Species structure of phytocenosis. Phytocenosis. Composition of phytocenosis: participation of species and its assessment (abundance, cover, phytomass). Vertical and horizontal composition of phytocenosis. The structure of phytocenoses should be understood

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STRUCTURE OF PHYTOCOENOSES

THE IMPORTANCE OF STUDYING THE STRUCTURE OF PHYTOCOENOSES

Considering the formation of phytocenoses, we saw that they arise as a result of plant reproduction in conditions of complex interactions between plants and the environment, between individuals and between plant species.

Therefore, a phytocenosis is by no means a random set of individuals and species, but a natural selection and association into plant communities. In them, certain types of plants are placed in a certain way and are in certain quantitative ratios. In other words, as a result of these mutual influences, each phytocenosis receives a certain structure (structure), both in its above-ground and underground parts.1

The study of the structure of the phytocenosis provides morphological characteristics of the latter. It has a double meaning.

Firstly, the structural features of the phytocenosis are most clearly visible and can be measured. Without an accurate description of the structure of phytocenoses, neither their comparison nor generalizations based on comparison are possible.

Secondly, the structure of a phytocenosis is the design of mutual relationships between plants, the ecotope and the environment of the phytocenosis in given local conditions and at a given stage of development. And if so, then the study of the structure makes it possible to understand why the observed phytocenosis developed the way we see it, what factors and what interactions between them were the cause of the structure of the phytocenosis we observed. This indicative (or indicator) significance of the structure of phytocenoses makes its study the first and most important task in geobotanical research. It is by the floristic composition and structure of the phytocenosis that the geobotanist determines the quality of soils, the nature of local climatic and meteorological conditions, establishes the influence of biotic factors and various forms

human activity.

The structure of the phytocenosis is characterized by the following elements:

1) floristic composition of the phytocenosis;

2) the total number and mass of the plant population of the phytocenosis and quantitative relationships between species and groups of species;

4) the distribution of plant species in the phytocenosis and the division of the phytocenosis into its structural parts based on it.

The distribution of plant species in a phytocenosis can be considered from the perspective of their distribution in the space occupied by the phytocenosis, and from the perspective of their distribution in time. Distribution in space can be considered from two sides: firstly, as a vertical distribution - a tiered (or sinusial) structure and, secondly, as a horizontal one, otherwise called addition and manifested in the mosaic of phytocenoses; distribution in time manifests itself as a change in synusia at different times.

FLORISTIC COMPOSITION OF PHYTOCOENOSES

Floristically simple and complex phytocenoses

Based on the number of species that make up the phytocenosis, floristically simple and floristically complex phytocenoses are distinguished:

simple - from one or a few types, complex - from many types. An extremely simple phytocenosis should consist of individuals of one plant species (or even one subspecies, variety, one race, ecotype, etc.). Such phytocenoses do not exist in natural conditions, or they are extremely rare and are found only in some completely exceptional environment.

Only in artificial pure cultures of bacteria, fungi and other plants can their extremely simple groups be obtained. Under natural conditions, there is only relative simplicity or low floristic saturation of some phytocenoses. These are, for example, natural “pure” thickets of some grasses (thickets of sharp sedge, canary grass, southern reed, etc.), almost weed-free crops, dense young forests, etc. We see them as extremely simple only until out of habit, we take into account only higher plants. But as soon as we remember that in any such thicket there are many species of lower plants - bacteria and other microphytes interacting with each other and with this thicket and with the soil - the relativity of its floristic simplicity becomes obvious. Nevertheless, during geobotanical study they can be considered relatively simple, since the higher plants in them determine the main and visible structural features, and microorganisms are still rarely taken into account in this kind of research (although taking into account their activities is absolutely necessary for understanding many aspects of the life of the phytocenosis of higher plants ).

Floristically complex phytocenoses are more complex the more species they contain and the more diverse they are in ecological and biological terms.

(1929) distinguished phytocenoses:

from one type - aggregation; from several ecologically homogeneous species - agglomeration; from several aggregations or agglomerations that can exist separately - semi-association; from similar aggregations and agglomerations, but capable of existing only together - associations.

Grossheim interpreted these types of phytocenoses as successive “stages” in the development of vegetation cover and its complexity. However, the terms he proposed did not receive general recognition in the indicated sense.

An example of very high floristic complexity, or saturation of higher plant species, is the phytocenoses of tropical rain forests. In the forests of tropical West Africa, covering an area of ​​100 m2 found from above 100 species of trees, shrubs and herbs, not counting the huge number of epiphytes growing on the trunks, branches and even leaves of trees. In the former USSR, floristically rich and complex sub rainforests humid regions of Transcaucasia and the lower zones of the southern part of Sikhote-Alin in the Primorsky region, but they still do not reach the complexity of tropical rain forests. The herbaceous communities of Central Russian meadow steppes are complex, where 100 m2 There are sometimes up to 120 or more species of higher plants. In a complex (with undergrowth) pine forest in the suburbs of Moscow on an area of ​​0.5 ha 145 species were found (8 species of trees, 13 species of undergrowth shrubs, 106 species of shrubs and grasses, 18 species of mosses). In taiga spruce forests, floristic saturation is less.

Reasons for differences in floristic complexity of phytocenoses

What determines the degree of floristic complexity, or saturation, of phytocenoses? What environmental features does the floristic richness or, conversely, the poverty of the phytocenosis indicate to us? There are several reasons for this or that floristic complexity, namely:

1. General physical-geographical and historical conditions of the area, on which the greater or lesser diversity of the flora of the region depends. And the richer and more ecologically diverse the flora of an area, the greater the number of species competing for any territory in this area, the more larger number under favorable conditions, they can live together in one phytocenosis.

The floristic richness of the Central Russian meadow steppes is replaced in the drier southern and southeastern regions by the much less floristic richness of the phytocenoses of the feather grass steppes. Central Russian oak forests are floristically more complex than coniferous taiga northern forests. Phytocenoses in the lakes of the Kola Peninsula are floristically poorer than similar phytocenoses in more southern lakes. In the Arctic, where the flora of higher plants is poor, the complexity of individual phytocenoses is also low.

2. Edaphic conditions of habitat. If soil and ground conditions are such that they allow the existence of only one or a few species of local flora that are most adapted to these conditions, then only they form phytocenoses (the latter, therefore, turn out to be relatively simple even in areas with a very rich flora). And vice versa, if the ecotope satisfies the requirements of many plant species, they form more complex phytocenoses.

Almost pure thickets of sharp sedge or reeds, thickets of saltwort on salt marshes, or pine forests with a carpet of cladonia on the soil therefore consist of very few species, because the inherent waterlogging in these places or too much poverty or dryness, or salinity of the soil, etc. . exclude all other plants. In areas of flooded meadows that annually receive thick deposits of sand or silt, phytocenoses of one or a few species are common that can survive the annual burial of their renewal buds by thick deposits of alluvium. Such are the thickets of the underbelly of the present (Petasitesspurius), bonfireless fire (Bromopsisinermis), ground reed grass (Calamagrostisepigeios) and other plants with long rhizomes that can quickly grow through the sediment that buries them. On soils very rich in nitrates, single-species thickets of creeping wheatgrass sometimes form (Elytrigiarepens) or nettle (Urticadioica) and other nitrophils.

Thus, any extreme conditions lead to the formation of phytocenoses of the most simple structure. In the absence of such extremes, more complex phytocenoses are obtained, which is what we see in the example of most forest, meadow, steppe and other phytocenoses.

3. Sharp variability of the ecological regime. The sharp variability of the water regime especially noticeably increases the floristic richness and ecological heterogeneity of the flora of the phytocenosis. Thus, the spring moistening of the feather grass steppe causes an abundance of ephemerals and ephemeroids, which end the growing season before the onset of dry and hot summer. In water meadows, spring moisture ensures the growth of moisture-loving species; summer dryness limits them, but is favorable for species growing here that are moderately demanding of moisture, but can tolerate spring waterlogging. As a result, a large number of ecologically diverse species are observed, together forming a complex phytocenosis. In some floodplain meadows (Ob River, middle Volga), moisture-loving plants (hydrophytes), for example, bogwort, literally grow side by side (Eleocharispalustris), and many mesophytes, and even xerophytes.

The variability of the light regime can have a similar significance. In oak-broad-leaved forests, every year during the growing season, two periods alternate in lighting: in the spring, when the leaves of trees and shrubs that have not yet blossomed do not prevent the penetration of light, many light-loving plants grow and bloom - Siberian scilla (Scitlasibirica), corydalis (Corydalis) and other spring ephemeroids, the later period - the period of shading by developed foliage - is used by other, shade-tolerant plants.

4. Biotic factors. The most obvious example is the influence of wild and domestic animals on vegetation. Livestock grazing changes soil and soil conditions and the species composition of plant groups: the soil either becomes compacted or, conversely, loosens, hummockiness appears, excrement left by animals fertilizes the soil - in short, the air-water, thermal, and salt regimes change. This entails a change in vegetation. Grazing directly affects plants: grazing and mechanical trampling select species that can withstand this impact.

Grazing, in combination with varying degrees of influence of climate, soil and original vegetation, can contribute to either the complication of the original phytocenoses or their simplification. For example, when grazing hummocks form on damp soil, the hummocky microrelief increases the heterogeneity of the environment and the range of species. When grazing animals on moderately moist soil, the turf is often disturbed, and repeated grazing weakens the dominant plants, which promotes the growth of weedy pasture grasses, i.e., the range of phytocenosis species increases. On the contrary, intensive grazing on dense, turfy soil allows the growth of only a few persistent species. Therefore, many previously floristically complex meadow and steppe phytocenoses, now, with their strong pasture use, have turned into extremely simplified ones, consisting of a few species. Mouse-like rodents, inhabiting various phytocenoses and loosening the turf and surface layers of soil with their moves, contribute to the settlement of many plants and thereby create and maintain a more complex structure of the vegetation cover.

5. Properties of some components of phytocenosis. For example, on abandoned arable land with fairly rich soil, often after 1–2 years an almost pure thicket of creeping wheatgrass grows. This plant, quickly spreading with the help of long branched rhizomes, takes over arable land faster than many other plant species that can grow here as well as wheatgrass, but spread more slowly. The latter only gradually penetrate into the wheatgrass phytocenosis and complicate it.

Similar and for the same reason, pure thickets of fireweed and ground reed grass grow in forest burnt areas. Here, as on abandoned arable land, there are all conditions for the growth of many species, i.e., for the formation of complex phytocenoses. But the two named species, having great energy in both seed and vegetative reproduction, spread faster than others. The penetration of other species into such thickets is usually delayed by the saturation of the soil with rhizomes and roots of the pioneer species, as well as by the density of their grass stand. Such thickets, however, quickly thin out, since the species that form them are demanding on soil looseness (aeration), and sometimes on its richness in nitrates; their proliferation compacts the soil, impoverishes it, which leads to self-thinning.

There are also plants that are capable of creating conditions for relatively poor flora coexisting with them and maintaining them for many tens and hundreds of years. That's what spruce is like. In a spruce mossy forest, strong shading, air and soil humidity, soil acidity, an abundance of slowly and poorly decomposing litter and other features of the air and soil environment caused by the spruce itself allow the settlement under its canopy of a few other species of higher plants adapted to the spruce forest environment. It is worth looking at a clearing in the middle of such a forest to be convinced by the abundance of many species that are absent in the surrounding forest that this ecotope is completely suitable for them. This means that the low floristic saturation of the spruce forest is the result of the influence of its environment.

The environment of a plant community can also complicate its floristic composition. For example, under the canopy of forest plantings in the steppe, various forest plants appear over time, and initially simple plantings turn into more complex forest phytocenoses.

Thinking about the reasons for the floristic richness or poverty of phytocenoses, we see that they can all be reduced to three groups of factors: firstly, to the influence of the primary environment (ecotope), secondly, to the influence of the environment of the phytocenosis itself (biotope) and, in -third, to the influence of biotic factors. These reasons operate within the framework of the richness or poverty of the area's flora and its ecological diversity, determined geographically, historically and ecologically.

By finding out the reasons for a particular floristic saturation of each phytocenosis, we thereby clarify its indicative significance for characterizing environmental conditions and the degree of their use by plants.

The degree of floristic saturation indicates the complete use of the environment by the phytocenosis. There are no two species that are completely identical in their relationship to the environment and in their use of it. Therefore than more types is located in a phytocenosis, the more versatile and complete the use of the environment it occupies. Conversely, a phytocenosis consisting of one or a few species indicates incomplete, one-sided use of the environment, often only because local flora there were no other species capable of growing here. For example, a forest without shrubs uses the energy of solar radiation less fully than a forest with a shrubby undergrowth. The undergrowth uses rays passing through the upper canopy of the forest. If there is also grass or green mosses under the undergrowth, then they, in turn, use the light passing through the undergrowth. In a forest without undergrowth, grasses and mosses, all the light penetrating through the tree crowns remains unused.

If we remember that green plants are the only natural agents that convert the energy of solar radiation into organic matter with a huge reserve of chemical energy, then it will become clear how important it is for plant communities to be as complex as possible.

The floristic composition of phytocenoses is sometimes increased artificially. This is achieved by sowing or planting other plant species in phytocenoses, even alien to the local flora, but suitable for the given conditions. Sometimes ecological and phytocenotic conditions are changed for the same purpose.

In Germany and Switzerland, spruce forests are converted into more profitable mixed forests by planting other tree species (beech). Instead of single-species crops of forage cereals and the same crops of legumes, they prefer to cultivate mixed cereal-legume crops, not only because they are more appropriate for improving the soil and the quality of hay, but also because their use of field resources and their productivity are greater than pure crops.

Identification of the complete flora of the phytocenosis

All plant species that make up the phytocenosis depend on the conditions of existence, and each species contributes its share to the formation of the phytocenosis environment. The more fully the floristic composition of the phytocenosis is known, the more data the researcher has to judge environmental factors.

Revealing full composition- not an easy task even for an experienced florist. Some species of higher plants present in a phytocenosis, at the time of observation, can only be found in the form of rhizomes, bulbs or other underground organs, as well as in the form of seeds in the soil, and because of this they often go unnoticed. It is difficult to determine the species of seedlings and juvenile forms. Recognizing the species of mosses, lichens, and fungi requires special training and skills, and identifying the microflora of a phytocenosis requires a special, complex technique.

When studying the floristic composition, as well as when studying other signs of the structure of a phytocenosis, it is necessary that the phytocenosis occupies an area sufficient to reveal all its features. Even the completeness of recording the floristic composition depends on the size of the recorded area. If there is, for example, a herbaceous phytocenosis of several dozen plant species, then by choosing an area of ​​0.25 m2 to take into account the floristic composition, we will find several species on it. Having doubled the area, we will find on it, in addition to those already noted, species that were absent on the first one, and the general list of species composition will be replenished. With a further increase in area to 0.75–2 m2, etc., the list of species will continue to increase, although with each increase in area the profit of the number of species in the general list becomes smaller. By increasing the sites to 4 m2, 5 m2, 10 m2, etc., we notice that at sites larger than, for example, 4 m2, there is little or no new addition to the list of species. This means that the 4 m2 area we took is the minimum area for identifying the entire species composition of the phytocenosis under study. If we limited ourselves to a smaller area, it would be impossible to fully identify the species composition. There are areas of vegetation cover that differ from neighboring ones, but are so small in size that they do not reach the area for identifying the floristic composition of the phytocenosis to which they belong. These areas are fragments of phytocenoses.

The term “detection area” has been proposed. Foreign authors use the term “minimum range”.

The area of ​​identification of the species composition of phytocenoses of various types is not the same. It is not the same for different parts of the same phytocenosis. For example, for a moss cover on soil in a forest, 0.25–0.50 m2 is often sufficient to meet all types of mosses present in a given phytocenosis in such a small area. For herbaceous and shrub cover in the same phytocenosis, a large area is required, often at least 16 m2. For a forest stand, if it consists of several species, the detection area is even larger (from 400 m2).

In various meadow phytocenoses, the minimum area for detecting floristic composition does not exceed or barely exceeds 100 m2. Finnish authors consider an area of ​​64 m2.

Bearing in mind the identification of not only the floristic composition of the phytocenosis, but also various other structural features, in the practice of Soviet geobotanists, when describing a complex forest phytocenosis, it is customary to take a sample area of ​​at least 400–500 m2, and sometimes up to 1000–2500 m2, and when describing herbaceous phytocenoses - about 100 m2 (if the area of ​​the phytocenosis does not reach such dimensions, all of it is described). Moss and lichen phytocenoses often have a detection area of ​​no more than 1 m2.

The phytocenosis is characterized by:

1. certain species composition;
2. structure, or otherwise, the features of the placement of components in space and time;
3. conditions of existence.

Species composition phytocenosis. The established phytocenosis has its own physiognomy and certain characteristics. The most important feature phytocenosisstated floristic composition- a set of plant species included in a phytocenosis. The number of species included in the phytocenosis may vary. Phytocenoses consisting of one plant species are very rare in nature. Single-species phytocenoses formed lower plants, usually denoted by the word “colony”. In the case when one type of higher plant, a “thicket,” takes part in the formation of a phytocenosis, next to the word “thicket” is placed the name of the higher plant that is part of the phytocenosis (nettle thickets, raspberry thickets, etc.).

In nature, there are predominantly complex phytocenoses, which include not only higher plants, but also lower plants. The total number of species found in the phytocenosis over the entire occupied area depends on the conditions of existence (habitat conditions) of the phytocenosis and the history of its development. The size of the area occupied by the phytocenosis is also of considerable importance. The number of species registered on the registration site located within the described phytocenosis gives an idea of ​​its species richness and species diversity.

Phytocenosis (from the Greek φυτóν - “plant” and κοινός - “general”) is a plant community that exists within the same biotope. It is characterized by relative homogeneity of species composition, a certain structure and system of relationships of plants with each other and with the external environment. Phytocenoses are the object of study of the science of phytocenology (geobotany).

Phytocenosis is part of the biocenosis along with zoocenosis and microbiocenosis. The biocenosis, in turn, in combination with the conditions of the abiotic environment (ecotope) forms a 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 cycle of substances and energy. The properties of soils, microclimate, the composition of the animal world, such characteristics of biogeocenosis as biomass, bioproductivity, etc., depend on vegetation. In turn, the elements of phytocenosis are cenopopulations of plants - collections of individuals of the same species within the boundaries of phytocenoses.

The layering was first described by the Austrian scientist L. Kerner in 1863. In the spruce forest, he distinguished: the tree layer, the fern layer and the moss layer. Then the Swedish scientist Gult identified 7 tiers in the forests of northern Finland:

1. top woody,
2. lower woody,
3. undergrowth,
4. top grass,
5. medium herbal,
6. lower grass,
7. ground

Vertical structure has two polar options, connected by smooth transitions: tiered and vertical continuum. Thus, layering is not a mandatory characteristic, but different heights of plants are a widespread phenomenon.

Tiering allows species of different ecological qualities to coexist in a community, makes the habitat more ecologically capacious, and creates a large number of ecological niches, especially in relation to the light regime.

In the series single-tiered - two-tiered - multi-tiered - imperfectly layered (vertical-continuous) communities, an increase in floristic richness is observed.

The consistent use of the concept of tiering has a number of theoretical difficulties due to the fact that:

1. not all communities are vertically discrete;
2. it is unclear whether tiers are layers or elements “inserted” into each other;
3. It is unclear where to include vines, epiphytes, and undergrowth.

To overcome these difficulties, Yu. P. Byalovich formulated the idea of ​​a biogeocenotic horizon - a vertically isolated and vertically indivisible structural part of the biogeocenosis. From top to bottom, it is homogeneous in the composition of biogeocenotic components, in their interrelationships, the transformations of matter and energy occurring in it, and in these same respects it differs from the neighboring, higher and lower located, biogeocenotic horizons.

The vertical parts of plant communities, accordingly, form phytocenotic horizons. Each of them is characterized not only by the composition of autotrophic plant species, but also by a certain composition of the organs of these plants. With this approach to the analysis of vertical structure, controversial issues disappear, including where to classify lianas, epiphytes or undergrowth.

Horizontal structure

Most plant communities are characterized by heterogeneity of horizontal composition. This phenomenon is called mosaic phytocenoses. Mosaic elements are most often called microgroups, although a number of researchers have proposed their own terms - microphytocenoses, coenoquants, coenocells. The concept of a parcel stands apart. - element of horizontal heterogeneity of biogeocenosis.

The uneven distribution of species is due to a number of reasons. There are types of mosaics based on their origin:

1. Phytogenic mosaic caused by competition, changes in the phytoenvironment or the specific life forms of plants (the ability to vegetative propagation and formation of clones).
2. Edaphotopic mosaic associated with the heterogeneity of the edaphotope (irregularities in the microrelief, different drainage, heterogeneity of soils and litter, their thickness, humus content, granulometric composition, etc.).
3. Zoogenic mosaic caused by the influence of animals, both direct and indirect (mediated) - eating, trampling, laying excrement, and the activity of burrowing animals.
4. Anthropogenic mosaic is associated with human activity - trampling due to recreational load, grazing of farm animals, mowing of grass and cutting down of forest plant communities, resource harvesting, etc.
5. Exogenous mosaic, caused by external abiotic environmental factors - the influence of wind, water, etc.

Mosaic- a special case of horizontal heterogeneity of vegetation cover. When studying the horizontal heterogeneity of vegetation in a region, researchers distinguish between two concepts, two circles of phenomena - mosaic and complexity.

In contrast to mosaicism, which characterizes intracenotic horizontal heterogeneity, complexity is the horizontal heterogeneity of plant cover at the supraphytocenotic level. It manifests itself in the natural alternation of individual phytocenoses or their fragments within the same landscape.

The complexity of the vegetation cover is determined by micro-or mesorelief, which serves as a kind of redistributor of the load of the main environmental factors and thereby differentiates the landscape into habitats with different ecological regimes.

There are complexes and combinations of communities. Complexes are communities related to each other genetically, i.e. being successive stages of one succession process.

Sometimes they talk about the sinusial structure of plant communities, thus highlighting the special structural elements of the phytocenosis - synusia.

Sinusia- these are structural parts of a plant community, limited in space or time (i.e., occupying a certain ecological niche) and differing from one another in morphological, floristic, ecological and phytocenotic terms.

The synusia of spring forest ephemeroids, the “pseudo-meadow” synusia in deserts, or the synusia of annuals in some types of vegetation are well distinguished in deciduous forests.

Phytocenosis is a plant community characterized by relative homogeneity of species composition, determined primarily by habitat conditions, and relative isolation from other communities, consisting of coenopopulations connected by the relations of differentiation of ecological niches and interference, located in conditions of relatively homogeneous habitat conditions and capable of independent existence.

Phytocenosis is a conditional concept, since, firstly, a community of some plants cannot really exist without interaction with other components of biogeocenosis - zoocenosis, microbiocenosis, biotope, and secondly, according to the dominant concept of continuity of vegetation cover today, any isolation of isolated communities from it are artificial and serve only for practical purposes of studying vegetation at all levels.

The modern idea of ​​phytocenosis as a conditional, really non-existent formation arose on the basis of an individualistic hypothesis developed by the Russian scientist L. G. Ramensky and the American G. Gleason. The essence of this hypothesis is that each species is specific in its relationship to the external environment and has an ecological amplitude that does not completely coincide with the amplitudes of other species (that is, each species is distributed “individually”). Each community produces species whose ecological amplitudes overlap under given environmental conditions. When any factor or group of factors changes, the abundance of some species gradually decreases and disappears, other species appear and increase in abundance, and in this way a transition is made from one type of plant communities to another. Due to the specificity (individuality) of the ecological amplitudes of species, these changes do not occur synchronously, and with a gradual change in the environment, the vegetation also changes gradually. Thus, plant communities do not form clearly isolated units, but are linked by transitional communities into a continuously varying system.

Depending on the specifics of the research in the concept of “biocenosis structure” V.V. Masing (1973) identifies three directions that he developed for phytocenoses.

1. Structure, as a synonym for composition (specific, constitutional). In this sense, they talk about species, population, biomorphological (composition of life forms) and other structures of the cenosis, meaning only one side of the cenosis - composition in the broad sense. In each case, a qualitative and quantitative analysis of the composition is carried out.

2. Structure, as a synonym for structure (spatial, or morphostructure). In any phytocenosis, plants are characterized by a certain affinity to ecological niches and occupy a certain space. This also applies to other components of the biogeocenosis. Between the parts of the spatial division (tiers, sinusia, microgroupings, etc.) you can quite easily and accurately draw boundaries, you can plot them on the plan, calculate the area, and then, for example, calculate resources useful plants or animal feed resources. Only on the basis of data on the morphostructure can one objectively determine the points at which certain experiments were performed. When describing and diagnosing communities, the spatial heterogeneity of cenoses is always studied.

3. Structure, as a synonym for sets of connections between elements (functional). The basis for understanding structure in this sense is the study of relationships between species, primarily the study of direct connections - the biotic connex. This is the study of chains and nutrition cycles that ensure the circulation of substances and reveal the mechanism of trophic (between animals and plants) or topical (between plants - competition for nutrients in the soil, for light in the above-ground sphere, mutual assistance).

All three aspects of the structure of biological systems are closely interrelated at the coenotic level: species composition, configuration and placement of structural elements in space are a condition for their functioning, i.e. vital activity and production of plant mass, and the latter, in turn, largely determines the morphology of cenoses. And all of these aspects reflect the environmental conditions in which the biogeocenosis is formed.

Morphological signs of phytocenosis

Plant communities, despite complex combinations of species, differ in structure. External characteristics that are used to evaluate the structure are called morphological. The main ones are: species composition, tiers, quantitative ratios of species in the phytocenosis. Let's look at each of these signs. The difference between each phytocenosis lies in its floristic composition, which is represented by a combination of certain plant species (trees, shrubs, grasses, mosses, etc.). To determine the species composition in the area, a description of botanical sites is made. The size of the site for grass phytocenoses is 1 m 2, for forest phytocenoses 1600 m 2 (80x20 m). Based on the descriptions, plant species are identified, their botanical identification is made, and the species richness of the phytocenosis as a whole is established.

Tiering in phytocenoses arises because plants have different attitudes to light, heat, moisture, and soil. In phytocenoses, plants of different heights are selected. Thanks to the layering, a larger number of species can settle on a unit area. Simply arranged phytocenoses consist of one tier (willows on sandy sediments); up to 5-9 tiers are found in forest phytocenoses (Fig. 61). The division of a phytocenosis into tiers represents a unique form of qualitative assessment of the ratio of species. As an example, we can cite the characteristics of the layering of a broad-leaved forest in the north of the Central Russian Upland. Typically, in oak forests, the first tier is formed by oak, the second tier by linden and maple, and the third by undergrowth of oak, linden, and aspen. The oak grove is characterized by a dense shrubby undergrowth (IV tier) of hazel, buckthorn, and honeysuckle. The grass cover of an oak forest can also be divided into tiers: fern (tier V), tall grasses (VI), oak forest broad grass (tier VII).

When characterizing a phytocenosis, it is important to establish the quantitative ratio or abundance of species. This characteristic is necessary to determine the predominant species (dominants) that make up the appearance of the phytocenosis. Currently, to determine abundance, the visual 4-point Drude scale is used, in which the following gradations are introduced: soc (sociales) - plants form the background; litter (copiosae) - abundantly represented; sp (sparsae) - found scatteredly; sol (solitarie) - rarely. Abundance can be more accurately determined by counting the number of species per unit area. The abundance indicator is complemented by the characteristic of the projective cover of species, when the area of ​​projections of the terrestrial parts of the species is calculated and expressed as shares (%) of the total surface occupied by the phytocenosis. This characteristic is introduced because abundance does not provide a complete picture of the participation of a species in the composition of the phytocenosis.

Variability of phytocenoses

There are daily, seasonal and annual variability of plant communities.

Daily variability. As a result of fluctuations in the intensity of a number of environmental factors - especially light and temperature - the basic physiological parameters of plants change. Some results of plant reactions to changing factors are visible to the naked eye. This includes the daily rhythm of flowering and pollination, characteristic of most plant species, the phenomena of heliotropism (movements of vegetative and generative organs associated with the position of the sun in the sky), and the phenomena of photoperiodism (plant response to light intensity). The structure of aquatic communities is especially susceptible to daily variability.

Seasonal variability caused by changes in conditions during the year and is associated with the presence in the community of groups of plants that differ in the rhythm of seasonal development (they are found in almost all phytocenoses). Seasonal variability occurs regularly from year to year and can usually be predicted. The exception is sharply anomalous years.
Climate seasonality is a widespread situation in most regions of the globe; it occurs almost everywhere, with the exception of tropical rainforest areas. Because of this, widespread and climatically determined seasonal variability communities associated with the fall and melting of snow cover, the dynamics of river water in floodplains, semi-rest or dormancy during the hottest period in steppes, semi-deserts, savannas and deserts.

Seasonal variability is not only related to climate. There is cenotically determined seasonal variability associated with changes in the phytoenvironment within the community. It is widely known, for example, the existence of two temporary synusia in the herbaceous layer deciduous forests- synusia of spring ephemeroids, developing in the spring during the period of absence of leaves on the trees, and synusia of shade-loving broad grasses, appearing with the leaves blooming on the trees and shading of the lower tiers. Finally, there is also anthropogenic seasonal variability associated with seasonal human activities (mowing plants in grass ecosystems, grazing by farm animals, etc.).

Interannual variability (fluctuation variability, fluctuations). The main reasons for the occurrence of fluctuations in phytocenoses include changes from year to year or over periods of years in various environmental conditions affecting the community. There are several types of fluctuations depending on the reasons that cause them: ecotopic fluctuations, caused by differences in meteo-, hydro- and other conditions of ecotopes from year to year, are widespread in meadow communities; anthropogenic fluctuations are caused by differences in the form and intensity of human impact on the phytocenosis. For example, in different years a meadow community can be used either as hayfields or as pasture. The timing of haymaking changes from year to year, which creates different conditions for seeding of individual plant species. The species composition of grazing animals also significantly influences; zoogenic fluctuations caused by differences in the impact of herbivores and burrowing animals (especially digging rodents and insects).

Changes in phytocenoses over time

No phytocenosis exists forever; sooner or later it is replaced by another phytocenosis. The ability to change is one of the most important properties of plant communities.
Irreversible and directed, i.e., changes in vegetation cover that occur in a certain direction, manifested in the replacement of one phytocenosis by another, are called succession. It is their irreversibility and directionality that distinguishes them from fluctuations. Changes in phytocenoses have long been noticed and described, but the theory of these processes was most thoroughly worked out by the American scientists Henry Cowles and F. Clements. Clemente created a system of ideas about succession, starting with the emergence of phytocenoses up to the formation of stable, self-renewing plant communities - climaxes. The final stage of any succession - climax - can occupy an area indefinitely and exist for many hundreds of years practically unchanged. The main property of the climax community is a zero balance of matter and energy throughout the year.

There are two main types of successions - primary and secondary. Primary successions are quite rare in nature. They begin with the emergence of phytocenoses on bare mineral substrates, where previously there was no vegetation. Examples of such substrates are scree in the mountains, frozen recent lava flows, bottoms and sides of valleys after glacier retreat, exposed seabed, blown aeolian sands, etc. At the first stages of primary succession, autotrophic nitrogen fixers - both free-living and symbiotic - are of decisive importance associated blue-green algae (lichens). Lichens, in addition, provide chemical and biological weathering of rocks. These successions take several hundred years.

Tundra vegetation. The tundra is distributed mainly in the northern hemisphere. It occupies large areas on the northern edge of the continents of Eurasia, North America, and is also found on the Antarctic islands southern hemisphere. In the USSR, the area occupied by tundra is 14.7% of the entire territory of the country.

The ecological conditions of the tundra are extremely unique and cause the appearance of a certain adaptability of plants.

In arctic and subarctic climates, a characteristic feature of the tundra is the absence of woody vegetation. Of the existing environmental factors, the thermal and chemical characteristics of tundra soils are of greatest importance, explaining the reasons for its treelessness. Many hypotheses have been put forward on the issue of treeless tundras. One of the main reasons should be considered the phenomenon of “physiological dryness”, which is created in supercooled thawed soil when tree roots, due to low temperatures, cannot “use” soil water (B.N. Gorodkov). According to some scientists, the ecological conditions for the germination of tree seeds in the tundra are deteriorating due to climate change (V.B. Sochava).

The flora of the tundra has a certain originality. Its species composition is poor and numbers no more than 500 species of higher plants. In the process of adaptation to living conditions in the tundra, certain phytocenoses were formed. A particularly important role in them is played by green mosses and lichens, as well as perennial plants adapted for development in conditions of a short growing season.

The herbaceous vegetation of the tundra is low-growing (5-15 cm), forms many shoots, due to which it often takes a semi-oval shape in the form of “pillows” (for example, semolina, saxifrage plants). Due to the abundance of light in summer time tundra plants have large and bright flowers (poppy, forget-me-not, tar, etc.).

Also common in the tundra are shrub plants with a characteristic woody stem and dull leathery leaves that have a waxy coating and pubescence (blueberry, cranberry, bearberry, dreadberry, etc.).

The only common shrubs in the tundra are dwarf birch and various types of willows. These low-growing shrubs have small, pubescent leaves, reclining trunks, often hidden in the moss cover. Among the coniferous shrubs, juniper is found at the southern border of the tundra, and in Eastern Siberia- dwarf cedar.

Distributed across three continents, the tundras do not remain homogeneous. Within their boundaries, from north to south, one can outline a natural change in certain types of tundra(formations).

Arctic tundra is common on the coast of the North Arctic Ocean. Its vegetation cover is characterized by sparseness (coverage area no more than 60%). Of the shrubs, only the Dread is found here. Herbaceous species are represented by sedge, cotton grass, polar poppy, etc. The moss cover is formed by polytrichous and green mosses. Lichens are characterized by scale forms. Areas not occupied by vegetation are rocky placers, areas complicated by stone polygons and polygons.

The moss-lichen tundra is characterized by a complex vegetation cover. On clay soils, a moss cover of green mosses is developed. The upper tier of this formation includes willows, blueberries, and dreadas; of herbs - sedge, arctic bluegrass.

Lichen associations are common on sandy soils. The following geographical pattern can be outlined in their distribution. In the western Arctic (up to the Yenisei River), in the presence of deep snow cover, moss tundras (lichen predominates - moss) are common, which provide valuable pastures for reindeer herding. In the eastern part of the Taimyr Peninsula, in conditions of little snow in winter, bushy lichens (Allectoria, Cetraria) are common.

Moss-lichen tundras are characterized by significant swampiness (up to 30%). The swamps are predominantly lowland moss and sedge with a characteristic hilly topography (Fig. 64).

Shrub tundra is a formation that replaces the moss-lichen tundra to the south. In the western sector of the Arctic

shrubs are represented by dwarf birch (erniki). East of the river Lena is dominated by various types of willows and alders. The widespread development of shrub plants is characteristic. Very large areas (up to 50%) are occupied by swamps.

In the south, the tundra is limited by forest-tundra. In this subzone there is an alternation of open forest and tundra areas. Thus, in the European and North American forest-tundra, birch and spruce woodlands are common, in the Asian forest - larch. In the forest-tundra, trees are far apart from each other, their height is no more than 6-8 m, have thin curved trunks. The ground cover is dominated by lichens, green mosses and grasses (Fig. 65).

Forest-tundra should be considered as a transition zone to the forest zone. Its border is very tortuous. On flat interfluves, the tundra moves south. On the contrary, along river valleys and mountain slopes of southern exposure, the forest moves north. The sparseness of the forest-tundra tree stand is a consequence of unfavorable climatic conditions associated with low rainfall.

It should be noted that the boundary between tundra and forest does not remain constant and is subject to certain dynamics. Facts such as the overgrowing of the tundra of the Far Northeast and North America with larch forest, the overgrowing of spotted and polygonal areas of the Arctic tundra indicate that the forest boundary tends to shift in a northerly direction.

Taiga vegetation.This type of vegetation is widespread in the temperate climate zone of the northern hemisphere - Eurasia and North America. Within the USSR, taiga occupies more than 11 million hectares. km 2.

Vegetation of the taiga type is classified as mesophilic and is represented by such life forms as coniferous trees, shrubs, grasses, etc. This type of phytocenosis is characterized by a complex structure and great variety. In the future, the characteristics of coniferous forests will be given using the example of the taiga of the USSR.

Forest classification is carried out taking into account forest-forming species, i.e. those tree species that predominate in the forest. On this basis, coniferous forests are divided into dark coniferous(spruce, fir, cedar) and light coniferous(pine, larch).

The distribution of coniferous forests is largely determined by the distribution area of ​​their forest-forming species (see Fig. 62). At the same time, in order to make the characteristics of forests more specific and show all the diversity, they use the concept of types of forest. Forest types are distinguished on the basis of the general physiognomic characteristics of the phytocenosis, its floristic composition and habitat conditions. In taxonomic meaning, the forest type approaches the concept of association.

Let us consider a brief description of the main formations of coniferous forests.

Spruce forests. This formation is most common among dark coniferous forests of the European part of the USSR and Western Siberia. The forest-forming species is spruce. In the USSR, spruce has up to 10 species, of which the most common is the common spruce ( European part USSR) and Siberian spruce (northeast of the European part of the USSR and Western Siberia).

Spruce is one of the shade-tolerant species, so spruce forests are dense and shaded. The undergrowth in the spruce forest does not develop widely. In the undergrowth there are shrubs: buckthorn, honeysuckle, juniper. The herbaceous cover is characterized by shrubs (lingonberries and blueberries), ferns, mosses, wood sorrel, wintergreen, etc. Green mosses and bearded lichen are abundant in the spruce forest.

Spruce forests form a large number of associations. Currently, to identify them, as well as determine patterns of distribution, ecological series method, developed by acad. V. N. Sukachev. Ecological series make it possible to identify the sequence of arrangement of plant associations in connection with changes in environmental conditions (Fig. 66).

If we consider the change in types of spruce forest depending on environmental conditions, the following pattern can be outlined. Optimal growing conditions (point ABOUT) corresponds to the association spruce-sorrel forest. With increasing dryness and decreasing soil fertility (a number of A) association is replaced spruce-lingonberry. In conditions of increased dryness it grows spruce-lichen forest. In moist areas with signs of stagnation

waterlogging (number IN) develops spruce-blueberry. A typical spruce forest association is spruce forest, which grows in low areas of excessive moisture. In swampy conditions it is replaced by sphagnum spruce forest- an association where spruce is heavily oppressed, and sphagnum moss forms a continuous cover (the final member of the series IN). Under conditions of flow humidification (row D) an association is formed along the stream valleys marsh-grass spruce forest(stream) with developed undergrowth. The association is also peculiar oak spruce forest, which is confined to the most fertile soils of the forest zone (a number WITH). Spruce usually contains an admixture of broad-leaved species (oak, linden), hazel in the undergrowth, and a cover where oak broad-grass predominates is also developed.

The given spruce forest associations do not exhaust all the diversity. The considered ecological series show how the composition of associations changes with changes in environmental conditions and position in the relief (Fig. 67). Thus, ecological series can be considered as one of the methods for studying plant associations with frequent changes in space.

A certain pattern is emerging in the distribution of dark coniferous forests on the territory of the USSR. Within the European part of the USSR, spruce forests predominate, which occupy wide and flat watersheds. In the West Siberian Lowland, forests of this type gravitate toward river valleys, as areas that are more drained. In southern Siberia they are found in the mountains, where the participation of fir and cedar increases (Tian Shan).

Fir forests are similar in characteristics to spruce forests. Their predominant associations belong to the “greenwashers” group.

Fir forests have a more limited distribution. They avoid both dry and wet places. Mixed fir forests with an admixture of Siberian spruce and cedar are often found (West Siberian Lowland, Ural, Altai, Sayan Mountains, etc.).

Larch forests occupy a large area in the USSR. The distribution area of ​​larch is in Eastern Siberia (north of 48° N), where Dahurian larch is widespread. This breed, having a superficial root system, is well adapted to growing in conditions of a sharply continental climate on marshy soils with close occurrence permafrost. Siberian larch is common in the mountains of southern Siberia.

A characteristic feature of larch forests is that they form pure stands of trees. Since the density of crowns in the forest is small, the larch forest has a park-like appearance. In the upper tier, larch reaches 30-35 m height. The ground cover is dominated by pine grasses and shrubs (reed grass, lingonberries), and in some places sphagnum mosses. Larch forests have a large supply of valuable industrial timber and are also valuable hunting grounds.

Pine forests. This is the most widespread type of coniferous forest in the temperate zone. The main forest-forming species is Scots pine. Other types of pine (Crimean, Pitsunda, etc.) have a very limited range.

Compared to other tree species, pine has a large ecological range. It is most widespread on sandy plains and river terraces. At the same time, it forms peculiar associations in peat bogs. Pine forests penetrate into the forest-steppe zone and are found in the mountains.

Pine forests, like larch forests, often have pure stands of one or two-tier structure. The grass cover in them is poor and is mainly characterized by the predominance of shrubs (heather, blueberries, lingonberries, etc.). In pine forests of dry habitats, a cover of lichens or green mosses is developed (Fig. 68, 1).

The main associations of a pine forest and the patterns of their change can be expressed by a system of ecological series, similar to spruce forests, which include associations of certain environmental conditions (lichen pine forest, green moss pine forest, sphagnum pine forest, etc.).

In terms of the composition of their associations, cedar forests are close to pine forests. Their distribution area is confined to the northeast of the European part of the USSR and Western Siberia. Cedar forests, like pine forests, are found in sphagnum bogs. In the mountains of Siberia there are cedar forests of a mixed type - cedar-larch (Altai, Sayan, etc.).

The geographical patterns of distribution of coniferous (taiga) forests in the northern hemisphere are quite complex. Distributed in the temperate climate zone, coniferous forests vary noticeably in composition both from north to south and from west to east.

Currently, geobotanists divide taiga-type forests into three groups of formations: northern taiga, middle and southern taiga, which are characterized by the predominance of certain forest types. Geographically, they represent wide stripes (subzones), which are clearly visible on the plains (Russian Plain, West Siberian Lowland). Thus, the northern taiga of the European part of the USSR, located south of the forest-tundra, is distinguished by the dominance of species of Siberian origin (spruce, cedar, larch). The predominant forest type here is a green moss spruce forest. The middle taiga is characterized by spruce (spruce-blueberry) and spruce-fir forests; southern taiga - spruce forests with an admixture of broad-leaved species (oak, elm, linden, maple). The northern and middle taiga are very swampy, and sphagnum pine forests are common in the raised bogs.

The taiga in the Asian part of the USSR retains the same division. Its distinctive feature is the large swampiness of forests (up to 50%).

In the northern taiga of the West Siberian Lowland (the southern border coincides with the latitudinal segment of the Ob River), pine, spruce-larch, and pine forests are common. East of the river In the Yenisei region, larch forests predominate in the area of ​​permafrost development.

The middle taiga in Western Siberia is characterized by the dominance of dark coniferous fir-spruce forests (“urmans”) and cedar forests. In Central Siberia and Yakutia they are replaced by larch-pine forests (Dahurian larch).

The southern taiga is characterized by a predominance of pine and birch forests, and in lower areas - spruce-fir (Western Siberia), cedar-fir (Central Siberia) and larch open forests (Transbaikalia). A special variety is represented by swampy larch forests “Mari”, widespread in Central and Eastern Siberia and the southern regions of Transbaikalia. The forests consist of Daurian larch, have an undergrowth of birch (birch) and a continuous sphagnum cover. This type of forest is confined to river valleys, where peat-bog soils are formed.

Coniferous forests Western Europe do not form marked subzones and grow only in the mountains (Alps, Pyrenees, Carpathians, etc.). In addition to ordinary pine and spruce, there are European larch and fir, which form a special forest belt.

Coniferous forests in North America occupy large areas (Labrador, Alaska, the mountains of the Pacific coast, the Atlantic plains). Unlike European coniferous forests of the American type, there is a wide variety of species of pine, spruce, fir, and larch. Specific species are also found in forests, especially on the west coast of the mainland, such as Douglas fir, tsuga, thuja, in the Sierra Nevada mountains - gigantic sequoia(mammoth tree). The named tree species are distinguished by their gigantic height (up to 80-100 m). The main reason for the species richness of the American taiga is the favorable conditions for species migration during the Ice Age.

Summer green deciduous forests. Deciduous forests in temperate latitudes become widespread in marine climates. In Eurasia, these forests are typical of Western Europe, the south of the Russian Plain, the Caucasus and the Carpathians. Further to the east they are replaced by coniferous forests. The habitat of deciduous forests is represented in the Far East of the USSR, in eastern China and in Japanese islands. Deciduous forests are found in Northern and South America(Patagonia).

Deciduous forests are divided into broad-leaved and small-leaved.

The broad-leaved forest-forming species are oak, beech, linden, maple, elm and ash. These forests have a well-developed crown, and the upper layer in them is usually composed of one forest-forming species. Since the forests are shady, the undergrowth and grass cover are poorly expressed. The predominant herbaceous species are ephemeroids, which develop intensively in spring and autumn. Typical broadleaf forest formations are as follows.

Beech forests are most widespread in Western Europe. Near the northern border of their range, they are distributed on the plains, in southern Europe - in the mountains, where they form a forest belt. Within the USSR, beech forests are found in western Ukraine, Moldova, as well as in the Carpathians, Crimea and the Caucasus, where they form a special belt.

The beech forests of Europe are of the same type. The forest-forming species in them is beech. Due to the large shade, the undergrowth and summer herbs, as a rule, are absent. In the mountains, beech's companions are fir and yew.

Beech forests in North America (eastern USA, Canada) differ from European ones. The forests have a wide variety of species, but are dominated by American beech and sugar maple. Vines made from wild grapes are characteristic.

Oak forests are the more common type of broadleaf forest. In the USSR, oak forests are common in the European part, where they form a subzone of broad-leaved forests. In oak groves, the main forest-forming species is pedunculate oak, to which maple, ash, linden, and elm are mixed. The oak groves are multi-tiered. They contain an undergrowth of hazel and euonymus. The grass cover includes plants - oak forest broad grass (sniffle, lungwort, hoofed grass etc.), the aspect of ephemeroids with subsnow development is also characteristic in spring (see Fig. 68, 1, 2). Compared to beech forests, oak forests have a wider range and are found in other subzones, for example, forest-steppe, where they form gulley forests. The forest-forming species in the oak forests of Western Europe are holm and downy oak, which are combined with evergreen rhododendron and yew (Ireland). In North America, oak forests are common in the continental west bordering the prairies. Unlike European ones, there is a large presence of broad-leaved species: several types of oak, maple, walnut, plane tree, etc. Oak forests are also characterized by lianas.

Small-leaved forests (birch, aspen, alder) Along with conifers and broad-leaved trees, they are especially widespread. By origin these forests are secondary, which became widespread after the cutting down of broad-leaved coniferous forests. However, examples of primary birch forests are known in the West Siberian forest-steppe (pegs) and in Kamchatka.

There is also a mixed type of forests - coniferous-broad-leaved, in which small-leaved species occupy a significant place. These forests are mainly distributed on the border of coniferous and broad-leaved forests. Depending on changing environmental conditions, there is an alternation various types coniferous and broad-leaved forests: oak forests are confined to the slopes of the southern exposure of river valleys, pine forests are common on terraces, and spruce forests are common on flattened watersheds. Mixed forests are especially typical for the European part of the USSR, where they form an entire subzone.

Steppe vegetation.Steppes are a herbaceous type of xerophytic vegetation with a closed grass stand, developing in a temperate climate with a lack of summer precipitation. The steppes occupy the largest areas in the USSR, stretching across a wide strip in the European and Asian parts. Steppe areas (Pashto) found within the Danube Lowland. In North America, steppes are called prairies.

Vast expanses of steppes (pampas) in subtropical parts of South America, Africa and Australia.

We will consider the main features of steppe vegetation using the example of the steppes of the USSR. In terms of physiognomic characteristics, steppe vegetation differs sharply from other herbaceous types (for example, meadows, swamps), since it expresses xerophytic features. To withstand summer droughts, plants have developed adaptations such as a waxy coating on the leaves, their pubescence, and in some cases, reduction of the leaf blade. All above-ground vegetative parts of plants have a dull green tint, which creates a certain steppe background.

Steppe vegetation is characterized by the predominance of special floristic groups. Are being widely developed turf grasses, having narrow rolled leaves and turf deep in the soil (feather grass, fescue, tonkonog). Also presented sedge, legumes, forbs, ephemerals.

The most distinctive feature of the steppe is its dynamism. The flora of the steppe consists of plants that do not coincide in their phenological phases. Therefore, the appearance of the steppe and its color background changes in different periods. Thus, in early spring, the appearance of the steppe is determined by the flowering of yellow tulips, blue hyacinths, golden goose onions and white crocuses. The silvery color of steph in May is due to feather grass. June marks the flowering of tumbleweed plants. The golden-green background of the steppe in July is associated with the flowering of feather grass. In August, wormwood and steppe asters begin to bloom.

During the entire flowering period in the steppe, there are up to 12 colorful phases (Streletskaya steppe). The noted change in aspects in the steppe should be considered as the adaptation of vegetation to certain environmental conditions.

V.V. Alekhine divided the steppes of the USSR into types: northern (meadow) steppes and southern steppes located on the border with semi-deserts.

The northern steppes are characterized by the development of colorful forbs. The participation of feather grasses is insignificant (common and angustifolia feather grass). The predominant cereals are loose turf (brome, wild oats, bentgrass, etc.). The maximum species richness was noted when the number of species per 1 m 2 reaches 80, and their number is up to 2000. Steppe phytocenoses have a complex layering.

The southern steppes are distinguished by the predominance of feather grasses, forming the aspect: feather feather grass (fescue) and feather grass “tyrsa”. There are very few forbs in the grass cover. Only the phase of spring ephemeroids (tulips) is clearly expressed and the number of tumbleweed plants is increased. In the southern steppes, the grass cover is very sparse and is generally characterized by low species richness compared to the northern steppes: by 1 m 2 area there are no more than 12 species.

The northern and southern steppes in the European part of the USSR are completely plowed. The remaining virgin areas have been declared nature reserves.

The Siberian steppes have many common features with the European ones. However, in conditions of a peculiar rugged topography (Barabinskaya steppe), they are combined with grass swamps and salt marshes. In the steppes of Western Siberia, feather grasses are prevalent. Near the border of the birch forest-steppe there are forest and swamp species, as well as saltwort plants.

The North American prairies are close in floristic composition to the European steppes. Three types of grasses are dominant in the American prairies: feather grass, wheatgrass and grama (the latter is not found in the European steppes). A feature of the prairies is the distribution of deep-rooting species, whose roots go to a depth of 1.6-2 m. At the same time, cereals are distinguished by their high height (80-120 cm).

The types of steppes in North America are extremely diverse. The tallgrass prairies of the Great Plains are close to the “northern” type steppes. Cereal formations are dominated by grasses such as bearded grass, Indian grass, feather grass, and wheatgrass. In spring there is an abundance of flowering herbs.

In the drier conditions of the Prairie Plateau, short-grass steppes are common, where dense-grass grasses (gram grass, endemic buffalo grass) predominate.

The “Pampas” of South America occupy vast plains in the south and east of the mainland (Argentina, Uruguay). The vegetation has all the features of xerophytes and is characterized by clearly defined changing aspects. The main elements of the steppes are perennial grasses of the genus feather grass, bearded grass, and millet. A variety of herbs.

Desert vegetation. The desert type of vegetation is characterized by a predominance of subshrubs and shrubs. The factors determining the development of deserts are essentially climatic, since they are formed under conditions of an arid climate with a high moisture deficit in extratropical and tropical regions of the globe (deserts of the USSR, central Asia, Sahara, Colorado, South America, Australia, etc.) - Edaphic conditions in deserts are also unfavorable: the soils are depleted in humus and saline, groundwater is located at great depths. Compared to steppe vegetation, it is typical for desert vegetation sharp increase drought-resistant species. In the process of plants adapting to unfavorable climate conditions, a number of life forms. Among them, the plants most adapted to tolerate dryness are xerophytes, having a developed taproot and superficial lateral roots, a rigid stem, and reduced leaves. The most typical representatives are subshrub plants, such as camel thorn, black and white saxaul, etc. (Fig. 69).

The other predominant life form is ephemeroids. These tuberous and bulbous perennial plants finish

growing season for 1-2 months before the onset of the dry period (bluegrass, tulips, onions). At this time, the deserts are covered with a continuous carpet of flowering plants.

A number of desert plants have the ability to accumulate water reserves in the hairs covering the leaves (for example, the kokpek subshrub) or in the tissues of the leaves and stem (plants succulents). The latter are very characteristic of many deserts around the world. Their main representatives are cacti, euphorbia, etc. The amount of water they accumulate can be 96% of their weight. The named life forms form a complex complex with saltwort plants.

According to the nature of environmental conditions and, first of all, according to the precipitation regime, the nature of the substrate, the deserts of the globe can be divided into a number of types: clayey, sandy, rocky, saline. Let us consider their main features using the example of the deserts of the USSR.

The deserts of Central Asia occupy more than 2 million hectares. km 2(10% of the area). According to climatic conditions, they can be divided into northern and southern.

Northern deserts are formed under conditions of a temperate continental climate with an even distribution of precipitation throughout the year. These are predominantly clay deserts (Ustyurt, Bet-Pak-Dala, etc.).

A common feature of their vegetation cover is the predominance of xerophyte shrubs in combination with saltworts. Depending on the soil, a number of typical phytocenoses are formed. The most common are wormwood deserts (clayey ones), which are characterized by the predominance of various types of wormwood and saltwort. The vegetation cover is monotonous and very sparse (cover does not exceed 40%).

In areas with highly saline soil, saltwort deserts are widespread, represented by a group of associations dominated by the low subshrub Kokpek and the cushion-shaped subshrub Biyurgun.

The named types of deserts do not occupy large areas. In conditions of complex microrelief, depending on the degree of soil salinity, they form complexes. For example, at the bottom of basins and saucer-shaped depressions there is a kokpek desert, on their slopes - a solyanka desert, and in higher areas - wormwood deserts (Fig. 70). This complexity of vegetation cover is reflected in the legends of geobotanical maps.

Climatically, the southern deserts are quite different in temperature regime and pronounced spring-autumn maximum precipitation. This explains their significant difference and the wide variety of types.

Clay deserts of the southern variant are formed on piedmont loess plains (Kopet-Dag, Pamir-Alai, Tien Shan). Their vegetation cover is mesophytic in nature. In spring, a continuous turf of grass forms, which can be compared to a meadow. The most typical plants are bulbous ephemera: sedge, bulbous bluegrass, which form a dense, albeit low (20 cm) turf. Projective coverage reaches 80-100%. In spring, the ephemeral desert is used as pasture. In summer, all ephemerals die off and the soil surface becomes very dry.

The greatest diversity of plant associations is distinguished by sandy deserts(Karakum, Kyzylkum, Muyunkum, Balkhash sands, etc.). There is a wide variety of life forms here, including ephemerals, shrubs and trees.

This is largely explained by the properties of sands, in which a favorable water regime is created (permeability, poor capillarity, ability to condense moisture). In the sandy desert at a depth of 100-150 cm There is a constant moisture horizon, which in spring is supplemented by a “hanging horizon.” Among the unfavorable environmental factors on sands is their mobility. Plants, as an adaptation for growing on moving sands, form deep-reaching adventitious roots.

The distribution of plant associations depends on the degree of sand fixation. Tall grass dominates on mobile dunes and dune chains Celine(up to 1 m), juzgun, sand acacia- low trees (up to 6 feet) with a characteristic “weeping” shape (Fig. 71).

In areas where ridged and hummocky sands develop, gnarled bushes are widespread white saxaul(up to 2-3 m). Its distinctive feature is the summer shedding of branches. Other shrubs include juzgun and tree-like solyanka. Under the canopy of white saxaul, a grass cover of ephemerals and ephemeroids develops.

Saline deserts are usually confined to river terraces (Amu Darya, Ili, etc. rivers), sea coasts and deep depressions where highly saline soils are developed. They are characterized by a peculiar solyanka (halophytic) vegetation, among which succulent plants predominate. The most typical plants are: sarsazan – subshrub with a fleshy stem (sparse thickets of sarsazan occupy large areas on the coast of the Caspian Sea), succulent solyanka(tamarix) - plants whose leaves are covered with a salt crust, and sulfur wormwood.

On slightly saline soils, associations are common black saxaul- leafless tree-like solyanka, reaching a height of 5-9 m. Dense thickets of black saxaul are common in the Balkhash region, in the lower reaches of the Amu Darya, etc. Saxaul is a good fuel, which is slightly inferior in calorific value to some types of coal.

The desert type of vegetation on the globe occupies significant areas. In Eurasia, outside the USSR, there are vast deserts that form in subtropical and tropical climates (Tar, Registan, Rub El Khali, Syrian, Gobi Desert, Alashan, etc.). These are predominantly mountainous deserts, which are characterized by the development of thorny cushion-shaped shrubs (astragalus), succulents, and wormwood.

Large areas (up to 40%) are occupied by desert in Africa (Sahara, Kalahari, etc.). The vegetation of the Sahara approaches to some extent the deserts of Central Asia. In sandy areas, shrubs (camel thorn, acacia) and grasses (related to seline) are common. Significant areas are also occupied by rocky desert (“gammada”), which is characterized by lichens that form a continuous crust on the stones and rare subshrubs. The deserts of South Africa are characterized by the dominance of succulents, which are distinguished by an abundance of species: aloe, milkweed (Karoo Desert).

In the sandy Kalahari Desert, cereals predominate, and acacia is the dominant tree species.

The Namib Desert (the Orange River basin) is most distinctive, where special forms of succulents dominate, which look like stones - "plant-stones" A very peculiar endemic relict plant Velvichia(obviously a representative of the Mesozoic flora). The lifespan of Velvichia is more than 100 years. Its woody stem is up to 1.5 in diameter m rises to a height of no more than 20 cm(Fig. 72).

The deserts of North America are unique: along with the indicated types (saltwort, black wormwood, etc.)

spreading creosote bush desert (Colorado plateau, California coast). Mexican highland deserts at altitudes 1000-2250 m above sea level are the center of education cactus flora. This area contains up to 500 species of cacti, Opuntia, agaves, and tree-like yuccas (Fig. 73). Giant cacti in the desert are combined with thorny bushes (mimosa, creosote bush, etc.). The vegetation cover of the Mexican desert is very sparse.

The deserts of South America and Central Australia are saline plains and plateaus, abundant in sand and salt marshes. The plant background in them is formed by halophytic shrubs, succulents and herbs. Specifically Australian are shrub deserts with a predominance acacia and shrubby eucalyptus trees Vast sandy spaces are occupied by the formation of hard and prickly grasses (spinifex), growing on loose sand and stones (Western Australia).

Subtropical shrub-woody vegetation.MoistureSubtropical forests are typical for areas of subtropical climate. This type of forest is common in eastern Asia, Central and South America and other areas and is represented by evergreen trees and shrubs. The dominant species in hard-leaved forests are laurel, plane tree, oak, boxwood. Ferns and mosses are abundant, often growing as epiphytes. The forests of Florida, Chile and Patagonia are dominated by evergreen beech.

A variety of this formation are evergreen hard-leaved forests and shrubs, typical for the countries

The Mediterranean, as well as California, southwestern Australia, South Africa (Cape Region), South America (Patagonia). The life forms of hard-leaved forests are very unique. Plants have xerophilic adaptations: hard leaves twig-like stems covered with resinous secretions. The dominant species in Mediterranean forests are stone And cork oak. The forests have an undergrowth of evergreen shrubs, such as myrtle And heather.

In Southern Europe, North Africa and the countries of Asia Minor, evergreen forests are beginning to be dominated by groves of pine pine and Lebanese cedar.

Hard-leaved forests of the subtropical zone are everywhere combined with thickets of various tall shrubs, which in the Mediterranean are called maquis. The maquis formation is characterized by strawberry tree, myrtle, and tree-like heather. In thickets of low evergreen shrubs called gariga, Shrubby oak, thyme, rosemary, gorse, etc. predominate (southern France). In North Africa and southern Spain, the gariga is represented by a dwarf palm. The hard-leaved eucalyptus forests of southern Australia are very distinctive, with evergreen undergrowth and bush thickets (scrab) of various types of acacias, bushy eucalyptus, etc.

Moist tropical (rain) forests. This type of forest formations is becoming widespread in the area equatorial climate. Forests occupy vast areas in Africa (the Congo and Niger river basins), Central and South America (the Amazon river basin) and southeast Asia. Tropical rainforests stand out among all other forest formations with a wide variety of species. The trees are dominated by tree ferns, different types of ficus palm trees(coconut, oilseed, wine) rubber plants(Hevea brasiliensis).

The structure of tropical forests is the most complex. The number of tiers in them reaches 4-5. Tall trees (up to 60 m and above), with characteristic plank-shaped roots. The shade of the forest is maximum and only 1/150 of the incoming light reaches the soil surface. It should also be noted that there is less diversity in the types of grass cover, where spore-bearing plants predominate: ferns, mosses. Another characteristic feature tropical forests are abundant lianas and epiphytes(Fig. 74). The distribution of such life forms is explained by the large shade of the tropical forest. The most common: palm vines (up to 300 m), vines from the family Philodendron, pepper, vanilla, etc. Epiphytes are herbaceous species from the fern and orchid families, as well as mosses and algae.

A very characteristic formation of tropical rainforests is mangrove vegetation, common in the tidal zone of bays and lagoons of the northern and east coast South America, West Africa, Hindustan, etc. Mangrove vegetation consists of thickets of evergreen shrubs. The participation of trees in them is small. In terms of species, this formation is extremely monotonous (rhizophora and some palm species predominate). This is explained by the specific environmental conditions, since the crowns of trees rise out of the water during high tide, and during low tide the trunks, stilted and breathing roots are exposed. This root system is a kind of adaptation for transmitting oxygen during coastal flooding. Mangrove plants also have features characteristic of halophytic plants (Fig. 75).

In the region of the equatorial monsoon climate, a special type of deciduous (winter-green) tropical rainforests develops (Indochina, Hindustan, Sunda Islands). The forests are similar to tropical ones, but during periods of drought the trees shed their leaves. These forests differ in the nature of the tree stand. In mixed forests, the forest-forming species are valuable tree species (sandalwood, rosewood), bamboo, and palm trees. There are many flowering shrubs and herbs in the forests. Also characteristic are lianas and epiphytes that lose their foliage during dry periods.

With increasing dryness in the tropical zone, winter-green tropical rainforests are replaced by dry xerophilous forests and thorny bushes. This formation occupies large areas in Africa (Rhodesia, Angola, Somalia),

Argentina, northern Australia. Xerophilous forests are stunted and sparse. They are dominated by leafless trees and shrubs such as acacia, palms, intertwined with vines. The undergrowth is dominated by thorny bushes. The xerophilic forests of Brazil are unique "caatinga" with many specific species: cacti, including tree-like ones, trees from the bombasaceae family, which have swollen barrel-shaped trunks with a diameter of several meters (Fig. 76). The distribution of these formations can be seen on the map of the world's vegetation.

This is a woody-herbaceous type of vegetation that is transitional from tropical forests to deserts tropical zone. Savannahs are becoming widespread in the southern and central Africa(basins of the Niger and Upper Nile rivers), South America (Brazil, Orinoco river basin) Australia.

In conditions of severe aridity of the tropical climate, evergreen trees in savannas have hard, pubescent leaves that are shed during the dry season. Another feature is the umbrella shape of the crown as a device for strong winds Trees in the savanna are scattered in small groups. The main representatives are umbrella-shaped acacia And baobab - giant tree reaching a height of up to 25 m and having a diameter of up to 9 m(can reach an age of 5000 years) (Fig. 77). In Australian savannas, trees are dominated by eucalyptus trees, in the savannas of South America, “llanos” are varieties of palm trees. The grass cover of savannas is dominated by tall xerophytic, rigid-stemmed grasses (such as bearded grass).

Swamp vegetation. Swamps develop in different climatic zones - from equatorial to subarctic. They are especially characteristic of the forest zone of temperate climates.

Swamps are characterized by hygrophilic plants growing in conditions of excessive moisture and experiencing the influence of “physiological dryness”. When plants die, peat accumulates.

Modern classification of swamps is based on the identification types(formations) according to the following characteristics: 1) position in the relief, 2) moisture and nutrition conditions, 3) predominant plant associations.

The most common type is lowland swamps. They form on the bottoms of valleys of streams, ravines, gullies and are characteristic of all natural zones. The moistening of the swamps is associated with the close occurrence of mineralized groundwater. The grass cover of lowland bogs is dominated by green mosses, various sedges and grasses. In older bogs, birch, alder and willows appear. This type of bog is characterized by weak peat (the thickness of the peat layer does not exceed 1-1.5 m).

A variety of grass and hypno-grass swamps are tall-grass swamps with thickets of reeds, reeds, cattails, widespread in floodplains and lake basins in the forest, forest-steppe and steppe subzones of the European part of the USSR, Siberia and the Far East.

Raised bogs have specific features. They form on flat watersheds and occupy vast areas of the forest zone (for example, the West Siberian and Pechora lowlands, Polesie). Moistening of raised bogs is associated exclusively with precipitation and in conditions of flattened relief

becomes excessively stagnant. The surface of the bog acquires a convex profile due to the uneven growth of peat. The excess of the central part of the swamp over the periphery reaches 3-4 m. During the development of the swamp, a complex microrelief is formed on its surface, represented by a combination of small ridges and depressions (see Fig. 82).

The ecological conditions of the raised bog are very unique. Plants adapt to growing in an environment depleted mineral nutrition, especially nitrogenous compounds. Common in high bogs sphagnum mosses and associated marsh species: cotton grass, wild rosemary, Cassandra, heather, cranberry etc. The peculiarity of their life forms is that they have adventitious roots and a moving growth point. The vegetation of the raised bog (Fig. 78) is also adapted to tolerate “physiological dryness.”

The shrub plants of the raised bog have narrow leathery leaves with a waxy coating and a woody stem. Sedges, cotton grass, etc., having narrow, hard leaves, also acquired a specific appearance. The most common tree species found in raised bogs is pine And birch, less commonly cedar and larch. The trees in the swamp are severely depressed and stunted.

The named plant dominants for raised bogs (trees, shrubs, mosses, etc.) form certain associations, depending on environmental conditions. The following pattern emerges in their distribution: in the central part of the raised bog, pine-sphagnum association, towards the periphery of the flywheel in places where the ridge-hollow complex develops, it is replaced by pine-shrub, on the edge of the swamp

is spreading pine-cotton grass association (the nature of the distribution of associations in the raised bog and their location in plan, see Fig. 79).

Raised bogs have a large practical significance. Their peat layer often reaches a thickness of 6-10 m. Peat is used as a fuel raw material, fertilizer and for the production of a number of chemicals.

Raised bogs are common in North America (mainly in the northeast). Here the swamps are similar in nature to European ones, but larch predominates among the tree species. In South America, sphagnum bogs are found in the Andes and on the island of Tierra del Fuego.

Transitional swamps are mixed in nature and form on terraces or concave slopes of interfluves. The vegetation cover of such bogs combines the features of lowland and raised bogs and is characterized by a predominant distribution sphagnum-cotton grass-sedge associations.

The process of development of wetlands is very complex. The death and accumulation of plant debris in the swamp is essentially related to its water regime, since the growth of the peat layer reduces the influx of groundwater. This, in turn, entails a change in ecology and corresponding marsh associations. The types of swamps mentioned above can be considered as certain stages this development. Lowland sedge-grass bogs of ground moisture are replaced by transitional sphagnum-sedge bogs of mixed nutrition. Raised bogs of exclusively atmospheric nutrition represent the final stage of bog development, at which the tendency for peat to grow in height appears.

The outlined scheme gives the most general idea about the development of swamps. At the same time, the reasons causing waterlogging are extremely diverse. During the development of spruce and pine formations, waterlogging is facilitated by the development of moss cover from cuckoo flax and sphagnum. Forest burnt areas and clearings often become swamped. And finally, swamps arise on the site of lakes and river oxbows, which are populated by wetland vegetation. Let's look at this process in general terms.

Lake waterlogging most often occurs through overgrowth. With gentle banks and a gradual increase in depth, aquatic vegetation is located in the form belts in the following sequence: 1) in the deepest places a belt of green algae stands out (at a depth of more than 6 m); 2) a belt of flowering plants immersed in water (hornwort, pondweed); 3) a belt of broad-leaved pondweeds with wide floating leaves and inflorescences on the surface of the water (at a depth of 4- 5 m); 4) belt of water lilies at a depth of 2-3 m(water lily); 5) belt of reeds up to 2 m(reed, reed, horsetail); 6) belt of large sedges at a depth of up to 0.7 m; 7) belt of small sedges (Fig. 80).

Each of the marked belts is not durable and is replaced by the neighboring one - less deep-sea. This is explained by the fact that deposited plant residues contribute to the shallowing of the reservoir. This is how associations consistently shift from the periphery to the center. Its last stage is the transformation of the lake into sedge bog.

Of all the listed marsh associations, the most widespread on the globe are reed swamps with a predominance of high reed thickets (up to 6-10 m). In African tropical swamps along the banks of rivers and lakes there are thickets of papyrus, reeds and reeds; in Indian swamps there are thickets of bamboo.

Meadow vegetation.Meadows are a herbaceous type of mesophilic vegetation that grows in conditions of moderate moisture in various natural zones of the globe (tundra, forest zone, tropical, etc.).

Based on their location, meadows can be divided into floodplain (flood) and watershed (dry) meadows. Floodplain meadows are of greatest interest as a type of plant formation. Their vegetation is formed on fertile soils under the influence of a long-term flood regime and the deposition of loose river sediments.

Floodplain meadows are characterized by a number of floristic features: predominance loose turf cereals(timothy grass, fescue, bluegrass, awnless bromegrass), legumes(clover, alfalfa, mouse peas) and forbs(meadow geranium, meadow cornflower, common cornflower and a number of others). The grassland of the meadows is of high quality and represents valuable hayfields!

On the floodplains of large rivers, which are distinguished by complex microrelief and varying moisture levels, a variety of environmental conditions are created. When crossing the floodplain from the river bed towards the slope, a complex ecological series.

In the elevated riverbed part of the floodplain, composed of sandy alluvium, the driest conditions are created. Here, the sparse grass cover is dominated by long-rhizome grasses (creeping wheatgrass, awnless bromegrass), and some steppe species are also found.

The central part of the floodplain is composed of clayey alluvium and has a high groundwater table. Loose turf grasses, legumes and flowering herbs with a closed herbage dominate here.

The character of the meadow changes dramatically in the near-terrace part of the floodplain. This low area of ​​the floodplain at the foot of the slope turns out to be the most moist due to the stagnation of hollow waters and the release of springs. The near-terrace floodplain is often forested. The indigenous type of forest is alder with an undergrowth of black currant.

In wet meadows, turf grasses (for example, pike) and sedges predominate.

In the forest zone there are also dry meadows that form on watersheds. Unlike floodplains, dry lands are of secondary origin, as they arise on the site of cut down or burned forests. Therefore, in their herbage, in addition to purely meadow mesophytes, there are elements of forest herbs and a well-developed moss cover. The productivity of such meadows is low.

In the steppe zone, watershed meadows form in depressions (estuaries, valleys, floods, etc.).

The vegetation of meadows is influenced by the type of vegetation (steppe, desert, etc.) among which it is formed. So, on the floodplain of the river. On the Oka River, which crosses the subzone of broad-leaved forests, there are steppe species; on the floodplain of the river. Teberdy - subalpine species. On the floodplains of the steppe rivers Sal and Manych, saltwort plants, characteristic of semi-deserts, predominate.

Alpine vegetation represents a special type of high-mountain low-grass meadows that are located above the upper border of the forest. Altitude position alpine meadows varies depending on the geographical latitude of the mountains, the exposure of the slopes, and the degree of continental climate. For example, in the Alps and the western Caucasus, alpine meadows are located at altitudes of 2200-3000 m above sea level.

Alpine vegetation is similar to tundra vegetation in a number of ways: the predominance of perennial shrubs, cushion plants, etc. All this is an adaptation of alpine vegetation to the conditions of a short growing season with sharp temperature contrasts during the day. In conditions of high light intensity, alpine plants acquire a low-growing, squat shape and bright color colors.

Alpine vegetation is divided into two altitudinal zones: the lower - subalpine, the upper - alpine meadows.

Subalpine meadows are most widespread in the mountains of Central Asia and the Caucasus. Their vegetation is distinguished by its extraordinary diversity and brightness. The grass cover is dominated by grasses and flowering herbs (geraniums, scabiosa, bluebells, alpine poppies, forget-me-nots, anemones, asters and many others). This type of herbal phytocenosis is characterized by complex tiers and high species richness. The subalpine meadows of the western Caucasus are characterized by the development tall grass, reaching a height of up to 2 m and more (bellflower, hogweed, elecampane, columbine). There are also thickets of Caucasian rhododendron, juniper, and willow.

Alpine meadows replaced by subalpine ones at altitudes above 3000 m. The grass cover of the Tien Shan meadows is dominated by mesophytic plants. Its important element is turf sedges(cobresia) with very large and bright flower. The size and brightness of the colors of the flowers are a characteristic feature of alpine vegetation. Flowering herbs are similar to the subalpine zone, but in appearance the vegetation of alpine meadows is distinguished by low grass stand. The leaves of herbs are arranged in the form of a rosette, often without a stem (chickweed, forget-me-nots, buttercups, alpine poppies and many others). There are many bulbous plants in the alpine meadow: tulips, hyacinths, mountain lilies etc. The alpine meadows of the Alps are distinguished by the nature of their vegetation by the abundance of species of tundra flora (for example, dryad); there are endemic species, such as edelweiss, primrose.

- Source-

Bogomolov, L.A. General Geography / L.A. Bogomolov [and others]. – M.: Nedra, 1971.- 232 p.

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Geobotany

Topic 3

PHYTOCENOSIS

Lecture1

Phytocenosis and its features

Phytocenology

Phytocenology studies plant communities (phytocenoses). The object of study is both natural phytocenoses (forest, meadow, swamp, tundra, etc.) and artificial ones (for example, crops and plantings of cultivated plants). Phytocenology is one of the biological sciences that studies living matter at the coenotic level, i.e. at the level of communities of organisms (slide 4-5).

The task of phytocenology includes the study of plant communities from different points of view (composition and structure of communities, their dynamics, productivity, changes under the influence of human activity, relationships with the environment, etc.). Great importance is also given to the classification of phytocenoses. Classification is a necessary basis for studying vegetation cover and for compiling maps of vegetation in various territories. The study of phytocenoses is usually carried out by their detailed description using a specially developed technique. At the same time, quantitative methods are widely used to take into account various characteristics of the phytocenosis (for example, the share of participation of individual plant species in the community).

Phytocenology is not only a descriptive science; it also uses experimental methods. The object of the experiment is plant communities. By influencing the phytocenosis in a certain way (for example, applying fertilizers to a meadow), the response of vegetation to this influence is revealed. The relationships between individual plant species in a phytocenosis, etc. are also studied experimentally.

Phytocenology is of great economic importance. Data from this science are necessary for the rational use of natural vegetation (forests, meadows, pastures, etc.) and for planning economic activities in agriculture and forestry. Phytocenology is directly related to land management, nature conservation, reclamation work, etc. Phytocenological data are used even in geological and hydrogeological surveys (in particular, when searching for groundwater in desert areas).

Phytocenology is a relatively young science. It began to develop intensively only from the beginning of our century. A great contribution to its development was made by domestic scientists L.G. Ramensky, V.V. Alekhin, A.P. Shennikov, V.N. Sukachev, T.A. Rabotnov and others. Foreign scientists also played a significant role, in particular J. Braun-Blanquet (France), F. Clements (USA), R. Whitteker ( USA).

Phytocenosis and its features

According to the generally accepted definition of V.N. Sukacheva, phytocenosis (or plant community) we must call any collection of higher and lower plants that live on a given homogeneous area of ​​the earth's surface, with only their characteristic relationships both among themselves and with habitat conditions, and therefore creating their own special environment, phytoenvironment(slide 6). As can be seen from this definition, the main features of a phytocenosis are the interaction between the plants that form it, on the one hand, and the interaction between plants and the environment, on the other. The influence of plants on each other occurs only when they are more or less close, touching their aboveground or underground organs. A collection of individual plants that do not influence each other cannot be called a phytocenosis.

The forms of influence of some plants on others are varied. However, not all of these forms have the same importance in the life of plant communities. In most cases, the leading role is played by transabiotic relationships, primarily shading and root competition for moisture and nutrients in the soil. Competition for nitrogenous nutrients, of which many soils contain little, is often particularly intense.

The joint life of plants in a phytocenosis, when they influence each other to one degree or another, leaves a deep imprint on their appearance. This is especially noticeable in forest phytocenoses. The trees that form a forest are very different in appearance from the single trees that grow on open place. In the forest, the trees are more or less tall, their crowns are narrow, raised high above the ground. Single trees are much lower, their crowns are wide and low.

The results of the influence of plants on each other are also clearly visible in herbaceous phytocenoses, for example in meadows. Here the plants are smaller in size than when growing alone, they bloom and bear fruit less profusely, and some do not bloom at all. In phytocenoses of any type, plants interact with each other and this affects their appearance and vital condition.

The interaction between plants, on the one hand, and between them and the environment, on the other, takes place not only in natural plant communities. It is also present in those sets of plants that are created by man (sowing, planting, etc.). Therefore, they are also classified as phytocenoses.

In the definition of phytocenosis V.N. Sukachev includes such a feature as the homogeneity of the territory occupied by the phytocenosis. This should be understood as the homogeneity of habitat conditions, primarily soil conditions, within the phytocenosis.

Finally, V.N. Sukachev points out that only a collection of plants that creates its own special environment (phytoenvironment) can be called a phytocenosis. Every phytocenosis, to one degree or another, transforms the environment in which it develops. The phytoenvironment differs significantly from the ecological conditions in an open space devoid of plants (light, temperature, humidity, etc. change).