As already mentioned, plant and environment are a dialectical unity. At present, no one doubts the environmental role of plants. If individual plant organisms are under the influence of the environment and in turn act on it, then the phytocenosis, that is, the totality of individual organisms, is also under the influence of the environment, which in turn is formed under the influence of vegetation.

When exposed to the environment, the phytocenosis essentially creates its own internal environment, which is called the phytoenvironment. When studying the phytoenvironment of a community, it is easy to notice that the phytoenvironment of one community, for example, a pine forest, differs sharply from the phytoenvironment of another community, a birch forest.

The mutual influence of the environment and phytocenosis is extremely diverse, each environmental factor has an impact on the structure and vital functions of the phytocenosis, but the structure of the phytocenosis has no less effect on the environment as a whole and on its individual factors.

Influence of phytocenosis on humidity. Any phytocenosis has a significant impact on soil and air moisture. This is especially noticeable in tree communities, where the moisture content of the soil surface is higher than in an open, treeless area, and vice versa at the depth of the soil. This is explained by the fact that in the forest on the soil surface there is a large amount of organic residues that absorb moisture, and the crown of trees reduces evaporation from the soil surface. At a certain depth of the soil, moisture is strongly absorbed by the powerful root system of woody vegetation. So, according to Vysotsky, soil moisture on the surface of black steam is 3.6%, virgin lands - 5.9%, forests - 15%; at a depth of 25 cm - respectively 24.2; 17.5 and 18.4%.

Phytocenoses, especially woody ones, delay precipitation with their foliage. The older the forest, the more precipitation is intercepted by its crown.

Different types of plants retain an unequal amount of precipitation, and therefore the soil moisture under the phytocenosis is different. For example, deciduous forest, as a rule, retains moisture with its leaves less than pine and spruce. This is due to the fact that water from the leaves of deciduous plants drains easily, and in coniferous plants it lingers in the form of drops on the needles.

Phytocenoses to a large extent affect the regime of water flow and thus protect soils from nutrient leaching and erosion. Phytocenosis has a strong influence on the water regime not only within the community itself, but also far beyond its borders. For example, shelterbelts contribute to the accumulation of a large amount of moisture inside the forest belts and in the fields adjacent to them.

Influence of phytocenosis on temperature. Vegetation cover strongly influences air and soil temperature. The air temperature inside the phytocenosis is always much lower than in the open. It is especially easy to find it in the forest. Shrub and herbaceous vegetation also affects the temperature regime of the soil and air. But the nature of the influence can change dramatically depending on the structure and geographical location of the phytocenosis.

The dense meadow vegetation always prevents the penetration of heat to the soil surface, and therefore in summer the soil in the meadows is colder than in open places.

The influence of phytocenosis on the thermal regime depends on many factors: species composition, age, layering, standing density, etc.

There is no doubt that plants of the same phytocenosis, but of different tiers, are in unequal temperature conditions.

Influence of phytocenosis on illumination. The amount of light penetrating into the phytocenosis largely depends on the layering, standing density, species composition of vegetation and other structural features of the phytocenosis. In any phytocenosis, part of the sun's rays is absorbed by plants, and the stronger the more pronounced the layering and leafiness of the community. It is well known that with the same plant density in a pine forest it is always lighter than in a deciduous one.

In different phytocenoses, the amount of light penetrating to individual tiers is not the same. First of all, it depends on the structure of the plants of the upper tier. The penetration of different amounts of light into the tiers also determines the species composition of plants in individual tiers. As already mentioned, depending on their relationship to light, plants are divided into 3 main groups: photophilous, shade-tolerant and shade-loving. Representatives of these ecological groups of plants grow better with a certain amount of light. So, for example, for such a photophilous plant as European larch, the minimum amount of light is 20% of full daylight. In the presence of less light, the larch dies. In another light-loving plant - Scots pine - the needles stop growing at 9.1% of full daylight. Whereas such a shade-loving plant as a forest beech can grow in the presence of only 1.3% of the light of full daylight. If beech trees grow in very low light, then the grassy vegetation of these forests receives even less light under the canopy of trees.

The effect of phytocenosis on illumination changes dramatically depending on the period of the year: in spring, when the trees are without leaves, the lower tier - herbaceous vegetation - receives much more light than in summer.

Influence of phytocenosis on wind speed and strength. The wind speed on a flat surface is always stronger in the upper layers of the atmosphere than in the lower ones. Phytocenosis has a great influence on wind speed, and the farther, for example, into the depths of the forest, the less wind force becomes. Different wind strength is also observed in the tiers: in the lower tier, the wind force is always less than in the upper one.

Influence of phytocenosis on the soil. As V. V. Dokuchaev, the largest soil scientist in our country, pointed out, soil-forming processes are influenced by parent rocks, topography, climate and living organisms. Phytocenoses play an important role in the soil-forming process. Different types of soils are formed under the influence of various phytocenoses, for example, the formation of chernozems took place under the influence of steppe herbaceous vegetation, podzolic soils in the northern regions were formed under the direct influence of coniferous woody vegetation, red soils were created with the participation of subtropical and tropical woody vegetation.

Soil-forming processes are inextricably linked with the accumulation of organic matter. Their main supplier is plants, which deposit these substances in the form of falling aerial parts, dead root systems, etc. The amount of deposited organic mass depends on the nature and structure of phytocenoses.

In various phytocenoses, the following number of above-ground parts (in tons) falls per 1 ha of soil: in the tundra and forest-tundra - 0.4, in a mixed forest - 5 ... 7, in the steppe - 6 ... 10, in the desert - 0, 4 ... 2.3, in a tropical rainforest - 100 ... 200.

Phytocenoses contribute to the accumulation of humus in the soil, the formation of soil structure, determine the various chemical and mechanical composition, soil fertility, its thermal regime, etc.

The formation of soils is greatly influenced not only by higher, but also by lower plants, which, in the course of their vital activity, accumulate a large amount of organic matter in the soil. Thus, in nature, there is always a significant influence of vegetation on the structure of the soil, and, conversely, the structure of the soil affects the nature of the vegetation.

Influence of phytocenosis on relief. As already noted, vegetation strongly regulates the nature of the water flow, its speed and uniformity, which is of particular importance on hilly and mountainous terrain. The organization of the correct use of the vegetation of phytocenoses, for example, the organization of planned grazing of animals, prevents the trampling of slopes and their erosion. Unreasonable deforestation usually leads, especially on mountain slopes, to the washing away of the soil cover, and, consequently, to the destruction of the phytocenosis.

Influence of human activity on phytocenoses. Human life is inextricably linked with plants, from which he receives various food products and raw materials for various types of industry. Human influence on the vegetation cover of the globe exceeds the influence of any other environmental factor. The vegetation of all continents has been greatly altered by man, and at present the influence of man on vegetation is increasing. Let us dwell on some examples of changes in phytocenoses by humans.

In 1501, an island was discovered in the Atlantic Ocean, called Saint Helena. At that time it was densely covered with local vegetation. The British brought goats to this island, which destroyed almost all the local vegetation.

A similar picture of the destruction of local phytocenoses by man and the creation of new ones can be observed in almost all regions of the globe. In the USA, on the site of the destroyed huge forests, agricultural plants imported from other countries of the world are cultivated, even weeds here are foreign.

However, although man is to blame for the disappearance of many plants, at the same time he did a lot to introduce new plants, he created new plant communities, which can be called cultural phytocenoses.

A number of laws on the protection of nature have now been issued in the Soviet Union. Many reserves have been created in various geographical zones, in which a lot of research work is being carried out to preserve the natural resources of both flora and fauna.

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To date, none of the environmental factors has such a significant and comprehensive impact on plant communities as human activity. This influence has been gradually increasing since the emergence of human civilization, and today it is almost impossible to find such a plant community that a person would not have influenced to one degree or another.

The nature of the anthropogenic influence on the vegetation cover differs significantly from the influence of abiotic and biotic natural factors. The fact is that anthropogenic influence is always external in relation to the ecosystem. In the final result, human action is reduced either to changing the parameters of the ecotope, i.e., changing abiotic factors, or to direct transformation of the structure and composition of the ecosystem.

The nature of human impact on plant communities is extremely diverse and, in most cases, negative. It, first of all, depends on the level of development of industry and agriculture: the degree of plowing of land, the development of a network of means of communication, the level of environmental pollution with production waste, and so on. At the same time, human impact on the vegetation cover can be conscious and unconscious, direct and indirect. So, often unconsciously, a person spreads many types of plants. Consciously, a person transforms individual phytocenoses and even entire landscapes: he cuts down or, conversely, plants forests, plows up land, extracts minerals, etc. Sometimes it is very difficult to distinguish between conscious and unconscious human influence on nature. So, for example, when extracting minerals in an open way, a person consciously destroys vegetation in the places of extraction. At the same time, when quarries are created, the groundwater level changes, which, in turn, can greatly affect the surrounding plant communities.

The main types of human anthropogenic impact on nature are the direct impact on the vegetation cover (deforestation, the creation of artificial phytocenoses, grazing of domestic animals, drainage or, conversely, irrigation, the impact on plants of emissions and discharges from industrial enterprises, etc.), as well as the importation of or another region of new plant species that, under new conditions, are able to be part of natural or semi-natural phytocenoses. All this ultimately leads to the reduction of ranges or the complete disappearance of various plant species and even entire plant communities.

Creation of cultural and semi-cultural phytocenoses Today, it is perhaps the most significant factor in human impact on the environment. According to the degree of human impact, it is customary to distinguish the following types of phytocenoses (Fursaev, Khokhlov, 1940):

· intact phytocenoses, i.e., those that have not been subjected to conscious or unconscious human influence in the process of development. Their species composition and structure have been preserved in a state that depends only on physiographic and biotic conditions;

· natural phytocenoses- have been subjected to involuntary human influence or have arisen as a result of his activities that are not directly aimed at changing the composition of the phytocenosis (cutting, grazing, etc.);

· cultivated phytocenoses- natural phytocenoses, in which, as a result of extensive human impact, the structure and composition have been changed to one degree or another;

· semi-cultural phytocenoses- purposefully created by man on the site of natural phytocenoses, radically changed (artificial forest plantations, sown meadows, etc.);

· cultural phytocenoses- created by a person who constantly controls them throughout the entire time of their existence, while a person creates and regulates the species composition, structure and even the conditions for the growth of species in a phytocenosis.

Intensive human activity has led to the fact that in many regions of the planet that are heavily developed by him, cultural, semi-cultivated and cultivated phytocenoses predominate, while untouched phytocenoses are practically absent. So, for example, only in Belarus on more than 30% of the territory natural communities are completely destroyed - the land is used as arable land, roads and human settlements. Another 20% of the area of ​​the republic is occupied by various semi-natural or strongly anthropogenically transformed territories: hayfields, pastures, gardens, wastelands, etc. Forest cultures also make up a significant proportion of forests, that is, forests planted by humans in clear cut areas or unforested areas. All this leads to the fact that today on the territory of the republic there are practically no intact phytocenoses that have not been subjected to human influence.

Deforestation may be of a different nature. Depending on the purpose, fellings can be sanitary, thinning, selective and clear cuts. During sanitary and maintenance felling in a forest phytocenosis, a person cuts down diseased or poorly growing trees, which contributes to better growth of other plants and, thereby, to the creation of more productive plant communities. During selective logging, a person selectively removes from the phytocenosis either trees of certain species, or trees that have reached a certain age, and leaves the rest of the species. In this case, the human impact on the plant community is deeper and can lead to the replacement of one phytocenosis by another. Finally, during clear cuttings, the phytocenosis is completely destroyed. At the same time, the restoration of forests in cleared areas will primarily depend on the nature of the further economic use of the territory by humans, and only then on the complex of physical and geographical conditions and environmental factors affecting this habitat. Thus, the use of the territory freed from under the forest as arable land or haymaking makes it impossible for the natural restoration of the forest, and grazing also hinders this process or greatly slows it down. Quite often, the disappearance of the forest can lead to a strong change in the ecological conditions of the habitat. For example, when the groundwater is shallow, deforestation can lead to waterlogging of the territory; the destruction of forests on mountain slopes and on the slopes of the primary banks of rivers can lead to severe soil erosion and even to their complete washing away.

The nature of the impact on phytocenoses grazing domestic animals largely depends on the characteristics of the vegetation cover, the duration and intensity of grazing, the breed of grazing animals. When grazing, animals selectively eat certain types of plants, branches of trees and shrubs, which leads to a change in the competitive relations between species in the phytocenosis. In addition, animals compact the soil, which changes its air and water regimes. In some regions of the planet, livestock grazing determines the composition and structure of the vegetation cover in large areas. So, in the Mediterranean countries, the excessive number of goats caused the almost complete disappearance of forests and their replacement by shrubs and shrubs and herbs. In damp meadows, overgrazing can lead to their swamping, and in the steppes, on the contrary, to greater xerophytization of vegetation and even to desertification; grazing on light loose soils - to their erosion.

dehumidification waterlogged areas dramatically changes the environmental conditions of the habitat (mainly the water and air regimes of soils), which leads to a radical change in plant communities. At the same time, melioration can lead both to positive changes in the composition and structure of vegetation (especially from the point of view of its economic use), and to sharply negative ones. Very often, people use territories transformed as a result of drainage as agricultural land, but often improper agricultural practices lead to complete or partial degradation of fertile peaty soils. The lowering of the groundwater level as a result of reclamation measures leads to the shallowing or even complete disappearance of many small rivers, a decrease in the catchment area of ​​medium and large rivers and, as a result, the transformation, in most cases negative, of the vegetation cover in large areas.

Irrigation also leads to significant changes in vegetation cover. As a result of irrigation, water, temperature, and salt regimes change, which leads to a change in xerophytic plant communities by more mesophytic or even hygrophytic ones. This allows a person to use irrigated areas as agricultural land. But, unfortunately, the problem of secondary soil salinization is very acute on irrigated lands. As a result of an increase in the level of groundwater and, as a result, increased evaporation of water, salts from deep horizons of the soil are gradually pulled up to its surface. Ultimately, this leads to the fact that initially non-saline or slightly saline soils turn into secondary solonchaks and solonets soils with corresponding vegetation.

Effects on plants of industrial emissions and discharges can be both direct and indirect. Thus, many organisms, especially conifers and lichens, are sensitive to the content of sulfur compounds (mainly oxides) in the air. Very often this leads to the complete or partial death of lichens, excessive defoliation and, accordingly, to a strong weakening of the trees. The consequence of this, as a rule, is a strong degradation of forest communities in the vicinity of large industrial enterprises. In addition, the so-called "acid rain" and dust released into the air greatly change the chemistry of soils, which also leads to changes in the composition and structure of plant communities. The dust covering the leaves negatively affects the processes of photosynthesis in plants. Heavy metals, which are emitted in large quantities into the atmosphere with vehicle exhaust gases, increase the level of mutations and adversely affect the generative reproduction of many plant species.

Human introduction of new plant species. Today, man is a significant factor influencing the change in the ranges of many plant species. In addition to the reduction of ranges, as mentioned above, in many cases it is a factor that contributes to the penetration and dispersal of a large number of plant species into unoccupied territories. At the same time, the development of a network of transport communications, trade relations and wars, the use of imported seeds of agricultural plants and many other factors play an important role. Such species, which are called adventive (adventive), may differ in the time and method of introduction, as well as in the degree of naturalization.

According to the time of skidding, they distinguish:

· archeophytes- species that appeared before the 16th century ( Atriplexpatula, Fallopia convolvulus, Urticaurens,Acoruscalamus and etc.);

· cenophytes (neophytes) are species that appeared at a later time.

According to the method of skidding, they distinguish:

· xenophytes- Species entered by chance. This group includes the vast majority of adventitious species;

· ergasiophytes– Species introduced intentionally. Most often, these are species cultivated by humans that have emerged from culture and settled without human help (for example, Pinusbanksiana,Acernegundo, Amelanchierspicata, Echinocystis lobata and etc.);

· xenoergasiophytes- a transitional group of species, the method of introduction of which has not yet been clarified.

According to the degree of naturalization, there are:

· ephemerophytes– species unable to establish themselves in a new territory;

· colonophytes– species that are firmly established in the new territory, but do not spread to new habitats;

· epecophytes– alien species that are able to invade only disturbed habitats with weakened competitive relations (for example, ruderal or segetal communities);

· agriophytes- species that are so competitive in a new habitat for themselves that they are more or less successfully included in natural plant communities.

79. Nature protection(English) environmentalism) - a set of measures for the conservation, rational use and restoration of natural resources and the environment, including the species diversity of flora and fauna, the richness of the subsoil, the purity of waters, forests and the Earth's atmosphere. Nature protection is of economic, historical, social and national importance

Nature protection measures

Activities related to nature protection can be divided into the following groups:

natural sciences

technical and production,

economic,

administrative and legal.

The danger of uncontrolled changes in the environment and, as a result, the threat to the existence of living organisms on Earth (including humans) required decisive practical measures to protect and protect nature, legal regulation of the use of natural resources. Among such measures are cleaning up the environment, streamlining the use of chemicals, stopping the production of pesticides, restoring land, and creating nature reserves. Rare plants and animals are listed in the Red Book.

In Russia, environmental protection measures are provided for in land, forestry, water and other federal legislation.

In a number of countries, as a result of the implementation of government environmental programs, it was possible to significantly improve the quality of the environment in certain regions (for example, as a result of a long-term and expensive program, it was possible to restore the purity and quality of water in the Great Lakes). On an international scale, along with the creation of various international organizations on certain problems of nature protection, the UN Environment Program operates.

The active impact of builders on the natural environment is primarily due to the fact that all buildings and structures being erected directly interact with many elements of the natural environment. To ensure this interaction, it is necessary to some extent to resort to the violation of the existing natural situation.

During the construction of the underground part of buildings and structures, natural conditions are primarily violated, therefore, when designing buildings and structures, as well as methods for their construction, it is necessary to predict possible changes in the natural environment and develop the necessary measures to protect and preserve nature.

The nature of the violation of the natural environment during the construction of the underground part of buildings and structures is diverse, and this nature is significantly influenced by the type of work performed.

Destruction of the natural relief "is associated with the implementation of earthworks and water-reducing works, as well as with other works on the construction of foundations. Violation of the natural relief is manifested in the form of landslides, landslides, collapses, failures, erosion, subsidence. The most dangerous is water erosion, which consists in the washing away of the top layer of the earth by melt and rain waters. With water erosion, vegetation and forests are destroyed, especially on the slopes of mountains and river valleys, which contributes to the development of ravines and the collapse of slopes. Deforestation contributes to the spread of erosion. Sometimes, improper organization of construction, lack of access and intra-site roads with a hard surface lead to the acceleration of water erosion. To prevent landslides, soil compaction by preliminary soaking and soaking using deep explosions on landslide-prone slopes is not allowed.

In the production of major water-reducing works, it is necessary to provide for measures to prevent shifts and precipitation of the earth's surface, for example, regulation of water-reducing works.

At the present stage, the anthropogenic impact on the vegetation cover of the Earth can be reduced to three main forms:

1. complete destruction of the vegetation cover;

2. creation of cultural phytocenoses in place of natural vegetation;

3. synanthropization of vegetation cover.

On the globe, 20 hectares of forests are cut down in one minute. The creation of cultural phytocenoses on the site of natural vegetation is the creation of crops, gardens, soil and field plantings. Vegetation synanthropization is a gradual change in the composition and structure of vegetation under the influence of anthropogenic factors. Synanthropization is manifested in the following: the replacement of indigenous phytocenoses by derivatives, the replacement of endemic plants by cosmopolites. All this leads to the impoverishment and monotony of the plant world. The impoverishment of the flora has two aspects: a decrease in species diversity; reduction in genetic diversity. The first is caused by the extinction of species. In this case, endemic species usually disappear faster. The second is related to the disappearance of the locality of the species. The more diverse the habitat conditions of a species, the richer the gene pool. Now there is a significant decrease in the species saturation of various phytocenoses. For example, in the Netherlands, on an area of ​​20 km2, on average, the number of species decreased from 250 to 180; hayfields, pastures, etc. were especially affected (losing up to 60-70% of species richness).

If before the appearance of man it is believed that one species disappeared on average for one thousand years, then from 1850 to 1950. this interval was 10 years, after 1950 - one year. It is now believed that one species disappears in one day. The flora of the islands, represented by often endemic species, is rapidly disappearing. For example, out of 1500 endemic species of the Hawaiian Islands, 500 species are considered rare and endangered. Small populations of species that are outside the main range or on its border are rapidly dying out. In densely populated, industrially developed areas (especially near large cities), the disappearance of plant species occurs more intensively than in agricultural areas.

Anthropogenic impact on the evolutionary process manifests itself in at least four directions:

1. reduction of genetic heterogeneity of species;

2. fragmentation of plant populations and their increasing isolation;

3. hybridization between previously separated taxa;

4. emergence of endemic technogenic substrates and contaminated sites.

Reducing the genetic diversity of individual species. Man reduces the number and size of populations, which leads to a decrease in the genetic diversity of species. The replacement of natural forest ecosystems by forest plantations has led to a reduction in the genetic diversity of woody plants by more than a hundredfold in some areas.

Fragmentation of plant populations and their increasing isolation. Formerly widespread plant communities are reduced in size and dissected into a number of isolated fragments. In accordance with this, plant populations are reduced and dissected. The geographical or ecological barriers that arise between them create for small populations an environment close to island populations. The existence of plant species in the form of small populations creates prerequisites for the emergence of a series of taxa of intraspecific and even species rank.

Hybridization between previously separated taxa. Under the influence of anthropogenic factors, geographical and environmental barriers between related, but previously isolated groups are often eliminated. This occurs as a result of habitat transformation, disruption of the structure of plant communities, mass introduction of introduced species, etc. For example, in England, two species of hawthorn - smooth and single-pistil - were initially ecologically separated. The smooth hawthorn grew in the forests, the single-petaled hawthorn grew in open places. Cuttings led to the thinning of forests, as a result, two species of hawthorn appeared on the same territory, and hybrids between species appeared. In Poland, hybrids between Polish and European larch appeared.

Emergence of endemic technogenic substrates and polluted places. In the process of activity, a person creates new substrates that are populated by plants. In the vicinity of Lake Bear in Canada, with a close occurrence of uranium ores, a large number of willow-herb and blueberry mutants have been noted.

Currently, there is an intensive dying off of forests in Europe. One of the causes of death is air pollution. The impact of air pollution is to weaken the vital activity of foliage and needles, tree trunks and roots.

Studies carried out in Germany have identified four main types of pollution impacts: 1 direct effect of gases on vegetation; 2 precipitation of heavy metals and their accumulation in soil; 3 acid action on plants and soil; 4 action of nitrogen saturation.

Three classes of interactions between atmospheric impurities and forest ecosystems have been identified. At a low content of pollutants (first-class interaction), the vegetation and soils of forest ecosystems function as their absorbers. Depending on the nature of pollutants, their influence may be imperceptible or stimulating (like fertilizers).

With an average content of pollutants (interaction of the second class), some tree species are negatively affected. This influence is expressed in a violation of the balance and metabolism of nutrients, a decrease in immunity to pests and diseases, and increased morbidity. The biomass and productivity of plants decrease, the species composition and structure of communities change.

Phytocenosis(from Greek φυτóν - "plant" and κοινός - "general") - vegetable community that exists within the same biotope. It is characterized by the relative homogeneity of the species composition, a certain structure and system of relationships between plants with each other and with the external environment. According to N. Barkman, phytocenosis is a specific segment of vegetation in which internal floristic differences are less than differences with surrounding vegetation. Phytocenoses are the object of study of the science of phytocenology (geobotany).

Phytocenosis is part of biocenosis as well as zoocenosis and microbiocenosis. Biocenosis, in turn, in combination with the conditions of the abiotic environment ( ecotope) forms biogeocenosis. Phytocenosis is the central, leading element of biogeocenosis, as it transforms the primary ecotope into a biotope, creating a habitat for other organisms, and is also the first link in the circulation of matter and energy. Soil properties, microclimate, composition of the animal world, such characteristics of biogeocenosis as biomass, bioproductivity, etc., depend on vegetation. In turn, the elements of phytocenosis are plant populations - aggregates of individuals of the same species within the boundaries of phytocenoses.

Formation of phytocenosis

The formation of phytocenoses can be considered both in a dynamic aspect (change of communities) and in terms of their formation in free areas of the earth's surface.

Primarily free areas are distinguished, which in the past were not inhabited by plants and do not contain their rudiments. Phytocenoses can form on them only when diaspores are introduced from outside. Such areas include rocky outcrops, fresh river and sea sediments, the exposed bottom of reservoirs, areas freed from glaciers, lava fields, etc. On the whole, they occupy insignificant areas on Earth.

Secondarily free areas are formed in places where vegetation used to exist, but was destroyed due to the impact of some unfavorable factor. Burnt areas, screes, unsown arable lands, areas of phytocenoses eaten away by pests or livestock can serve as an example. In most cases, soil and diaspores are preserved on them, and the formation of phytocenoses occurs much faster than in the initially free areas. The formation of a phytocenosis is a continuous process, but can be conditionally divided into stages:

• according to V. N. Sukachev:

1. Lack of phytocenosis- random composition of species; lack of interaction between plants; very little impact on the environment; unexpressed structure.
2. Open phytocenosis- unstable composition, mainly from annuals; structure with separate cenopopulations that do not interact with each other.
3. Closed undeveloped phytocenosis- loss of a significant part of the pioneer species; patchy structure with penetration of individual plants into clusters of other species; tiering is indicated.
4. Closed developed phytocenosis- relatively constant species composition; difficulty in the entry of new species; interaction of all cenopopulations; pronounced tiering.

• according to A.P. Shennikov:

1. Pioneer grouping- cenopopulations are small, there are no relationships between them
2. Group-thick community- cenopopulations are distributed in clumps in which interaction between plants occurs
3. diffuse community- cenopopulations mix, a system of interspecific interactions is developed

• according to F. Clements:

1. Migration- importation of diasporas
2. ecesis- consolidation of the first settlers
3. Aggregation- formation of offspring groups around mother plants
4. Invasion- mixing of cenopopulations
5. Competition- development of competitive relations due to a sharp increase in density
6. Stabilization- formation of a stable closed community

E. P. Prokopiev, summing up the various division schemes of the process of phytocenosis formation, proposes to distinguish three stages in it:

1. Receipt of primordia on a free site. The species composition of the emerging phytocenosis will depend on the species composition of plants in the surrounding area and the nature of the distribution of their diaspores, with the main role played by the rudiments of allochoric species, mainly anemochores.
2. Ecotopic (abiotic) selection. Not all of the diaspora that got to the free area will take root on it: some will not germinate, and some of the germinated ones will die in a young state due to an unfavorable combination of abiotic factors. The established plants will be pioneer for this territory.
3. Phytocoenotic selection. Due to the reproduction and settlement of pioneer species in the area, they will begin to influence each other and change the ecotope, forming a biotope (habitat). The primary abiotic environment of the ecotope turns into a secondary biotic - phytoenvironment. Under the influence of the phytoenvironment and mutual influences of plants, some pioneer species that are not adapted to it fall out. This can occur, for example, due to shading or allelopathy. At the same time, new species are fixed on the site, already adapted to this phytoenvironment.

Factors of organization of phytocenosis

Factors of plant community organization can be conventionally divided into four groups: characteristics of the environment (ecotope), the relationship between plants, the effect of heterotrophic components (animals, fungi, bacteria) on vegetation, and disturbances. These groups of factors determine the combination and characteristics of species coenopopulations in a phytocenosis.

Ecotop is the main factor in the organization of phytocenosis, although it can be largely transformed by the biotic influences of plants or disturbances. Abiotic factors influencing community organization include:

• climatic (light, heat, water regimes, etc.)
• edaphic (granulometric and chemical composition, humidity, porosity, water regime and other properties of soils and soils)
• topographic (relief characteristics)

plant relationships subdivided into contact and mediated : transabiotic- through abiotic environmental factors and transbiotic through third organisms.

Influence on the organization of phytocenoses heterotrophic components biogeocenoses are extremely diverse. The influence of animals is manifested in pollination, eating, dispersal of seeds, changing the trunks and crowns of trees and related characteristics, loosening the soil, trampling, etc. Mycorrhizal fungi improve the supply of plants with mineral nutrients and water, increase resistance to pathogens. Nitrogen fixing bacteria increase the supply of nitrogen to plants. Other fungi and bacteria, as well as viruses, can be pathogens.

Violations, both anthropogenic and natural genesis, can completely transform the phytocenosis. This occurs during fires, clearings, grazing, recreational pressure, etc. In these cases, derivative phytocenoses are formed, which gradually change towards the restoration of the original one, if the impact of the disturbing agent has ceased. If the impact is long-term (for example, during recreation), communities are formed that are adapted to exist at a given level of load. Human activity has led to the formation of phytocenoses that did not previously exist in nature (for example, communities on toxic dumps of industrial production).

Interactions of organisms in phytocenoses

The presence of a system of relationships between plants is one of the main signs of an established phytocenosis. Studying them, due to the large overlap and strong influence of abiotic factors, is a difficult task and can be implemented either in the form of an experiment in which the relationship between two specific species is studied, or by isolating such relationships from a complex of others using the methods of mathematical analysis.

Direct (contact) interactions

Symbiotic relationship are manifested in the coexistence of plants with fungi and bacteria (including cyanobacteria). Accordingly, they distinguish mycosymbiotrophy and bacteriosymbiotrophy.

Plants that form mycorrhiza, according to the requirements for the presence of a mycosymbiont, can be divided into two groups:

• obligate mycosymbiotrophs - not capable of development without a mycosibiont (fam. Orchidaceae)
• facultative mycosymbiotrophs - able to exist without a mycosymbiont, but develop better in its presence

Bacteriosymbiotrophy - symbiosis of plants with nodule bacteria ( Rhizobium sp.). It is not as widespread as mycosymbiotrophy - about 3% of plants of the world flora enter into symbiosis with bacteria (mainly of the legume family (about 86% of the species of the family), as well as some species of the families Bluegrass, Birch, Lokhovye, Krushinovye). Nodule bacteria play the role of nitrogen fixers, converting atmospheric nitrogen into forms available to plants. There are root and leaf forms of interaction. In the root form, the bacteria infect the roots of the plant, causing intense local divisions of cells and the formation of nodules. Leaf bacteriosymbiotrophy occurs in some tropical plants and is still poorly understood.

One of the methods of three-field culture is based on the ability of plants of the legume family to enter into symbiosis with nodule bacteria.

Epiphytes living on plants phorophytes use the latter only as a substrate, without entering into physiological interactions with them. Epiphytic forms are found in the groups of angiosperms, ferns, mosses, algae and lichens. Epiphytes reach the greatest diversity in humid tropical forests.

In ecological terms, the relationship between epiphytes and phorophytes is usually represented by commensalism, but elements of competition may also appear:

• epiphytes partially intercept light and moisture from phorophytes
• retaining moisture, contribute to the decay of phorophyte
• shading the phorophyte, epiphytes reduce its effective photosynthetic surface
• growing profusely, can cause deformation or breakage of phorophytes

Lianas, bringing their leaves closer to the light during growth, benefit from cohabitation with the supporting plant, while the latter is mainly harmful, both direct - due to the mechanical impact of the vine and the breakdown / death of the supporting plant, and indirectly - due to the interception of light by the liana, moisture and nutrients.

The greatest variety of creepers also reach in humid, tropical forests.

Transabiotic interactions

Influences of plants on each other, mediated by abiotic environmental factors. They arise due to the overlap of phytogenic fields of neighboring plants. Subdivided into competition and allelopathy.

Competition develops either due to the initial limitation of habitat resources, or as a result of a decrease in their share per plant due to overpopulation. Competition leads to a decrease in the consumption of resources by a plant and, as a result, a decrease in the rate of growth and storage of substances, and this, in turn, leads to a decrease in the number and quality of diaspores. Distinguish inside- and interspecific competition.

Intraspecific competition affects the fertility and mortality rates in the cenopopulation, determining the tendency to maintain its numbers at a certain level, when both values ​​balance each other. This number is called ultimate density and depends on the amount of habitat resources. Intraspecific competition is asymmetric - it affects different individuals differently. The total phytomass of the cenopopulation remains constant in a fairly wide range of density values, while the average weight of one plant begins to decrease steadily upon thickening - law of constancy of harvest(C=dw, where C is the yield, d is the coenopopulation density and w is the average weight of one plant).

Interspecific competition is also widespread in nature, since the vast majority of phytocenoses (except for some agrocenoses) are multispecific. The multispecies composition is ensured by the fact that each species has an ecological niche characteristic only for it, which it occupies in the community. At the same time, the niche that a species could occupy in the absence of interspecific competition - fundamental, shrinks to realized. In a phytocenosis, differentiation of ecological niches occurs due to:

• different plant heights
• different depths of penetration of the root system
• contagious distribution of individuals in the population (separate groups / spots)
• different periods of vegetation, flowering and fruiting
• unequal efficiency in the use of habitat resources by plants

With a weak overlap of ecological niches, the coexistence of two cenopopulations can be observed, while with a strong overlap, a more competitive species displaces a less competitive one from the habitat. The coexistence of two highly competitive species is also possible due to the dynamics of the environment, when one or another species gains a temporary advantage.

allelopathy- the influence of plants on each other and on other organisms by releasing active metabolites into the environment both during the life of the plant and during the decomposition of its residues. The allelopathic activity of a particular species is determined by a certain set of chemicals of various nature, the qualitative and quantitative composition of which significantly depends on external conditions. Allelopathically active substances are secreted both by aboveground organs (mainly leaves) and underground, mainly in three ways:

• active excretion via glands or hydathodes
• precipitation washout
• isolation by decomposition of litter by microorganisms

The amount of secretions of various plants in a phytocenosis is its biochemical environment. Since the composition of the secretions is not constant, we can talk about the existence of an allelopathic regime of phytocenosis, along with water, air, etc.

Transbiotic interactions

Indirect influences of some plants on others through third organisms (other plants, animals or fungi). The impact can be manifested both at the level of an individual organism and at the level of the whole cenopopulation. Transbiotic interactions can be:

During the formation of a phytocenosis, the primary abiotic environment of an ecotope turns into a phytoenvironment, and the ecotope itself becomes a biotope. At the same time, phytocenosis affects almost all abiotic factors, changing them in one direction or another.

Light regime of phytocenosis

Inside any phytocenosis, the light regime will differ from the light regime of an open area not occupied by vegetation. Such differences arise due to the fact that the light in the phytocenosis is redistributed in a certain way and the following processes occur:

• reflection of part of the world outside the phytocenosis
• absorption of part of the world by plants (including in the process of photosynthesis)
• penetration of light into the phytocenosis

Due to the reflection and absorption of light by plants, only a small part of it reaches the soil level, which is especially clearly seen in multi-tiered forest phytocenoses: under the canopy of a pine forest, illumination is, on average, 25-30%, oak - about 3%, and a humid tropical forest - about 0.2% of total illumination (on an open surface in the same geographical conditions).

Illumination in the phytocenosis is heterogeneous: it changes both in the vertical and horizontal directions. When moving from the upper boundary of the phytocenosis to the soil level, the illumination drops abruptly, primarily due to the peculiarities of leafing (density and arrangement of leaves in space) on each tier.

In herbal phytocenoses, two types of illumination are distinguished: cereal and dicotyledonous. The cereal type is typical for communities with a predominance of plants with vertically oriented leaves (grasses, sedges) and is characterized by a gradual decrease in illumination from top to bottom. Dicotyledonous type - for communities with horizontally oriented leaves; characterized by sharp jumps in illumination and is similar in this regard to changes in illumination in forest communities.

In aquatic ecosystems, in addition to plants, water and particles suspended in it also participate in the absorption and reflection of light, as a result of which the existence of plants becomes impossible at great depths. In transparent fresh water bodies, illumination becomes less than 1% at depths of more than 5-10 meters, as a result of which higher plants in such conditions are found at depths of no more than 5, and algae - no more than 20 meters, however, in the clear waters of the seas and oceans, certain types of red algae penetrate to a depth of several hundred meters.

Plants in phytocenoses also change the qualitative composition of the spectrum, selectively absorbing and reflecting light with a certain wavelength. Hard UV radiation (λ< 280 нм), вредное для живых структур растительной клетки, практически полностью (до 95-98 %) поглощается эпидермисом листьев и другими покровными тканями. Видимая часть солнечного спектра (физиологически активная радиация) до 70 % поглощается фотосинтетическими пигментами, при этом интенсивнее поглощается сине-фиолетовая и красная части спектра, а зелёная - значительно слабее. ИК-излучение с λ >7000 nm is absorbed up to 97%, and with λ< 2000 нм - очень слабо.

The permeability of leaves to light is also not the same and depends primarily on the thickness and structure of the leaf, as well as the wavelength of light. So, leaves of medium thickness transmit up to 10-20% of the light, very thin ones - up to 40%, and thick, hard leaves covered with a wax coating or pubescence may not transmit light at all. IR and green light have the highest penetrating power, the rest of the spectrum penetrates much less through the leaves.

The light regime also changes during the day, during the year, and depending on the age composition of phytocenosis plants.

Thus, phytocenoses change the lighting conditions of the ecotope, forming a special, spatially heterogeneous light regime. The specificity of this regime in each specific phytocenosis determines the set of species, their distribution and the structure of the phytocenosis as a whole.

Thermal regime of phytocenosis

An area of ​​the Earth's surface, devoid of vegetation, receives heat both directly from the Sun and indirectly - through the scattered light of the sky and the return radiation of the heated atmosphere. The received heat is partly reflected back into the atmosphere, partly absorbed and removed to the deeper layers of the Earth, and partly radiated by the heated soil back into the atmosphere. All processes of heat input and removal form a heat balance.

The heat balance changes during the day: during the day, during the insolation phase, it turns out to be positive, and at night it is negative. The heat balance is also affected by weather conditions, terrain, seasons and geographic location of the ecotope.

Phytocenoses significantly change the thermal regime of the ecotope, since plants:

• reflect part of the sunlight back into the atmosphere, reducing the flow of heat into the phytocenosis
• absorb sunlight and spend it on physiological processes in the future
• release some heat during respiration
• carry out transpiration and guttation
• absorb some of the heat radiated by the soil
• reduce evaporation from the soil surface
• slow down the movement of air masses

Also, a change in the thermal regime of the ecotope occurs due to condensation and physical evaporation of moisture from the surface of plants.

The main energy exchange in the phytocenosis is carried out not at the soil surface, as in an area devoid of vegetation, but in the upper closed phytocoenohorizon, which heats up most during the day and cools most at night.

In general, the thermal regime of a phytocenosis has the following features compared to that of a site devoid of vegetation:

• maximum temperatures are falling and minimum temperatures are rising
• daily and seasonal temperature amplitudes are smoother
• average annual temperature below

Air regime of phytocenosis

The influence of phytocenosis on the air regime is manifested in a change in the speed of movement and composition of the air. The wind speed in phytocenoses decreases from top to bottom and from a more open area to a less open one. The dynamics of air composition is determined mainly by changes in the concentrations of oxygen and carbon dioxide in the process of photosynthesis and respiration. The content of CO 2 is subject to more significant fluctuations: in the first half of the day it decreases, which is associated with the intensification of photosynthesis, in the second half of the day it rises and reaches a maximum at night. The change in the oxygen content in the air occurs synchronously, but in the opposite direction. There is a certain variability in the content of CO 2 and O 2 by the seasons of the year: for example, in the forests of the temperate zone, the lowest concentration of CO 2 is observed in spring, when leaves bloom and life processes intensify in plants.

Phytocenosis humidity regime

Phytocenosis structure

Depending on the specifics of research in the concept of "structure of the biocenosis", V.V. Mazing distinguishes three directions developed by him for phytocenoses.

1. Structure as a synonym for composition (species, 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 confinement to ecological niches and occupy a certain space. This also applies to other components of biogeocenosis. Between the parts of the spatial division (tiers, synusia, micro-groups, etc.) one can easily and accurately draw boundaries, put them on the plan, calculate the area, and then, for example, calculate the resources of useful plants or animal feed resources. Only on the basis of data on the morphostructure, it is possible to objectively determine the points of setting up certain experiments. When describing and diagnosing communities, a study of the spatial heterogeneity of cenoses is always carried out.

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

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

Phytocenosis consists of a number of structural elements. There are horizontal and vertical structure of phytocenosis. The vertical structure is represented by tiers identified by visually determined horizons of phytomass concentration. The tiers consist of plants of different heights. Examples of layers are 1st tree layer, 2nd tree layer, ground cover, moss-lichen layer, undergrowth layer, etc. The number of layers may vary. The evolution of phytocenoses goes in the direction of increasing the number of layers, as this leads to a weakening of competition between species. Therefore, in the older forests of the temperate zone of North America, the number of layers (8-12) is greater than in similar younger forests of Eurasia (4-8).

The horizontal structure of the phytocenosis is formed due to the presence of tree canopies (under which an environment is formed that is somewhat different from the environment in the inter-canopy space), relief heterogeneities (which cause changes in the groundwater level, different exposure), species characteristics of some plants (reproducing vegetatively and forming monospecies "spots" , changes in the environment by one species and response to this by other species, allelopathic effects on surrounding plants), animal activities (for example, the formation of spots of ruderal vegetation on rodent burrows).

Regularly repeating spots (mosaics) in a phytocenosis, differing in the composition of species or their quantitative ratio, are called microgroups, and such a phytocenosis is mosaic.

Heterogeneity can also be random. In this case it is called variegation.

Dynamics of phytocenoses

Phytocenoses are characterized by the constancy of species composition, habitat conditions, but continuous changes still occur there. The property to change is called dynamic.

Dynamic processes are reversible and irreversible.

reversible

1. Diurnal - associated with the daily rhythm of the vital activity of plants that form a phytocenosis; expressed in changes in the activity of transpiration, respiration, photosynthesis, in the daily movements of flowers and leaves, in the rhythm of opening and closing flowers. They are determined by the characteristics of the phytoclimate created by the plant community.

2. Seasonal - determined by the peculiarities of the rhythm of development of the species that form the phytocenosis. These changes allow a greater number of plant species to exist together than if they developed simultaneously. For example, in spring - early ephemeroids, in summer - late summer grasses, shrubs, trees.

3. Fluctuations are year-to-year changes associated with unequal conditions for the existence of plants in different years. The composition does not change; the size and age composition of the population may change.

irreversible

(successions, community evolution, community disturbances).

Successions are gradual changes in phytocenoses, irreversible and directed, caused by internal or external causes, in relation to phytocenoses, causes. There are primary and secondary successions. Primary successions begin on lifeless substrates (rocks, cliffs, river sediments, loose sands), while secondary ones begin on substrates on which vegetation was, but disturbed (restoration after a forest fire).

Classification of phytocenoses

When classifying phytocenoses, similar communities are combined into groups - classification units.

The lowest unit of classification is association(a set of homogeneous phytocenoses that have more or less the same appearance, similar floristic composition and the same dominant species by tiers). The names of the associations are given by listing the Russian names of the dominant plants of each phytocenosis tier, starting from the uppermost tier (Pinus sylvestris + Picea abies - Vaccinium vitis-idaea + Vaccinium myrtillus - Pleurozium schreberi) with the addition of suffixes lat. -etum, -osum, -estosum: Piceetum oxalidosum (from Picea and Oxalis) - sour spruce forest.

A formation is a set of associations in which the same type of plant dominates in the upper tier (for example, pine forests, oak forests, etc.)

Ordination is the construction of a series of phytocenoses by a gradual change in any environmental factor in a certain direction. So, it is possible to carry out ordination according to the factor of soil moisture. In this case, a series of communities will be obtained, where each will take its appropriate place depending on the moisture conditions in which it develops, and the extreme of them will correspond to the wettest soils, and the opposite to the driest.