Diversity of phytocenoses message. Species composition of phytocenoses. Phytocenosis: variety of phytocenoses, structure of phytocenosis
Subject : Variety of phytocenoses.
Goals: to form an idea of the diversity of plants in natural communities. To develop the ability to find relationships in the community, to recognize plants by external signs.
Lesson type: Discovery of new knowledge based on the activity approach technology using ICT
Educational Resources: presentation [Electronic resource].
Technical support: computer, multimedia projector and screen, herbarium specimens of plants.
Software security : Microsoft PowerPoint, Microsoft Word
Planned educational results:
subject (volume of development and level of competencies): learn to give examples of the relationship between plants and environmental factors; will have the opportunity to learn to evaluate their actions in relation to nature and talk about them; make assumptions and prove them; understand the educational task of the lesson and strive to fulfill it; work in groups using the information provided to gain new knowledge; answer final questions and evaluate your achievements in the lesson.
Metasubject (components of cultural competence experience / acquired competence): use various methods of searching (in reference sources and a textbook), collecting, processing, analyzing, organizing, transmitting and interpreting information in accordance with communicative and cognitive tasks; define a common goal and ways to achieve it; be able to agree on the distribution of functions and roles in joint activities; exercise mutual control in joint activities; adequately evaluate their own behavior and the behavior of others.
Personal: formation of a holistic, socially oriented view of the plant world in its organic unity and diversity of nature, a respectful attitude towards a different opinion; the development of ethical feelings, goodwill and emotional and moral responsiveness, the development of motives for educational activities and the personal meaning of learning; mastering the logical actions of comparison, analysis, synthesis, generalization, classification according to the generic characteristics of plants; readiness to listen to the interlocutor and conduct a dialogue, to recognize the possibility of the existence of different points of view and the right of everyone to have their own, express their opinion and argue their point of view and assessment of events.
Universal learning activities (UUD):
Cognitive: general educational - extracting the necessary information during the development of a new topic on plant diversity;brain teaser - addition and expansion of existing knowledge and ideas about the plant world.
Communicative: are able to exchange opinions, listen to each other, build understandable speech statements; accept a different opinion and position, allow for different points of view.
Regulatory: orientation in the textbook and workbook; accept and save the learning task; evaluate the result of their actions; predict the results of the level of assimilation of the studied material.
Personal: understand the importance of knowledge about natural communities for humans and accept it.
Methods and forms of education: partially search, group, individual.
During the classes.
IMotivation for learning activities
IIKnowledge update.
1… Hello guys!!! We have words scattered on the board, we need to make a logical scheme from them so that all the words are interconnected.
2 ... This scheme tells us the topic of our lesson. What theme? (Variety of phytocenoses). Today we will have an unusual lesson, a lesson-journey. We will go on a journey through natural communities.
3. ...What do we need to know on the way???
We will find out what plant floors are in different natural communities, what plant world is characteristic of them, and how it is connected by invisible threads with factors of inanimate nature.
4..
So, let's go on a trip.
You, my friend, look do not let us down!
Promise to be truthful and kind!
Don't hurt a bird or a cricket,
Do not buy a net for a butterfly.
Love flowers, forests, expanse of meadows, fields -
All that is called your homeland.
IIIInclusion in the system of knowledge and repetition.
TEST: (5 min)
IVLearning new material.
Practical work with herbarium specimens of plants.
Now let's do some practical work. We will work in groups. Each group has its own herbariums of plants corresponding to the phytocenosis.
The class is divided into groups according to the name of the biogeocenosis: “Spruce forest”, “Meadow”, “Pine forest”, “Oak forest”, “Swamp”. "Field and Garden".
Select a team captain who will lead the group.
The team captain distributes tasks.
The students work in groups.
They protect their phytocenoses by responding according to plan. Demonstrate herbarium specimens. Answer students' questions.
VPhysical education minute (exercises for the eyes and to improve cerebral circulation)
A set of exercises for gymnastics for the eyes
1. Blink quickly, close your eyes and sit quietly, slowly counting to 5. Repeat again.
2. Close your eyes tightly (count to 3), open your eyes and look out the window (count to 5). Repeat 2 times.
A set of exercises to improve cerebral circulation
Starting position - sitting on a chair. 1–2. Gently tilt your head back, tilt your head forward without raising your shoulders. Repeat 3-4 times. The pace is slow.
2) Starting position - sitting, hands on the belt. 1. Turning the head to the right. 2. Starting position. 3. Turning the head to the left. 4. Starting position. Repeat 3 times. The pace is slow.
VI.Summing up the lesson. Evaluation of student work in class.
Our journey has come to an end.
Let's remember where we were today? (By groups)
How are plants located in any natural community? (by tiers)
Name these layers.
Why do plants of different natural communities differ from each other? (different biotope)
Team captains hand over sheets of achievements to the teacher.
VII. Homework
By the next lesson you should be fineknow:
1. The name of the organisms that make up the natural community;
2. Tiers of natural communities.
Shouldbe able to :
1. Distinguish plants.
2. Establish their relationship in nature.
3. Always take care of the environment.
The constitutional structure of phytocenoses
concept constitutional structure phytocenosis proposed by T.A. Rabotnov (1965), reflects its composition in a broad sense, including species, population, ecological and biological composition, composition of phytocoenotypes and coenogenetic groups, etc. The main features of the constitutional structure of phytocenoses are briefly considered below.
Species composition of phytocenoses
Each phytocenosis is characterized by a special species composition peculiar to it. The complexity or simplicity of it is determined by the indicator in species (floristic) saturation, which is understood as the number of species per unit area of a phytocenosis. The dependence of the value of this indicator on the accounting area is determined by the regression curve, which initially goes up sharply, and then becomes flatter (Fig. 12). The nature of such a curve indicates that in order to identify the species composition of a phytocenosis, the counting area should not be less than a certain threshold value (S), which very much depends on the size of the plants forming the cenosis. Therefore, when establishing the species composition of communities of different types, trial plots(registration areas) of unequal sizes, for example, forest phytocenoses are usually described on a trial plot of 0.25 hectares, grass - 100 sq.m, moss and lichen - 1 sq.m. m.
According to the value of the species saturation indicator, phytocenoses can be divided into three groups: a) floristically simple, consisting of a small number of species (up to one to two dozen), b) floristically complex, including many dozens of species, c) phytocenoses, occupying an intermediate position in terms of species saturation . However, when determining species saturation, only higher plants and macrophytic lichens are usually taken into account. If we take into account that the composition of phytocenoses also includes species of algae, fungi, bacteria, the number of which is usually several times greater than the number of higher plants, then it must be recognized that in nature, apparently, there are no floristically simple phytocenoses, as evidenced by the following table 3.
The species diversity of phytocenoses is influenced by a number of factors. A certain role in this regard is played by the general physiographic and historical conditions, on which the species richness of the flora of each particular region depends. And the richer the flora of the area, the more there will be candidate species that can settle in each specific phytocenosis. So, for example, the species saturation of phytocenoses of humid tropical forests, which are formed in conditions of exceptionally rich tropical flora, is estimated by hundreds of species of higher plants, and the species saturation of Siberian taiga forests, which are formed against the background of poor boreal flora, varies, as a rule, within 15-30 species. .
Table 3
Complete species composition of phytocenoses of the deserted steppes of Kazakhstan (Rabotnov, 1978)
| Numbers of phytocenoses | |||||||||
| plant groups | Number | % | Number | % | Number | % | Number | % | |
| Flowering | 12,5 | 10,5 | 10,5 | 12,0 | |||||
| mosses | 0,8 | 0,5 | |||||||
| Lichens | 4,6 | 6,0 | 9,0 | 7,0 | |||||
| Seaweed | 9,9 | 17,0 | 11,5 | 4,5 | |||||
| microscopic mushrooms | 32,3 | 34,5 | 34,0 | 39,0 | |||||
| Bacteria and actinomycetes | 39,9 | 32,0 | 34,5 | 38,0 | |||||
| Total | |||||||||
The floristic diversity of phytocenoses also depends on the habitat conditions: the more favorable they are, the more complex the species composition, and, conversely, floristically simple phytocenoses are formed in unfavorable habitats. For example, in the undisturbed phytocenoses of the meadow steppes of the European part of Russia, associated with moderately moistened fertile chernozem soils, there were (Alekhin, 1935) per 100 sq. m. up to 120 or more species of higher plants, while in the same areas along the banks of reservoirs with unfavorable highly waterlogged soils or on salt marshes, phytocenoses of 5-10 species of higher plants are formed.
Thus, the unfavorable factors of the ecotope exclude the possibility of many species growing in it and create the so-called ecotopic isolation phytocenosis, which in this case determines the simplicity of its composition. Therefore, M.V. Markov (1962) rightly considered the species richness of a phytocenosis as an indicator of the ecological capacity of a habitat.
In addition to ecotopic factors, the species diversity of phytocenoses is also influenced by coenotic conditions, which manifests itself, firstly, in the competitive exclusion of some plant species by others and, secondly, in the formation of a specific internal environment in communities that prevents the introduction of species adapted to a given environment into them. environment. So, for example, on the site of the destroyed dark coniferous forests of the taiga zone of the Western Siberian Plain, derivative birch forests are formed, which over time are replaced by birch with dark coniferous tree species. Together with it, some of its satellites disappear from the lower tiers and later on, they can not stand the significant shading created in dark coniferous forests by abundant coniferous litter, increased soil acidity. This phenomenon, named by A.K. Kurkin (1976) cenotic isolation phytocenoses, widespread in nature. At the same time, the ecotopic and coenotic aspects of isolation are interrelated with each other and jointly determine the general ecological the isolation of the phytocenosis and limit the capacity of its habitat.
Animals and humans can also influence the species diversity of phytocenoses. Thus, prolonged intensive grazing of domestic animals leads to a significant simplification of the species composition of the initially floristically rich meadow and steppe phytocenoses. A person sometimes deliberately destroys undesirable plants in phytocenoses and thereby simplifies their species composition. For example, this is done when clearing agrophytocenoses from weeds. In other cases, on the contrary, a person introduces new useful plants into the composition of natural phytocenoses, complicating the species composition. This is done when improving the composition of natural pastures by overseeding valuable fodder grasses. Most often, a person consciously or unconsciously influences the habitat, changing it and thereby causing a change in the species composition of phytocenoses: fertilizing meadows, draining swamps, irrigating natural phytocenoses of steppes and deserts.
In addition, the species diversity of a phytocenosis may depend on the mode of entry of plant primordia into its territory from outside, which is primarily determined by the landscape position of the phytocenosis. The more diverse and in greater quantities the primordia of plants enter the phytocenosis from the outside, the higher the probability that this phytocenosis will be floristically rich. And although this pattern is not always realized in nature, but the tendency of its manifestation is constantly preserved. Back in the early twenties, L.G. Ramensky (1971) drew attention to the fact that in natural phytocenoses there are by no means always viable rudiments of all those plant species that could grow in them. Considering this circumstance, he introduced the concepts floristic fullness and floristic incompleteness phytocenoses and proposed to distinguish between two similar categories of phytocenoses.
Floristically full members phytocenoses include all species capable of growing in them. It was later established (Rabotnov, 1978) that apparently, absolutely complete phytocenoses do not exist in nature, since in any case there will be species from other floristic regions that can grow in one or another particular phytocenosis. This is evidenced by the facts of the wide distribution and introduction into natural phytocenoses of species accidentally introduced by humans from other regions. Therefore, one can only assume the existence of native full-membered phytocenoses, which include all types of local flora that can grow in them. Such phytocenoses should be sought among resistant "ecological-phytocenotic closed"(Kurkin, 1976) communities.
Obviously not full members phytocenoses do not contain all types of local flora that can grow in them. When the rudiments arrive naturally or with the help of humans, these species take root in these phytocenoses. Apparently, most natural phytocenoses are floristically incomplete (Vasilevich, 1983), as evidenced, in particular, by the facts of the successful artificial introduction of useful plants into many natural phytocenoses.
In general, the question of the completeness or incompleteness of phytocenoses is not easily solved, since it is based on long-term observations of the fate of new species sown or replanted in order to verify the results of their establishment. At the same time, this issue is of great practical importance, since the presence of floristic incompleteness of phytocenoses is associated with the possibility of deliberately introducing plants useful to humans into natural phytocenoses, successfully controlling weeds, increasing the productivity of natural hayfields and pastures, and solving a number of other problems of rational use of vegetation.
These are the main factors that determine the species diversity of phytocenoses. In addition, there are some other reasons that affect species saturation, for example, a sharp variability of ecological regimes in a number of habitats, some ecological and biological features of species, etc.
cenopopulations
Each species in a phytocenosis is almost always represented by a more or less significant number of individuals, which together form cenopopulation. The concept of cenopopulation was developed in the forties and early fifties of TA. Rabotnov (1945, 1950a, etc.), and the term coenopopulation was introduced into geobotany later by V.V. Petrovsky (1960) and A.A. Korchagin (1964). In the future, the doctrine of cenopopulation was intensively developed by A.A. Uranov and his students, who published many interesting works, including the two-volume monograph "Cenopopulations of Plants" (1975, 1989).
To date, an idea has been formed about the cenopopulation as one of the main elements of the composition of the phytocenosis, and phytocenosis often defined as a system of coenopopulations associated with each other and with the environment. Each cenopopulation occupies its own ecological niche. When species grow together in a phytocenosis, the niches of coenopopulations partially overlap, but their centers are always differentiated (Mirkin and Rozenberg, 1978). Cenopopulations are a heterogeneous formation. It consists of individuals that differ in age, size, life condition, reaction to external influences, etc. It is believed that the internal differentiation of the coenopopulation is a stability factor. Due to the continuity of the vegetation cover and the weak discreteness of natural phytocenoses, coenopopulations of one species from neighboring phytocenoses turn out to be connected by gradual, continuum-like transitions and are not clearly delimited from each other (Mirkin, Rozenberg, 1983).
41. Phytocenosis: variety of phytocenoses, structure of phytocenosis.
Phytocenosis (from the Greek φυτóν - "plant" and κοινός - "general") - a plant community that exists within the same habitat. 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. The term was proposed by the Polish botanist I. K. Pachoski in 1915. Phytocenoses are the object of study of the science of phytocenology (geobotany).
Phytocenosis is a part of biocenosis along with zoocenosis and microbiocenosis. The biocenosis, in turn, in combination with the conditions of the abiotic environment (ecotope) forms a biogeocenosis. Phytocenosis is the central, leading element of biogeocenosis, as it transforms the primary ecotope into a biotope, creating a habitat for other organisms, and is also the first link in the 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 cenopopulations - aggregates of individuals of the same species within the boundaries of phytocenosis.
Depending on the specifics of research in the concept of “biocenosis structure”, VV Mazing (1973) 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). Understanding the 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 (Yaroshenko, 1961), and such a phytocenosis is called mosaic.
Heterogeneity can also be random. In this case, it is called variegation.
Forest phytocenosis - a forest community, a community of woody and non-woody vegetation, united by the history of formation, the common conditions for development and the territory of growth, the unity of the circulation of substances. The forest community reaches its maximum degree of homogeneity within the geographic facies, where various plant species are in complex relationships with each other and with the ecotope. Depending on the ecotope, composition, ecology of tree species, stage of development, simple (single-tier) and complex (multi-tier) forest communities are distinguished.
The forest is a complex complex. Parts of this complex are in continuous interactions between themselves and the environment. In the forest there are a variety of tree and shrub species, their combinations, a variety of tree ages, their growth rate, ground cover, etc.
Thus, the main component of the forest as a whole - woody vegetation, in addition to a separate forest cenosis, receives a more definite shape. A relatively homogeneous set of trees within these boundaries is called a forest stand. Young woody plants included in the forest phytocenosis, depending on their age and development, are usually called self-seeding or undergrowth in a natural forest. The youngest generation - seedlings.
In a forest plantation, along with woody vegetation, there may also be shrubs. Forest phytocenosis is also characterized by ground cover. Therefore, the Plantation is a forest area that is homogeneous in terms of tree, shrub vegetation and living ground cover.
Meadow phytocenosis
Meadow - in a broad sense - a type of zonal and intrazonal vegetation, characterized by the dominance of perennial herbaceous plants, mainly grasses and sedges, under conditions of sufficient or excessive moisture. A property common to all meadows is the presence of herbage and sod, due to which the upper layer of the meadow soil is densely penetrated by the roots and rhizomes of herbaceous vegetation.
An external manifestation of the structure of meadow phytocenoses is the features of vertical and horizontal placement in space and time of aboveground and underground plant organs. In the existing phytocenoses, the structure took shape as a result of a long-term selection of plants that have adapted to growing together in these conditions. It depends on the composition and quantitative ratio of the phytocenosis components, the conditions of their growth, the form and intensity of human impact.
Each stage of phytocenosis development corresponds to a special type of their structure, which is associated with the most important property of phytocenoses - their productivity. Separate types of phytocenoses differ greatly from each other in terms of the volume of the aboveground environment used by their components. The height of low-grass stands is not more than 10-15 cm, tall-grass - 150-200 cm. Low-grass stands are typical mainly for pastures. The vertical profile of the herbage varies seasonally from spring to summer and autumn.
Different types of meadows are characterized by a different distribution of phytomass within the volume of the medium used. The most obvious manifestation of the vertical structure is the distribution of mass in layers (along the horizons) from 0 and further along the height.
Usually the first tier is made up of cereals and the tallest species of herbs, the second tier is dominated by low species of legumes and herbs, the third tier is represented by a group of small herb and rosette species. Low-lying (waterlogged) and floodplain meadows often have a layer of ground mosses and lichens.
In anthropogenically disturbed grass stands, the typically formed layered structure is also disturbed.
In meadow communities, especially multi-species and polydominant ones, there is always a more or less pronounced horizontal heterogeneity of the herbage (spots of clover, strawberry, golden cinquefoil, etc.). In geobotany, this phenomenon is called mosaic or microgrouping.
Mosaic in meadow phytocenoses arises as a result of an uneven distribution of individuals of individual species. And each species, even its age groups, is specific in the vertical and horizontal placement of its aboveground and underground organs. The uneven distribution of species within the phytocenosis is also due to the randomness in the dispersal of seeds (bulbs, rhizomes), the survival of seedlings, the heterogeneity of the ecotope, the influence of plants on each other, the peculiarities of vegetative propagation, the impact of animals and humans.
The boundaries between individual types of mosaicity cannot always be clearly drawn. Often, the horizontal division of phytocenoses is determined not by one, but by several reasons. Episodic mosaicity, along with phytogenic, is the most common. It is especially pronounced in the distribution of some species (angelica, cow parsnip) in places of their mass seeding (under shocks, near generative individuals), spots appear with a predominance of these species. Their power and participation in the creation of phytomass initially increases, and then decreases due to the mass extinction of individuals as a result of the completion of the life cycle.
In the meadows (unlike forests), small-contour mosaics are common. Meadows are also characterized by the movement of microgroups in space: disappearance in some places and appearance in others. Mosaic is widespread, represented by various stages of vegetation restoration after disturbances caused by deviations from average weather conditions, animals, human activities, etc.
Ruderal phytocenosis
Ruderal plants are plants that grow near buildings, in wastelands, landfills, in forest belts, along communication lines, and in other secondary habitats. As a rule, ruderal plants are nitrophils (plants that grow abundantly and well only on soils sufficiently rich in assimilable nitrogen compounds). Often they have various devices that protect them from destruction by animals and humans (thorns, burning hairs, poisonous substances, etc.). Among the ruderal plants there are many valuable medicinal plants (dandelion officinalis, common tansy, motherwort, large plantain, horse sorrel, etc.), melliferous (medicinal and white melilot, narrow-leaved Ivan tea, etc.) and fodder (awnless bonfire, creeping clover, wheatgrass creeping, etc.) plants. Communities (ruderal vegetation) formed by ruderal plant species, often developing in places completely devoid of ground cover, give rise to restorative successions.
Coastal water phytocenosis
forest ruderal phytocenosis vegetation
The floristic composition of coastal aquatic vegetation depends on various environmental conditions of water bodies: the chemical composition of water, the characteristics of the soil that makes up the bottom and banks, the presence and speed of the current, pollution of water bodies with organic and toxic substances.
The origin of the reservoir is of great importance, which determines the composition of phytocenoses. Thus, lake-type floodplain water bodies, located in similar natural conditions and characterized by similar hydrological characteristics, have macrophyte flora similar in composition.
The species composition of plants inhabiting the coastal zone of reservoirs and the aquatic environment is quite diverse. In connection with the aquatic environment and lifestyle, three groups of plants are distinguished: real aquatic plants, or hydrophytes (floating and submerged); air-water plants (helophytes); coastal aquatic plants (hygrophytes).
Theme 3
Geobotany
PHYTOCENOSIS
Phytocenosis and its features
Phytocenology
Phytocenology studies plant communities (phytocenoses). The object of study is both natural phytocenoses (forest, meadow, swamp, tundra, etc.) and artificial ones (for example, crops and plantings of cultivated plants). Phytocenology is one of the biological sciences that study living matter at the cenotic level, i.e. at the level of communities of organisms (slide 4-5).
The task of phytocenology is to study plant communities from different points of view (the composition and structure of communities, their dynamics, productivity, changes under the influence of human activities, relationships with the environment, etc.). Great importance is also given to the classification of phytocenoses. Classification is a necessary basis for studying the vegetation cover, for compiling vegetation maps of various territories. The study of phytocenoses is usually carried out by their detailed description according to a specially developed technique. At the same time, quantitative methods for accounting for various signs of phytocenosis (for example, the share of participation of individual plant species in the community) are widely used.
Phytocenology is not only a descriptive science, it also uses experimental methods. Plant communities serve as the object of the experiment. By influencing the phytocenosis in a certain way (for example, by applying fertilizers to the meadow), the reaction of vegetation to this effect is revealed. Experimentally, they also study the relationship between individual plant species in a phytocenosis, etc.
Phytocenology is of great national economic importance. The data of this science are necessary for the rational use of the natural vegetation cover (forests, meadows, pastures, etc.), for the planning of economic measures in agriculture and forestry. Phytocenology is directly related to land management, nature protection, reclamation work, etc. Phytocenology data are used even in geological and hydrogeological surveys (in particular, when searching for groundwater in desert regions).
Phytocenology is a relatively young science. It began to develop intensively only from the beginning of our century. A great contribution to its development was made by domestic scientists L.G. Ramensky, V.V. Alekhin, A.P. Shennikov, V.N. Sukachev, T.A. Rabotnov and others. Foreign scientists also played a significant role, in particular J. Braun-Blanquet (France), F. Clements (USA), R. Whitteker (R. Whitteker) ( USA).
Phytocenosis and its features
According to the generally accepted definition by V.N. Sukachev, a phytocenosis (or plant community) should be called any combination of higher and lower plants that live on a given homogeneous area of the earth's surface, with only their characteristic relationships both among themselves and with habitat conditions, and therefore creating their own special environment, phytoenvironment (slide 6). As can be seen from this definition, the main features of a phytocenosis are the interaction between the plants that form it, on the one hand, and the interaction between plants and the environment, on the other. The influence of plants on each other takes place only when they are more or less close, touching their aboveground or underground organs. A set of separate plants that do not affect each other cannot be called a phytocenosis.
Forms of influence of some plants on others are diverse. However, not all of these forms are of equal importance in the life of plant communities. The leading role in most cases is played by transabiotic relationships, primarily shading and root competition for moisture and nutrients in the soil. Competition for nitrogenous nutrients, which are scarce in many soils, is most often fierce.
The joint life of plants in a phytocenosis, when they influence each other to one degree or another, leaves a deep imprint on their appearance. This is especially noticeable in forest phytocenoses. The trees that form the forest are very different in appearance from single trees that have grown in the open. In the forest, the trees are more or less tall, their crowns are narrow, raised high above the ground. Single trees are much lower, their crowns are wide and low.
The results of the influence of plants on each other are also clearly visible in herbal phytocenoses, for example, in meadows. Here the plants are smaller than when growing alone, bloom and bear fruit less abundantly, and some do not bloom at all. In phytocenoses of any type, plants interact with each other and this affects their appearance and vitality.
The interaction between plants, on the one hand, and between them and the environment, on the other, takes place not only in natural plant communities. It is also present in those aggregates of plants that are created by man (sowing, planting, etc.). Therefore, they are also classified as phytocenoses.
In the definition of phytocenosis V.N. Sukachev includes such a feature as the homogeneity of the territory occupied by the phytocenosis. This should be understood as the homogeneity of habitat conditions, primarily soil conditions, within the phytocenosis.
Finally, V.N. Sukachev points out that only such a set of plants that creates its own special environment (phytoenvironment) can be called a phytocenosis. Any phytocenosis to some extent transforms the environment in which it develops. The phytoenvironment differs significantly from the ecological conditions in an open space devoid of plants (illumination, temperature, humidity, etc. change).
Composition of phytocenoses
Speaking about the composition of phytocenoses, they primarily mean the floristic (species) composition, as well as the composition of life forms, ecological groups of plants, and a number of other features.
Different phytocenoses to a greater or lesser extent differ from each other in their composition.
Floral composition. In a particular phytocenosis, as a rule, dozens of plant species can be counted. Small-species phytocenoses are relatively rare and occupy small areas. The number of species of vascular plants forming a phytocenosis can vary from 1–3 to 500–1000 or more.
The species richness of plants in a phytocenosis is closely related to climatic and soil conditions. The more favorable these conditions, the more species are included in the phytocenosis. There are especially many species in tropical rainforests, which develop in a very warm and humid climate. There are relatively many species in the phytocenoses of the meadow steppe and floodplain meadows, where soils are rich in nutrients. In extreme, especially unfavorable conditions, the species richness is the smallest (slide 7). Very few species are included, for example, in the composition of phytocenoses developing on solonchaks. Here, an excess of salts in the soil is extremely unfavorable for plants. In such conditions, only a few plant species can exist.
composition of life forms. (slides 8-10) Plants that form a phytocenosis, as a rule, belong to different life forms. The diversity of life forms is especially great in forest phytocenoses, where trees, shrubs, shrubs (stunted shrubs), herbaceous plants, mosses, lichens, etc. . Each of the listed larger life forms, in turn, is subdivided into smaller ones (for example, shrubs - into evergreen and deciduous, etc.).
A significant variety of life forms is also observed in herbal phytocenoses (meadow, steppe, etc.). Individual plant species vary greatly in terms of growth form, methods of reproduction and overwintering, etc.
Ecological groups of plants. (slides 11-15). The phytocenosis often includes plants belonging to different ecological groups in terms of their requirements for light, moisture, nutrients in the soil, etc. For example, in the same forest phytocenosis, light-loving trees coexist, forming the upper tier of the forest, and relatively shade-tolerant forest grasses . In the swampy forest of black alder, mesophyte plants are common on elevations near tree trunks, and hygrophyte plants are common in flooded depressions. The diversity of ecological groups is better expressed in those cases when, within the phytocenosis, areas differing in environmental conditions (for example, microhighs and microlows) alternate.
Dominant Species Different types of plants differ in their participation in the formation of phytocenosis. Some of them are represented by very many copies. Such species are called dominant or dominant. Thus, oxalis is often the dominant herb-shrub cover in spruce and pine forests. In addition to dominants, there are other species that are found in the phytocenosis with a lower degree of abundance, and in different species it is different. The degree of abundance of a species is most often assessed by its projective cover (the part of the total area of the site occupied by the projections of the aerial organs of the species onto a horizontal plane).
Different phytocenoses differ significantly from each other in the number of dominant species. In some communities, only one species dominates (for example, reeds in swamps). Such phytocenoses are called monodominant. Phytocenoses, where there are several dominant species, are called polydominant (many types of floodplain meadows).
Monodominant phytocenoses, as a rule, develop in less favorable climatic and soil conditions, polydominant - in more favorable ones. In some phytocenoses, it is generally impossible to distinguish dominant species (for example, in tropical rainforests).
Species-edifiers. In phytocenoses, there are also types of edificators. This is the name of plants that are not only found in a large number of specimens, but also have a strong impact on the environment, determine the living conditions of other plants. An example of an edificator species would be a spruce in a spruce forest. Under the canopy of spruce, a very peculiar environment is created, which differs sharply from the conditions in the open (strong shading, high humidity, etc.). Spruce is one of the strong edificators, its transformative effect on the environment is very large.
Composition of phytocoenotypes. A phytocoenotype is a group of plant species characterized by a certain "life strategy". The most common classification of phytocenotypes proposed by L.G. Ramensky. (slides 16-17) He distinguished three phytocoenotypes: violets, patients and explerents. Violentas are competitively powerful plants that occupy strong, stable positions in the phytocenosis (spruce in a spruce forest, feather grass in the steppe). Patients are hardy plants. Although they do not have competitive strength, they are constantly present in the phytocenosis due to the fact that they tolerate the effects of violets well (oxygen in a spruce forest). Explerents are weak competitors. They easily capture any territory devoid of plants, but do not hold it for long, and then "migrate" to a new free area (coltsfoot). The phytocenosis includes plant species belonging to different phytocenoses. For example, in forest phytocenoses, many plants are violents and patients, and there are very few explerents (coltsfoot and willow-herb on overgrown campfires).
Coenotic populations of species. Each species is represented in the phytocenosis, as a rule, by many individuals (slide 18). They are different in size, age, vitality (some bloom, others only vegetate). The totality of individuals of a species in a particular phytocenosis is called the cenotic population of a given species. The composition of the coenotic population includes: 1) living seeds contained in the soil, 2) seedlings, 3) young plants, 4) adults that do not bloom, 5) adults that form flowers, 6) senile individuals that are in the extinction stage . The quantitative ratio between the listed groups indicates how stable the position of the species in the phytocenosis is, what is the future of this species (whether it will remain in the same number, whether it will become more abundant or, on the contrary, will disappear). For example, if there are no seeds in the soil, seedlings and young plants in the coenotic population, but there are many senile specimens, this means that the species may soon disappear from the phytocenosis. In the knowledge of coenotic plant populations, T.A. Rabotnov (slide 19).
The constancy of the species composition. Throughout the territory occupied by the phytocenosis, the species composition of plants is quite homogeneous. In different areas within the phytocenosis, the same dominant species are found and, in addition, a number of other species that are not dominant. Only some rarer species are not present at every site. Consequently, in different parts of the phytocenosis, the species composition of plants is generally similar. Each phytocenosis is characterized by a certain species composition of plants and in this respect differs from other phytocenoses.
The structure of phytocenoses
The structure of phytocenosis is understood as the features of the placement of plants in space (in horizontal and vertical directions)
Among the structural signs of phytocenosis is the degree of closeness of the vegetation cover (slide 20). It is characterized by the general projective cover of plants (the part of the area occupied by the projections of the aboveground plant organs). The degree of density of the vegetation cover in different communities varies greatly. This is often associated with the provision of plants with moisture. In those areas where there is less moisture in the soil, the vegetation cover is usually more sparse.
Layered. The composition of the phytocenosis, as a rule, includes plants that more or less differ in their height. This is especially noticeable in forest phytocenoses. Here there are plants of very different heights - from very tall trees, reaching several tens of meters, to small mosses and lichens that do not exceed a few centimeters.
Plants, more or less similar in height, form separate tiers, which are structural elements of the phytocenosis. For example, in forest phytocenoses, one can distinguish a layer of trees (tree stand), a layer of shrubs (undergrowth), a grass-shrub layer, a moss-lichen cover (slide 21). The tiers are especially well expressed in the coniferous forests of the taiga zone. However, it is sometimes impossible to distinguish clearly separated layers in a phytocenosis (for example, in many types of meadows).
It is legitimate to single out tiers only when the plants included in them are quite numerous, more or less closed. Otherwise, one should say that one or another tier is not expressed or is weakly expressed.
A distinction is made between above-ground and underground tiering (in the latter case, they mean the tiered arrangement of underground plant organs in the soil). A well-defined underground layering is observed very rarely (for example, in plant communities on solonetzes) (slide 22).
In forest phytocenoses, in addition to plants that are part of a certain tier, there are plants that do not belong to any tier. This includes, in particular, creepers and epiphytes (epiphytes are called plants that settle in the forest on the trunks and branches of trees). There are very few lianas in the forests of our country, and mainly mosses and lichens are found as epiphytes. Epiphytes are autotrophic plants capable of photosynthesis. They use the tree only as a place of settlement, but not as a source of food.
Usually, young tree specimens in the forest (self-sowing and undergrowth) do not form a separate permanent layer either.
Mosaic. A characteristic feature of phytocenoses is heterogeneity in the horizontal direction. Often there is a more or less pronounced spotting, mosaic of the vegetation cover within the phytocenosis. For example, in the larch forests of Yakutia, green mosses predominate on the soil under the crowns of trees, and lichens outside the crowns. In the oak-spruce forests of central Russia, under oak trees, some herbaceous plants (snot) dominate, and under spruce trees - others (oxalis), etc.
Sometimes, in the lower tiers of forest phytocenoses, the spots of one plant alternate with those of another, and this is not due to the influence of the tree layer. For example, in a spruce forest, one can find oxalis spots, mainik spots, etc.
Mosaic is characteristic not only of forest phytocenoses. It is also observed in meadows, swamps, tundra, steppes, and deserts. This phenomenon is very widespread.
In the case when the mosaicity of the vegetation cover is well expressed, within the limits of the phytocenosis, separate structural units are distinguished - microphytocenoses. So, if in a spruce forest there are areas with the dominance of sour and areas with the dominance of green mosses, then two microphytocenoses are distinguished - spruce-oxalis and spruce-green-moss.
If we consider not phytocenosis, but a wider natural formation - biogeocenosis, then parcels should be considered structural units of mosaicity (this term was proposed by N.V. Dylis). Each parcel includes not only vegetation, but also other components of animate and inanimate nature (soil, animal components, fungi, microorganisms, etc.). However, territorially, the parcels coincide with microphytocenoses, since the boundaries of the parcels are drawn along the plant component.
The mosaic structure of the vegetation cover within the same phytocenosis can be due to various reasons. One of the main reasons is the heterogeneity, patchiness of environmental conditions. Often mosaic is due to microrelief. In this case, more moisture-loving plants develop in microlows, and less moisture-loving plants develop on microhighs. The mosaic nature of the grass-shrub cover in the forest is often caused by the fact that certain types of plants are able to grow in thickets, forming spots. This is due to the growth of horizontal rhizomes in the soil or creeping above-ground shoots. There may be other reasons for the mosaicity of phytocenoses (activities of animals, humans, etc.).
The area of detection of phytocenosis. The characteristic features of a phytocenosis (its species composition, quantitative relationships between species, structure) are found only in a certain area. They are completely revealed throughout the territory occupied by the phytocenosis, but with sufficient completeness and in some part of it. The minimum dimensions of such a plot are not the same for different phytocenoses. For forest phytocenoses, many hundreds of square meters are needed, for herbal ones, as a rule, 100 m is enough. The minimum area on which the main features of a phytocenosis can be found is called the detection area.
It should be noted that the detection area is not the same for different forest communities, depending on their complexity. Thus, for forests with a rich tree species composition (for example, coniferous-broad-leaved forests of the Far East), the detection area is much larger than for forests where there are few tree species (pure spruce forests, pine forests, etc.).
Phytocenosis as a system. Phytocenoses are complex formations that can be considered as original natural systems.
They are made up of various components that are related to each other in one way or another. However, the level of organization of such systems is quite low and the connections between the components are relatively weak. This can be proved by the fact that when some components are excluded, for example, certain plant species, the system is not destroyed.
In those systems where the connections are closer, the exclusion of individual components leads to the disintegration of the system as a whole.
The main properties of phytocenoses
This section considers only natural phytocenoses and, at the same time, indigenous, or climax ones.
Stability over time. One of the most important properties of natural phytocenoses is the ability to independently maintain their existence without any human intervention. In forests, this happened in the past due to the fact that after the death of some trees, others grew in their place and the forest as a phytocenosis was preserved for many centuries.
Independently, without human help, not only forest, but also other natural phytocenoses - steppe, tundra, marsh, etc., supported their existence in the past for a long time. The ability to restore is characteristic of all natural plant communities.
In the modern era, not all natural phytocenoses have retained the ability to independently maintain their existence. This is explained by the fact that as a result of intensive human impact on the natural vegetation cover and the environment, the conditions for the existence of plants have changed dramatically in an unfavorable direction.
In contrast to natural phytocenoses, the communities of cultivated plants created by man do not have the ability to recover at all.
The ability to recover from violations. If the natural phytocenosis has undergone any violation, it is able to return to its original state again, but on condition that the violation is not too great and it will not happen again. So, in suburban forests, where there are many vacationers, the herb-shrub and moss-lichen layers noticeably change, trees and shrubs suffer (slide 23-24). But if human impact stops completely, then the forest can return to its original state. Of course, recovery does not occur immediately, but over a more or less long period (at least 10-15 years). In the same way, meadow, steppe and desert phytocenoses, disturbed by overgrazing, are being restored (slide 25-26). But even in this case, for the complete restoration of vegetation, it is necessary to stop any impact for a rather long time.
Ability to recover after destruction. If the natural phytocenosis in any area is destroyed, it can recover again after a certain time. Thus, after a clear cutting of a spruce forest, the forest of the former composition is usually restored, but such restoration, as a rule, occurs through an intermediate stage of birch forest. To restore the spruce forest, it is necessary that spruce seeds from neighboring forest areas fall into the cut area in sufficient quantities.
In the place of the plowed steppe, the original steppe vegetation can subsequently be restored again, but restoration is possible only if there is a virgin steppe nearby, which is the source of the seeds of steppe plants.
Change of phytocenoses under changing environmental conditions. Natural phytocenoses have the ability to respond to changes in habitat conditions (primarily soil). Changes of this kind are varied: a decrease in soil moisture in some area due to drainage, an increase in moisture in the territory adjacent to a newly created reservoir, etc. When habitat conditions change, a radical restructuring of the phytocenosis occurs, dominants and species composition of plants change. Ultimately, one phytocenosis is replaced by another.
Each phytocenosis can exist only under certain environmental conditions, and if the conditions change, then a new phytocenosis is formed (slide 27).
Variability of phytocenoses in time
Phytocenoses change continuously over time. There are the following types of variability of phytocenoses: daily, seasonal, multi-year and age.
Daily variability is a change in phytocenosis during the day. - Such variability is expressed in the fact that different types of plants bloom at a certain time of the day, in some plants the leaves of a complex leaf are folded at night (clover, oxalis), etc.
Seasonal variability is the changes in phytocenosis that occur throughout the year. They are due to changes in the conditions of existence of plants from season to season (temperature, humidity, etc.). Seasonal variability is manifested in a change in the appearance of vegetation and many other features of the phytocenosis (quantitative relationships between plant species, structure, productivity, etc.). However, the composition of the phytocenosis remains unchanged. An example of seasonal variability is the death of the above-ground organs of some herbaceous plants in autumn and their regrowth the following spring.
Seasonal variability of phytocenoses is observed in those regions of the globe where plant life conditions change dramatically throughout the year. Where this is not the case, there is no seasonal variability of phytocenoses (in tropical rainforests).
Year-to-year variability, or fluctuations, are changes in phytocenosis from year to year. They are most often associated with the fact that the conditions for the existence of plants in different years are not the same, and sometimes they differ to a great extent (for example, in some years there is a lot of precipitation, in others - little).
Year-to-year variability of phytocenoses is well expressed in floodplain meadows flooded in spring when rivers flood. In these meadows, in different years, some plants grow strongly and become dominant, then some plants, then others. The quantitative ratio of different plant species varies greatly from year to year, although the overall species composition remains unchanged. Year-to-year changes in this case are due to the fact that individual years differ greatly in the duration of the spring flood. In years with prolonged floods, more moisture-loving plants grow strongly (for example, meadow foxtail), in years with short-term floods, less moisture-loving plants (for example, red clover).
Year-to-year changes in phytocenoses are also well expressed in the steppes. Here, in some years, feather grass blooms very abundantly and the steppe in summer resembles a gray sea, which sways from the wind. In other years, feather grasses bloom, on the contrary, rather weakly and do not give a solid background. The noted phenomenon is explained by the fact that in different years there is either more or less precipitation. In the conditions of the steppe, against the background of a general lack of moisture, this is very important.
If from year to year the living conditions of plants do not change sharply, then the year-to-year variability of phytocenoses is weakly expressed. This takes place, for example, in taiga coniferous forests, where plants are always provided with moisture. The phytocenoses of the taiga change comparatively little from one year to another.
With year-to-year changes in phytocenoses, the species composition of plants remains the same. Only the dominant plants, the number of flowering specimens, etc., change.
There are fluctuations around a certain "average" level. They do not lead to the restructuring of the phytocenosis and its replacement by any other.
Age variability observed only in forest phytocenoses, moreover, such trees are more or less similar in age (a forest stand is usually of the same age when the forest has formed on a clear-cut, conflagrated, abandoned arable land, etc.). During the life of one generation of trees forming a forest stand, significant changes occur in the lower tiers of forest phytocenosis - undergrowth, grass-shrub layer, moss-lichen cover. This is clearly seen, for example, in the spruce forests of the taiga zone. In a young, very dense spruce forest, due to strong shading, no plants develop on the soil. In an older spruce forest, where there is more light under the canopy, first a moss cover appears, and then individual grasses and shrubs. In the old spruce forest, both moss and grass-shrub cover are usually well developed (slide 28). Age-related changes in the lower tiers of forest phytocenoses are due to the fact that with the age of the forest, the illumination under the canopy of trees increases, the intensity of root competition in the soil for moisture and nutrients weakens, etc. Age-related changes also occur in the tree layer.
As the age of the trees increases, they become larger, their number per unit area decreases, and so on.
Age-related changes in forest phytocenoses are usually cyclical. Having reached old age, the tree layer disintegrates and dies. An open space is formed, on which a forest phytocenosis begins to form again. He again goes through various age stages in his development.
The influence of the environment on phytocenoses
The climatic and soil conditions of any territory largely determine the nature of the phytocenoses that develop here (the species composition of plants, the composition of dominants, etc.). This is especially well manifested in the course of primary successions, the final stage of which is root (climax) phytocenoses, most corresponding to the climatic and soil conditions of the territory. Thus, the environment determines the direction of primary successions and their final stage, i.e. ultimately affects the formation of phytocenoses.
The formed phytocenoses also experience the influence of the environment, and it is very diverse. Consider it on the example of forest phytocenoses. The impact of fires and hurricanes is especially dangerous for the forest. The sticking of large masses of snow on trees also has a significant effect, which leads to their breakage and fall.
Fires are a natural, natural factor that has affected forest phytocenoses for many millennia. The fires were caused by lightning strikes. Coniferous forests are predominantly affected by fire. Horse fire, when coniferous trees burn in mass, destroys all tiers of the forest. A ground fire, during which only fallen dry needles burn on the ground, causes significant changes in the lower tiers of the forest phytocenosis and in the species composition of coniferous trees that form the forest. Pine, whose trunks are covered with thick bark, is not very sensitive to fire. Therefore, a ground fire does not cause her much harm. Spruce trunks are covered with thin bark, which does not protect well from fire. Spruce is severely affected by ground fires, and most of the trees die.
The impact of hurricanes has a particularly strong effect on forest phytocenoses formed by coniferous trees. At the same time, some trees turn out to be felled, while others are broken (slide 4-6). A hurricane can cause serious damage to a coniferous forest over a large area. Not only coniferous, but also deciduous forests suffer from the hurricane.
The sticking of large masses of snow on trees also has a significant impact on forest phytocenoses (slide 7-8). Coniferous trees either break or are completely felled. Spruce usually suffers more than pine, since especially a lot of snow sticks to its dense crown.
The influence of the animal world on phytocenoses
Phytocenoses are significantly influenced by various representatives of the fauna - both vertebrates (mammals, birds) and invertebrates (insects, worms, etc.). This influence manifests itself in very different forms, and its scale can be quite significant.
The influence of invertebrates is especially great in forest phytocenoses. Some leaf-eating insects, if they appear in large numbers, greatly harm the forest. For example, caterpillars of the Siberian silkworm butterfly during the years of mass reproduction are able to destroy coniferous forests over a vast area. Dark coniferous forests (cedar, fir, spruce) are especially affected by the Siberian silkworm.
Great damage to deciduous forests is caused by caterpillars of the gypsy moth and oak leafworm appearing in the mass, eating leaves on trees.
Not only the needles and foliage of trees, but also their fruits suffer from insects. Thus, the larvae of some insects (acorn moth, acorn weevil) cause massive death of oak acorns, affecting them at an early stage of development, when they are still on trees.
Ants have a noticeable positive effect, especially on forest phytocenoses. They destroy a large number of pests, spread the seeds of some herbaceous plants (hoof, various types of violets, etc.) (slides 9-10).
There are other forms of influence of insects on phytocenoses. Some types of insect activity are widespread and cause significant changes in phytocenoses up to the replacement of some phytocenoses by others (slides 11-12).
Of the invertebrates, earthworms have a very large, and positive, effect, the number of which in the soil can be extremely high (many tens per 1 m) (slide 13). Worms process dead plant residues, enrich the soil with nutrients, improve its structure, loosen and ventilate the soil layer, etc. There are especially many earthworms in the soils of broad-leaved forests (up to 500 per 1 m) and northern or meadow steppes (over 100).
The impact on the phytocenoses of mammals is also quite large and manifests itself in various forms. Steppe phytocenoses, for example, have been exposed to wild herbivorous ungulates for many millennia, which systematically destroyed some of the plant mass. This type of influence of animals, if their numbers are not too large, is a necessary condition for the normal development of steppe phytocenoses. The steppe, which is now in conditions of absolute conservation, is gradually reborn, losing its characteristic features (the role of feather grasses is sharply decreasing, some plants that are alien to the steppes are growing strongly) (slides 14-15).
The influence of mammals on forest phytocenoses is very significant. Larger animals (moose, deer), feeding on the aboveground plant organs, cause certain harm to forest phytocenoses. These animals destroy the undergrowth, eat the foliage of shrubs, etc. Small mammals (mouse-like rodents) also harm forest phytocenoses, which sometimes destroy a huge amount of fruits and seeds of trees that have fallen to the ground (especially oak acorns). Due to this, seed propagation of tree species is greatly hampered.
The burrowing activity of some small mammals (moles, mice, voles, etc.) has a significant impact on phytocenoses (slide 16). These animals contribute to the penetration of air and precipitation into the soil layer, which is favorable for plants. But at the same time, they can severely damage the plants themselves, i.e. act as a negative factor.
The influence of burrowing animals on phytocenoses is diverse. In places of their mass accumulation, the vegetation cover is more or less thinned out. In the meadows, the activity of moles leads to spotting of the vegetation cover, since emissions of fresh earth constantly appear on the surface of the meadow, on which plants settle. Thanks to these emissions, the vegetation cover of the meadows becomes mosaic.
Sometimes the activity of earthmovers leads to catastrophic consequences. Thus, in the steppes of Mongolia, during the years of their mass reproduction, voles dig up the soil so strongly that this causes the death of sod grasses characteristic of the steppe (feather grass, fescue).
Earthmovers have the greatest impact on the vegetation cover in the southern steppes and semi-desert.
Mammals play an important role in the dispersal of seeds and fruits of plants. Some small mammals, such as squirrels, make reserves of seeds and fruits, but in the process of transferring them to their pantries, they lose some of them, which contributes to the settling of plants.
The role of birds in the life of phytocenoses is also significant. Some birds feed on plant foods (buds of trees, their unblown catkins, juicy fruits, etc.). The destruction of buds and catkins harms plants to a certain extent. However, eating juicy fruits (elder, buckthorn, mountain ash, etc.) promotes the spread of seeds and brings certain benefits. Some birds, like small mammals, play the role of peddlers of tree seeds (for example, the jay spreads oak acorns, the nutcracker - pine nuts, etc.). However, eating a large amount of dry fruits and seeds (oak acorns, pine nuts, etc.), birds to a certain extent impede the seed propagation of trees.
The examples given show that the importance of fauna in the life of phytocenoses is quite large, and the forms of influence are very diverse. Representatives of the animal world play both a positive and a negative role in relation to phytocenoses.
Human influence on phytocenoses
In the modern era, natural phytocenoses are strongly influenced by humans. Its scope and intensity is constantly increasing. Human activity today is one of the most significant factors influencing the vegetation cover. The forms of anthropogenic (anthropogenic) influence are diverse: air pollution with harmful emissions, recreation (the use of the territory for mass recreation of the population), deforestation, grazing, haymaking, drainage or flooding of the territory, the use of mineral fertilizers, herbicides, etc. Each of these types of impact causes certain changes in the vegetation cover.
Atmospheric pollution has a particularly strong effect on forest phytocenoses, primarily on coniferous forests. The most common air pollutant is sulfur dioxide (sulfur dioxide). This substance has a negative effect on plants even in very small concentrations (on the order of a millionth part).
Due to human activities, sulfur dioxide enters the Earth's atmosphere in large quantities. It is thrown out by pipes of many plants and factories, thermal power plants, various types of boiler houses, etc. Exposure to sulfur dioxide leads to severe inhibition of trees, especially conifers, and often to their death. As a result, more valuable coniferous forests are replaced by less valuable small-leaved forests (birch forests, etc.). There are changes not only in the forest stand, but also in other tiers of the forest (undergrowth of tree species, many types of forest grasses, shrubs, mosses and lichens disappear). The higher the concentration of sulfur dioxide in the air, the faster the forest phytocenoses degrade (slide 17). Sulfur dioxide not only poisons plants, but also sharply worsens the properties of the soil, strongly acidifying it (acid rain falls).
In addition to sulfur dioxide, dangerous atmospheric pollutants are also nitrogen oxides, ammonia, phenols, magnesite dust, soot, etc.
Influence recreation for phytocenoses is very significant and also negative (slide 18-19). The presence of a large mass of people in any area causes a strong compaction of the soil. Under the influence of compaction, the soil layer, especially in its uppermost part, is greatly depleted of oxygen. As a result, the conditions for the existence of roots deteriorate sharply, which leads to the oppression of plants, and sometimes to their death. In addition, plants suffer from mechanical damage during trampling (breaking off of above-ground shoots, damage to buds on rhizomes shallow in the soil, etc.). One of the consequences of recreation is a sharp reduction in the number, and sometimes the complete disappearance of some beautifully flowering plants, which are collected in large quantities for bouquets.
The influence of recreation strongly affects forest phytocenoses. As a result of soil compaction, trees begin to dry out, and plants of the lower tiers of the forest suffer greatly from trampling. Different forest plants are not equally sensitive to trampling (slide 20). Lichens developing on the soil are especially severely damaged, and to a lesser extent, small grass forests. The most persistent shrubs and green forest mosses.
Intensive and prolonged use of the forest as a place of recreation for a large number of people leads to the degradation of forest phytocenoses of cenoses, to the replacement of multi-species complex plant communities with low-species, simple ones. So, an oak forest with various types of trees, with a well-developed undergrowth and a rich grass cover, under the influence of intensive recreation, is highly degraded (slide 21). It turns into a rare forest of drying oaks and a grass cover, in which plants dominate that are not characteristic of the forest, but tolerate trampling well (Annual bluegrass, Highlander bird, Large plantain, etc.) (slides 22-24).
Deforestation is one of the strongest forms of human impact on natural phytocenoses. As a result, the forest phytocenosis is replaced by herbal ones, and the forest is restored again. But it is often completely different, the one that was before cutting down (for example, a birch forest is formed in place of a spruce forest).
It is better restored after cutting down deciduous, for example oak (if it is not very old). In this case, a shoot is formed from tree stumps and there is no change from one forest phytocenosis to another. The stage of open treeless space with grass cover is very short.
Livestock grazing is also one of the most common forms of anthropogenic impact. If the grazing is moderate, corresponding to the established norms, then it does not cause serious harm to phytocenoses. There are certain rules for grazing domestic animals. They are not the same for different animal species and different types of phytocenoses. Overgrazing leads to negative consequences. Plants that are more valuable in terms of fodder disappear, and their place is taken by less valuable or not eaten by livestock at all (slide 25).