Geobotany

Theme 3

PHYTOCENOSIS

Lecture1

Phytocenosis and its features

Phytocenology

Phytocenology studies plant communities (phytocenoses). The object of study is both natural phytocenoses (forest, meadow, swamp, tundra, etc.) and artificial ones (for example, crops and plantings of cultivated plants). Phytocenology is one of the biological sciences that 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 areas).

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

Phytocenosis and its features

According to the generally accepted definition by V.N. Sukacheva, phytocenosis (or plant community) should be called any set 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).

Forest phytocenosis - a forest community, a community of woody and non-woody vegetation, united by the history of formation, common development conditions and growing area, 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 multispecies 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).

Phytocenosis (or plant community) is any set of plants that live on a given homogeneous area of ​​the earth's surface, only with their inherent relationships both between themselves and habitat conditions and therefore creating their own special environment, phytoenvironment (Sukachev, 1954).

Phytocenosis is any specific grouping of plants throughout the space it occupies, relatively homogeneous in appearance, floristic composition, structure, conditions of existence and characterized by a relatively similar system of relationships between plants and with the environment (Shennikov, 1964).

Phytocenosis - a set of co-growing plants - is a part of a biocenosis - a set of co-living organisms. The science of biocenoses is called biocenology (from the Greek bios - life). Thus, phytocenology is a part of biocenology (Voronov, 1963).

V. N. Sukachev proposed to call biogeocenosis (1940) a plant community, together with its animal population and the corresponding part of the earth's surface, characterized by certain properties of the microclimate, geological structure, soil and water regime.

The first definition of a plant community was given by G. F. Morozov (1904) for a forest, and then (1908) extended by V. N. Sukachev to all plant communities. The term "phytocenosis" was used by I.K. Pachosky for "pure thickets" (formed by one plant species) in 1915 and for all communities - by Sukachev in 1917 and Hams in 1918.

Phytocenosis, or plant community, is a set of plants growing together in a homogeneous area, characterized by a certain composition, structure, composition and relationships of plants both with each other and with environmental conditions. The nature of these relationships is determined, on the one hand, by the vital, otherwise, ecological properties of plants, on the other hand, by the properties of the habitat, i.e. the nature of the climate.

Between plants in a phytocenosis there are relations of two genera. Firstly, growing side by side, plants of the same species or plants of several species (plants of different species often grow side by side in a phytocenosis) compete with each other for the means of life; between them there is a struggle for existence (in the broad metaphorical sense, as Charles Darwin understood it). This competition, on the one hand, weakens plants, but on the other hand, it forms the basis of natural selection, the most important factor in speciation and, consequently, in the process of evolution. Secondly, plants in a phytocenosis have a beneficial effect on each other: shade-loving herbs live under the canopy of trees, which cannot grow or grow poorly in open places; plants with weak climbing or climbing stems - lianas - rise on tree trunks and branches of shrubs; epiphytes not associated with the soil settle on them (Sukachev, 1956).

A phytocenosis is characterized by a certain set of plants that form it (species composition), a certain structure, and confinement to a certain habitat. Due to the change in the environment by plants, the phytocenosis creates its own environment - the phytoenvironment.

Phytoenvironment is the environment of plant communities (Dudka, 1984).

The term phytocenosis (plant community) can be applied both to specific areas of vegetation cover and to designate taxonomic units of various ranks: for an association, for a formation, for a type of vegetation, etc.

Four types of phytocenosis boundaries can be distinguished: sharp, mosaic, bordered, diffuse. Sharp boundaries of phytocenoses can be observed both with a sharp change in environmental conditions and with a gradual one. Even with very sharp boundaries, the introduction of the edificator of one community to the outskirts of another community is usually observed. Mosaic borders are characterized by the fact that in the contact zone of two phytocenoses, small areas of one cenosis are included in the array of another, that is, as if the complexes formed by both bordering phytocenoses are developing. Border boundaries differ from other boundaries in that a narrow border of a community is observed in the contact zone, which differs from both bordering communities. Diffuse boundaries are characterized by a gradual change in space of one phytocenosis by another.

Phytocenosis with its animal population is a biocenosis. Biocenosis - a set of plants and animals inhabiting a habitat area with more or less homogeneous conditions of existence (biotope), formed naturally or under the influence of human activity, continuously developing and characterized by certain relationships between members of the biocenosis and between the biocenosis and the habitat (Pavlovsky, Novikov, 1950).

A population is a group of individuals of a species that is geographically or ecologically isolated from other groups of individuals of the same species. A group of individuals of a species in a phytocenosis is a population of this species.

Different individuals of the same species in the phytocenosis are present in a different state, in other words, the population of each species is heterogeneous in composition. Its individuals may differ from each other, for example, by age phases. The following main periods of plant life are distinguished: latent period (period of primary dormancy); the virgin (virgin) period, in itself three states of plants: shoot, juvenile (youthful) and premature (adult virgin); generative period; senile (senile) period (Rabotnov, 1945, 1950).

There are many definitions of life forms. IG Serebryakov (1962) points out that the doctrine of life forms has now acquired at least two aspects - ecological-morphological and ecological-cenotic, closely related to each other.

From an ecological and morphological point of view, a life form, according to I. G. Serebryakov, is “a peculiar general appearance (habitus) of a certain group of plants (including their aboveground and underground organs - underground shoots and root systems), arising in their ontogenesis as a result of growth and development in certain environmental conditions. This habitus historically arises in given soil and climatic conditions as an expression of the adaptability of plants to these conditions.

From an ecological-coenotic point of view, a life form is “an expression of the ability of certain groups of plants to spatially settle and fix on a territory, to participate in the formation of vegetation cover.”

Raunkier in 1905-1913 built a system of life forms based on the position of the buds of plant renewal when the plant endures an unfavorable period caused by a decrease in temperature or lack of moisture. This system was subsequently modified and supplemented by I.K. Pachosky (1916), who proposed to base it on the amount of losses incurred by a plant when its organs die off during an unfavorable season (Voronov, 1963).

The main characteristics of a phytocenosis include the species and age composition of the plants that form it, as well as its spatial structure.

Species composition of phytocenoses. Each phytocenosis is characterized by a special species composition peculiar to it. Its complexity or simplicity is determined by the indicator of species (floristic) saturation, which is understood as the number of species per unit area of ​​a phytocenosis.

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 .

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.

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.

Animals and humans can also influence the species diversity of phytocenoses (Prokopiev, 1997).

The age composition of populations is the distribution of individuals of the coenotic population by age and development phases. The age of plants is the lifespan of a whole plant or its separate part, from its inception to the moment under study. Age is measured in units of time (calendar age) or in the number of leaves or plastochrones laid down (physiological age) (Dudka, 1984).

Depending on the ratio of age groups, T. A. Rabotnov (1995) distinguishes three types of cenopopulations: invasive, normal, and regressive.

Analysis of the age composition of cenopopulations is important in the study of phytocenoses. It allows you to find out the current state of individual cenopopulations and phytocenosis as a whole, predict the direction of their further development, helps develop a regime for the rational use of phytocenoses, and solve problems of their optimization and protection (Yaroshenko, 1969).

The vertical structure of phytocenoses is due to the fact that the plants growing in it have an unequal height, and their root systems penetrate the soil to different depths. As a result, the phytocenosis is divided in the vertical direction (in its aboveground and underground spheres) into separate more or less separated layers, which leads to a more complete use of habitat resources by plants.

There are three main elements of the vertical structure: layer, canopy and phytocenotic horizon.

In herbaceous plants, layering is expressed in points.

1 point Tall plants (stems of cereals and tall forbs).

2 points. Plants of the second largest size (stalks of lower cereals, forbs and other plants).

3 points. Low growing plants.

4 points. Mosses, lichens and very low herbaceous plants 1-5 cm tall (Zorkina, 2003).

The horizontal structure of phytocenoses is determined primarily by the nature of the distribution of plants over their area. Currently, it is customary to distinguish three main types of distribution of cenopopulations - regular, random and contagious.

The uneven distribution of plants in phytocenoses depends on several reasons and, first of all, on the characteristics of their reproduction and growth form. In this regard, V.N. Sukachev (1961) proposed to distinguish between two types of plant growth: 1) solitary growth, in which individuals of the cenopopulation grow apart from each other, developing one, sometimes two or three shoots from the root and multiply exclusively by generative means; 2) group growth is characterized by the fact that individual individuals or their shoots grow crowded, in groups.

The following main forms of group growth are distinguished: a) a bunch (or a bush); b) turf (or pillow); c) patch; d) curtain; d) spot.

Depending on the type of distribution of dominant coenopopulations, two types of horizontal structure arise - diffuse and mosaic. The diffuse structure is characterized by a more or less uniform (homogeneous) horizontal structure. It arises in those cases when the dominant cenopopulations are distributed evenly - according to regular or random types. True, practice shows that there are practically no completely homogeneous natural phytocenoses, since in nature there are no and cannot be cases of an absolutely uniform distribution of all phytocenosis cenopopulations. Therefore, we can only talk about a relatively diffuse composition of phytocenoses.

The mosaic structure is characterized by a clearly heterogeneous (spotted) distribution of dominant cenopopulations, as a result of which small areas are distinguished in the phytocenosis, differing from each other in composition and structure. There are three main categories of elements of the mosaic structure: a) elements of a larger volume that stand out within the entire above-ground part of the phytocenosis; b) elements of the smallest volume that stand out within one subordinate tier; c) elements of an intermediate volume that stand out within several subordinate tiers. In the naming of these structural parts of the phytocenosis, there is a great discrepancy. Following A. A. Korchagin (1976), they are respectively designated as: a) microcenosis, b) microgrouping, c) congregation.

In accordance with the above factors of uneven distribution of cenopopulations, L. G. Ramensky (1938) and T. A. Rabotnov (1974) distinguish the following types of mosaic: 1) episodic; 2) ecotopic; 3) phytogenic; 4) clonal; 5) zoogenic; 6) anthropogenic.

Later, T. A. Rabotnov (1995) added several more types of mosaic: a) age mosaic, associated with a change in the impact of plants on the environment with increasing age; b) demutational mosaicism associated with the restoration of vegetation in disturbed areas of the community; c) mosaic, due to the formation of nanorelief by plants - tussocks, pillows, etc.; d) mosaicity arising under the influence of two factors, for example, eolian-phytogenic mosaicity, common in arid areas and due to the accumulation of fine earth carried by the wind in shrub clumps.

In the Anglo-American geobotanical literature, patterns or spots are considered as structural parts of the horizontal heterogeneity of the vegetation cover (Korchagin, 1976), which, in the understanding of most authors, do not have definite boundaries and regular repetition. In connection with the continuous change in the area of ​​the phytocenosis of environmental conditions, the patterns form a motley carpet of continuously changing unstable combinations of various species. Thus, the patterns differ from the microcenoses, congregations, and microgroups that are more or less stable in time and are apparently characteristic of some herbaceous phytocenoses with a highly variable structure.

The productivity of a plant is the amount of organic mass (biomass) produced by one plant per year, and the seed productivity is the number of seeds produced by one copy of the plant per year. In the same sense as productivity, the terms productivity of phytocenosis, annual growth of plant mass, and productivity are used (Voronov, 1963).

Community products - organic substances produced by biocenosis, or phytocenosis. They differ: total primary production - the amount of organic matter introduced into the cenosis system by producers through photosynthesis and chemosynthesis; net primary production - the same, but minus the substances spent on respiration and consumed by heterotrophic organisms; total secondary production - the amount of organic matter created by heterotrophic organisms - consumers; net secondary production - the same, but minus the substances spent on respiration and consumed by other heterotrophs; stock of products (Bykov, 1973).

Productivity - the amount of useful products obtained from a certain area of ​​a phytocenosis or agrocenosis (Dudka, 1984).

Phytomass (from Greek phyton - plant and mass) - expressed in units of mass, the amount (wet, dry or deashed) of plant matter (populations, phytocenoses, etc.) per unit area or volume. In different phytocenoses, the phytomass has different stratigraphy and different fractional composition (Bykov, 1973).

Composition, structure and structure of phytocenoses

Phytocenology (from Phytocenosis and ... Logia - the doctrine of phytocenoses (plant communities); a branch of geobotany (See Geobotany) (often identified with geobotany) and biogeocenology (See Biogeocenology). At the end of the 19th century in a number of countries in as a result of studying their vegetation cover, an idea arose about the regular combinations of co-growing plants - plant communities, the need for their study as a special object was justified, and the tasks of a scientific discipline that studies plant communities were formulated, the name of phytotopography (I. P. Norlin), florology (Polish botanist Yu. Pachosky, 1891), later phytosociology (Pachosky, 1896; Soviet botanist P. N. Krylov, 1898), and then F. (German geobotanist H. Gamay, 1918; Soviet botanist L. G. Ramensky, 1924 The latter name has become widespread in the USSR and some European countries, in other countries the terms phytosociology and plant ecology are used.

The tasks of phytocenoses include the study of the floristic, ecobiomorphic (see Ecobiomorpha) and cenopopulation composition of phytocenoses, the relationships between plants, the structure, ecology, dynamics, distribution, classification, and history of phytocenoses. F.'s development proceeded in several directions. The founder of the geographical direction was A. Humboldt, who established at the beginning of the 19th century. the main patterns of vegetation distribution depending on the climate; the results of research by Humboldt and his followers summarized it. the geographer of plants A. Grisebach, who in 1872 published The Vegetation of the Globe According to Its Climatic Distribution (Russian translation 1874-1877). The development of this direction was greatly influenced by the works of V. V. Dokuchaev. Owl research. geobotanists G. N. Vysotsky, A. Ya. Gordyagin, B. A. Keller, and others went in the direction of studying vegetation, taking into account soil conditions. The greening of the study of vegetation was largely influenced by the "Textbook of the ecological geography of plants" dates. botanist I. Warming (Russian translation in 1901 and 1902). phytocenology phytocenosis science

In the 19th century significant material was accumulated on the structure (layering, mosaicity) of phytocenoses (Austrian botanists I. Lorenz, 1858, and A. Kerner, 1863; Finnish botanist R. Hult, 1881, etc.) and the study of successions, the doctrine of which especially developed in the USA (F. Clemente). In the 20th century after the 3rd International Botanical Congress (1910), at which the association was accepted as an elementary taxonomic unit (See Association), schools were formed that differed in the methods of studying phytocenoses and identifying associations. The dominant idea was that the vegetation cover was composed of discrete, well-delimited units. There was also an idea about the continuity of the vegetation cover, about the absence of sharp boundaries between phytocenoses (if the growing conditions change gradually). The doctrine of the continuity of the vegetation cover and the associated idea of ​​the ecological individuality of plant species were substantiated independently by Ramensky (1910, 1924), Amer. scientist G. Gleason (1926), Italian G. Negri (1914), French. scientist F. Lenoble (1926). This direction at first did not receive recognition, but starting from the 40s. began to develop successfully in the USA (J. Curtis, R. Whittaker, and others), and then in other countries. Supporters of the continuity of the vegetation cover substantiated the methods of ordination - the allocation of types of phytocenoses based on their placement in a coordinate system that characterizes changes in certain environmental conditions (moisture, soil fertility, etc.). Ordination is also successfully used by supporters of the discreteness of phytocenoses, for example, V.N. Sukachev, who distributed the groups of forest associations he identified into ecological-phytocenotic series.

Ecological studies of the vegetation of our planet are summarized in the monograph by G. Walter “Vegetation of the Globe. Ecological and physiological characteristics "(Russian translation 1968-1975). In the USSR, and then in the USA, an idea arose about the possibility of using vegetation as an indicator of the conditions for plant growth (B. Keller, 1912, F. Clements, 1920). Subsequently, methods were developed for compiling ecological scales and using them to indicate the environment by the composition of vegetation (Ramensky, 1938; Ramensky et al., 1956; G. Ellenberg, 1950, 1952, 1974, and others). It also turned out to be possible to use vegetation as an indicator in geological and hydrogeological studies (Sov. botanist SV Viktorov and others).

The biological direction of the study of phytocenoses was substantiated by Schweitz. botanist O. P. Decandol (1820, 1832). It was developed after the publication by Charles Darwin of The Origin of Species (1859). The followers of Decandole and Darwin believed that the composition, structure, and change of plant communities are determined not only by climate and soil conditions, but also by the relationships between plants. In the 70-80s. 19th century this direction was developed in the works of Rus. scientists N. F. Levakovsky and S. I. Korzhinsky, and then (in the 20th century) in the works of G. F. Morozov and V. N. Sukachev. To study the relationship of plants in phytocenoses, V. N. Sukachev and A. P. Shennikov used an experiment; then. an experimental F.

From the 40s. 20th century based on the representation of Sukachev and English. botanist A. Tensley about biogeocenoses (ecosystems), a new direction arose in the study of phytocenoses as components of more complex bio-inert systems. Stationary complex studies (in addition to botanists, zoologists, microbiologists, soil scientists, climatologists) began to develop, in which they studied the amount of organic matter and energy produced by a phytocenosis (primary production), the role of phytocenoses in energy flows and the transformation of substances, consortia (See Consortia ), the relationship of autotrophic plants with each other and with heterotrophic organisms, etc. As a result of these studies, the species composition of phytocenoses (including vascular plants, mosses, lichens, algae, fungi, bacteria and actinomycetes), the composition of cenopopulations, structure, dynamics, including including the changes caused by human activity, find out the conditions that ensure the maximum production of phytocenoses, including the creation of artificial highly productive phytocenoses. Mathematical methods, including mathematical modeling, are increasingly being used in phytocenoses, and the statistical and mathematical study of phytocenoses has arisen.

A great contribution to the development of F. was made by owls. botany. They studied the vegetation of one sixth of the Earth's territory, developed theoretical problems and methods for studying phytocenoses: V. N. Sukachev, G. F. Morozov and A. Kayander - in the forest F., B. N. Gorodkov, V. B. Sochava, V. N. Andreev, B. A. Tikhomirov - vegetation of the tundra, L. G. Ramensky and A. P. Shennikov - meadows, V. V. Alekhin, E. M. Lavrenko - steppes, etc.

F. is the theoretical basis for the protection, proper use, and increase in the productivity of natural and man-made phytocenoses. The results of phytocenological studies are used for planning and rational use of forest, fodder and other lands, in geological and hydrogeological studies, etc.

Research on F. is conducted in many countries in botanical, ecological, geographical, and also specialized scientific institutions, in the corresponding universities. F.'s problems are covered. in botanical, ecological and general biological journals: in the USSR - in the Botanical Journal (since 1916), Bulletin of the Moscow Society of Nature Testers. Biological Department (since 1829), Ecology (since 1970), Forest Science (since 1967) and Journal of General Biology (since 1940), and abroad - Journal of Ecology (L. - Camb., since 1913), Ecology (N. Y., c 1920), Ecological Monographs (c 1931), Vegetatio (The Hague, since 1948), Folia geobotanica et phytotaxonomica (Prague, since 1966), Phytocoenologia (V., since 1973). The USSR also publishes a series of works by the BIN of the Academy of Sciences of the USSR devoted to phytogenesis—Geobotany (since 1932) and Geobotanical Mapping (edited by V. B. Sochava, since 1963). Phytocenosis structure

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

• 1. Structure as a synonym for composition (species, constitutional). In this sense, they talk about species, population, biomorphological (composition of life forms) and other structures of the cenosis, meaning only one side of the cenosis - composition in the broad sense. In each case, a qualitative and quantitative analysis of the composition is carried out.
• 2. Structure, as a synonym for structure (spatial, or morphostructure). In any phytocenosis, plants are characterized by a certain confinement to ecological niches and occupy a certain space. This also applies to other components of biogeocenosis. Between the parts of the spatial division (tiers, synusia, micro-groups, etc.) one can easily and accurately draw boundaries, put them on the plan, calculate the area, and then, for example, calculate the resources of useful plants or animal feed resources. Only on the basis of data on the morphostructure, it is possible to objectively determine the points of setting up certain experiments. When describing and diagnosing communities, a study of the spatial heterogeneity of cenoses is always carried out.
• 3. Structure, as a synonym for sets of connections between elements (functional). 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, and such a phytocenosis is called mosaic.

STRUCTURE OF PHYTOCENOSES

SIGNIFICANCE OF STUDYING THE STRUCTURE OF PHYTOCENOSES

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

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

The study of the structure of phytocenosis gives a morphological characteristic of the latter. It has two meanings.

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

Secondly, the structure of a phytocenosis is the design of mutual relations between plants, an ecotope and the environment of a phytocenosis under given conditions of a place and at a given stage of development. And if so, then the study of the structure makes it possible to understand why the observed phytocenosis has developed the way we see it, what factors and what interactions between them were the cause of the phytocenosis structure we observed.

This indicative (or indicator) value of the structure of phytocenoses makes its study the first and most important task in geobotanical research. It is by the floristic composition and structure of the phytocenosis that the geobotanist determines the quality of soils, the nature of local climatic and meteorological conditions, and establishes the influence of biotic factors and various forms of human activity.

The structure of phytocenosis is characterized by the following elements:

1) floristic composition of phytocenosis;

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

3) the state of individuals of each species in a given phytocenosis;

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

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

FLORAL COMPOSITION OF PHYTOCENOSIS

Floristically simple and complex phytocenoses

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

simple - from one or a few species, complex - from many species. An extremely simple phytocenosis should consist of individuals of one plant species (or even one subspecies, variety, one race, ecotype, etc.). There are no such phytocenoses under natural conditions or they are extremely rare and occur only in some completely exceptional environment.

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

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

(1929) distinguished phytocenoses:

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

Grossheim interpreted these types of phytocenoses as successive "steps" in the development of the vegetation cover, its complication. However, the terms he proposed have not received general acceptance in the sense indicated.

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

Causes of differences in the floristic complexity of phytocenoses

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

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

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

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

Almost pure thickets of sharp sedge or reeds, saltwort thickets on salt marshes, or pine forests with a carpet of cladonia on the soil, therefore, consist of very few species, because the overmoistening inherent in these places or too great poverty or dryness, or salinity of the soil, etc. exclude all other plants. In areas of water meadows that annually receive thick deposits of sand or silt, phytocenoses are distributed from one or a few species that can survive with the annual burial of their renewal buds by a thick alluvium deposit. Such are the undergrowth of the present (Petasitesspurius), awnless bonfire (Bromopsisinermis), ground reed grass (Calamagrostisepigeios) and other plants with long rhizomes capable of quickly growing through the sediment that buries them. On soils very rich in nitrates, single-species thickets of couch grass are sometimes formed. (Elytrigiarepens) or nettle (Urticadioica) and other nitrophils.

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

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

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

4. Biotic factors. The most obvious example is the effect of wild and domestic animals on vegetation. Livestock grazing changes the soil and soil conditions and the species composition of plant groups: the soil either becomes compacted or, conversely, loosens, hummocks appear, the excrement left by animals fertilizes the soil - in short, the air-water, thermal, and salt regimes change. This entails a change in vegetation. Grazing also directly affects plants: grazing and mechanical trampling produce a selection of species that endure such an impact.

Grazing in combination with varying degrees of influence of climate, soil, and initial vegetation can contribute either to the complication of initial phytocenoses or their simplification. For example, when grazing on wet soil, hummocks form, and the hummocky microrelief increases the heterogeneity of the environment and the set of species. When grazing animals on moderately moist soil, turfing is often disturbed, and repeated grazing weakens the dominant plants, which contributes to the growth of pasture weeds, i.e., the set of phytocenosis species increases. Conversely, intensive grazing on dense, soddy soil makes it possible for only a few resistant species to thrive. Therefore, many previously floristically complex meadow and steppe phytocenoses, now, with their strong pasture use, have turned into extremely simplified ones, consisting of a few species. Mouse-like rodents inhabiting various phytocenoses and loosening the sod and surface layers of the soil with their moves contribute to the settlement of many plants and thus create and maintain a more complex structure of the vegetation cover.

5. Properties of some components of phytocenosis. For example, on abandoned arable lands with fairly rich soil, almost pure thickets of creeping wheatgrass often grow in 1–2 years. This plant, spreading rapidly by means of long, branched rhizomes, captures arable land sooner than many other plant species that can grow here as well as wheatgrass, but settling more slowly. The latter are only gradually introduced into the couch grass phytocenosis and complicate it.

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

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

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

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

Finding out the reasons for this or that floristic saturation of each phytocenosis, we thereby find out its indicative value for characterizing ecological conditions and the degree of their use by plants.

The degree of floristic saturation indicates the completeness of the use of the environment by phytocenosis. There are no two species that are completely identical in their relation to the environment, in its use. Therefore, the more species are in the phytocenosis, the more versatile and fuller the environment occupied by it is used. And vice versa, a phytocenosis consisting of one or a few species indicates an incomplete, one-sided use of the environment, often only because there were no other species in the local flora that could grow here. For example, a forest without shrubs uses the energy of solar radiation to a lesser extent than a forest with shrub undergrowth. The undergrowth uses rays that pass through the upper canopy of the forest. If there is also grass or green mosses under the undergrowth, then they in turn use the light passing through the undergrowth. In a forest without undergrowth, grasses and mosses, all the light penetrating through the crowns of trees remains unused.

If we recall that green plants are the only natural agents that convert the energy of solar radiation into organic matter with a huge supply of chemical energy, it becomes clear how important it is that plant communities be of the most complex composition.

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

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

Identification of the complete flora of phytocenosis

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

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

When studying the floristic composition, as well as when studying other signs of the structure of a phytocenosis, it is necessary that the phytocenosis occupies an area sufficient to reveal all its features. Even the completeness of accounting for the floristic composition depends on the size of the recorded area. If there is, for example, a herbaceous phytocenosis of several dozen plant species, then by choosing a site of 0.25 m2 to take into account the floristic composition, we will find several species on it. Having doubled the site, we will find on it, in addition to those already noted, species that were absent on the first one, and the general list of species composition will be replenished. With a further increase in area to 0.75-2 m2, etc., the list of species will increase, although with each increase in area, the profit of the number of species in the general list becomes smaller. By increasing the sites to 4 m2, 5 m2, 10 m2, etc., we notice that on sites larger, for example, 4 m2, new replenishment of the list of species does not occur or almost does not occur. This means that the area of ​​4 m2 taken by us is the minimum area for revealing the entire species composition of the studied phytocenosis. If we had limited ourselves to a smaller area, it would have been impossible to fully identify the species composition. There are areas of vegetation that differ from neighboring ones, but are so small that they do not reach the area of ​​detection of the floristic composition of the phytocenosis to which they belong. These sites are fragments of phytocenoses.

The term "area of ​​detection" is proposed. Foreign authors use the term "minimal area".

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

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

Bearing in mind the identification of not only the floristic composition of a phytocenosis, but also various other structural features, it is customary in the practice of Soviet geobotanists when describing a complex forest phytocenosis to take a sample area of ​​at least 400–500 m2, and sometimes up to 1000–2500 m2, and when describing herbaceous phytocenoses - about 100 m2 (if the area of ​​the phytocenosis does not reach such sizes, it is described in its entirety). Moss and lichen phytocenoses often have an area of ​​detection not more than 1 m2.