Structure, layering and mosaic of plant communities. The phenomenon of layering, preconditions and reasons for its formation. Biological and morphological interpretation of the concept of "layer". The concept of extra-tiered plants, undergrowth, canopy, synusia Layering and species composition

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Phytocenosis- a plant community that exists within the same biotope. It is characterized by the relative homogeneity of the species composition, a certain structure and system of relationships between plants with each other and with external environment. Phytocenosis is a part of biocenosis along with zoocenosis and microbiocenosis. Biocenosis, in turn, in combination with conditions abiotic environment(ecotope) forms biogeocenosis. Phytocenosis is the central, leading element of biogeocenosis, as it transforms the primary ecotope into a biotope, creating a habitat for other organisms, and is also the first link in the circulation of matter and energy.

The structure of the plant community (phytocenosis)-- features of the distribution of its components in the space occupied by the community. Distinguish horizontal and vertical distribution of community components.

vertical structure phytocenosis called the distribution of plant organs of various species on different heights above the soil surface and at different depths in the soil.

The vertical structure is often expressed in tiered, i.e., in horizontal layers of different ecomorphs. In full-fledged multi-species developed forest plant communities, there are up to 7-8 tiers. A tier may be composed of one or more species.

The plant species that make up the plant community have their aboveground and underground parts at different levels. It depends on the hereditary properties of each species, as well as on the condition environment. Thus, the arrangement is called tiered separate parts plants according to their size. The above-ground and underground tiers are distinguished, i.e. layering of root systems.

Aboveground layering

plant community structure

Plants that have reached the usual sizes for this type should be attributed to one or another tier. Young plants that are temporarily part of the lower tiers should not be included in them. It is not necessary to allocate to a special tier those specimens of a particular species that are temporarily so oppressed that they are not able to reproduce by seed or vegetative means.

Thus, each species is included in only one layer, and in other layers, specimens of this species are present temporarily and temporarily form canopies located between the layers of the phytocenosis.

Usually, among the tiers of the community, the main one is distinguished, which determines the conditions for existence in the phytocenosis. In the aerial part of the phytocenosis, the main tier is usually one of the upper ones: either the upper arboreal one in forests or the most closed grassy one in meadows and steppes, etc. However, in some cases, the main tier (which includes the phytocenosis edificator) is the lower one, for example, the sphagnum layer mosses in peat bogs or wetlands.

Each tier, which is part of the phytocenosis, influences other tiers and, in turn, is influenced by them. Therefore, phytocenosis must be considered as something whole, and phytocenosis tiers - as its structural parts, which in some cases can be relatively independent.

Underground layering

Underground tiers are distinguished on the basis of the depth of penetration of the roots into the soil and the placement of active, i.e., capable of absorbing water and nutrients, part of root systems, usually provided with root hairs. In forests, one can often observe three to six underground tiers. For example, in a broad-leaved ash-oak forest, a tier of occurrence of rhizomes and roots of shallow-rooted herbs, a tier of roots of more deeply rooted herbs, one or two tiers of shrub roots (more superficially and more deeply rooted) are distinguished, and these tiers can coincide and then combine with underground tiers of grasses, two tiers of tree roots (the upper one is formed by ash roots, the lower one is deeper oak roots).

It is generally accepted that root systems plants included in one or another underground layer use the moisture and nutrients of those soil horizons in which this layer is located. However, in phytocenoses with insufficient moisture, thin active, so-called ephemeral roots are formed in the near-surface layers, which appear very quickly and die just as quickly when these layers dry out.

In communities with a predominance of drought-resistant plants, the mass of roots is often many times greater than the mass of above-ground plant parts.

Often, root systems close in such communities where the above-ground parts of plants are separated. Sometimes, for example, on gravelly slopes, differentiation of root systems occurs: absorbing and attaching roots are formed.

The concept of layering was formed in the late 19th - early 20th century in the works of phytocenologists who studied the boreal and broad-leaved forests of the temperate zone. So, for the first time, layering was described in 1863 by the Austrian scientist A. Kerner. In a spruce forest, he identified a tree layer, a fern layer, and a moss layer.

Then the Swedish scientist R. Gult identified 7 tiers in the forests of northern Finland:

1. upper tree layer;

2. lower tree layer;

3. undergrowth;

4. upper grass layer;

5. medium grass layer;

6. lower grass layer;

7. ground layer.

Reasons for the formation of tiers. Ecological and biologicale value of such differentiation

The main reason for layering is the inhomogeneous environmental conditions.

There are light-loving and shade-tolerant plants; their root systems are located on different depth; they need various elements mineral nutrition and unequal amount of water; in different time they bloom and bear fruit; have their own pollinators.

The longline structure of phytocinosis gives plants the opportunity to more fully use the resources of the environment. Plants of different tiers live in different conditions which reduces competition and increases species diversity. The more favorable the habitat conditions, the more complex the layering.

The layering of the phytocenosis is of great ecological importance. It is the result of a long and complex process of interspecific competition and mutual adaptation of plants to each other. Thanks to it, phytocenosis is formed by species that are very different in their ecology and have different life forms (tree, shrub, grass, moss, etc.).

For plants aquatic environment, for example, freshwater reservoirs, the corresponding layering is characteristic, which reflects their adaptability to this particular environment with its own light and temperature regime.

Animals change their position during the day, year, life, spending a longer time in one or another layer than in others. Its various invertebrate inhabitants are associated with certain depths of the soil, but they do not have a strict confinement to the underground layers.

The distribution of plants over the aboveground layers is determined by uneven illumination, which leads to differences in temperature regime and humidity mode.

In the same tiers there are plants of the same height, similar or different in their ecological characteristics (for example, conifers and deciduous species), but having approximately the same need for lighting.

Plants of different tiers influence each other. Plants of the upper aboveground tiers are more photophilous than plants lower tiers, and better adapted to fluctuations in temperature and humidity. Under their crowns, they create conditions of low light and stable temperature and humidity. Therefore, the lower tiers are formed by plants in which the need for light is less.

In turn, the plants of the lower tiers affect the plants of the upper tiers. So, for example, a layer of mosses in a spruce or fir forest accumulates a significant amount of moisture; the grass cover of the forest is involved in the process of soil formation, forming litter, etc.

Not all tiers are the same. Some of them, formed only by trees or only by shrubs and shrubs, are permanent and retain a system of trunks and branches, and in some cases even leaves, all year round. Others are fickle. They are educated herbaceous plants, the aerial parts of which completely or partially die off for an unfavorable period of the year.

When selecting tiers, two (or three) tiers of trees, one or two tiers of shrubs, three tiers of herbs, one tier of ground cover are distinguished

Plants that develop their foliage in different tiers are called intertier (or extratier) plants.

The underground layering of phytocenoses has been studied worse than the above-ground layering. The distribution of plant roots in underground layers is determined by the change in the degree of soil moisture with depth, its richness in nutrients, and the decrease in the degree of soil aeration with depth.

The underground tiers, as well as the above-ground ones, influence each other. The roots that form the upper underground layer can intercept rain water in plants whose roots are in deeper layers. In turn, the roots that make up the deeper underground tiers intercept the rising capillary water from the roots of the upper underground tiers.

Phytocenotic horizon - this is an element of the vertical structure of the plant community, which is characterized not only by the composition of species, but also by a certain composition of autotrophic plant species, by the stepped filling of space with these organs. So, in the forests of the temperate zone, 4 horizons can be distinguished:

- crown, including crowns of trees (branches, leaves, together with epiphytes);

- stem, including tree trunks with epiphytes and lianas, as well as undergrowth;

- herbal, grass-shrub or shrub, including the basal part of the trunks with epiphytes, herbs and shrubs, as well as the lower part of the undergrowth;

- subsoil, including ground mosses and lichens, low growing herbs, the lower parts of plants that are part of higher horizons.

Thus, some species take part in the formation of all four phytocenotic horizons (trees), others only three (shrubs), two (grasses and shrubs), or only one (ground mosses and lichens) horizons.

vegetable continuum - the property of vegetation to exist in the form of a continuous cover. It manifests itself in the gradual transition of plant communities into each other with a gradual change in environmental conditions.

One type of plant continuum is vertical continuum - the type of vertical structure of the ecosystem, when a clear division along the vertical into delimited layers-tiers is not observed by eye.

Classic example - vertical structure rainforest. The vertical structure of meadow and steppe grass stands is continuous.

The mass of above-ground organs and the surface of the sheets vertically changes gradually, forming a vertical continuum.

There are also:

- spatial continuum-- gradual change in the composition and properties of the vegetation cover in space

- time continuum-- gradual change in the composition and properties of the vegetation cover over time (with seasonal and long-term fluctuations, succession and evolution of vegetation)

- syntaxonomic continuum-- reflects the presence of transitional (intermediate) communities between their types (syntaxa).

- horizontal continuum-- a smooth transition of some communities to others when environmental conditions change.

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plant community structure

The distribution of plants over the above-ground tiers is determined by unequal illumination, which leads to differences in temperature and humidity conditions.

Plants of different tiers influence each other. The plants of the upper aboveground layers are more photophilous than the plants of the lower layers, and are better adapted to fluctuations in temperature and humidity. Under their crowns, they create conditions of low light and stable temperature and humidity. Therefore, the lower tiers are formed by plants in which the need for light is less.

Thus, each species is included in only one layer, and in other layers, specimens of this species are present temporarily and temporarily form canopies located between the layers of the phytocenosis.

Not all tiers are the same. Some of them, formed only by trees or only by shrubs and shrubs, are permanent and retain a system of trunks and branches, and in some cases even leaves, all year round. Others are fickle. They are formed by herbaceous plants, the aerial parts of which completely or partially die off during an unfavorable period of the year.

Plant groupings consist of a large number of plants that form a complex spatial architecture that changes over time.

The structure of a plant group is understood as the distribution of the aboveground and underground masses of plants in space and time.

The structure of phytocenosis is very complex and consists of the following elements:

aboveground and underground layering;

mosaic phytocenosis;

synusiality;

consortium.

When plant organisms are placed in space, in accordance with their requirements for environmental conditions, peculiar tiers of plants are created.

Layering is the dismemberment of a phytocenosis of structural or functional horizons that have varying degrees closeness and take a different part in the assimilation and accumulation of substances and energy that directly or indirectly affect the life of organisms in a phytocenosis.

A tier is a part of the layer of a plant group in which the assimilation organs of plants are located - leaves, stems, sucking roots, underground organs that store nutrients (roots, rhizomes, tubers, bulbs).

The tiered structure is especially clearly visible in forest phytocenoses: one or more tiers of tree species, shrubs, shrubs. herbaceous plants, mosses, lichens (Fig. December 6).

Rice. 12.6. Scheme of tiers in the forest

The layering of forests depends on environmental conditions (Fig. 12.7). Multilayer tropical forests are especially complex (Fig. 12 8). The forests of the temperate zone are quite diverse. The most complex are broad-leaved forests, in which 7-8 tiers can be distinguished. seed plants(three tree tiers, three tiers of shrubs, three herbaceous tiers). Highly complex structure plant grouping occurs in an oak forest that grows on rich soils with sufficient moisture in favorable climatic conditions. At the same time, the layering of such a forest is somewhat simplified when it grows in adverse environmental and climatic conditions. On the poor (with deep ground water) forest phytocenoses are also simplified in the sand dunes of Polissya Ukraine. In such forests, two tiers are clearly distinguished: Scotch pine and lichen. As you leave the dune, the plant grouping becomes more complicated, three tiers can be clearly distinguished in it - pines, blueberries, green mosses. The tiered arrangement of the aerial parts of plants allows for a more complete use of environmental conditions, especially light and heat. The better these conditions, the more complex the layering of plant groups. Thus, it can be stated that in more favorable conditions growth, plant groupings that are more complex in layering arise.

Plants of different tiers live in different phytoclimatic and soil conditions, so they differ not only in height, but also in ecological and biological features, exactingness to light, heat, moisture, soil conditions, methods of seed distribution. However, within the same tier, the conditions for existence are similar. Therefore, plants that live within the same tier have some similarities. Layering has a deep ecological significance, because thanks to it, plants of different species can grow on the same area. life forms. Of course, in this case we are dealing with a very long and complex process adaptations of plants, both one to another, and to the conditions of existence. At the same time, certain natural complexes species that not only did not interfere with each other, but also had certain advantages in cohabitation. Layering is also present in herbaceous phytocenoses, but it is not so noticeable, and the number of layers is most often two to three, rarely four (Fig. 12. 9).

The vegetation layers have a certain independence and stability. So, as we have already noted, Scotch pine forms various associations with various plant species that make up the lower tier. At the same time, in the mountains one can observe how the plants that made up the lower tiers of forest phytocenoses rise significantly higher than the tree species that formed the upper tier on the plain.

Rice. 12.7. Layer structure of some forest plant communities

(After P. W. Richards, 1956)

Rice. 12.8. Elevated view of primary rainforest, Dulit Mountain, Kalimantan Peninsula

(After P. W. Richards, 1956)

Rice. 12.9. Aboveground and belowground layering in the herbaceous cover of a coniferous forest

The layering of herbaceous groups also has certain features. Here the difference in height of the plants is less noticeable, because they themselves are much lower than the tree. The plants of the meadow phytocenosis, which form the first tier, include the hedgehog ( Dactylis glomerata) awnless fire ( Bromopsis inennis) timothy meadow ( Phleum pratense) meadow cornflower ( Centaurea jacea). In the second tier, meadow kitnik grows ( Alopecurus pratensis), red clover ( Trifolium pratense) soddy meadow ( Deschampsia caespitosa) meadow bluegrass ( Roa pratensis), common queen ( Leuanthemum vulgare), meadow geranium (Geranium pratense). In the third tier there are grassroots grasses, such as annual bluegrass (R. annua), bent grass thin (Agrostis tenuis), and creeping clover (T. repens), plants of the genera verbosilla (Lysimachia) and dandelion (Leontodon) other. The plants of the upper tiers are always more photophilous than the plants of the lower tiers, they are better adapted to fluctuations in humidity and temperature. In their lives important role wind plays. It stirs the air, cools the leaves, transports pollen, disperses fruits and seeds. Plants of the lower tiers are shade-tolerant, they do not withstand sudden changes in temperature, dust in them occurs with the help of insects, fruits and seeds are distributed by animals. Plants of low tiers have wide dark green leaf blades, white flowers, they are self-pollinating very well reproduce vegetatively.

Spatial differences in the distribution of plants are also observed in the underground part of the phytocenosis. Thanks to underground tiers different kinds plants absorb water and nutrients from different soil horizons. This allows a large number of organisms to grow in one area. The largest number roots in the upper horizons of the soil, it decreases with depth. But the roots of tree species go deep enough. For example, in broad-leaved forests of the temperate zone - up to 5 - 6 m deep. It is believed that the roots use moisture and nutrients from the horizons in which they are located. This is usually the case, but in phytocenoses with insufficient moisture (steppes, deserts), many plants with a deep root system during the rainy season quickly form thin active roots in the surface layers of the soil. Thanks to this, plants use water from seemingly unusual horizons. In dry weather, these ephemeral roots die off.

Underground layers are more difficult to distinguish than aboveground ones. But experts distinguish 2-3, sometimes 4 tiers. For example, in broad-leaved ash-oak plantations, there are:

The layer of occurrence of rhizomes and roots of herbaceous plants, rooted in top layer soil;

Layer of herbaceous plants with deep roots;

Shrub root layer;

Tier of ash roots;

Tier of oak roots.

Inherent underground layering and herbaceous groups. In the typical steppes of Ukraine, the following underground layers can be noted:

Layer of ephemeral roots (up to a depth of 15-20 cm);

Root layer of herbaceous plants, mainly one- or two-year-old dicots (up to a depth of 50 - 70 cm);

Root layer of soddy grasses, shear root perennials and large biennial dicotyledonous plants.

In all phytocenoses, the main number of roots (regardless of their size) is located in the upper soil horizons. Their number decreases with depth, but the length of the root system can significantly exceed the height of the above-ground part of the plant (Fig. 12-10). Quite often, especially in conditions of lack of moisture, one can observe very sparse groupings of plants, but after studying the root systems, their complete closure turns out to be (Fig. 12-11). It is also a kind of adaptation for providing plants with water in conditions of its shortage.

Highly complex issue layering in aquatic plants, because some of them are attached to the soil and are always under water, others are also attached to the bottom of the reservoir, but their leaves and flowers are on the surface of the water, and still others float freely in the water column (Fig. 12. 12). For aquatic plants, it is recommended to separate the tiers of attached species (in this case, it is proposed to indicate the depth at which the leaves of plants forming a certain tier are located), as well as the tiers of plants that float freely. However, the latter, as well as epiphytes in terrestrial phytocenoses, may not be associated with a certain depth and, therefore, will be related to mid-layer plants.

An important characteristic of the structure of plant grouping is mosaic. Usually, phytocenosis is not exactly the same over its entire area. For example, in the forest there are more or less illuminated places under a canopy of tree species, there are bumps in swamps, small depressions can often be found on a flat area of meadows, the bottom of a reservoir can have deep holes or, conversely, come to the surface, and the like. Obviously, in such places, different in ecological conditions, plants will grow that differ from those that grow in neighboring areas.

Rice. 12.10. Root system layouts

(By D. Weaver and F. Clement, 1938)

The reasons for the mosaic are different. Most often, this is the unevenness of the conditions of existence: differences in lighting, chemical features litter, Nanorelief, food conditions, animal activity and the like. Quite often, mosaicism is associated with the way the plants themselves grow. Thus, high hummocks formed by soddy sedge in swamps are covered with plants that are rarely found in the space between the hummocks.

Areas that differ from each other in the structure of the vegetation cover are called microcenosis.

Some authors call them microphytocenoses or microgroups. It should be noted that microcenosis exists in all tiers of phytocenoses. These microcenoses form small spots with an area of 4 - 10 m2 each, their combination forms a mosaic structure of a phytocenosis (Fig. 12-13). The heterogeneity of the composition of tree species and their closeness, in turn, ensures the mosaic nature of the lower tiers of vegetation.

Rice. 12.11. Vertical projection of semi-desert vegetation cover

Rice. 12.12. Scheme of vegetation layers in a shallow pond

Rice. 12.13. Fragment of a birch-larch forest with three microcenoses

a - birch and larch microcenosis (crown density 0.6)

b - larch microcenosis (crown density 0.4)

c - birch microcenosis (crown density 0.3)

Mosaic is a horizontal disjunction in the middle of a phytocenosis, which can be clear or weakly expressed.

In addition to the above, there is another definition of mosaic phytocenosis.

Mosaic phytocenosis is a phytocenosis, in which naturally repeat themselves are timed to certain conditions microcenosis. The mosaic pattern of vegetation, which is associated with the fine mosaic pattern of miscellaneous growth, should not be confused with the gradual spatial changes in growth conditions and vegetation that are observed in large areas. For example, the gradual change in environmental conditions and vegetation that is observed along a slope is not mosaic. In this case, this is a kind of ecological series of growth conditions and the corresponding dynamics of vegetation cover, which is associated with changes in humidity, salinity, and the like.

The idea of synusia, as a phenomenon that characterizes phytocenosis, is rather ambiguous. The term "sinusia" was introduced by X. gams in 1918. He proposed to unite in synusia a group of plants of the same (sinusia of the first order) or several types (sinusia of the second order), that belong to the same life form. But Gamay did not offer an appropriate classification of life forms. In the future, this term was specified and changed until it received its modern meaning.

Synusia (from the Greek Synusia - coexistence, community and lat. Usus - custom) are ecologically close groups of plants within a plant group (phytocenosis), which belong to the same life form.

The application of this term is currently quite debatable. Many scientists consider its use inappropriate. For example, according to A. G. Voronova, "the understanding of this term does not add anything new to the understanding of the structure of phytocenosis." Say, first-order synusias correspond to populations of a given species in a phytocenosis, and second-order synusias are a collection of plants of the same life form. But other authors actively use this concept and it is found in the literature.

In natural biocenoses, the specialization of plants (and other organisms), their mutual complementation and use is the result of intense competition, the most severe between plants that are similar in their biology and ecology, and somewhat weakened in the case of heterogeneous species. Different specialization of organisms is a means of facilitating their struggle for existence. At the same time, as a result of the specialization and heterogeneity of the components of the biocenosis, the stability of the grouping and the completeness of the use of natural resources- light, heat, moisture, nutrients. In the biocenosis, in addition to tiers, microcenosis and synusia, there is another type of structuredness - consortia.

Consortia (from lat. Consortio - complicity, community) - a system of heterogeneous organisms that are closely connected in their life with one species, the central one in the group.

Within any biogeocenosis, it is almost always possible to find various groups of organisms that are confined to a single species, without which they cannot exist. Most often, such an association occurs around a species that is important for creating an environment (an edifier species). An example can be such tree species as spruce, pine, oak, birch, around which a whole complex is formed. various plants and animals.

The species around which a consortium is formed are called determinants.

Species that unite around determinants are called consorts.

Most often, a consortium is formed on the basis of a plant population (spruce, pine, birch, feather grass). A consort can be associated with determinants:

trophic(get energy and nutrients from them)

topical(find storage or dwelling in them).

For example, various phytophages associated with trophic determinants, and epiphytes, birds - topical. The latter can be associated and trophic. The composition of the consortium, in addition to the type that defines it, may include:

Mycorrhizal fungi;

epiphytes;

Lichens;

Seaweed;

Phytophagous animals permanently and temporarily live on determinants or use them (collect pollen, nectar, etc.).

Groups A consort of a certain order is called concentres.

Each consortium consists of a large number of species that change over time. Let's say that young pine plantations are dominated by butter mushrooms, and 50-year-old mushrooms, porcini mushrooms and others. Spruce stem pests also appear in more mature stands, and seed-eating animals in the fruiting stage of trees. The disappearance of the determinant from the biogeocenosis is accompanied by the disappearance of many consorts, especially monophages, that is, those that feed exclusively on the basis of this consortium. Therefore species based on multiple consortia have best opportunities survive. Thus, more biological diversity is the key to the formation of more stable phytocenoses.

Rice. 12.14. Scheme of the structure of the consortium

(According to V.V. Mazing, 1970)

I, II, III - concentrates

1 - consortium determinant;

2 - consort of the first order (phytophages, epiphytes, symbionts)

3 - consort of the second, third and higher orders (zoophages).

The distribution of plants over the above-ground tiers is determined by unequal illumination, which leads to differences in temperature and humidity conditions.

Allocate tiered aboveground and underground. Due to the tiered arrangement of plants in the community, the most fully used natural conditions(light, heat, soil). The quality of life depends on belonging to a certain tier, since environmental conditions in different tiers are not the same.

In forests, tiers are formed by plants of individual life forms (according to Serebryakov), the following tiers are distinguished:

Tier A - tree stand (tier of trees);

Layer B - undergrowth (shrub layer);

Tier C - herbaceous (tier of herbaceous plants);

Layer D - moss-lichen layer.

One of the important indicators of the tree layer is the degree of crown density.

The degree of crown closure is the ratio of the area occupied by crowns to the total area of the site being described. This indicator is evaluated visually, expressed in tenths of a unit (or as a percentage).

For herbaceous communities and herbaceous forest layer, one of the characteristics is the aspect - this appearance phytocenosis (its physiognomy, color), changing in accordance with the alternation of the phases of plant development and the season.

Abundance is an external characteristic - this is the number of individuals of a certain plant species within a given vegetation cover of a trial plot. Determining the number of individuals can be done by direct counting or by using a subjective eye estimate. It is customary to use the five-point scale of the German scientist O. Drude to determine the abundance.

In some meadows, tiers can also be distinguished - tall grass, medium grass and short grass.

The presence of layers is not a mandatory feature of phytocenoses and is mainly characteristic of forest phytocenoses.

coexistence different types and life forms in the plant community leads to their spatial isolation. This is expressed in the horizontal and vertical division of the phytocenosis into separate elements, each of which plays its role in the accumulation and transformation of matter and energy.

Vertically, the plant community is divided into tiers - horizontal layers, strata, in which the above-ground or underground parts of plants of certain life forms are located.

This layering is especially pronounced in forest phytocenoses. There are usually five or six tiers here: tree tiers, shrubs, grass-shrub, moss or lichen, litter (leaf litter). Along with such diverse phytocenoses as forest, there are so-called low-tiered communities - meadow, steppe, swamp - have only two or three tiers. Plants have one type of nutrition: the diet of almost all species includes a solution of minerals, carbon dioxide and sunlight. However, their ecological niches are differentiated.

A canopy (Sukachev, 1930) is a temporary layer formed by young plants or plants oppressed by factors outside the phytocenosis (for example, logging).

Not all tiers are the same. Some of them, formed only by trees or only by shrubs and shrubs, are permanent and retain a system of trunks and branches, and in some cases even leaves, all year round. Others are fickle. They are formed by herbaceous plants, the aerial parts of which completely or partially die off during an unfavorable period of the year.

When selecting tiers, two (or three) tiers of trees, one or two tiers of shrubs, three tiers of herbs, one tier of ground cover are distinguished

Plants that develop their foliage in different tiers are called intertier (or extratier) plants.

The underground tiers, as well as the above-ground ones, influence each other. Roots that form the upper underground layer can intercept rainwater from plants that have roots in deeper layers. In turn, the roots that make up the deeper underground tiers intercept the rising capillary water from the roots of the upper underground tiers.

Underground tiers are distinguished on the basis of the depth of penetration of the roots into the soil and the location of the active, i.e., capable of absorbing water and nutrients, part of the root systems, usually equipped with root hairs. In forests, one can often observe three to six underground tiers. For example, in a broad-leaved ash-oak forest, a tier of occurrence of rhizomes and roots of shallow-rooted herbs, a tier of roots of more deeply rooted herbs, one or two tiers of shrub roots (more superficially and more deeply rooted) are distinguished, and these tiers can coincide and then combine with underground tiers of grasses, two tiers of tree roots (the upper one is formed by ash roots, the lower one is deeper oak roots).

It is generally accepted that the root systems of plants included in one or another underground layer use the moisture and nutrients of those soil horizons in which this layer is located. However, in phytocenoses with insufficient moisture, thin active, so-called ephemeral roots are formed in the near-surface layers, which appear very quickly and die just as quickly when these layers dry out.

In communities with a predominance of drought-resistant plants, the mass of roots is often many times greater than the mass of above-ground plant parts.

Then the Swedish scientist R. Gult identified 7 tiers in the forests of northern Finland:

1. upper tree layer;
2. lower tree layer;
3. undergrowth;
4. upper grass layer;
5. medium grass layer;
6. lower grass layer;
7. ground layer.

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