The upper tier in the oak forest is formed by plants. §41. The structure of the biocenosis as the basis for maintaining its integrity. Exercises on the covered material

Take a look at Figures 198, 200-202 with groups of organisms living together in biocenoses. What are the connections between them?

Various types of existing relationships of organisms in biocenoses contribute to the preservation of their species composition and maintenance of the optimal number of species populations that make up the biocenosis.

The structure of the biocenosis is expressed in the species composition of its population and the quantitative ratio of organisms by species (species structure), in the regular distribution of organisms of different species relative to each other in the occupied space (spatial structure), in food (trophic) and other relationships of organisms.

The species structure of the biocenosis. Any biocenosis is formed by species of organisms characteristic of it with a certain number of each of them. The total number of species in one biocenosis can reach several tens of thousands. Coral reefs and tropical forests are especially rich in species of organisms (Fig. 197, 1, 2). For biocenoses that have developed in the harsh living conditions of organisms, for example, in the Arctic, a much smaller number of species are characteristic (Fig. 197, 3).

Fig. 197. Biocenoses rich and poor in species: 1 - coral reef; 2 - a tropical forest; 3 - polar tundra

The number of organisms of each species in the biocenosis is different. The most abundant species, or dominant (dominant) ones, make up its “species core”. In some spruce forests, for example, in oxalis spruce forests, spruce dominates among trees, oxalis dominates among herbaceous plants, kinglet, robin, chaffinch among birds, and bank voles and red-gray voles among mammals (Fig. 198).

Fig. 198. Numerous species of organisms of the sorrel spruce forest: 1 - Norway spruce; 2 - common oxalis; 3 - finch; 4 - red-gray vole

The number of small species in biocenoses is always greater than that of numerous. Scarce species create the species richness of biocenoses and increase the diversity of its connections. The same species serve as a reserve for replacing dominant species when environmental conditions change. The richer the species composition of the biocenosis, the better it is ensured its resistance to changing environmental conditions.

The spatial structure of the biocenosis. The distribution of organisms in terrestrial biocenoses is mainly associated with the layering, or vertical arrangement of vegetation.

Layered, or vertical, composition of biocenoses is most clearly expressed in forests, where there can be up to 5-6 layers of plants (Fig. 199). Thus, in deciduous forests, or oak forests, oak, linden and other tall deciduous trees with large leaves form the first (upper) tier. Less light-loving, for example, Norway maple, elm and other companion trees of oak - this is the second tier. Hazel (hazel), honeysuckle, euonymus, wild rose, viburnum, buckthorn and other shrubs - the third tier (underbrush). Perennial herbaceous plants (corydalis, anemone, goose onions, lungwort, lily of the valley, green zelenchuk, European hoof, raven's eye) form the fourth tier. Mosses, lichens, and fungi grow in the lower (fifth) tier of deciduous forest and are rare, without forming a continuous cover.

Fig. 199. Layered distribution of plants in the biocenosis of deciduous forest - oak grove

The tier structure of the forest allows plants to use sunlight more efficiently: light-loving plants form the upper tier, and plants of other tiers have adapted to life in low-light conditions or develop and bloom in early spring before the leaves bloom on the trees (woodlands, anemone, corydalis, goose onions).

The vertical distribution of animals and other organisms is associated with the layers of biocenoses (Fig. 200). So, in the crowns of trees of the first and second tiers of the forest, various leaf-eating insects, insectivorous birds (blackbirds, orioles, cuckoos), and small animals (squirrels, dormouse) live. There are also birds of prey here, such as the sparrowhawk. The population of animals in the lower forest layer is especially diverse. Moose, hares, wild boars, hedgehogs, forest mice, wolves, foxes and other animals live here.

Fig. 200. Longline distribution of animals in the mixed forest biocenosis

Many animals, due to their mobility, live in several tiers. For example, the common squirrel builds nests and feeds its young in trees, and gathers food for itself both in trees and on bushes and on the ground. Grouse, wood grouse, hazel grouse feed mainly in the lower layer of the forest, spend the night in trees, and breed their offspring on the ground.

The distribution of animals over the tiers in the biocenosis reduces the competition between them in nutrition and the choice of places for building nests. Thus, the pied flycatcher hunts insects in the crowns of trees, and the garden redstart - in the bushes and above the soil. Great spotted woodpecker and nuthatch feed on insects and their larvae usually in the middle layer of the forest. However, they do not compete with each other: the woodpecker takes insects, their larvae and pupae from under the bark of trees, and the nuthatch collects insects from the surface of the bark.

Layering, like floors, is also observed in the location of the roots. The roots of the trees in the upper tiers go deepest into the soil. In each layer of the soil there are bacteria and fungi, due to which the transformation of organic residues into humus (humus) and its mineralization occur. Many insects, ticks, worms and other animals live here permanently or temporarily. The number of species and individuals of animals associated with the soil exceeds the number of land animals. The soil population is most numerous in areas where the soil is rich in organic matter and has a great influence on soil formation.

Food (trophic) structure of the biocenosis. All organisms of biocenoses are interconnected by the relationship "food - consumer" and each of them is included in one or another link of the food chain - a sequential series of organisms that feed on each other. There are two main types of food chains: grazing (grazing chains) and detrital (decomposition chains).

Plants (autotrophic organisms) and animals (heterotrophic organisms) form the basis of pasture food chains. Herbivorous animals such as locusts, leaf beetles, crossbills, waxwings, voles, hares, deer are first-order consumers; carnivores (frogs, toads, lizards, snakes, insectivorous birds, many birds of prey and animals) - consumers of the second order; and predatory animals feeding on consumers of the second order are consumers of the third order (Fig. 201).

Fig. 201. Oak grove pasture food chain

In detrital food chains (from Lat. Detritus - worn out, small organic particles), the food source of first-order consumer organisms is the remains of decomposed animals, plants, fungi, together with the bacteria they contain. Detrital food chains are most common in forests (Fig. 202). Thus, a significant part of plant production (leaf litter) is not consumed directly by herbivorous animals, but dies and undergoes decomposition and mineralization by saprotrophs (from the Greek sapros - rotten) - rotting bacteria. Earthworms, centipedes, mites, insect larvae feeding on detritus serve as food for the consumers of the next link.

Fig. 202. Detrital food chain of deciduous forest

So, the species, spatial and food (trophic) structures of the biocenosis form the basis for maintaining its integrity. Species composition organisms are formed in accordance with the environmental conditions in which a particular natural community exists. The species that make up the biocenosis, distributed over the tiers and connected with each other by food chains, ensure the long existence of various natural communities on our planet.

Exercises on the covered material

What is the structure of the biocenosis expressed in?
How does the species structure of the biocenosis differ from the spatial and food (trophic) structure?
What types of organisms of the biocenosis are classified as dominant?
What is the role of small species in the biocenosis?
What is the vertical distribution of organisms associated with in biocenoses?
What are food chains? How do grazing food chains differ from detrital ones?

From the listed organisms and products of their vital activity, make up several grazing and detrital food chains: herbaceous plants, leaves of trees and shrubs, plant litter, earthworms, caterpillars of butterflies, slugs, meatfly larvae, frogs, snakes, dead crow, tits, hawks, hedgehogs.

Biogeocenosis Is a homogeneous area of \u200b\u200bthe earth's surface with a certain composition of living organisms and certain conditions habitats that are united by metabolism and energy into a single natural complex.

In each biogeocenosis, there are species that are predominant in number or occupy a large area. They are called species - dominants. However, not all dominant species have the same effect on the biogeocenosis. Those that determine the composition, structure and properties of an ecosystem by creating an environment for the entire community are called edifiers... Now let's consider the biogeocenosis of the oak forest.

Among terrestrial biogeocenoses, one of the most complex is a broad-leaved forest, for example, an oak forest. Dubrava is a perfect and stable ecological system that can exist for centuries under unchanged external conditions. The biogeocenosis of oak forests is made up of more than a hundred species of plants and several thousand species of animals.

Plants of oak groves. In terrestrial biogeocenoses, the main biological products are created by higher plants... In the forest, these are mainly perennial tree species.

There is intense competition between plants for basic living conditions: space, light, water with minerals dissolved in it. As a result of long-term natural selection, the oak forest plants have developed adaptations that allow different types coexist. This is clearly manifested in the layering characteristic of the oak forest.

The upper tier is formed by the most light-loving tree species: oak, ash, linden. Below there are less light-loving trees accompanying them: maple, apple, pear, etc. Even lower is the undergrowth layer formed by various shrubs: hazel, buckthorn, viburnum, etc. Finally, a layer of herbaceous plants grows on the soil. The lower the tier, the more shade-tolerant the plants forming it.

Due to the complex layering, the total area of \u200b\u200bleaves of plants growing on each hectare reaches 4-6 hectares. Net production in the form of an increase in organic matter is almost 10 t / ha per year.

Food chains in oak groves. The richness and diversity of plants is the reason for the development in oak forests of consumers from the animal world, from protozoa to higher vertebrates - birds and mammals.

The food chains in the forest are intertwined in a very complex food web, so the loss of any one species of animals usually does not significantly disrupt the entire system. The disappearance, for example, in most of our oak forests of all large herbivorous ungulates: bison, deer, roe deer, elk would have little effect on the overall ecosystem, since their biomass was never large and did not play a significant role in the general circulation of substances. But if herbivorous insects disappeared, the consequences would be very serious, since insects perform an important pollinator function in biogeocenosis, participate in the destruction of litter and serve as the basis for the existence of many subsequent links in the food chain.

Ecological systems

Biogeocenosis

Pond and oak forest as examples of biogeocenoses
Changes in biogeocenoses
Biogeocenoses created by man

Food connections
Energy losses in power circuits

Biogeocenosis.

Biogeocenosis is a stable community of plants, animals and microorganisms that are in constant interaction with the components of the atmosphere, hydrosphere and lithosphere. This community receives the energy of the Sun, mineral substances of the soil and gases of the atmosphere, water, and heat, oxygen, carbon dioxide, and waste products of organisms are released from it. The main functions of biogeocenosis are the accumulation and redistribution of energy and the circulation of substances. Biogeocenosis is an integral self-regulating and self-sustaining system. It includes the following mandatory components: inorganic (carbon, nitrogen, carbon dioxide, water, mineral salts) and organic matter (proteins, carbohydrates, lipids, etc.); autotrophic organisms - producers of organic substances; heterotrophic organisms - consumers of ready-made organic substances of plant origin - consumers (consumers of the first order) and animal (consumers of the second and next orders) origin. Heterotrophic organisms include destroyers - reducers, or destructors, which decompose the remains of dead plants and animals, turning them into simple mineral compounds.
Speaking about biocenoses, only interconnected living organisms that live in a given area are considered. Biocenoses are characterized by species diversity, i.e. the number of species of living organisms that form it; population density, i.e. the number of individuals of a given species per unit area or per unit volume (for aquatic and soil organisms); biomass - the total amount of animal organic matter, expressed in mass units.
Biomass is formed by binding solar energy. The efficiency with which plants assimilate solar energy is not the same in different biocenoses. The total production of photosynthesis is called primary production. Plant biomass is used by first-order consumers - herbivorous animals - as a source of energy and material to create biomass; and it is used extremely selectively (Figure 17.7), which reduces the intensity of the interspecies struggle for existence and contributes to the conservation of natural resources. Herbivorous animals, in turn, serve as a source of energy and material for second-order consumers - predators, etc. Figure 17.8 shows comparative data on the productivity of various biogeocenoses. The largest number biomass is formed in the tropics and in the temperate zone, very little - in the tundra and the ocean.
Organisms that make up biogeocenoses are influenced by inanimate nature - abiotic factors, as well as from living nature - biotic influences.

Biocenoses are - holistic, self-regulating biological systems, in soy * becoming which includes living organisms that live on the same territory.
The energy of sunlight is assimilated by plants, which are subsequently used by animals as food.

Food connections .

Energy losses in power circuits

All species that make up the food chain live off the organic matter created by green plants. At the same time, there is an important law related to the efficiency of use and conversion of energy in the process of nutrition. Its essence is as follows.
In total, only about 1% of the radiant energy of the Sun falling on a plant is converted into potential energy of chemical bonds of synthesized organic substances and can be used later by heterotrophic organisms for nutrition. When an animal eats a plant, most of the energy contained in the food is spent on various life processes, turning into heat and dissipating. Only 5-20% of the food energy goes into the newly built substance of the animal's body. If a predator eats a herbivore, then again most of the energy contained in the food is lost. Due to such large losses of useful energy, food chains cannot be very long: they usually consist of no more than 3-5 links (food levels).

The amount of plant matter that serves as the basis of the food chain is always several times greater than the total mass of herbivorous animals, and the mass of each of the subsequent links of the food chain also decreases НН o This very important regularity is called the rule of the ecological pyramid.

Pond and oak forest as examples of biogeocenoses

1.Biogeocenosis of a fresh water body.

Any natural body of water, such as a lake or pond, with its plant and animal population is a separate biogeocenosis. This natural system, like other biogeocenoses, is capable of self-regulation and continuous self-renewal.
Plants and animals inhabiting the reservoir are unevenly distributed in it. Each species lives in the conditions to which it is adapted. The most varied and favorable conditions for life are created in the coastal zone. Here the water is warmer, as it is warmed up by the sun's rays. It is sufficiently oxygenated. The abundance of light penetrating to the bottom ensures the development of many higher plants. Small algae are also numerous. Most animals live in the coastal zone. Some are adapted to life on aquatic plants, while others actively swim in the water column (fish, predatory swimming beetles and water bugs). Many are found at the bottom (barley, toothless, larvae of some insects - caddis flies, dragonflies, mayflies, a number of worms, etc.). Even the surface film of water serves as a habitat for species specially adapted to it. In quiet backwaters, you can see predatory water striders running on the surface of the water and swirling beetles quickly swimming in circles. The abundance of food and other favorable conditions attract fish to the coastal zone.
In the deep bottom areas of the reservoir, where sunlight penetrates poorly, life is poorer and more monotonous. Photosynthetic plants cannot exist here. The lower layers of water remain cold due to poor mixing. The water here contains little oxygen.
Special conditions are created in the water column of open areas of the reservoir. It is inhabited by a mass of the smallest plant and animal organisms, which are concentrated in the upper, more warmed up and well-illuminated layers of water. Various microscopic algae develop here; algae and bacteria feed on numerous protozoa - ciliates, as well as rotifers and crustaceans. This whole complex of small organisms suspended in water is called plankton. Plankton plays a very important role in the circulation of substances and in the life of a reservoir.

2. Food connections and stability of the pond biogeocenosis.

Consider how the system of the inhabitants of the reservoir exists and how it is maintained. Power supply chains consist of several successive links. For example, protozoa feed on plant debris and bacteria developing on them, which are eaten by small crustaceans. Crustaceans, in turn, serve as food for fish, and the latter can be eaten by predatory fish. Almost all species eat more than one type of food, but use different food items. Food chains are intricately intertwined. An important general conclusion follows from this: if any member of the biogeocenosis falls out, then the system is not disturbed, since other food sources are used. The greater the species diversity, the more stable the system.
The primary source of energy in the aquatic biogeocenosis, as in most ecological systems, is sunlight, thanks to which plants synthesize organic matter. Obviously, the biomass of all animals existing in the reservoir completely depends on the biological productivity of plants.
Often the reason for the low productivity of natural water bodies is the lack of minerals (especially nitrogen and phosphorus) necessary for the growth of autotrophic plants, or the unfavorable acidity of the water. The introduction of mineral fertilizers, and in the case of an acidic environment, liming of water bodies contribute to the reproduction of plant plankton, which / feed animals that serve as food for fish. In this way, the productivity of fishery ponds is increased.

3. Biogeocenosis of deciduous forest.

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Among terrestrial biogeocenoses, one of the most complex is a broad-leaved forest, for example, an oak forest. Dubrava - a perfect and stable ecological system that can exist for centuries under constant external conditions. The biogeocenosis of oak forests is made up of more than a hundred species of plants and several thousand species of animals.

Plants of oak groves

In terrestrial biogeocenoses, higher plants create the main biological products. In the forest, these are mainly perennial tree species (Figure 39).

Figure 39. Biogeocenosis of deciduous forest.

Characteristic deciduous forest is the species diversity of vegetation. There is intense competition between plants for basic living conditions: space, light, water with minerals dissolved in it. As a result of long-term natural selection, the oak forest plants have developed adaptations that allow different species to coexist. This is clearly manifested in the layering characteristic of the oak forest.

Finally, a layer of herbaceous plants grows on the soil. The lower the tier, the more shade-tolerant the plants forming it.

Tiering is also expressed in the location of root systems. Trees in the upper tiers have the deepest root systems and can use water and minerals from the deeper layers of the soil.

Dubrava is characterized by high biological productivity. Due to its complex multi-tiered structure, the total area of \u200b\u200bleaves of plants growing on each hectare reaches 4-6 hectares. Such a powerful photosynthesizing apparatus captures and transforms about 1% of the annual influx of solar radiation into potential energy of organic matter. The latter in middle latitudes is about 3.8 10 7 kJ / ha. Almost half of the synthesized substance is consumed by the plants themselves during respiration. Net production in the form of an increase in organic matter in the aboveground parts of plants is 5-6 t / ha per year. To this should be added 3-4 t / ha of annual growth of underground parts. Thus, the production of oak forests reaches almost 10 t / ha per year.

Food chains in oak groves.

The richness and diversity of plants that produce an enormous amount of organic matter that can be used as food, become the reason for the development in oak forests of numerous consumers from the animal world, from protozoa to higher vertebrates - birds and mammals.

The food chains in the forest are intertwined in a very complex food web, so the loss of any one species of animals usually does not significantly disrupt the entire system. The significance of different groups of animals in the biogeocenosis is not the same. The disappearance, for example, in most of our oak forests of all large herbivorous ungulates; bison, deer, roe deer, elk - would have little effect on the overall ecosystem, since their number, and therefore, biomass has never been large and did not play a significant role in the general circulation of substances. But if herbivorous insects disappeared, the consequences would be very serious, since insects perform an important pollinator function in biogeocenosis, participate in the destruction of litter and serve as the basis for the existence of many subsequent links in the food chain.

Self-regulation in the forest biogeocenosis.

The process of self-regulation in the oak forest is manifested in the fact that the entire diverse population of the forest exists together, not completely destroying each other, but only limiting the number of individuals of each species to a certain level. How great is the importance of such regulation of the number in the life of a forest can be seen from the following example. Several hundred species of insects feed on oak leaves, but under normal conditions, each species is represented by such a small number of individuals that even their general activity does not significantly harm the tree and forest. Meanwhile, all insects are highly fertile. The number of eggs laid by one female is rarely less than 100. Many species are capable of producing 2-3 generations per summer. Therefore, in the absence of limiting factors, the number of any species of insects would increase very quickly and would lead to the destruction of the ecological system.

Mineralization of organic residues.

The processes of decomposition and mineralization of the mass of dying leaves, wood, remains of animals and products of their vital activity are of great importance in the life of the forest. Of the total annual increase in the biomass of aboveground parts of plants, about 3-4 tons per hectare naturally dies and falls off, forming the so-called forest litter. Dead underground parts of plants also make up a significant mass. With litter, most of the minerals and nitrogen consumed by plants return to the soil.

Animal remains are very quickly destroyed by dead eating beetles, skin eaters, larvae of carrion flies and other insects, as well as putrefactive bacteria. Fiber and other durable substances, which make up a significant part of plant litter, decompose more difficult. But they also serve as food for a number of organisms, such as fungi and bacteria, which have special enzymes that break down fiber and other substances into easily digestible sugars.

Figure 40. Comparison of the general structure of terrestrial and aquatic biogeocenoses:

I - plants producing organic matter: a - higher plants; b - algae;

II - animals - consumers of organic matter: a - herbivorous, b - carnivorous, c - eating mixed food.

Once the plants die, their substance is completely used up by the destroyers. A significant part of the biomass is made up of earthworms, which do a huge job of decomposing and moving organic matter in the soil. The total number of insects, mites, worms and other invertebrates reaches many tens and even hundreds of millions per hectare. In the decomposition of litter, the role of bacteria and lower, saprophytic fungi is especially great.

ECOSYSTEM DUBRAVA: EXCURSION

1. Dubrava as a natural community (biogeocenosis), is one of the most complex terrestrial biogeocenoses. Well, first of all, what is biogeocenosis? Biogeocenosis is a complex of interrelated species (populations of different species) living in a certain area with more or less homogeneous living conditions. This definition will be needed for future use. Dubrava is a perfect and stable ecological system that can exist for centuries under unchanged external conditions. The biogeocenosis of oak forests is made up of more than a hundred species of plants and several thousand species of animals. It is clear that with such a variety of species inhabiting the oak forest, it will be difficult to shake the stability of a given biogeocenosis by exterminating one or several species of plants or animals. It is difficult, because as a result of the long-term coexistence of plant and animal species from scattered species, they have become a single and perfect biogeocenosis - an oak forest, which, as already mentioned above, is capable of existing for centuries under constant external conditions.

2. The main components of biogeocenosis and the relationship between them; plants are the main link in the ecosystem. The vast majority of biogeocenosis is based on green plants, which are known to be producers of organic matter (producers). And since herbivorous and carnivorous animals are necessarily present in the biogeocenosis - consumers of living organic matter (consumers) and, finally, destroyers of organic residues - mainly microorganisms that bring the decomposition of organic substances to simple mineral compounds (reducers), it is not difficult to guess why plants are the main link in the ecosystem. But because everyone in the biogeocenosis consumes organic matter, or compounds formed after the decay of organic matter, and it is clear that if plants, the main source of organic matter, disappear, then life in the biogeocenosis will practically disappear.

3. The cycle of substances in the biogeocenosis.Significance in the cycle of plants using solar energy Cycle of substances in biogeocenosis - necessary condition existence of life. It arose in the process of the formation of life and became more complicated in the course of the evolution of living nature. On the other hand, in order for the cycle of substances to be possible in the biogeocenosis, it is necessary to have organisms in the ecosystem that create organic substances from inorganic ones and convert the energy of the sun's radiation, as well as organisms that use these organic substances and turn them back into inorganic compounds. All organisms are divided into two groups according to the way of feeding - autotrophs and heterotrophs. Autotrophs (mainly plants) use inorganic compounds of the environment for the synthesis of organic substances. Heterotrophs (animals, humans, fungi, bacteria) feed on ready-made organic substances that are synthesized by autotrophs. Consequently, heterotrophs are dependent on autotrophs. In any biogeocenosis, all the reserves of inorganic compounds would very soon be exhausted if they were not renewed in the course of the life of organisms. As a result of respiration, decomposition of animal corpses and plant residues, organic substances are converted into inorganic compounds, which return again to the natural environment and can again be used by autotrophs. Thus, in the biogeocenosis, as a result of the vital activity of organisms, a flow of atoms is continuously carried out from inanimate nature to living nature and vice versa, closing into a cycle. For the circulation of substances, an inflow of energy from the outside is required. The energy source is the Sun. The movement of matter, caused by the activity of organisms, occurs cyclically, it can be used many times, while the flow of energy in this process is unidirectional. The radiation energy of the Sun in the biogeocenosis is converted into various forms: into the energy of chemical bonds, into mechanical and, finally, into internal energy. From all that has been said, it is clear that the circulation of substances in biogeocenosis is a necessary condition for the existence of life and plants (autotrophs) in it the most important link.

4. Diversity of species in biogeocenosis, their adaptability to cohabitation.A characteristic feature of the oak forest is the species diversity of vegetation. As already mentioned above, the biogeocenosis of oak forests comprises more than a hundred species of plants and several thousand species of animals. There is intense competition between plants for basic living conditions: space, light, water with minerals dissolved in it. As a result of long-term natural selection, the oak forest plants have developed adaptations that allow different species to coexist. This is clearly manifested in the layering characteristic of the oak forest. The upper tier is formed by the most light-loving tree species: oak, ash, linden. Below there are less light-loving trees accompanying them: maple, apple, pear, etc. Even lower is the undergrowth layer formed by various shrubs: hazel, euonymus, buckthorn, viburnum, etc. Finally, a layer of herbaceous plants grows on the soil. The lower the tier, the more shade-tolerant the plants forming it. Tiering is also expressed in the location of root systems. Trees in the upper tiers have the deepest root systems and can use water and minerals from the deeper layers of the soil.

7. Changes in biogeocenosis in spring: in the life of plants and animals.
Spring changes in plant life.
Some willows, alder, and hazel are blooming before the leaves have blossomed; on thawed patches, even through the snow, the sprouts of the first spring plants... By mid-spring, leaves are blooming on almost all trees. The flowering period for plants and flowers. In general, plants come to life from the winter calm.
Spring changes in animal life.
Arrive migratory birds, overwintered insects appear, some animals wake up from hibernation. The period of formation of couples and the mating season.

8. Possible directions of changes in biogeocenosis.Any biogeocenosis develops and evolves. Plants play a leading role in the process of changing terrestrial biogeocenoses, but their activity is inseparable from the activity of other components of the system, and the biogeocenosis always lives and changes as a whole. The change goes in certain directions, and the duration of the existence of various biogeocenoses is very different. An example of a change in an insufficiently balanced system is the overgrowth of a reservoir. Due to the lack of oxygen in the bottom layers of water, part of the organic matter remains unoxidized and is not used in further circulation. In the coastal zone, remains of aquatic vegetation accumulate, forming peaty deposits. The reservoir grows shallow. Coastal aquatic vegetation spreads towards the center of the reservoir, peat deposits are formed. The lake is gradually turning into a swamp. The surrounding terrestrial vegetation is gradually moving towards the site of the former reservoir. Depending on local conditions, a sedge meadow, a forest or another type of biogeocenosis may appear here. Dubrava can also turn into a different type of biogeocenosis. For example, after cutting down trees, it can turn into a meadow, a field (agrocenosis) or something else.

9. Influence of human activity on biogeocenosis; measures that need to be carried out in order to protect it. Recently, man has become very active in influencing the life of biogeocenosis. The economic activity of people is a powerful factor in the transformation of nature. As a result of this activity, peculiar biogeocenoses are formed. These include, for example, agrocenoses, which are artificial biogeocenoses arising from human agricultural activities. Examples are artificially created meadows, fields, pastures. Man-made artificial biogeocenoses require tireless attention and active intervention in their lives. Of course, in artificial and natural biogeocenoses there are many similarities and differences, but we will not dwell on this. Man also influences the life of natural biogeocenoses, but, of course, not so much as on agrocenoses. An example is the forestry established for planting young trees, as well as to restrict hunting. Reserves and national parks created to protect certain species of plants and animals can also serve as an example. Mass societies are also being created that promote the preservation and protection of the environment, such as the society of "green", etc.

10. Conclusion.Using the example of an excursion walk through the natural biogeocenosis - an oak forest, they found out and disassembled why the oak forest is integral and stable, what are the main components of the biogeocenosis, what is their role and what connections exist between them, they also analyzed why the circulation of substances in the biogeocenosis is a necessary condition for the existence of life, they also found out how all the diversity of species living in the oak grove does not conflict with each other, allowing each other to develop normally, sorted out what food connections exist in the oak grove and disassembled such a concept as an ecological pyramid, substantiated the factors causing a change in numbers and such a phenomenon as self-regulation, found out what changes occur in the biogeocenosis in the spring and analyzed the possible directions of the evolution of biogeocenosis, as well as how a person affects life in biogeocenoses. In general, the life of biogeocenoses was completely analyzed using the example of oak forests.

The life of forest plants has its own characteristics. The trees that form the forest grow more or less closely together, influencing each other and all other forest vegetation. Plants in the forest are arranged in tiers that can be compared to floors. The upper, first tier is represented by the main trees of the first degree of importance (spruce, pine, oak). The second tier is formed by trees of the second size (bird cherry, mountain ash, apple tree). The third tier consists of shrubs, for example, wild rose, hazel, viburnum, euonymus. The fourth tier is the herbaceous cover, and the fifth is mosses and lichens. The access of light to plants of different tiers is not the same. The tree crowns of the first tier are better illuminated. From the upper to the lower tiers, the illumination decreases, since the plants of the upper tiers retain the proportion of sunlight. Mosses and lichens occupying the fifth tier receive very little light. These are the most shade-tolerant plants in the forest.

Different forests have a different number of layers. For example, in a dark spruce forest, only two or three tiers are distinguishable. The first tier contains the main trees (spruce), the second is a small number of herbaceous plants, and the third is formed by mosses. Other woody and shrubby plants do not grow in the second tier of a spruce forest, as they cannot stand strong shading. Also, grassy cover is not observed in the spruce forest.

The tiered arrangement is typical not only for the aboveground parts of plants, but also for their underground organs - the roots. Tall trees have roots that penetrate deep into the ground, while root system trees of the second tier are shorter and conditionally form the second tier of roots. The roots of other plants in the forest are even shorter and are located in the upper layers of the soil. Thus, the plants in the forest absorb nutrients from different soil layers.

Trees of the first size (oak, pine, spruce) close with their crowns and form a forest canopy, under which a small proportion of sunlight penetrates. Therefore, herbaceous plants of the forest, as a rule, are shade-tolerant and have wide leaf blades. Many of them cannot withstand exposure to direct sunlight and may die on open space... A feature of broadleaf forest grasses is flowering in early spring, when the trees still have no foliage. With the help of wide leaves, forest plants accumulate organic matter in low light and deposit them in underground organs, for example, lungwort - in rhizomes. In gloomy thickets of spruce, flowers of herbaceous plants have corollas whiteso that they are visible from a distance to pollinating insects. For example, such flowers are in a lily of the valley, a wintergreen, a week, a dream, a mine. But, despite these adaptations, the flowers of forest herbs often do not pollinate and do not form seeds. Therefore, the reproduction of many herbaceous plants is carried out by dividing the rhizomes, for example, in the acid plant, lily of the valley, kupena, weekly, and mine. This explains the placement of these herbs in the forest in groups.

The forest litter covering the soil consists of fallen leaves or needles, respectively, in deciduous or coniferous forests, as well as bark and branches of trees, dead areas of grasses, mosses. Loose forest litter is moist, which is favorable for the development of mold and cap fungi. Myceliums of various fungi penetrate the litter through and through, gradually converting organic matter into humus and mineral salts to nourish the green plants of the forest.

Dubrava, as a natural community (biogeocenosis), is characterized by integrity and stability.

Dubrava is one of the most complex terrestrial biogeocenoses. Biogeocenosis are complexes of interconnected species (populations of different species) that live on certain territory with more or less homogeneous conditions of existence. The biogeocenosis of oak forests is made up of more than a hundred species of plants and several thousand species of animals. It is clear that with such a variety of species inhabiting the oak forest, it will be difficult to shake the stability of a given biogeocenosis by exterminating one or several species of plants or animals. It is difficult, because as a result of the long-term coexistence of plant and animal species from scattered species, they have become a single and perfect biogeocenosis - an oak forest, which, as already mentioned above, is capable of existing for centuries under constant external conditions.

The overwhelming majority of biogeocenosis is based on green plants, which are known to be producers of organic matter (producers). In the biogeocenosis, herbivorous and carnivorous animals are necessarily present - consumers of living organic matter (consumers) and, finally, destroyers of organic residues - mainly microorganisms that bring the decomposition of organic matter to simple mineral compounds (decomposers). Plants are the main source of organic matter, and if they disappear, then life in the biogeocenosis will practically disappear.

The circulation of substances in biogeocenosis is a necessary condition for the existence of life. It arose in the process of the formation of life and became more complicated in the course of the evolution of living nature. On the other hand, in order for the cycle of substances to be possible in the biogeocenosis, it is necessary to have organisms in the ecosystem that create organic substances from inorganic ones and convert the energy of the sun's radiation, as well as organisms that use these organic substances and turn them back into inorganic compounds. All organisms are divided into two groups according to the way of feeding - autotrophs and heterotrophs. Autotrophs (mainly plants) use inorganic compounds of the environment for the synthesis of organic substances. Heterotrophs (animals, humans, fungi, bacteria) feed on ready-made organic substances that are synthesized by autotrophs. Consequently, heterotrophs are dependent on autotrophs. In any biogeocenosis, all the reserves of inorganic compounds would very soon be exhausted if they were not renewed in the course of the life of organisms. As a result of respiration, decomposition of animal corpses and plant residues, organic substances are converted into inorganic compounds, which return again to the natural environment and can again be used by autotrophs. Thus, in the biogeocenosis, as a result of the vital activity of organisms, a flow of atoms is continuously carried out from inanimate nature to living nature and vice versa, closing into a cycle. For the circulation of substances, an inflow of energy from the outside is required. The energy source is the Sun. The movement of matter, caused by the activity of organisms, occurs cyclically, it can be used many times, while the flow of energy in this process is unidirectional. The radiation energy of the Sun in the biogeocenosis is converted into various forms: into the energy of chemical bonds, into mechanical and, finally, into internal energy. From all that has been said, it is clear that the circulation of substances in the biogeocenosis is a necessary condition for the existence of life and plants (autotrophs) in it the most important link.

A characteristic feature of the oak forest is the species diversity of vegetation. As already mentioned above, the biogeocenosis of oak forests comprises more than a hundred species of plants and several thousand species of animals. There is intense competition between plants for basic living conditions: space, light, water with minerals dissolved in it. As a result of long-term natural selection, the oak forest plants have developed adaptations that allow different species to coexist. This is clearly manifested in the layering characteristic of the oak forest. The upper tier is formed by the most light-loving tree species: oak, ash, linden. Below there are less light-loving trees accompanying them: maple, apple, pear, etc. Even lower is the undergrowth layer formed by various shrubs: hazel, euonymus, buckthorn, viburnum, etc. Finally, a layer of herbaceous plants grows on the soil. The lower the tier, the more shade-tolerant the plants forming it. Tiering is also expressed in the location of root systems. Trees in the upper tiers have the deepest root systems and can use water and minerals from the deeper layers of the soil.