the forest is determined by the density of the trees. Heavy precipitation is softened by the treetops and the rainwater is slowly drained downwards. The tree layer can be further divided into the upper (crown layer) and lower tree layer.
The vegetation layer of the shrubs in a habitat with heights of between one and a half to about five meters is called the shrub layer. Young, regrowing trees are included in these layers. A distinction can be made between the first and second shrub layers (low and high shrubs). The shrub layer needs sun and only a little moisture, unlike the moss layer, which, on the other hand, needs a lot of moisture. This floor only gets the filtered light from the crowns, ie penumbra or shadow plants prefer to grow here , which would not tolerate bright sunlight. Blackbirds, song thrushes, robins and blackcaps like to stay in the shrub layer, which consists of young trees and shrubs. They build their nests protected in the bushes and are therefore called bush breeders. In addition to the shrubs such as elder, hazel, hawthorn , raspberry and blackberry, the linear clematis can also occur. The bush layer on the edge of the forest acts as a windbreak and prevents the soil from drying out.
The herb layer (also known as the field layer) is that of the non-woody vegetation that is bound to the ground and grows up to about one and a half meters high. The herb layer consists of various herbaceous plants , grasses, dwarf shrubs ( hemikryptophyte , geophyte , therophyte and chamaephyte ) and young plants of the woody plants. Early bloomers first appear in forests before the canopy closes. After that, the plants have little light available. Plants then come to flower which are adapted to these conditions. Only layers of moss and weeds have developed in the grassland. Occasionally there are layers of shrubbery in transition to forest cover ( succession ) , usually when it is abandoned .
Vegetation directly on the surface up to about 0.15 meters is called a moss layer, soil or cryptogamous layer . First there is a layer of dead plant and animal material (litter) on the floor. Countless small and tiny soil organisms such as bacteria , fungi , algae and microorganisms live in this layer and the upper centimeters of the topsoil below , which decompose the dead organic substances and return them to the soil. In places the ground is overgrown with lichens and mosses .
The subterranean area of a plant stand is called the root layer. The “basement” of the forest extends down to five meters. All plants that grow in the forest take root here. Mice and foxes dig their tunnels and burrows between the underground roots . Typical inhabitants of the root layer are millipedes and earthworms . In winter, some insects , reptiles and amphibians also withdraw from the soil layer there. In addition, there are modified parts of the shoots such as rhizomes , bulbs or tubers in the root layer .
Vertical structure in aquatic plant populations
A special stratification results in waters. In adaptation to the life forms of the aquatic and marsh plants, the following layers can be divided:
- Pleuston layer : Plants floating freely on the surface of the water.
- Nymphaeidenschicht : Plants rooted in the ground and floating on the surface of the water.
- Elodide layer : Plants that are mainly rooted in the ground and fill the water space .
- Isoetic layer : plants that take root and grow directly on the ground.
- Halophyte layer : cryptogams attached to solid substrates.
- Helophyte layer : Plant parts of different heights that are rooted in the ground and protrude from the water.
Due to the vertical and horizontal division, the vegetation requires a structuring of the plant population, which creates habitats with habitat properties such as living and resting options, hiding places, food and nutrition options and / or a suitable microclimate for living beings. The more structured a stock is, the more ecological niches are available to the living world. The stratification is most diverse in tropical rainforests . Accordingly, the biodiversity near the equator is very high. In addition, small plants benefit from the dead leaves of the "jungle giants", as these are converted into useful minerals by microorganisms.
- H. Dierschke: Plant Sociology . Ulmer, Stuttgart 1994, ISBN 3-8252-8078-0 .
- CS Elton: Animal Ecology. Sidgwick & Jackson, London 1927.
- M. Schaefer: Dictionary of Ecology. Spectrum, Jena 1992. ISBN 3-8252-0430-8 .