The emergence of biocenosis begins with the appearance of the first organisms in areas deprived of life (lava flows, volcanic islands, talus, exposed rocks, sandy deposits and dried bottoms of reservoirs). Settlement begins with an accidental introduction of organisms from territories already developed by them and depends on the properties of the substrate. This site for many seeds of plants and animals that have penetrated here may not be suitable for reproduction. Often, especially in the humid zone, the first settlers are representatives of algae, mosses and lichens.

As a rule, only a few of the introduced plant species develop successfully. Animals-consumers settle somewhat later, since their existence without food is impossible, but an accidental visit by them to the developed areas is a rather frequent occurrence. This stage of development of biocenosis is called pioneer. Although the community has not yet formed at this stage, it already has an impact on the abiotic environment: soil begins to form.

The pioneer stage is replaced by an unsaturated one, when plants begin to renew themselves (by seeds or vegetatively), and animals multiply. Not everyone is employed in an unsaturated biocenosis ecological niches.

Gradually, the rate of settlement of the site increases due to both an increase in the number of individuals of pioneer vegetation before the formation of thickets, and the introduction of new species. The species composition of such a community is still unstable, new species are introduced quite easily, although competition begins to play a significant role. This stage of development of the biocenosis is a grouping.

With the subsequent development of the community, the vegetation cover is differentiated by tiers and synusia, its mosaic pattern acquires stable constancy, species composition, food chains and consortia. Ultimately, all ecological niches are occupied, and further invasion of organisms becomes possible only after the displacement or destruction of the old-timers. This final stage of biocenosis formation is called saturated. However further development biocenosis does not stop and random deviations in the species composition and relationships both between organisms and with environment may still take place.

Random deviations in the structure of the biocenosis are called fluctuations. As a rule, they are due to random or seasonal changes in the abundance of species included in the biocenosis as a result of adverse meteorological phenomena, floods, earthquakes, etc.

Although the biocenosis is a rather conservative natural system, however, under the pressure of external circumstances, it can give way to another biocenosis. The successive change in time of some communities by others in a certain area of ​​​​the environment is called succession. As a result of succession, one community is successively replaced by another without returning to its original state. The interaction of organisms, mainly wounds, with each other and with the environment leads to succession.

Successions are divided into primary-historical. Primary ones occur on soils that are primarily free from soil - volcanic tuff and lava fields, loose sands, stony placers, etc. As the phytocenosis develops from the pioneer stage to saturated, the soil becomes more fertile and more and more involved in the biological cycle chemical elements in increasing numbers. With an increase in fertility, plant species that develop on nutrient-rich soils displace less demanding species in this regard. At the same time, the animal population also changes. Secondary successions are carried out in the habitats of destroyed communities, where soils and some living organisms have been preserved. Secondary successions are typical for degraded pastures, burnt areas, deforestation, arable lands and other lands excluded from agricultural use. as well as for artificial forest plantations. For example, often under the canopy of middle-aged pine crops on sandy soils, abundant natural renewal of spruce begins, which will eventually displace pine, provided that regular clear-cutting of pine stands and silvicultural work are not carried out.

The change of one biocenosis to another during the succession forms a successional series, or series. The study of successional series has great importance in connection with the increasing anthropogenic influence on biocenoses. The end result of this kind of research can be the prediction of the formation of natural-anthropogenic landscapes. The study of secondary successions and the factors that cause them plays an important role in solving the problems of protection and rational use of biological and land resources.

If the natural course of succession is not disturbed, the community gradually comes to a relatively stable state in which a balance is maintained between organisms, as well as between them and the environment - to a climax. Without human intervention, this biocenosis can exist indefinitely, for example, blueberry pine forest, lichen tundra on sandy soils.

The concept of menopause was developed in detail by the American botanist X. Kauls and is widely used in foreign botanical and geographical literature. According to this concept, the climax is the terminal stage of community evolution, which corresponds to a soil of a certain type - pedoclimax. Successions leading to this stage are called progressive, and those that remove the biocenosis from it are called regressive.

Biocenoses that, when disturbed, return to their original state, are called indigenous.

Transformed biocenoses do not return to their original state.

Different ecosystems exist on the same biotope over time. The change of one ecosystem to another can take both rather long and relatively short (several years) periods of time. The duration of the existence of ecosystems in this case is determined by the stage of succession. A change in ecosystems in a biotope can also be caused by catastrophic processes, but in this case, the biotope itself changes significantly, and such a change is not usually called succession (with some exceptions, when a catastrophe, for example, a fire, is a natural stage of cyclic succession)

Succession is a consistent, regular change of some communities by others in a certain area of ​​the territory, due to internal factors in the development of ecosystems. Each previous community determines the conditions for the existence of the next and its own disappearance. This is due to the fact that in ecosystems that are transitional in the succession series, there is an accumulation of matter and energy that they are no longer able to include in the cycle, transformation of the biotope, changes in the microclimate and other factors, and thus a material and energy base is created, as well as the environmental conditions necessary for the formation of subsequent communities. However, there is another model that explains the mechanism of succession as follows [: the species of each previous community are replaced only by consistent competition, inhibiting and "resisting" the introduction of subsequent species. However, this theory considers only competitive relations between species, not describing the whole picture of the ecosystem as a whole. Of course, such processes are underway, but the competitive displacement of previous species is possible precisely because of the transformation of the biotope by them. Thus, both models describe different aspects of the process and are correct at the same time.

An example of the stage of autotrophic succession - a forest grows on the site of a fallow.

Succession can be autotrophic (for example, succession after a forest fire) and heterotrophic (for example, a drained swamp).

An example of a heterotrophic succession stage is a swampy meadow

In the early stages of succession, the species diversity is low, but as the development progresses, the diversity increases, the species composition of the community changes, species with complex and long life cycles begin to predominate, larger organisms usually appear, mutually beneficial cooperations and symbioses develop, and the trophic structure of the ecosystem becomes more complex. It is usually assumed that the terminal stage of succession has the highest species biodiversity. This is not always true, but for climax communities rainforest this statement is true, but for communities temperate latitudes the peak of diversity occurs in the middle of the succession series or closer to the terminal stage. On early stages communities consist of species with a relatively high rate of reproduction and growth, but a low ability for individual survival (r-strategists). In the terminal stage, the impact of natural selection favors species with a low growth rate, but a greater ability to survive (k-strategies).

As you move along the successional series, there is an increasing involvement of biogenic elements in the cycle in ecosystems, a relative closure within the ecosystem of the flows of such biogenic elements as nitrogen and calcium is possible. Therefore, in the terminal stage, when most of the biogens are involved in the cycle, ecosystems are more independent of the external supply of these elements.

To study the process of succession, various methods are used. mathematical models, including stochastic ones.

climax community

Elnik (spruce forest) is a typical example of a climax community that develops on some loamy soils in the North-West of Russia in the southern taiga subzone. The concept of succession is closely related to the concept of a climax community. The climax community is formed as a result of a successive change of ecosystems and is the most balanced community] that uses material and energy flows as efficiently as possible, that is, it maintains the maximum possible biomass per unit of energy entering the ecosystem.

Pine forest as a climax community, on the contrary, develops on sandy and sandy loamy soils.

Theoretically, each successional series has a climax community (ecosystem), which is the terminal stage of development. However, in reality, the succession series is not always closed by the climax; a subclimax community can be realized, which is a community that precedes the climax, sufficiently developed structurally and functionally. Such a situation may arise due to natural causes - environmental conditions or as a result of human activity (in this case it is called disclimax).

Although the biocenosis is a rather conservative natural system, however, under the pressure of external circumstances, it can give way to another biocenosis. The successive change in time of some communities by others in a certain area of ​​​​the environment is called succession (from Lat. successia succession, inheritance). As a result of succession, one community is successively replaced by another without returning to its original state. The interaction of organisms, mainly wounds, with each other and with the environment leads to succession.

Successions are divided into primary - historical. Primary ones occur on soils that are primarily free from soil - volcanic tuff and lava fields, loose sands, stony placers, etc. As the phytocenosis develops from the pioneer stage to saturated, the soil becomes more fertile and more and more chemical elements are involved in the biological cycle in increasing quantities. With an increase in fertility, plant species that develop on nutrient-rich soils displace less demanding species in this regard. At the same time, the animal population also changes. Secondary successions are carried out in the habitats of destroyed communities, where soils and some living organisms have been preserved. The destruction of biocenoses can be caused by natural natural processes(hurricanes, heavy rains, floods, landslides, prolonged droughts, volcanic eruptions, etc.). as well as a change in the habitat by Organisms (for example, when a reservoir overgrows, the aquatic environment is replaced by peat deposits). Secondary successions are typical for degraded pastures, burnt areas, deforestation, arable lands and other lands excluded from agricultural use. as well as for artificial forest plantations. For example, often under the canopy of middle-aged pine crops on sandy soils, abundant natural renewal of spruce begins, which will eventually displace pine, provided that regular clear-cutting of pine stands and silvicultural work are not carried out. On burnt areas with sandy and loamy soils, pioneer vegetation of willow-herb and warty birch eventually gives way to spruce plantations.

In recent decades, large-scale drainage and irrigation works have acquired particular importance in changing the vegetation cover. In swamp forests that are in the zone of influence of drainage channels, hygrophyte plants disappear (sedge ols, for example, are transformed into nettles). The transformation of the species composition, including the animal population, also affects the forests arriving to the drained swamps. Irrigation reclamation, on the contrary, contributes to the active penetration of plants of hygrophilic and mesophilic groups into waterlogged areas as a result of the accumulation of water used for irrigation. Industrial pollution also has a noticeable effect on biocenoses. All these changes are secondary successions.

The change of one biocenosis to another during the succession forms a successional series, or series. The study of successional series is of great importance in connection with the increasing anthropogenic influence on biocenoses. The end result of this kind of research can be the prediction of the formation of natural-anthropogenic landscapes. The study of secondary successions and the factors that cause them plays an important role in solving the problems of protection and rational use of biological and land resources.

If the natural course of succession is not disturbed, the community gradually comes to a relatively stable state in which a balance is maintained between organisms, as well as between them and the environment - to the climax. Without human intervention, this biocenosis can exist indefinitely, for example, blueberry pine forest, lichen tundra on sandy soils.

The concept of climax was developed in detail by the American botanist X. Kauls and is widely used in foreign botanical and geographical literature. According to this concept, climax is the terminal stage of community evolution, which corresponds to a soil of a certain type - pedoclimax. Successions leading to this stage are called progressive, and those that remove the biocenosis from it are called regressive. It is impossible, however, to give the concept of "climax" an absolute meaning and to believe that when it is reached, the community stops development.

Biocenoses that, when disturbed, return to their original state, are called indigenous. A birch forest will grow on the site of felling of blueberry pine forest or sour spruce forest, and it, in turn, will again be replaced by blueberry pine forest or sour spruce forest. In this case, we are talking about indigenous forest types.

Transformed biocenoses do not return to their original state. Thus, a low-lying sedge bog drained and developed for crops, after the depletion of the peat deposit and the destruction of the reclamation network, with the cessation of agricultural use for some reason, develops in the direction of the formation of birch or alder undergrowth. The zoocenosis of this small forest differs from the animal species community of the open grassy swamp.

1.6 Classification

In order to scientific knowledge biocenoses and the practical application of knowledge about them, communities of organisms must be classified according to their relative size and complexity of organization.

The classification is designed to put in order all their diversity with the help of a system of taxonomic categories, i.e. taxa, uniting in this case groups of biocenoses with varying degrees of commonality of individual properties and characteristics, as well as structure and origin. At the same time, a certain subordination of simple taxa to complex taxa, taxa of small (local) dimension to taxa of planetary dimension, and a gradual complication of their organization must be observed. In addition, when classifying biocenoses, the presence of possible boundaries between them should be taken into account.

There are no particular difficulties in establishing boundaries when neighboring biocenoses have clear indicative features. For example, an upland bog with rosemary–moss cover and a low-growing pine stand contrasts with the surrounding pine forest. forest community on sandy soils. The boundary between the forest and the meadow is also clearly visible. However, since the conditions for the existence of communities change more gradually than the communities themselves, the boundaries of biocenoses are usually blurred. The gradual transition from one phytocenosis to another with their proximity and the change of one phytocenosis by another in time is reflected in the concept of a continuum (from Latin continuum - continuous) of vegetation developed by the Soviet geobotanist L. G. Ramensky, American ecologist P. X. Whittaker.

The boundaries between communities appear more sharply in cases where edificators have the greatest transformative effect on the environment, for example, the boundaries between woodlands, formed by different tree species - pine, spruce, oak and others. In steppes, semi-deserts, and deserts, the boundaries between communities are more gradual, since the role of herbaceous species in transforming the environment is less contrasting.

The classification of communities uses taxonomic categories adopted in plant geography and based on the identification of dominants and edificators, which indicates the recognition of phytocenosis as an ecological framework that determines the structure of biocenosis. The taxonomic system of communities built on the basis of dominants and edificators can be expressed as follows: association - group of associations formation group of formations class of formations type of biome - biocenotic cover.

The lowest taxonomic category is association. It is a collection of homogeneous microbiocenoses with the same structure, species composition and similar relationships both between organisms and between them and the environment. IN field conditions The main features of its identification are the same layer structure, a similar mosaic (spotted, scattered), the coincidence of dominants and edificators, as well as the relative homogeneity of the habitat. The name of an association for multi-tiered communities consists of the generic names of the dominant tier (condominant) and edificators in each tier, for example, juniper-mossy pine forest, birch-bilberry spruce forest, etc. The name of complex meadow associations is formed by listing dominants and subdominants, with the dominant being called the last , for example, a caustic-meadow-bluegrass association. Meadow associations are usually denoted by Latin: Ranunculus + Roa pratensis.

The group of biocenotic associations is formed by associations that differ in the composition of one of the tiers. The bilberry pine forest, for example, combines associations with an undergrowth layer of juniper, buckthorn, and birch undergrowth. The group of grass–sedge–forb associations includes meadow communities with a set of named groups of meadow grasses (grasses, small sedges, forbs).

The biocenotic formation includes groups of associations. The formation is distinguished according to the dominant, according to which it is called: the formation of Scots pine, black alder, English oak, white saxaul, caustic buttercup, wormwood, etc. This is the main unit of the middle rank, widely used in mapping forest vegetation.

The composition of ecosystems is a dynamic process. Ecosystems are constantly undergoing changes in the state and vital activity of their members and the ratio of populations. The diverse changes that take place in any community are classified into two main types: cyclical and progressive.

Cyclical changes communities reflects the daily, seasonal and long-term periodicity external conditions and manifestation of internal (endogenous) rhythms of organisms.

Daily cycles are associated mainly with rhythm. natural phenomena and is strictly periodic. Seasonal variability of biocenoses is expressed in a change not only in the state and activity, but also in the quantitative ratio of individual species, depending on the cycles of their reproduction, seasonal migrations, and the death of individual generations during the year.

The tiered structure of the biocenosis is often subject to seasonal variability: individual tiers of plants can completely disappear in the corresponding seasons of the year, for example, a herbaceous tier consisting of annuals.

Long-term cyclicity depends on changes in meteorological conditions over the years (climatic fluctuations), uneven precipitation over the years, with periodic recurrence of droughts, or other external factors affecting the community (for example, the degree of river flooding). In addition, the long-term periodicity may be related to the features life cycle edificatory plants, with the repetition of mass reproductions of animals or microorganisms pathogenic for plants, etc.

Progressive changes in a community lead ultimately to the replacement of this community by another, with a different set of dominant species. The reason for such changes may be factors external to the cenosis, long time acting in one direction, for example, the drying up of bog soils increasing as a result of melioration, increasing pollution of water bodies, increased grazing, etc. The resulting changes of one biocenosis to another are called exogenetic. Endogenetic shifts arise as a result of processes occurring within the community itself.

Successions

The successive change of one biocenosis by another is called (from lat. Succession - sequence, change) - succession. Succession is a process of self-development of ecosystems. Succession is based on the incompleteness of the biological cycle in a given biocenosis. Every living organism, as a result of its vital activity, changes the environment around itself, removing some of the substances from it and saturating it with metabolic products. With a more or less long-term existence of populations, they change their environment in an unfavorable direction and, as a result, are forced out by populations of other species, for which the resulting environmental transformations turn out to be ecologically beneficial. Thus, in the community there is a change in the dominant species. A successive series of communities gradually and regularly replacing each other in succession is called successional series.

Distinguish between primary and secondary succession. primary succession begins on places deprived of life (on rocks, sands, cliffs). secondary succession- this is a successive change of one community that existed on a given substrate by another more perfect for these abiotic processes. Secondary successions, as a rule, take place faster and easier than primary ones, since the soil profile, seeds, primordia, and part of the former population and former connections are preserved in the disturbed habitat.

In any successional series, the rate of change gradually slows down. The end result is the formation of a relatively stable stage - climax community or menopause. The initial, pioneer groupings of species are characterized by the greatest dynamism and instability. Climax ecosystems, on the other hand, are capable of long-term self-maintenance in the appropriate range of conditions, since they acquire such features of the organization of biocenoses that allow maintaining a balanced circulation of substances.

7. Artificial ecosystems: agro- and urban ecosystems

A person receives a lot of products from natural systems, however, agriculture is the main source of food for him.

Agroecosystems are created by man to obtain a high yield - pure production of autotrophs. Summarizing everything that has already been said about agroecosystems, we emphasize the following main differences from natural ones:

1. The diversity of species is sharply reduced in them: a decrease in the species of cultivated plants also reduces the species diversity of the animal population of the biocenosis; the species diversity of animals bred by man is negligible compared to the natural one; Cultivated pastures (with undersowing of grasses) are similar in species diversity to agricultural fields.

2. Plant and animal species cultivated by man "evolve" through artificial selection and are not competitive in the fight against wild species without human support.

3. Agro-ecosystems receive additional energy subsidized by man, in addition to solar energy.

4. Pure products (crop) are removed from the ecosystem and do not enter the food chains of the biocenosis, and its partial use by pests, losses during harvesting, which can also fall into natural trophic chains, are suppressed in every possible way by humans.

Ecosystems of fields, gardens, pastures, kitchen gardens and other agrocenoses are simplified systems maintained by man in the early stages of succession, and they are just as unstable and incapable of self-regulation as natural pioneer communities, therefore they cannot exist without human support. .

More than 50% of the world's population lives in cities today. Process urbanization- this is the growth of the urban population, the number and size of cities, the increase in the role of the city in people's lives, the spread of the urban lifestyle. Today, urbanized areas occupy 1% of the land, but concentrate 50% of the world's population, produce 80% of the gross domestic product (GDP), give 80% of all emissions.

metropolis It is an overgrowth of cities. The relationship of all components and phenomena of the urban and natural environment is called urban ecosystem. Urban ecosystems have a specific place in geographic space. These are open systems, managed. Their important feature is anthropocentrism.

Succession. Examples of Ecosystem Succession

Succession

Types of successions

secondary succession

Types of successional changes

Duration of succession

Examples of Ecosystem Succession

Communities are constantly changing. Their species composition, the number of certain organisms, the trophic structure, and other indicators of the community are changing.

The community changes over time.

Succession is a consistent, regular change of some communities by others in a certain area of ​​the territory, due to internal factors in the development of ecosystems.

In order to understand the nature of ecological succession, imagine an IDEAL community (that is, the total production of autotrophs in energy terms exactly corresponds to the energy costs that go to ensure the vital activity of its constituent organisms).

In ecology, the total energy consumption is called - common breath of the community.

It is clear that in such an ideal case, the processes of production are balanced by the processes of respiration.

Consequently, the biomass of organisms in such a system remains constant, while the system itself remains unchanged or in equilibrium.

If the "total respiration" is less than the gross primary production, the ecosystem will accumulate organic matter;

If more, decrease it.

Both in the first and in the second case there will be changes in the community

With an excess of a resource, there will always be species that can master it, and with a shortage, some of the species will die out.

Such a change is the essence of ecological succession.

The main feature of such a process is that changes in the community always occur in the direction of an equilibrium state.

1.1 Types of successions

A succession that begins in a place devoid of life (for example, on a newly formed sand dune) is called primary succession.

In nature, primary successions are relatively rare and last much longer than secondary ones - up to several centuries.

primary succession- this is the overgrowing of a place previously not occupied by vegetation: bare rocks or hardened volcanic lava.

Example:

Formation of a community on an exposed area of ​​rock, an area of ​​hardened volcanic lava, on a newly formed sand dune, or after a glacier retreats.

Only a few plants are able to live on such soil, they are called the pioneers of successions. Typical pioneers are mosses and lichens. They change the soil, releasing acid, which destroys and loosens the stones. Dying mosses and lichens decompose under the action of decomposer bacteria, and their remains are mixed with loose stony substrate (sand).

This forms the first soil on which other plants can already grow. The need to destroy the parent rock - main reason slow progress of primary successions; note the increase in the thickness of the soil layer as the succession progresses.

On soil poor in nutrients, grasses settle, which are more specifically capable of and displace lichens and mosses. The roots of herbs penetrate into the cracks in the rock, pushing these cracks apart and destroying the stone more and more.

Grasses are replaced by perennials and shrubs, such as alder and willow. On the roots of the alder there are nodules - special organs containing symbiotic bacteria that fix atmospheric nitrogen and contribute to the accumulation of large reserves in the soil, due to which the soil becomes more and more fertile.

Now it can already grow trees, such as pine, birch and spruce.

Thus, the driving force behind succession is that plants change the soil beneath them, influencing its physical properties And chemical composition, so that it becomes suitable for competing species that displace the original inhabitants, causing a change in the community - succession, due to competition, plants do not always live where conditions are better for them.

The course of primary successions takes place in several stages.

For example, in the forest zone: dry lifeless substrate - lichens - mosses - annual forbs - grasses and perennial grasses - shrubs - trees of the 1st generation - trees of the 2nd generation; in the steppe zone, succession ends at the grass stage, etc.

1.2 Secondary succession

The term "secondary succession" refers to communities that develop on the site of a pre-existing previously formed community.

In places where economic activity people does not interfere in the relationship of organisms, a climax community is formed that can exist indefinitely - until any external impact (plowing the land, cutting down forests, fire, volcanic eruption, flood) does not violate its natural structure.

In the event of the destruction of the community, succession begins in it - a slow process of restoring the original state.

Examples of secondary successions: overgrowing of an abandoned field, meadow, burnt area or clearing.

Secondary succession lasts for several decades.

It begins with the fact that annual herbaceous plants appear on the liberated plot of soil. These are typical weeds: dandelion, thistle, coltsfoot and others. Their advantage is that they grow quickly and produce seeds adapted to spread over long distances with the help of wind or animals.

However, after two or three years they are replaced by competitors - perennial grasses, and then - shrubs and trees, primarily aspen.

These rocks shade the ground, and their extensive root systems take all the moisture out of the soil, so it becomes difficult for seedlings of the species that first hit the field to grow.

However, the succession does not stop there; a pine appears behind the aspen; and last - slow-growing shade-tolerant species, such as spruce or oak. A hundred years later, the community that was on the site of the field before the deforestation and plowing of the land is restored on this site.

VEINIK- a genus of perennial herbaceous plants of the family Cereals, or Bluegrass

Rice. 8.7. Secondary succession of the Siberian dark coniferous forest (fir-cedar taiga) after a devastating forest fire.

1.4 Duration of succession

The duration of succession is largely determined by the structure of the community. The study of primary succession in places such as sand dunes, indicates that, under these conditions, many hundreds of years are required for the development of the climax. Secondary successions, for example in clear cuts, proceed much faster. Nevertheless, it takes at least 200 years for the forest to be able to recover in a temperate humid climate.

If the climate is particularly severe (as, for example, in the desert, tundra or steppe), the duration of the series is shorter, since the community cannot significantly change the unfavorable physical environment. Secondary succession in the steppe, for example, lasts about 50 years.

The main stages of secondary succession in temperate climate:

· the first stage of herbaceous vegetation lasts about 10 years;

· the second stage of shrubs? from 10 to 25 years;

· the third stage of deciduous trees? from 25 to 100 years;

the fourth stage of coniferous trees? over 100 years.

Successions can be of various sizes. They can go slowly, for thousands of years, or they can go quickly - in a few days.

The duration of succession is largely determined by the structure of the community.

In primary succession, it takes many hundreds of years to develop a sustainable community.

Pay attention!

The need to destroy the parent rock is the main reason for the slow progress of primary successions.

Secondary successions proceed much faster. This is because the primary community leaves behind a sufficient number of nutrients, developed soil, which creates conditions for the accelerated growth and development of new settlers.

Example:

In Europe at the end Pliocene (3 million years ago) the ice age began. The glacier destroyed all life under its cover. He tore and smoothed the soil cover, crumbled rocks. With its retreat and the warming of the climate, vast expanses of bare, lifeless land were exposed. Gradually, it was inhabited by various plants and animals. Of course, these changes happened very slowly. Where the glacier destroyed the tropical forests, their restoration continues to the present. These areas have not yet reached a steady state. So they did not have enough to complete the succession and millions of years.

Slowly, the changes that led broadleaf forests Miocene (20 million years ago) to the current northern Central Asian deserts.

Successions pass much faster after a forest fire, when, in a certain sequence, one biocenosis is replaced by another, which finally leads to the restoration of a stable community.

Fouling of bare cliffs occurs relatively quickly: rock sections as a result of erosion or landslide.

The fastest successions are observed in a temporary reservoir or when communities change in a decomposing animal corpse, in a rotting tree trunk, in hay infusion.

General patterns of succession

IN general view The phenomenon of ecological succession can be characterized by the following provisions:

Succession is a natural process, the course of which can be foreseen.

Succession is the result of changes that the communities themselves make to the habitat, that is, the process is not set from the outside.

Succession ends with the formation of a climax biocenosis, which is distinguished by the greatest diversity, and, consequently, the most numerous connections between organisms.

Thus, the climax biocenosis is maximally protected from possible disturbances from external factors and is in a state of equilibrium.

The main feature of ecological succession is that community changes always occur in the direction of an equilibrium state.

When an ecosystem approaches the final stable state (climax state), in it, as in all equilibrium systems, all development processes slow down.

Observations of successions show that some certain properties of biocenoses change in the same direction, whatever the type of succession.

Let's formulate them.

Plant and animal species are constantly changing.

The species diversity of organisms is increasing.

The size of organisms increases in the course of succession.

Linear food chains dominated by herbivores evolve into complex food webs. Detritivorous forms (consumers of dead organic matter) begin to play an increasingly important role in them.

Biological cycles are lengthening and becoming more complex, organisms are becoming more and more ecologically specialized.

The biomass of organic matter is increasing. There is a decrease in the net production of the community and an increase in the intensity of respiration.

1.5 Significance of succession

A mature community, with its greater diversity, richness in organisms, more developed trophic structure, and balanced energy flows, is able to withstand changes in physical factors (such as temperature, humidity) and even some types of chemical pollution to a much greater extent than a young community. However, the young community is able to produce new biomass in much greater quantities than the old one. The remains of civilizations and deserts, the emergence of which is due to human activity, are excellent evidence that man has never realized his close connection with nature, the need to adapt to natural processes, and not command them. Nevertheless, even the knowledge that has been accumulated at the present time is enough to make sure that the transformation of our biosphere into one vast carpet of arable land is fraught with great danger. For our own protection, certain landscapes must be presented to natural communities.

In this way, a person can reap a rich harvest in the form of pure products, artificially supporting the community in the early stages of succession. After all, in a mature community at the climax stage, the net annual production is spent mainly on the respiration of plants and animals and may even be zero.

On the other hand, from a human point of view, the stability of a community in the climax stage, its ability to withstand the effects of physical factors (and even control them) is a very important and highly desirable property. A person is interested in both the productivity and the stability of the community. To maintain human life, a balanced set of both early and mature stages of succession is needed, which are in a state of energy and matter exchange. The surplus food created in young communities allows the maintenance of older stages that help resist external influences.

Arable land, for example, should be considered young successional stages. They are maintained in this state thanks to the continuous labor of the farmer. Forests, on the other hand, are older, more diverse, and more stable communities with low net production. It is extremely important that people pay equal attention to both types of ecosystems. If the forest is destroyed in pursuit of a temporary income from timber, water supplies will decrease and the soil will be blown off the slopes. This will reduce the productivity of the districts. Forests are of value to humans not only as a supplier of wood or a source of additional areas that can be occupied by cultivated plants.

Unfortunately, people are little aware of the consequences of environmental violations that occur in the pursuit of economic gain. This is partly due to the fact that even ecologists cannot yet give accurate predictions of the consequences that various disturbances of mature ecosystems lead to. The remains of civilizations and deserts, the emergence of which is due to human activity, are excellent evidence that man has never realized his close connection with nature, the need to adapt to natural processes, and not command them.

Nevertheless, even the knowledge that has been accumulated at the present time is enough to make sure that the transformation of our biosphere into one vast carpet of arable land is fraught with great danger. For our own protection, certain landscapes must be represented by natural communities.

FIXING:

Indicate the stages of overgrowing of the reservoir from the proposed vegetation: sphagnum, sedge, marsh pine, mixed forest, wild rosemary (sedge, sphagnum, wild rosemary, marsh pine, mixed forest).

Arrange the stages of succession in right order: annuals, shrubs deciduous trees, perennials, conifers (annual plants, perennials, shrubs, deciduous trees, conifers)

Arrange the ongoing stages of succession in time: the settlement of the territory with mosses. germination of seeds of herbaceous plants, colonization by shrubs, formation of a stable community, colonization of bare rocks by lichens

1. colonization of bare rocks by lichens

2. settlement of the territory with mosses

3. germination of seeds of herbaceous plants

4. settlement with shrubs

5. building a sustainable community

The course of evolution (development) of a community cannot be predicted.

Most general patterns evolution of biocenoses:

1. Species of plants and animals in the course of community development can be predicted

2.Reduces variety of organisms.

3. Sizes of organisms in the course of succession are declining.

4,Food chains shortened and simplified. They are playing an increasingly important role detritophages.

5. Biological cycles become more complicated organisms are becoming more ecologically specialized.

6. Biomass of organic matter during community development increases. going on height clean community products and slowdown breathing intensity.