Phytocenosis is a plant community characterized by relative homogeneity of species composition, determined mainly by habitat conditions, and relative isolation from other communities, consisting of coenopopulations connected by relations of differentiation of ecological niches and interference, located in conditions of relatively homogeneous habitat conditions and capable of independent existence.

Phytocenosis is a conditional concept, since, firstly, a community of some plants cannot really exist without interaction with other components of biogeocenosis - zoocenosis, microbiocenosis, biotope, and secondly, according to the concept of vegetation cover continuity that is dominant today, any isolation of isolated communities from it are artificial and serve only for the practical purpose of studying vegetation at all levels.

The modern concept of phytocenosis as a conditional, non-existent entity arose on the basis of an individualistic hypothesis developed by the Russian scientist L. G. Ramensky and the American G. Gleason. The essence of this hypothesis is that each species is specific in its relationship to the environment and has an ecological amplitude that does not completely coincide with the amplitudes of other species (that is, each species is distributed "individualistically"). Each community forms species whose ecological amplitudes overlap under given environmental conditions. When any factor or group of factors changes, the abundance of some species gradually decreases and disappears, other species appear and increase in abundance, and in this way the transition from one type of plant communities to another is carried out. Due to the specificity (individuality) of the ecological amplitudes of species, these changes do not occur synchronously, and with a gradual change in the environment, the vegetation also changes gradually. Thus, plant communities do not form distinctly isolated units, but are connected by transitional communities into a continuously varying system.

Depending on the specifics of research in the concept of "biocenosis structure" V.V. Mazing (1973) distinguishes three directions developed by him for phytocenoses.

1. Structure as a synonym for composition (species, constitutional). In this sense, they speak of species, population, biomorphological (composition of life forms) and other structures of the cenosis, meaning only one side of the cenosis - the composition in the broad sense. In each case, a qualitative and quantitative analysis of the composition is carried out.

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

3. Structure, as a synonym for sets of connections between elements (functional). The understanding of 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 coenotic level: the species composition, configuration and placement of structural elements in space are a condition for their functioning, i.e. 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.

Morphological signs of phytocenosis

Plant communities, despite complex combinations of species, differ in structure. External features that are used to assess the structure are called morphological. The main ones are: species composition, layering, quantitative ratios of species in the phytocenosis. Let's look at each of these signs. The difference of each phytocenosis lies in the peculiarity of the floristic composition, which is represented by a combination of certain types of plants (trees, shrubs, cereals, mosses, etc.). To determine the species composition on the ground, a description of botanical sites is made. The size of the site for herbal phytocenoses is 1 m 2, for forest 1600 m 2 (80x20 m). Based on the descriptions, plant species are identified, their botanical definition is made, and the species richness of the phytocenosis as a whole is established.

Layering in phytocenoses occurs because plants have different attitudes to light, heat, moisture, and soil. Plants of various heights are selected in phytocenoses. Due to layering, a larger number of species can settle on a unit area. Simply arranged phytocenoses consist of one tier (willows on sandy deposits), up to 5-9 tiers are found in forest phytocenoses (Fig. 61). The division of the phytocenosis into tiers is a kind of qualitative assessment of the ratio of species. As an example, one can cite a characteristic of the layering of a broad-leaved forest in the north of the Central Russian Upland. Usually in oak forests, the 1st tier is formed by oak, the 2nd tier - by linden and maple, the 3rd - by undergrowth of oak, linden, and aspen. The oak grove is characterized by dense shrub undergrowth (IV tier) of hazel, buckthorn, and honeysuckle. The herbaceous cover of an oak forest can also be subdivided into tiers: fern (V tier), high grasses (VI), oak broad grass (VII tier).

When characterizing a phytocenosis, it is important to establish the quantitative ratio or abundance of species. Such a characteristic is necessary to determine the dominant species (dominants) that make up the appearance of the phytocenosis. At present, to determine the abundance, the Drude eye 4-point scale is used, in which the following gradations are introduced: soc (sociales) - plants form the background; sor (copiosae) - presented abundantly; sp (sparsae) - found scattered; sol (solitarie) - rare. More accurately, abundance can be determined by counting the number of species per unit area. The abundance indicator is supplemented by the characteristic of the projective cover of species, when the area of ​​projections of the terrestrial parts of the species is calculated and expressed in fractions (%) of the entire surface occupied by the phytocenosis. This characteristic is introduced because the abundance does not give a complete picture of the participation of the species in the composition of the phytocenosis.

Variability of phytocenoses

There are daily, seasonal and year-to-year variability of plant communities.

daily variability. As a result of fluctuations in the intensity of a number of environmental factors - especially light and temperature - the main physiological parameters of plants change. Some results of the reaction of plants to changing factors are visible to the naked eye. These include the daily rhythm of flowering and pollination, characteristic of most plant species, the phenomena of heliotropism (movements of the vegetative and generative organs associated with the position of the sun in the sky), the phenomena of photoperiodism (the reaction of plants to light intensity). The structure of aquatic communities is especially susceptible to diurnal variability.

seasonal variability is caused by changes in conditions during the year and is associated with the presence in the community of plant groups that differ in the rhythm of seasonal development (they are found in almost all phytocenoses). Seasonal variability repeats regularly from year to year and can usually be predicted. The exception is sharply anomalous years.
The seasonality of the climate is a widespread situation in most regions of the globe, it manifests itself almost everywhere, with the exception of areas of tropical rainforests. Because of this, the climatically determined seasonal variability of communities is also widespread, associated with the fall and melting of snow cover, the dynamics of river water in the floodplains, semi-rest or rest in the hottest period in the steppes, semi-deserts, savannahs and deserts.

Seasonal variability is not only related to climate. There is a cenotically determined seasonal variability associated with changes in the phytoenvironment within the community. For example, the existence of two temporary synusia in the grass layer of broad-leaved forests is widely known - the synusia of spring ephemeroids, which develops in the spring during the absence of leaves on the trees, and the synusia of shade-loving broad-leaved grass, which appears with the leaves blooming on the trees and shading the lower tiers. Finally, there is also anthropogenic seasonal variability associated with seasonal human activities (mowing plants in grassy ecosystems, grazing farm animals, etc.).

Year-to-year variability (fluctuation variability, fluctuations). The main reasons for the occurrence of fluctuations in phytocenoses include changes from year to year or over periods of years of various environmental conditions affecting the community. There are several types of fluctuations depending on the causes that cause them: ecotopic fluctuations caused by differences in weather, hydro and other conditions of ecotopes from year to year are widespread in meadow communities; anthropogenic fluctuations are due to differences in the form and intensity of human impact on phytocenosis. For example, in different years the meadow community can be used either as a hayfield or as a pasture. From year to year, the timing of haymaking changes, which creates different conditions for the seeding of individual plant species. The species composition of grazing animals also has a significant effect; zoogenic fluctuations caused by differences in the impact of herbivorous and burrowing animals (in particular, rodents-diggers and insects).

Changes in phytocenoses over time

Not a single phytocenosis exists forever, sooner or later it is replaced by another phytocenosis. The ability to change is one of the most important properties of plant communities.
Irreversible and directed, i.e., passing in a certain direction, changes in the vegetation cover, manifested in the replacement of some phytocenoses by others, are called succession. It is the irreversibility and directionality that distinguishes them from fluctuations. Changes in phytocenoses have long been noticed and described, but the most detailed theory of these processes was worked out by American scientists Henry Cowles and F. Clements (Frederich Clements). Clemente created a system of ideas about successions, starting with the emergence of phytocenoses up to the formation of stable, self-renewing plant communities - climaxes. The final stage of any succession - the climax - can occupy the territory indefinitely and exist for many hundreds of years practically unchanged. The main property of the climax community is the zero balance of matter and energy throughout the year.

There are two main types of succession - primary and secondary. Primary successions are quite rare in nature. They begin with the emergence of phytocenoses on exposed mineral substrates, where previously there was no vegetation. Examples of such substrates are scree in the mountains, frozen recent lava flows, bottoms and sides of valleys after the retreat of the glacier, the exposed seabed, blown aeolian sands, etc. Autotrophic nitrogen fixers, both free-living and symbiotically, play a decisive role in the first stages of primary successions. related blue-green algae (lichens). Lichens, in addition, provide chemical and biological weathering of rocks. These successions go on for several hundred years.



1. The structure of phytocenoses should be understood as:

a) the diversity of species in them and the ratio of abundance and biomass of all populations included in them;

b) the ratio of ecological groups of plants, which develops over a long time in certain climatic, soil and landscape conditions;

c) spatial mutual arrangement of plants (and their parts) in a plant community;

e) a + b + c.

2. The structure of phytocenoses is determined by:

a) the composition and quantitative ratio of the components of plant communities;

b) growing conditions of plants;

c) exposure to zoocomponents;

d) the form and intensity of human impact;

e) a + b + c;

e) All answers are correct.

3. The structure of phytocenosis gives an idea of:

a) the amount of media used by the community;

b) the features of the contact of its constituent plants with the environment;

c) the efficiency and completeness of the use of natural resources by the plant community;

e) All answers are correct.

4. The structure of phytocenosis depends on:

a) ecobiomorphic composition of the plant community;

b) the number and vital status of individuals of vascular plants belonging to the main forms of growth (trees, shrubs, shrubs, grasses);

c) the presence and quantitative participation of mosses and lichens, protists, algae and macromycetes;

d) height and closeness of aboveground shoots of community components;

e) all answers are correct

5. The most important features of the phytocenosis structure are:

a) the degree of closeness of the vegetation cover and the features of the vertical distribution of the leaf surface;

b) the presence of sufficiently differentiated stages or, conversely, their absence;

c) homogeneity or heterogeneity of the horizontal division;

e). a + b + c.

6. The vertical structure of phytocenoses has two polar variants connected by smooth transitions:

a) tiered;

b) phytocenotic horizons

c) vertical continuum;

7. The main factor determining the vertical distribution of plants is:

a) the amount of light that determines the temperature regime and humidity regime at different levels above the soil surface in the biogeocenosis;

b) tough competitive relations between various plant species and their consorts;

c) edaphic, or soil-ground, habitat conditions;

d) terrain

8. The universal synthetic characteristic of the vertical structure of any phytocenosis (both with tiers and with a vertical continuum) is:

a) inversion of vertical belts;

b) aggregation index;

c) leaf surface index;

d) index of homogeneity;

e) index of phytocenotic plasticity.

a) the ratio of the surface area of ​​the leaves to the surface area of ​​the soil on which they are located;

b) the ratio of the total area of ​​leaves of a phytocenosis (or its layer) to the area of ​​the territory it occupies, expressed in m 2 /m 2, or ha / ha;

c) the ratio of the total area of ​​leaves of plants of different tiers;

d) the ratio of the surface area of ​​the leaves of different plant species.

10. The smallest value of the leaf surface index is typical for:

a) meadow phytocenoses;

b) open desert communities;

c) spruce forests;

d) mixed forests

11. Ceteris paribus, the leaf area index in the meadows increases:

a) from less acidic to more acidic soils;

b) from more acidic to less acidic soils;

c) from the beginning of the growing season to the period of the culmination of the development of the herbage;

d) after each mowing and grazing;

e) when increasing the intensity of lighting and applying full mineral fertilizer (NPK)

f) b + c + d + e;

g) b + c + e;

h) a + c + e;

12. For the addition of the underground part of phytocenoses, a decrease in the mass of plant organs from top to bottom is characteristic. This is established for plant communities such as:

a) meadow;

b) steppe;

c) desert;

d) forest;

e) All answers are correct.

13. The mass of underground organs is usually several times (sometimes 10 or more) higher than the mass of above-ground organs in such communities as:

a) meadow;

b) semi-shrub;

c) tundra;

d) desert;

e) All answers are correct.

14. To the main cenoelements of phytocenoses according to Kh.Kh. Track (1970) include:

b) phytocenotic horizons;

c) price cells;

d) microgroups.

15. An element of the vertical structure of phytocenoses, which manifests itself when the community is formed by life forms of plants contrasting in height, is:

a) price element;

b) synusia;

d) cenotype;

e) phytocenotic horizon.

16. Tiers differ:

a) environmental conditions in the horizons to which the aboveground organs of the plants that form them are confined;

b) features of light and temperature regimes;

c) air humidity;

e). a + b + c + d.

17. There are several types of tiers (according to Rabotnov T.A.):

a) resistant to seasons and years (for example, layers of evergreen trees, shrubs, shrubs, mosses, lichens);

b) year-round existing, but sharply changing from the growing season to the non-growing season (layers formed by deciduous trees, shrubs, shrubs);

c) formed by herbs;

d) ephemeral, existing for a short time, formed by herbs (ephemers, ephemeroids), sometimes mosses;

e) are formed only in certain years, for example, a layer of annual grasses in those deserts where atmospheric precipitation falls in sufficient quantities only in some years;

f) re-forming during the growing season due to the alienation of above-ground organs as a result of mowing or grazing;

and). a + b + c + d.

18. Longline arrangement of plants:

a) allows species of different quality in their ecology to coexist in the community;

b) makes the habitat ecologically more capacious;

c) creates a large number of ecological niches, especially in relation to the light regime;

d) reduces competition and ensures the sustainability of the community;

e) All answers are correct.

19. In the series single-tier - two - low-tier - multi-tier - imperfect-tier (vertical-continuous) communities, the following is observed:

a) increase in floristic richness;

b) decrease in floristic richness;

c) a clear correlation between the number of layers and the number of species that make up the phytocenosis;

d) the absence of a certain pattern.

20. In the forests of the temperate zone, the following tiers are usually distinguished:

a) the first (upper) tier is formed by trees of the first size (pedunculate oak, heart-shaped linden, smooth elm, etc.)

b) the second - trees of the second size (rowan, apple, pear, bird cherry, etc.);

c) the third tier is undergrowth formed by shrubs (common hazel, brittle buckthorn, etc.)

d) the fourth tier consists of tall grasses (nettle, common gout) and shrubs (blueberries);

e) the fifth tier is composed of low grasses;

f) in the sixth tier - mosses and lichens;

g) All answers are correct.

21. The consistent use of the concept of tiering has a number of theoretical difficulties associated with the fact that:

a) not all phytocenoses are vertically discrete;

b) it is not clear whether the tiers are layers or “inserted” elements into each other;

c) it is not clear where to attribute the undergrowth, creepers, epiphytes;

e) All answers are correct.

22. There is no division into tiers in such types of phytocenoses as:

a) most herbal;

b) tropical rainforests;

c) certain types of deciduous forests;

d) a + b + c.

23. The absence (or weak expression) of layering in herbaceous communities can be explained by:

a) the presence of only one life form;

b) small height of plants;

c) the presence of predominantly perennial grasses;

d) approximately the same illumination of all plant individuals, regardless of their height and ecological characteristics.

24. There is no underground tiering:

a) in spruce forests;

b) in meadow phytocenoses;

c) on solonchaks and solonetzes;

d) in steppe and desert communities;

e) a + b + d;

g) All answers are correct.

25. Phytocoenotic horizon is:

a) a vertically isolated and vertically further undivided structural part of the biogeocenosis;

b) the vertical part of the plant community, characterized by a certain floristic composition and a certain composition of the organs of these plants;

c) artificial morphological division of the vegetation cover, in which (unlike tiered division 26. In the forests of the temperate zone, the following phytocenotic horizons are usually distinguished, formed:

a) crowns of trees;

b) the undercrown part of the trunks of tall trees, as well as trees of a smaller height, shrubs and corresponding consorts (for example, plants) are, as it were, cut vertically, forming horizontal layers;

d) all answers are correct.

lichens);

c) shrubs or grasses, which, in addition to grasses and shrubs, include the lower parts of tree trunks and shrubs with their characteristic epiphytes;

d) mosses, lichens, creeping plants, including the lower parts of taller plants and their seedlings;

e) All answers are correct.

27. When identifying phytocenotic horizons, such controversial issues that arise when delimiting tiers, such as:

a) how many tiers this or that phytocenosis includes;

b) at what closeness of the aboveground organs of the corresponding plant species should the layer be considered expressed or unexpressed;

c) where to place creepers, epiphytes, undergrowth;

d) all answers are correct.

28. Lianas and epiphytes are part of:

a) upper horizons;

b) lower horizons;

c) those horizons to which parts of trees and shrubs belong, serving as their support;

29. Each phytocenotic horizon is characterized by:

a) a certain floristic composition;

b) the composition of the organs of these plants;

c) the degree of occupancy of the space by these organs;

e) All answers are correct.

30. A section of vegetation cover, within which it is impossible to draw boundaries according to given characteristics and thresholds adopted to determine the boundary, is called:

a) parcel;

b) price cell;

c) microgrouping;

d) price quant;

e) price element.

a) one life form;

b) united by individual topical and trophic competitive relations;

c) one type;

d) different tiers.

32. The morphological severity of the cell of woody vegetation is determined by:

a) the age of the stand;

b) group placement of trees and stands;

c) the height of the forest stand and plants forming the undergrowth;

d) plant vitality.

33. The structural part of a phytocenosis, limited in space or time (occupying a certain ecological niche) and differing from other similar parts in morphological, floristic, ecological and phytocenotic terms, is called:

a) cenopopulation;

b) cenotype;

c) synusia;

d) price quant.

34. As sinusia can be considered:

a) each well-limited layer of forest phytocenoses;

b) a collection of epiphytes, creepers, epiphytic lichens;

c) spring forest ephemeroids;

d) groups of annuals that exist in deserts only in years with heavy precipitation;

e) All answers are correct.

35. Among temporary synusias there are:

a) seasonal;

b) daily allowance;

c) fluctuation;

d) demutational;

e) a + c + d;

f) a + b + c.

36. The most important signs of sinusia are the following:

a) synusia is formed by plants of one or more closely related life forms;

b) plants in synusia are close together, closed in underground or aboveground parts;

c) ecological similarity of plants included in one synusia;

d) morphological isolation, spatial expression;

e) certain interactions between plants, their impact on the environment and, as a result, the creation of their own eco-environment;

f) relative autonomy, expressed in the fact that synusias of the same type can exist with synusias of other types in different combinations;

g) a + c + e + e;

h) All answers are correct.

37. Synusia are:

a) a forest stand formed by spruce, pine or any other species;

b) blueberry or heather cover;

c) a spot of hairy sedge in an oak forest;

d) mixed stand of spruce and fir;

e) a tree stand formed by a mixture of oak, maple, ash;

f) a cover of ephemeroids in an oak forest;

g) lichen carpet of bushy forms in a pine forest;

h) a + b + d + g;

i) All answers are correct.

38. Synusia are characterized by the following functional features:

a) the plants that make up the synusia have a similarity in needs, coenotypic kinship, similarity in the transformation of the environment in a direction favorable for themselves and their partners;

b) in synusia there is a single coenotic process;

c) coenotic and ecological selections take place in the synusia;

d) all answers are correct.

39. An example of fluctuation sinusia can be:

a) a group of spring ephemeroids, well limited in time from synusia of herbs of summer vegetation, which differ from spring ones in their species composition, structure, ecologically and coenotypically.

b) thickets of willow-herb on burned areas and clearings, existing for a short time;

c) a group of annual grasses that occur in some deserts in years with a large amount of precipitation;

d) synusia of creeping ranunculus in water meadows with prolonged stagnation of spring floods.

40. Synusial analysis of phytocenoses is reduced to:

a) the establishment of synusia that make up the phytocenosis;

b) study of their species composition and structure;

c) study of the relationship between them and the environment;

e) a + b + c.

41. Synusial analysis of plant communities helps to determine:

a) environmental conditions of the habitat;

b) the completeness of the use of environmental resources by the phytocenosis;

c) the ecological niche occupied by each particular synusia;

d) a + b + c.

42. Most plant communities are characterized by heterogeneity of horizontal composition; this phenomenon is called:

a) discontinuity;

b) mosaic;

c) continuum;

d) emergence.

43. Within phytocenoses, special structural formations can be distinguished, called:

a) microgroups, or microphytocenoses;

b) price elements;

c) price quants;

d) price cells;

e) a + c + d;

e) All answers are correct.

44. The horizontal division of phytocenoses - mosaic - is expressed by the presence in the biocenosis of various microgroups that differ:

a) species composition;

b) the quantitative ratio of different species;

c) closeness;

d) productivity and other features and properties;

e) All answers are correct.

45. There are the following variants of mosaicity of phytocenoses (Rabotnov, 1984; Mirkin, 1985):

a) regeneration mosaics- heterogeneity of phytocenosis associated with the renewal process;

b) clone mosaics- heterogeneity of phytocenosis associated with vegetative propagation of plants;

in) phytoenvironmental mosaics- heterogeneity of phytocenosis associated with a change in the environment by one of the species and the response of other species to this change;

G) allelopathic mosaics due to the release of some plant species of strongly smelling aromatic substances;

e) zoogenic mosaics are formed as a result of the impact of animals;

f) a + b + c + d + e.

46. ​​Irregularity in the distribution of plant species within a plant community and the resulting mosaic pattern is due to a number of reasons. By origin, the following types of mosaics are distinguished:

a) phytogenic, due to competition, changes in the phytoenvironment or characteristics of life forms of plants;

b) edaphotopic associated with the heterogeneity of the edaphotope (roughness of the microrelief, different drainage, heterogeneity of soils, etc.);

in) zoogenic caused by direct or indirect influence of animals (trampling, eating, deposition of excrement);

G) anthropogenic, the reason for which is human economic activity (grazing of farm animals, selective felling of trees in the forest, campfires, etc.)

e) exogenous, due to the action of abiotic environmental factors - the influence of wind, water, etc.

f) a + b + d;

g) All answers are correct.

47. Mosaic in the forest is least pronounced where:

a) the tree layer is formed by one species;

b) the tree layer is formed by species similar in their influence on the environment;

c) different ecobiomorphs (coniferous and softwood tree species) are represented in the tree layer;

d) shrubs are absent and poorly developed;

e) growing conditions for most species are unfavorable;

f) a + c + e;

g) a + b + d + e;

h) All answers are correct.

48. Mosaic is most pronounced:

a) in floodplain meadows;

b) in mixed coniferous-deciduous forests;

c) on raised bogs;

e) in coniferous forests.

49. The causes of phytogenic mosaicity in coniferous-deciduous forests, represented mainly by spruce and linden, can be the following:

a) lower illumination and temperature under spruce than under linden;

b) 2.0 - 2.5 times less precipitation in the form of rain penetrates under the crowns of spruce than under the crowns of deciduous trees;

c) rainwater flowing from the crowns of trees has a more acidic reaction than water flowing under a linden tree;

d) soil with a poorly developed humus horizon and a well-defined podzolic horizon is formed under the spruce;

e) a + b + e;

e). a + b + c + d.

50. Characteristic signs of mosaicity of many types of phytocenosis are:

a) stability in time and space;

b) dynamism;

c) change in time of some microgroups by others;

d) change due to the passage of the life cycle of plants;

e) b + c + d.

51. The English scientist Watt (Watt, 1947) distinguished the following phases of the age variability of plants and, accordingly, the variability of microgroups:

a) pioneer

b) invasive;

c) construction phase;

d) maturity;

e) degeneration;

f) a + c + d + e;

g) a + b + d + e.

52. There are the following types of horizontal addition of phytocenoses (according to A. P. Shennikov):

a) separate;

b) separate-group;

c) closed-group;

d) diffuse;

e) mosaic;

c) a + b + c + e;

g) a + b + c + d + e.

53. Mosaic phytocenosis, with all the diversity of composition and division into fragments, is combined:

a) the dominance of one from the tiers;

b) the absence of the dominance of any tier;

c) small sizes of mosaic elements mutually influencing each other;

d) significant sizes of mosaic elements.

54. In contrast to mosaic characterizing the intracenotic horizontal heterogeneity, complexity is the horizontal heterogeneity of the vegetation cover at the supraphytocenotic level. The complex is formed not from fragments, but from different phytocenoses, which:

a) occupy large areas;

b) are highly dependent on each other;

c) are less dependent on each other;

d) are not connected by a common tier;

e) mosaically alternate in space;

f) a + c + d + e;

g) a + b + d + e.

55. The transition zone between phytocenoses (contact phytocenosis) is called:

a) ecoid;

b) ecoclin;

c) ecotone;

d) ecotope.

56. Ecotone can be:

a) narrow or wide;

b) sharp or absent;

c) diffuse or bordered;

d) mosaic-island;

e) All answers are correct.

57. The absence of a pronounced transitional band between phytocenoses is most often due to:

a) a sharp change in growing conditions (for example, on a steep slope, in a clearly defined depression, etc.);

b) human impact (for example, a meadow clearing in the middle of a forest that arose at a clearing site);

c) environmental impact of dominant species in one of the adjacent phytocenoses (for example, spruce, sphagnum mosses, etc.);

e) a + b + c.

CHAPTER 5

Dynamics of phytocenoses.

1. Under the dynamics of phytocenoses and vegetation in general (syndynamics) is understood:

a) reversible changes in plant communities within a day, year and from year to year;

b) changes in phytocenoses with an increase in the age of edificators;

c) various options for gradual directed changes that can be caused by both internal and external factors and, as a rule, are irreversible;

d) long-term cyclical changes caused, for example, by regularly recurring forest fires;

e) a + b + d;

e) All answers are correct.

2. The main forms of vegetation dynamics are:

a) violations of phytocenoses;

b) succession of phytocenoses;

c) evolution of phytocenoses;

d) a + b + c.

3. There are the following types of variability of phytocenoses:

a) daily;

b) seasonal;

c) multi-year;

d) age;

e) all answers are correct

4. Unlike shifts, the variability of phytocenoses is characterized by the following features:

a) variability of floristic composition;

b) it takes place against the background of an unchanged floristic composition;

c) the observed changes are reversible;

d) irreversibility of changes;

e) the observed changes are non-directional;

f) a + d + e;

g) b + c + e.

5. Daily variability of phytocenoses appears only during the period:

a) vegetation;

b) the beginning of flowering;

c) flowering;

d) formation of seeds and fruits;

e) fruit ripening

6. During the day, such vital functions of plants change as:

a) photosynthesis;

b) intensity of absorption of water and mineral elements;

c) transpiration;

d) excretion of metabolites, which, in turn, leads to fluctuations in the composition of the air within phytocenoses (the content of CO2, specific emissions, etc.);

e) All answers are correct.

7. Seasonal variability of phytocenoses is due to changes during the year:

a) light and temperature regimes;

b) general climate;

c) hydrological regime;

d) phytoclimate;

e) all answers are correct

8. The stages of phenological development of phytocenoses differ from one another:

a) features of the biotope (phytoenvironment);

b) the intensity of growth and reproduction of plants;

c) the degree and methods of influence of some components on others;

d) features of the structure and floristic composition;

e) aspect (appearance) and economic use;

g) all answers are correct

9. Phenological spectra give an idea of:

a) floristic composition of the studied phytocenosis;

b) change in the participation of certain species in phytocenoses during the season or year;

c) composition of life forms;

d) the beginning and end of the growing season, as well as the duration of the growing season;

e) the timing of the onset and duration of individual phases of vegetation;

f) changes in the rhythm of seasonal vegetation depending on the characteristics of the environment in the studied cenoses;

g) All answers are correct.

10. Changes occurring in phytocenoses over years or periods of years, associated with unequal meteorological and hydrological conditions of individual years, are called:

a) succession;

b) transformation;

c) fluctuation;

d) demutation.

11. In accordance with the causes of occurrence, the following types of fluctuations are distinguished:

a) ecotopic, associated with differences in weather, hydro and other conditions of ecotopes from year to year;

b) anthropogenic, due to differences in the form and intensity of human impact on phytocenosis;

in) zoogenic, caused by differences in the effects of herbivorous and burrowing animals;

G) phytocyclic, associated with the peculiarities of the life cycle of certain plant species and (or) with their uneven seed or vegetative reproduction over the years;

e) All answers are correct.

12. Ecotopic fluctuations are the least pronounced:

a) in the forests;

b) in the meadows;

c) in the steppes;

d) in sphagnum bogs.

13. The most significant fluctuation changes are observed in adult individuals of herbaceous plants, which are manifested:

a) in the number and power of shoots;

b) in their vitality;

c) in the ratio of individuals in the generative and vegetative state;

d) a + b + c;

14. According to the degree of severity, fluctuations are divided into several types:

a) hidden;

b) oscillatory (oscillations);

c) cyclic;

d) digression-demutation;

e) all answers are correct

15. Latent fluctuations occur:

a) in monodominant grass cenoses;

b) in phytocenoses formed by species with perennial aboveground organs (woody plants, mosses, lichens);

c) in complex floristically rich multi-tiered forest communities

16. Oscillations are described for:

b) coniferous forests;

c) mixed forests;

17. Examples of oscillation can be:

a) change of dominants in some types of meadows in wet and dry years;

b) seasonal changes in the floristic and ecobiomorphic composition of phytocenoses;

c) fluctuations with alternating year-to-year changes at the level of subdominants;

d) seasonal dynamics of productivity

18. Digression-demutation fluctuations are characterized by:

a) the change of dominants and subdominants in floodplain meadows as a result of a sharp deviation from the average meteorological and hydrological conditions for these biogeocenoses;

b) changes in the ecobiomorphic composition of phytocenoses;

c) a strong violation of phytocenoses with their subsequent demutation - a return and a state close to the original, as soon as the cause that caused the change ceased to operate;

d) seasonal changes in the quantitative ratio of the components of phytocenoses

19. Factors causing digression of phytocenoses can be:

a) severe prolonged drought;

b) prolonged stagnation of water on the soil surface in spring;

c) the formation of a powerful ice crust;

d) severe winter with little snow;

e) mass reproduction of phytophages;

e) All answers are correct.

20. The most significant violations of phytocenoses occur if the adverse effects of meteorological and hydrological conditions, as well as zoocomponents:

a) is especially pronounced during the growing season of plants;

b) lasts no more than two years (seasons), as a result of which there is no strong oppression or mass extinction of dominant species;

c) continues in a row for several years or several seasons, which leads to mass extinction or severe suppression of the main components of phytocenoses;

d) lead to disruption of vegetative reproduction of plants of the lower tiers.

21. The duration of the demutation period is determined by:

a) the intensity of community disturbance;

b) the degree of conservation of plants that dominated before the disturbance;

c) growth conditions during the demutation period;

d) all answers are correct.

22. Examples of digression-demutation fluctuations can be:

a) the replacement of grass stands by creeping grass stands under the influence of spring stagnation of hollow waters, followed by the return of the predominance of grasses;

b) transformation into creeping cenoses with a predominance of various types of cereals;

c) the ability of individuals of many plant species under the influence of drought to go into a dormant state, and after the cessation of the drought - the possibility of a quick return of phytocenoses to their original state;

e) All answers are correct.

23. The practical significance of studying fluctuations in forage phytocenoses (meadow, steppe, etc.), aimed at their effective use and improvement, is determined by the fact that by years:

a) their productivity and the quality of the feed obtained from them fluctuate;

b) the terms and even the possibility or expediency of using fodder lands change;

c) the effectiveness of methods for improving fodder lands is changing

(irrigation, fertilization, overseeding, etc.);

d) all answers are correct.

24. The primary productivity of biogeocenoses is the creation of organic matter:

a) autotrophic organisms (photosynthetic green plants);

b) heterotrophs (bacteria, fungi, animals);

c) all living organisms of the ecosystem

25. When studying biological products, it is necessary to determine the mass:

a) only living plants;

b) only living plants and litter;

c) living plants, litter, dead trunks of trees and shrubs - waste, as well as dead underground organs;

e) All answers are correct.

26. Biomass is:

a) expressed in mass, the amount of living matter per unit area or volume of habitat (g / m 2, kg / ha, g / m 3, etc.);

b) the increase in primary production per unit of space per unit of time (for example, g / m 2 per day);

c) the total mass of individuals of a species, group of species or community of organisms, expressed in units of mass of dry or wet matter, per unit area or volume of habitat (kg / ha, g / m 2, g / m 3)

27. Biomass of living matter in terrestrial ecosystems is represented by:

a) plants, animals, fungi and bacteria in approximately equal proportions;

b) predominantly animals and microorganisms;

c) more than 95% by plants.

28. The highest functional activity, i.e. the rate of increase in biomass per unit of time, is characteristic of:

a) marine phytoplankton;

b) a complex of plants of rivers and lakes;

c) vegetation of meadows, steppes, arable land;

d) woody vegetation.

29. Gross primary production (gross production) is the amount of organic matter:

a) remaining in plants after using part of it for respiration;

b) created by plants in the process of photosynthesis;

c) created by all living organisms that are part of a particular biocenosis.

30. Vegetation production is determined by:

a) temperature conditions and humidity;

b) provision of plants with elements of mineral nutrition;

c) the absence of limiting factors, such as salinity;

d) all answers are correct

31. Succession is called:

a) repeated variability of phytocenoses over years or periods of years;

b) seasonal variability of phytocenoses, due to sharp fluctuations in temperature during the growing season;

c) irreversible and directed, i.e., occurring in a certain direction, a change in the vegetation cover, manifested in the change of some phytocenoses by others

32. The main difference between the evolution of phytocenoses and their succession is:

a) in the course of evolution, the composition and structure of phytocenoses remain practically unchanged (the composition can even be simplified), and as a result of succession, new phytocenoses always arise;

b) in the course of evolution, new phytocenoses are formed, and in the case of succession, phytocenoses do not arise, but combinations of species that already existed in the area are formed;

c) succession is always a “repetition of the past”, and in the course of evolution new, previously absent combinations of plant populations arise.

33. The main differences between succession and fluctuations are:

a) the irreversibility of the changes;

b) continuity of succession;

c) direction of changes;

e) All answers are correct.

34. By origin, two main types of successions are distinguished:

a) permanent;

b) temporary;

c) primary;

d) fluctuation;

e) secondary.

35. Primary successions begin with the emergence of phytocenoses on:

a) rocks;

c) deposits of water streams;

d) cooled lava after a volcanic eruption;

e) glades in the forest;

f) a + c + d;

g) All answers are correct.

36. There are the following processes occurring in the case of primary succession:

a) the formation of a substrate;

b) plant migration, their engraftment and aggregation;

c) interaction of plants;

d) change by plants of the environment;

e) change of phytocenoses;

f) a + b + d + e;

g) All answers are correct.

37. Migration (distribution) of plants is carried out by transferring from one place to another:

a) seeds, spores and other germs;

b) whole plants;

c) vegetative organs of plants;

e) All answers are correct.

38. The survival of plants arising from germs brought from outside is possible if:

a) they find themselves in favorable ecotopic conditions;

b) seedlings develop with the homeostatic composition of consorts;

c) they have the ability to reproduce by seeds;

d) all answers are correct.

39. The period from the initial phases of successions to the achievement of a stable state of phytocenoses varies depending on:

a) climate;

b) initial substrate;

c) opportunities for diasporas to enter;

e) a + b + c.

40. Primary successions proceed faster:

a) warm, humid climates

b) in cold dry climatic regions;

c) on rocky ground;

d) on fine-grained substrates

41. Available data on primary succession rates suggest that (tick the correct answer):

a) in the Alps they pass in 100 years, in Japan - in 700 years, in the Arctic - in more than 7000 years, on poor quartz sand dunes along the coast of Lake Michigan (USA) - in about 5000 years;

b) in the Alps - for 100 years, in the USA (oak forests on the dunes of the coast of Michigan) - for 700 years, in Japan - for 1000 years, in the Arctic - for more than 5000 years;

c) in the Alps - for 100 years, in Japan - for 700 years, in the USA (on the dunes of the coast of Michigan) - for 1000 years, in the Arctic - for more than 5000 years;

42. Secondary successions differ significantly from primary ones in that they begin in conditions of already formed soil, which contains:

a) numerous microorganisms (bacteria, protists, fungi);

b) spores and seeds of plants, their resting underground organs;

c) soil mesofauna;

d) mineral and organic substances;

e) All answers are correct.

43. Secondary successions:

a) occur much faster (about 5-10 times) than the primary ones;

b) pass much more slowly than the primary ones;

c) in terms of the rate of origin, they practically do not differ from the primary ones.

44. For reasons of changes in biogeocenoses, the following types of successions are distinguished:

a) syngenetic (syngenesis);

b) autochthonous;

c) endoecogenetic (autogenous, or endodynamic);

d) exoecogenetic (allogenic, or exodynamic);

g) all answers are correct

45. Syngenesis is a process:

a) settlement by plants of places not yet covered with vegetation;

b) colonization of places by plants after the destruction of pre-existing vegetation;

The term phytocenosis and the name of the science phytocenology derived from it (the science of plant communities, the relationship of plants with each other in conditions of joint growth) was proposed by the Austrian geobotanist Helmut Gama in 1918.

The concept of a phytocenosis, or plant community, is one of the central ones in phytocenology and in.

A plant community is an open biological system that represents an essential part (in material and energetic terms) of a more complex bio-inert system - a biogeocenosis, consisting of plants, mainly autotrophic (phototrophic), which are in complex relationships with each other, with other components and with an environment that, as a result of the vital activity of its autotrophic components, fixes solar energy and - with the participation of other organisms - its transformation and the biological cycle of substances, as well as the fixation of atmospheric nitrogen and has a certain composition and a more or less homogeneous structure within the occupied space.

In other words, a phytocenosis, or plant community, should be called any combination of both higher and lower plants that live on a given homogeneous area of ​​​​the earth's surface, with only their inherent relationships both with each other and with habitat conditions.

Two more specific but very important comments follow from these definitions:

a) combinations of plants existing in nature, in which there are practically no relationships between plants, are not phytocenoses; these combinations are called plant groups (for example, the vegetation of steep rocky walls, the vegetation of high arctic islands, etc.);

b) combinations of plants artificially created by man - forest plantations, crops, etc. - in almost all respects correspond to phytocenoses; in order to separate natural communities from communities created by man, the concept of agrophytocenoses (agrocenoses) was introduced.

Morphological structure of phytocenoses

The morphological structure of any system is determined by the spatial arrangement of individual structural elements.

As a rule, phytocenoses can be subdivided into elementary structures that are fairly well delimited in space (vertically and horizontally), and sometimes in time. They are called price elements.

The main cenoelements of phytocenoses are layers and microgroups. The first characterize the vertical, the second - the horizontal dismemberment of plant communities.

Vertical structure

The layering was first described by the Austrian scientist L. Kerner in 1863. In the spruce forest, he distinguished: tree layer, fern layer and moss layer. Then the Swedish scientist Gult identified 7 tiers in the forests of northern Finland: 1) upper tree, 2) lower tree, 3) undergrowth, 4) upper grass, 5) middle grass, 6) lower grass, 7) ground.

The vertical structure has two polar variants connected by smooth transitions: tiered and vertical continuum. Thus, layering is not an obligatory characteristic, but the difference in height of plants is a widespread phenomenon.

Layering allows coexistence in the community of species of different quality in terms of their ecology, makes the habitat ecologically more capacious, creates a large number of ecological niches, especially in relation to the light regime.

In the series single-tier - two-small-tier - multi-tier - imperfectly tier (vertical-continuous) communities, an increase in floristic richness is observed.

Consistent use of the concept of tiering has a number of theoretical difficulties associated with the fact that:

1) not all communities are vertically discrete;

2) it is not clear whether the tiers are layers or “inserted” elements into each other;

3) it is not clear where to attribute the creepers, epiphytes, undergrowth.

To overcome these difficulties, Yu. P. Byallovich formulated the concept of a biogeocenotic horizon - a vertically isolated and vertically further inseparable structural part of a biogeocenosis. From top to bottom, it is homogeneous in the composition of biogeocenotic components, in their interconnection, the transformations of matter and energy occurring in it, and in the same respects it differs from neighboring, above and below, biogeocenotic horizons.

The vertical parts of plant communities, respectively, form phytocoenotic horizons. Each of them is characterized not only by the composition of autotrophic plant species, but also by a certain composition of the organs of these plants. With this approach to the analysis of the vertical structure, there are no controversial issues, including where to attribute lianas, epiphytes, or undergrowth.

horizontal structure

Most plant communities are characterized by heterogeneity of horizontal composition. This phenomenon is called the mosaic of phytocenoses. Mosaic elements are most often called microgroups, although a number of researchers have proposed their own terms - microphytocenoses, cenoquants, cenocells. The notion of a parcel stands apart. - element of horizontal heterogeneity of biogeocenosis.

The uneven distribution of species is due to a number of reasons. There are types of mosaic according to their origin:

1) Phytogenic mosaicism due to competition, changes in the phytoenvironment or the specifics of plant life forms (the ability to vegetatively reproduce and form clones).

2) Edaphotopic mosaicity associated with the heterogeneity of the edaphotope (roughness of the microrelief, different drainage, heterogeneity of soils and litter, their thickness, humus content, granulometric composition, etc.).

3) Zoogenic mosaicism caused by the influence of animals, both direct and indirect (indirect), - grazing, trampling, deposition of excrement, the activity of digging animals.

4) Anthropogenic mosaicism is associated with human activities - trampling due to recreational load, grazing of farm animals, mowing grass and cutting down forest plant communities, resource harvesting, etc.

5) Exogenous mosaicity due to external abiotic environmental factors - the influence of wind, etc.

Mosaic is a special case of horizontal heterogeneity of vegetation cover. Studying the horizontal heterogeneity of the vegetation of any region, researchers distinguish between two concepts, two circles of phenomena - mosaic and complexity.

In contrast to mosaic characterizing the intracenotic horizontal heterogeneity, complexity is the horizontal heterogeneity of the vegetation cover at the supraphytocenotic level. It manifests itself in the regular alternation of individual phytocenoses or their fragments within the same landscape.

The complexity of the vegetation cover is determined by the micro- or mesorelief, which serves as a kind of redistributor of the load of the main environmental factors and thus differentiates the landscape into habitats with different ecological regimes.

There are complexes and combinations of communities. Complexes are communities that are genetically related to each other, i.e. which are consecutive stages of one successional process.

Sometimes they talk about the synusial structure of plant communities, thus highlighting the special structural elements of the phytocenosis - synusia.

Synusia are structural parts of a plant community, limited in space or time (i.e., occupying a certain ecological niche) and differing from one another in morphological, floristic, ecological and phytocenotic respects.

Well distinguished in broad-leaved forests is the synusia of spring forest ephemeroids, the "pseudo-meadow" synusia in deserts, or the synusia of annuals in some types of vegetation.

Community dynamics. Successions. Mechanisms and causes of successions

Among the most important features of phytocenoses is their temporal variability. In nature, there are 2 classes of phenomena - variability and change.

Variability is characterized by the following features:

a) it takes place against the background of an unchanged floristic composition;

b) the observed changes are reversible;

c) the observed changes are not directed.

Changes, on the contrary, are characterized by:

a) variability of floristic composition;

b) irreversibility of changes;

Quantitative ratios between species

The floristic composition is a very important, but far from exhaustive, characteristic of a plant community. In practice, it is quite realistic (not to mention the theoretical possibility) to meet communities that have the same floristic composition, but nevertheless differ significantly from each other in their appearance (as geobotanists say - in physiognomy), in a number of structural parameters. These differences are associated with differences in the quantitative ratio between species in communities.

Thus, another important indicator is the quantitative ratios between species, to the assessment of which there are several approaches:

a) Number, or "abundance" - the number of conventional counting units (shoots) per unit area of ​​the community. The most widely used quantitative eye scale Dru-de-Uranov:

litter 3 - very plentiful - less than 20 cm between shoots.

litter 2 - plentifully - 20-40 cm.

litter 1 - quite plentiful - 40-100 cm.

sp - scattered - 100-150 cm.

sol - rarely - more than 150 cm.

soc - when the view forms a solid wall, the background.

rr - 2-3 copies per 100 sq. m.

un is the only instance in the playground.

In the meadow steppes, for example, this figure is 4 thousand/sq. m., and in the meadows of Taimyr - 6.5-12 thousand / sq.m.

b) Projective cover.

It is clear that the same number of individuals can play a different role in different communities due to different ages, different sizes, and, therefore, different habitat-forming properties of the species. Differences in numbers also do not reflect differences in the cenotic significance of species. For example, even 20 individuals of common sorrel (Oxalis acetosella) will not play such a role in the plant community as a single individual of Siberian hogweed (Heracleum sibiricum). Therefore, a very important indicator is the projective cover, which reflects the proportion of the area of ​​projections of the organs of individuals of a given plant species relative to the area of ​​the entire community. This indicator is expressed as a percentage. The projective cover can be estimated fairly accurately with tools; expert evaluation can be made visually using, for example, the logarithmic six-point scale of T. A. Rabotnov.

c) Weight ratios provide the most accurate assessment of the role of a particular species in a community or ecosystem. This is a very important indicator that indicates the role of this species in the processes of transformation of matter and energy in this ecosystem.

The first two approaches are based on the above-ground sphere of the community, but one should not forget that a noticeable, sometimes significant part of the plants, and hence the phytomass, is “underground” (below the soil level). Moreover, for different types of communities, for different types of vegetation, the ratio of above- and below-ground phytomass is a fairly constant value and, thus, is an important feature of communities.

d) Volume ratios. In some types of communities, for example, in communities of aquatic ecosystems, volumetric ratios are a fairly informative indicator.

Coenotypes and their relationships in the plant community (differences in the cenotic significance of species)

At the beginning of the 20th century, researchers I. K. Pachosky, V. N. Sukachev and others drew attention to the fact that the role of some species in the plant community practically does not change from year to year, while the role of other species changes significantly over years or periods. years. These groups of species L. G. Ramensky called cenotypes.

“Cenotypes, according to the ideas of L. G. Ramensky, are groups of plant species with a similar change in their cenotic significance depending on the growing conditions or the characteristics of their life cycle.” They identified three groups of coenotypes:

1) violets (siloviki) - plants that are powerful in competitive terms;

2) patients (hardy) - plants that do not have great energy of vitality and growth, but are able to endure harsh environmental conditions;

3) explerents (performing) - weakly competitive plants capable of quickly capturing habitats that are temporarily freed from the influence of competitors.

In 1979, the English ecologist J. Grime singled out three types of plant life strategies, in many respects similar to Ramensky's coenotypes, and also characterized the basic ecological and biological properties and characteristics of plants that allow them to implement these types of strategies in nature.

K - competitors; long-living plants that form a small number of large seeds, in which there are relatively many reserve substances; have low morphological plasticity;

S - stress tolerance; plants with morphological and ecophysiological adaptations for existence in harsh environmental conditions;

g - ruderals; short-lived, non-competitive plants; produce a large number of relatively small seeds; have great morphological plasticity.

Composition and structure of cenopopulations of species

A coenotic population, or cenopopulation, is a set of individuals of the same species in a phytocenosis.

Each coenotic population in a plant community has only its own peculiarities - abundance, sex and age (ontogenetic) composition, productivity, phytomass reserve, etc.

Of particular importance for understanding the history of a population and predicting its development is the age (ontogenetic) composition. Individuals of the species in the community are in different age states. The following age groups (states) are distinguished:

I. viable seeds in the soil, fruits, vegetative primordia and other diaspores;

II. seedlings;

III. juvenile ("youthful") plants;

IV. adult vegetative (virginile) individuals;

V. adult generative individuals;

VI. senile ("senile") individuals.

In accordance with these age states, the following stages of the life cycle are distinguished: latent, virginal, generative and senile periods. Depending on the ratio of individuals at different stages of the life cycle, several main types of populations are distinguished - populations of the normal type, populations of the invasive type and populations of the regressive type. The former, in which plants of all age groups are equally well represented, can exist in a plant community for an indefinitely long time. Invasive populations, represented by individuals of predominantly “young” age stages, are in the phase of introduction into the plant community; populations of the regressive type consist predominantly of senile individuals, and because of this they gradually fall out of the composition of plant communities.

The study of the composition and structure of cenopopulations, among other things, is of great practical importance, making it possible to predict the development of a population, which is important, for example, when addressing issues of protection of rare and endangered plant species, issues of rational use of resource plant populations, issues of effective control of populations of malicious weeds, etc.

Ecobiomorphic composition of the community, or the spectrum of life forms

The concept of "life form" was introduced into scientific use in the 80s of the XIX century by the famous Danish botanist Eugene Warming, professor of botany at the University of Copenhagen, director of the Botanical Garden in Copenhagen, one of the founders of plant ecology.

The life form of a plant, according to Warming, is "... a form in which the vegetative body of a plant (individual) is in harmony with the external environment throughout its life, from cradle to coffin, from seed to death ...".

The appearance of plants (habitus) is determined by the shape and size of their vegetative aboveground and underground organs, which together make up the shoot system and root system. Depending on the conditions, part of the shoots and roots, or even all of them, can be significantly modified.

Warming was the first to draw attention to the adaptability of the vegetative sphere of a plant to environmental conditions. This was also emphasized by the largest domestic researchers I. G. Serebryakov and E. M. Lavrenko. They believed that the life form is a kind of habitus of certain groups of plants that arises in ontogeny as a result of growth and development under certain environmental conditions and historically developed in given soil-climatic and coenotic conditions as an expression of adaptability to these conditions. Life forms, or ecobiomorphs, are typical adaptive organism systems that exist in certain environmental conditions.

The reason for the adaptability of life forms of plants is a different degree of conservatism of vegetative and generative organs. Generative organs as a temporary formation "leave" the mechanisms of natural selection. Only the vegetative sphere falls into this "millstone". The attached way of life, the inability to respond to environmental changes behaviorally, like animals, leads to the need to respond with the “vegetative sphere”.

Among the numerous systems of life forms and approaches to their classification, one of the most popular so far is the classification proposed by the Danish botanist K. Raunkier (1918). He very successfully singled out one extremely important trait from the totality of plant traits, which characterizes the adaptation of plants to the experience of an unfavorable season - cold or dry. This trait is the position of the renewal buds on the plant in relation to the level of the substrate or snow cover (a very logical thesis, since the adaptability of a trait can be assessed through the prosperity of a species, and prosperity is directly dependent on how successfully it is renewed). Based on this feature, Raunkier identified 5 groups of life forms:

phanerophytes - Ph (from Greek phaneros - open), plants with buds exposed to adverse factors (trees and large shrubs);

hamefites - Ch (from the Greek hame - low), plants with relatively low-lying buds of renewal, covered with snow in winter;

hemicryptophytes - NK (from the Greek. hemi - semi), plants with renewal buds located on the soil surface;

cryptophytes - K (from the Greek cryptos - hidden), plants with renewal buds located below the level of the soil surface;

terophytes - Th (from the Greek. Theros - summer), plants that do not have renewal buds, that is, annuals wintering in the form of viable seeds.

Phytocenosis- a plant community characterized by relative homogeneity of the species composition, determined mainly by habitat conditions, and relative isolation from other communities, consisting of cenopopulations connected by relations of differentiation of ecological niches and interference, located in conditions of relatively homogeneous habitat conditions and capable of independent existence.

Forest phytocenosis

Phytocenosis is a conditional concept, since, firstly, a community of some plants cannot really exist without interaction with other components of biogeocenosis - zoocenosis, microbial cenosis, biotope, and secondly, according to the concept of continuum of vegetation cover that is dominant today, any isolation of isolated communities from it are artificial and serve only for the practical purposes of studying vegetation at all levels.

The modern concept of phytocenosis as a conditional, non-existent entity arose on the basis of an individualistic hypothesis developed by the Russian scientist L. G. Ramensky and the American G. Gleason. The essence of this hypothesis is that each species is specific in its relationship to the environment and has an ecological amplitude that does not completely coincide with the amplitudes of other species (that is, each species is distributed "individualistically"). Each community forms species whose ecological amplitudes overlap under given environmental conditions. When any factor or group of factors changes, the abundance of some species gradually decreases and disappears, other species appear and increase in abundance, and in this way the transition from one type of plant communities to another is carried out. Due to the specificity (individuality) of the ecological amplitudes of species, these changes do not occur synchronously, and with a gradual change in the environment, the vegetation also changes gradually. Thus, plant communities do not form distinctly isolated units, but are connected by transitional communities into a continuously varying system.

The main directions in the interpretation of the concept of "phytocenosis structure"

Depending on the specifics of research in the concept of "biocenosis structure" V.V. Mazing (1973) distinguishes three directions developed by him for phytocenoses.

1. Structure as a synonym for composition (species, constitutional). In this sense, they speak of species, population, biomorphological (composition of life forms) and other structures of the cenosis, meaning only one side of the cenosis - the composition in the broad sense. In each case, a qualitative and quantitative analysis of the composition is carried out.

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

3. Structure, as a synonym for sets of connections between elements (functional). The understanding of 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 coenotic level: the species composition, configuration and placement of structural elements in space are a condition for their functioning, i.e. 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 in the system of organization of living matter

Phytocenosis is a part of biocenosis along with zoocenosis and microbiocenosis. The biocenosis, in turn, in combination with the conditions of the abiotic environment (a biotope consisting of an edaphotope and a climatotope) form a biogeocenosis. Phytocenosis is the central, leading element of biogeocenosis, as it transforms the primary ecotope and creates a coenotic habitat for living organisms, and is also the first link in the energy cycle. Soil properties, microclimate, composition of the animal world, such characteristics of biogeocenosis as biomass, bioproductivity, etc. depend on vegetation.

In turn, the elements of the phytocenosis are the coenopopulations of plants - the totality of individuals of the same species within the boundaries of the phytocenosis. Cenopopulations of the same species have different characteristics in different phytocenoses.

Factors of organization of phytocenosis

Factors of plant community organization can be conventionally divided into four groups: environmental characteristics, relationships between plants, influence of heterotrophic components on vegetation, and disturbances. These three groups of factors determine the combination and characteristics of species coenopopulations in a phytocenosis.

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

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

• competitive relations;
• non-competitive environment formation (plants can affect the environment in different ways, through shading, drying, litter thickness, etc., and through it - on the composition and structure of the community). Among plants, edificators stand out, which have a decisive effect on the organization of phytocenosis (for example, an oak in an oak forest);
• allelopathy (plants affect each other with secreted substances);
• positive interactions (a little-studied form of interaction, manifested in the "mutual assistance" of plants);
• the influence of vines and epiphytes (can be manifested in the destruction of the bark, the "suffocation" of the prop plant, the formation of the environment in which the adventitious roots of the prop plant can develop by the products of the vital activity).

The influence on the organization of phytocenoses of heterotrophic components of biogeocenoses is extremely diverse. Influence animals manifests itself in pollination, eating, dispersal of seeds, changes in tree trunks and crowns and related characteristics, loosening of the soil, the appearance of pores, trampling, etc. Mycorrhizal mushrooms improve the supply of plants with mineral nutrients and water, increase resistance to pathogens. bacteria Nitrogen fixers increase the supply of nitrogen to plants. Other bacteria as well viruses may be pathogens.

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

Structural elements of phytocenosis

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 mosaic.

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

The main characteristics of phytocenosis

The main characteristics of a phytocenosis include the species composition of the plants that form it, diversity and abundance, ecological structure, and the spectrum of life forms.

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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 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. 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 the conditions of the habitat, 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).