Examples of types of phytocenoses. Phytocenosis and its main characteristics. In meadow communities, the dominant families were Poaceae and Fabacea

In order to understand the diversity of phytocenoses that make up the vegetation cover of a certain region, they are systematized using the classification of subordinate units. Of the classification units, we have to deal with the association (the basic lower taxonomic unit) and the vegetation type (the higher taxon). Other classification units (group of associations, formation, group of formations, class of formations) are used to one degree or another only when constructing a legend for a profile.

There are a large number of definitions of association - short and lengthy. The main thing is that phytocenoses that are similar in species composition, structure and habitat conditions belong to the same association.

Basic methods for isolating (differentiating) associations

In our country, most researchers, when assigning phytocenoses to a certain association, use dominant species (dominants) as the main, main criterion - species that clearly predominate in the phytocenosis over other species, i.e. The same association includes phytocenoses with the same dominants, but which may differ in the composition of species with low abundance.

To get a fairly complete picture of the association, it is necessary to describe and analyze species composition and the structure of several specific similar phytocenoses.

The dominant principle of identifying associations is most accessible and acceptable for short-term reconnaissance studies.

However, in polydominant communities (with a large number of dominant species, for example, in meadow and steppe) it can be very difficult to distinguish dominants. In addition, dominants can change dramatically during the growing season or from year to year, and then the same phytocenosis, depending on when the description is made, can be attributed to completely different associations.

Currently, geobotanists have other more objective and universal methods for identifying associations. The most promising methodological technique is to use as the main criterion for identifying associations - groups of species indicating the ecological community of phytocenoses united in the same association. Only limited time does not usually allow the use of other methods of identifying associations, since they require not only a certain skill, but also time-consuming, labor-intensive processing field descriptions phytocenoses.

Methodology of geobotanical research Compilation of flora

Before starting a comprehensive geobotanical study, a reconnaissance study of the flora is carried out - compiling a list of plants growing in the area according to the main types of biotopes (landscape areas). This is done, on the one hand, in order to obtain a general idea of ​​the vegetation of the area under study, and on the other hand, for educational and training purposes. When conducting “in-line” geobotanical surveys, this stage of geobotanical research can be omitted.

It is better to compile a list of plant species along a pre-planned route, covering diverse and contrasting habitats, typical and atypical for a given area.

It is better to lay out the route using a topographic map, forest management map, or using other information about the landscape structure of the area. In any case, the floristic route must pass through the main structural units of the landscape (“from bottom to top”: the riverbed part of the river, floodplain, terraces, slope of the bedrock bank, bedrock bank of the valley, watershed), as well as various types of plant communities (forests, meadows, swamps, agricultural landscape, populated areas, etc.).

In each biotope, work is carried out in the following order;

1) the field diary indicates the point number;

2) describe the physical features of the habitat and the characteristics of the plant community (position in the relief, surroundings of the point).

3) a list of all plant species growing at a given point is recorded.

If it is impossible to determine plant species in the field, they should be herbarized.

Establishment of trial plots and platforms

Descriptions of phytocenoses are made on sample plots, the sizes of which are different for different communities. However, in any case they should not be less area identification of phytocenosis - the smallest area on which all the main signs of phytocenosis appear.

When exploring forests temperate zone It is customary to lay out trial plots measuring 400 square meters. m (20 x 20 meters), and herbaceous vegetation - 100 sq. m (10 x 10 meters).

It is advisable to lay out the test area in the shape of a square.

If the phytocenosis is small in size, smaller than the detection area, then such areas of vegetation are called association fragments. Such areas are described within natural boundaries, indicating their sizes.

Trial plots should be laid out in the most typical places within the characterized phytocenoses, i.e. It is not recommended to establish a trial plot near the border with another phytocenosis, near roads or other anthropogenic disturbances (quarries, fire sites, peat mining, etc.).

Test plots (or registration plots) should be distinguished from trial plots, which can have different, but always small sizes (from 0.1 - 0.25 to 1 - 4 sq. m). They count seedlings and regrowth of tree species, take into account the absolute number of herbaceous plants, take cuttings to determine the yield of the grass stand, determine the occurrence of plant species, etc.

The number of sample sites may vary depending on the purposes of the study, the specified accuracy of the census, as well as the characteristics of the phytocenosis itself. However, they cannot replace trial plots, i.e. serve only as an addition and clarification to the analysis carried out on trial plots.

Description of phytocenoses

The description of the phytocenosis is carried out in a certain sequence on special forms. Depending on the tasks assigned to the researcher, the description can be made with varying degrees of detail. Most often, one standard form is used to describe both forest and herbaceous phytocenoses (Fig. 1). When characterizing the latter, the columns related to the tree and shrub layers are not filled in.

Before going on descriptions, you should prepare a sufficient number of forms by replicating the insert on pages 10-13 of this manual in the form of an A5 brochure (standard A4 sheet folded in half - 297 x 210 mm).

Filling out the form is one of the important stages of geobotanical research of the territory, and a formal attitude towards this operation sharply reduces the quality of the material or makes it completely unsuitable. Below is a description of those points of the form that require additional explanation or have special methodological significance.

Association name

The name of the association is given according to the dominant species.

The name of forest associations is compiled according to the dominants of each layer, starting with the tree layer. If there are several dominants in a tier, then in the name of the association they are connected by a hyphen and the dominant one is placed in last place.

For example, an association with the dominance of oak in the forest stand and a slightly lower abundance of linden, with the dominance of common hazel in the undergrowth and in the grass cover - hairy sedge and yellow greensedge with a predominance of sedge - can be called: linden-oak hazel-hairy-sedge.

In the names of herbaceous associations with this method of naming, the belonging of the dominants to a certain tier is usually not taken into account. Dominant species are joined by a hyphen in an order that puts the dominant species with the greatest abundance in last place. For example, a meadow association with dominant pike, buttercup and sedge hare with a clear predominance of pike can be called: sedge-buttercup-pike.

If the grass stand is dominated by one grass, for example, meadow bluegrass, there are no sedges, there are few representatives of legumes, and there are no dominant species among forb species, but collectively they play a noticeable role in the phytocenosis, then such a phytocenosis should be classified as a forb-bluegrass association.

Another way of composing the name of an association is to list the dominants of each tier, starting from the top, separated by a dash.

If a layer is formed by several dominants, then they are connected to each other by a plus sign, and in this case the dominant dominant is put in first place: pedunculate oak + common linden - common hazel - hairy sedge + yellow green grass.

When composing the names of polydominant associations, one should still strive to ensure that the names are not too cumbersome. The name of the association should be given after completing the description of the phytocenosis, i.e. after a detailed analysis of the floristic composition and structure of this phytocenosis with the final clarification of the name during the period of office processing of the forms.

tiers

Tiers are the largest structural parts of the vertical structure of a phytocenosis.

When identifying and describing tiers, you should understand the following basic principles:

1 The tiered (vertical) division of phytocenoses is determined by the fact that each phytocenosis is formed by plants of different heights and belonging to different biomorphs (life forms) - trees, shrubs, shrubs, grasses, mosses, etc.

2. The tiers are counted from above, i.e. The tallest plants belong to the first tier.

3 One tier should include all the above-ground parts of the plants included in it, i.e. tiers in a phytocenosis are not located in separate layers or floors one below the other, but are, as it were, nested one within the other.

4. The tiers should be well delimited from each other, and the plants included in them should form fairly closed formations. If this is not the case, then we should talk about tiered lack of expression. For example, in a forest community, individually growing shrubs or small scattered clumps of mosses do not form, respectively, either an undergrowth layer or a moss layer.

5. Each tier occupies a specific ecological niche. In the same tier there are plants that are similar in ecology.

Thanks to the tiered structure, it gets along well in the phytocenosis. a large number of plant species that make the most of their habitat.

There are different principles for interpreting the allocation of tiers.

The simplest, although more formal, approach is to differentiate tiers according to the height of the crowns and leafy parts of plants. With this approach, the same species can be included in different tiers.

In forest phytocenoses, the division of tiers is often carried out according to life forms, when the entire community is divided into woody, shrub, herbaceous-shrub and moss-lichen tiers. You can also distinguish several tiers of woody, shrubby, herbaceous or within woody, shrubby, etc. distinguish sub-tiers (i.e. floors that differ in composition and height within a tier).

However, the layer is not only a morphological concept, but an ecological and phytocenotic one (Sukachev, 1972). According to this understanding of the tier, the same species cannot be included in different tiers. If in a forest trees of the same species have different heights due to youth or their decline, then individuals that are lower in height (compared to the maximum height of trees) are separated into different canopies.

For herbaceous phytocenoses, it is usually difficult to establish a layered structure (especially during a one-time visit), since most of the plants during the growing season are part of different canopies, the height of which changes all the time. In such cases, the actual height distribution of the plants should be taken into account.

For herbaceous plants, the height of the tiers is determined by maximum height the plants included in it, regardless of whether they are represented by vegetative or generative shoots.

When the layering is not clearly expressed and individual tiers are difficult to distinguish, then it is enough to note the upper level of that part of the grass stand, above which the density of the grass stand drops sharply. The latter is especially important in the economic assessment of hayfields and pastures (Yaroshenko, 1969).

Tiers are designated by Roman numerals. The height of trees and shrubs is given in meters, herbaceous plants and shrubs - in centimeters.

Mosaic.

The horizontal structure of a phytocenosis is called mosaic. It characterizes spottiness and variegation of the phytocenosis. The main structural units of mosaic are microphytocenoses and microgroups.

Microphytocenoses are structural units of horizontal division of the entire phytocenosis, including all tiers.

Microgroups are structural units within one tier.

Lists of species

A very important step is to identify the floristic composition of the tiers, i.e. compiling a list of species for each tier. Species composition - main feature phytocenosis, and its identification is the basis of any geobotanical research.

Doubtful species and those plants for which it is impossible to establish species identity in the field should be included in the description form under serial numbers and collected in a herbarium under the corresponding numbers to determine and clarify their names in office conditions. For plants that are difficult to identify and visually difficult to distinguish in the field (such as mosses, lichens or plant seedlings), it is advisable to compile special collections of the most typical and frequently occurring species of these groups in the study area.

Compiling a species list of a tree stand and shrub layer does not cause much difficulty, since trees and shrubs are represented by a small number of species that are easily distinguished and therefore well remembered. Trees and shrubs are ranked in the list according to the degree of their participation; species with greater abundance are given first place (for characteristics of abundance, see below).

Herbaceous plants are usually found in the sample plot in greater numbers compared to trees and shrubs, therefore, for the herbaceous layer, the list is most often compiled in the order in which the species are encountered when walking around it.

In order not to miss species growing in the trial plot, it is advisable to enter plants into the description form in the following way. First, include all species occurring at any point near the boundary of the trial plot. Then, moving along the boundaries of the trial plot, gradually add new species to the list, after which the trial plot is intersected diagonally in order to include plant species that have not yet been included in the list.

This method of compiling a floristic list makes it possible to make it the most complete and save the area from trampling for further characterization of the vegetation (especially when describing a sample plot in a group).

In meadow phytocenoses, you can enter a list by agrobotanical groups, separately highlighting cereals, sedges, legumes, and forbs.

Coenotic groups.

Different species in a phytocenosis play different roles or otherwise have different coenotic significance. This is the basis for the division of plant species into certain groups, the name and number of which vary among different authors.

In the simplest classification, three main groups are distinguished:

Edifiers are species that can steadily dominate and have a significant impact on the formation of the phytoenvironment of a community, i.e. these are the builders of this phytocenosis.

Dominants are dominant species, but characterized by weak environment-forming ability in the phytocenosis.

Assectators are species that are unable to dominate, although collectively their role in the formation of the phytoenvironment in some phytocenoses can be significant.

Abundance

To assess the coenotic role of a species in a phytocenosis, determining its abundance is of great importance, i.e. its quantity in the trial plot. Abundance is determined by various indicators. The most accessible accounting methods are expressed in points; numerical methods of individuals of each species are less commonly used.

When describing forest stands, the composition of the forest stand is determined to assess the role of each tree species in the forest phytocenosis. The composition of a forest stand is usually understood as the degree of participation of each species in the forest stand of a given phytocenosis. The composition of the forest stand is determined by the method of relative accounting, i.e. when assessing the relationship between numbers different breeds; for a forest stand it is expressed as a formula on a 10-point scale. Total number trunks in the trial plot are taken as 10 units (which corresponds to 100%), the participation of each species in mixed plantings is estimated in fractions of 10. Tree species are designated in the formula by the first letters of their name (E - spruce, C - pine, Lp - linden, D - oak, Ol - alder, etc.). The coefficients in front of the name of tree species show their relative participation in the forest stand.

Examples: formula 6E4B means that the forest stand is 60% spruce and 40% birch; formula 10E means that the planting is clean and consists of one tree species - spruce. If the participation of any species in a planting is less than one (i.e. less than 10%), then in the forest stand composition formula the presence of this species is marked with a plus sign. So, for example, the formula 10E+B means that in the forest stand, in addition to spruce, there is a slight admixture of birch. Counting the trunks takes a little time, especially when, to avoid mistakes, each counted tree is numbered with chalk.

The most accurate data for assessing the abundance of tree species can be obtained only by determining the mass or volume of each species, which is most often unacceptable in the conditions of reconnaissance research. However, in some cases it is necessary to resort to an eye assessment of the mass, for example, when in a forest community the number of oak trunks is small, but it has a significant height and large diameter, and the birch is represented by a large number, but thin trunks. If in this case the participation of species is taken into account only by the number of their trunks, then an incorrect idea will be formed about this phytocenosis. The role of edificator and dominant here is played by oak; it predominates in mass and the forest should be called birch-oak, and not oak-birch, despite the predominance of birch trunks.

The abundance of plant species of all other tiers of forest phytocenoses is determined by absolute counting methods, when the number of individuals of a given species is taken into account regardless of the number of individuals of other species. Visual accounting methods are used, since numerical methods are labor-intensive and are usually used in stationary studies.

Visual quantitative assessment of abundance is carried out using various scales, where points indicate different degrees of abundance.

TABLE 1. Abundance assessment scale according to Drude (with additions by A.A. Uranov)

TABLE 2. Drude scale scores

The most widely used for assessing the abundance of herbaceous plants is the Drude scale as interpreted by A.A. Uralov (Table 1). A.A. Uralov, based on the principle that the more individuals of a species are found in an area, the smaller (on average) the distance between them should be, made an attempt to characterize the scores on the Drude scale by the average values ​​of the smallest distances between plants of a given species. Some authors believe that when using scale estimates of abundance, one inevitably has to combine the idea of ​​the number of specimens of each species (assessed by a certain scale point) with the idea of ​​its coverage (Yaroshenko, 1969).

However, abundance and projective cover characterize different properties of phytocenoses, so correlation of the ratios of these categories does not always give correct results. Thus, plants with spreading numerous densely leafy branches with a small abundance will have a significant projective cover, and, on the contrary, small leafy plants, found in large abundance, will be characterized by a small projective cover. For such species, both abundance and projective cover must be reported.

In addition to the listed abundance levels, the im (unicum) stage is sometimes used for species found in a single copy throughout the entire area being described. Sometimes combined abundance estimates are used, for example, sol-sp, sp-cop. Such estimates show that abundance fluctuates between two levels.

Among the methods of indirect absolute accounting of abundance (when not the abundance of a species itself is taken into account, but some of its features expressed quantitatively) for herbaceous plants, the definition of projective cover is very widely used individual species. For more precise definition a scale bar is used. However, this method requires the development of a certain skill in order to obtain fairly accurate results.

Despite fair criticisms regarding the Drude scale (its subjectivity and approximate quantitative assessment), the speed and very little labor involved in its use make this scale convenient for conducting route studies. In addition, replacing abundance (even if determined by eye) only with projective cover for each species is not always justified, since projective cover is a less constant value than abundance.

When characterizing tree layers (tree stands), you should have an idea of ​​the content of the following paragraphs of the description form (see also the methodological manual in this series, “The simplest method of geobotanical description of a forest”).

Crown density

Closeness is the area occupied by the projections of tree crowns without taking into account the gaps inside the crowns. The degree of crown closure is determined by eye in tenths of one or as a percentage. Thus, the degree of crown closure equal to 0.6 means that the crown projection accounts for 0.6, and the gaps account for 0.4 of the entire area.

Tree height

Measured using an eclimeter, altimeter or eye.

trunk diameter

The measurement is made using a measuring fork at a height of 1.3 m from the base of the trunk. In the absence of a measuring fork, the diameter of the trunk is determined according to the circumference. For this purpose, using a soft centimeter tape, measure the circumference of the trunk and divide the resulting value by 3.1 (Pi).

Tree age

Age is determined by counting the growth rings (layers) of wood.

To determine the age of standing trees, there is a special Pressler drill. Unfortunately, it is very difficult to acquire.

Age can also be determined by fresh stumps or felled trees. However, this is not always possible to use.

As a result, determining the age of trees is always fraught with great difficulties. Forest taxation data for the study area can be used.

Bonitet

Bonitet (from the Latin Bonitas - quality factor) is an indicator of the productivity of given habitat conditions. The better the soil and climatic conditions, the more wood the plant produces and the higher its quality. The quality rating is established based on the age and height of the trees, using tables or graphs.

Reforestation

Includes seedlings and undergrowth. Seedlings are usually considered to be one or two year old trees. Foresters conventionally classify all trees up to 10 cm in height as seedlings, and taller trees as undergrowth, but not higher than 1/4 or 1/2 the height of adult trees. Neither seedlings nor undergrowth can be considered independent layers, since this is a young generation of trees; many of them will die in the struggle for existence, and the stronger ones will eventually reach the height of the upper tier of the plantation and take the place of the old tree stand.

The importance of studying seedlings and regrowth is great, since it allows us to judge the degree of provision for natural regeneration, the stability of a given phytocenosis, the possibility of changing tree species, etc.

When characterizing the grass cover, you should pay attention to the following points of the form.

General projective coverage

This is the area occupied by the projections of the above-ground parts of plants, expressed as a percentage.

When determining the projective cover, the observer looks from top to bottom and takes into account the ratio of the projection of the above-ground parts of all plants to the total area on which the projective cover is determined. For a more accurate determination, a Ramensky grid is used, divided into 10 square cells, usually with a side of 1 cm.

True cover (turf)

This is the covering of the soil surface by the bases of plant stems. It is always less than the total projective coverage and, if the latter is the same, it can vary.

Aspect

Aspect is the appearance (physiognomy) of the phytocenosis. The aspect of the community changes repeatedly throughout the growing season and depends on the phenological state of the dominant plant species. This sign of phytocenosis is expressed exclusively by verbal descriptions. The names of the aspects are given according to the color of the aspectual species. Example entry: yellow aspect caused by mass flowering of ranunculus. For open phytocenoses, an aspect can serve as a sign of delimiting one phytocenosis from another.

Phenological state of plants

The plants that make up the herbage of each community are in different developmental phases (phenophases) at the time of description. Comparison of phenological phases of the same plant species in different conditions habitat allows us to draw some conclusions about how favorable these conditions are for a particular plant species, what conditions accelerate or delay its development. To designate phenophases, the following notation system is used.

TABLE 3. Designation system for phenophases according to V.V. Alekhine (with additions)

Nature of plant placement

The following symbols are most often used to indicate the uneven distribution of plants: gr (gregaria) - the plant is found in rare (cloudy) clusters, among which there is an admixture of individuals of other species.

These designations are placed on the form in a special column “Nature of placement” or attached to the abundance icon according to Drude, for example, sp gr, copj cum, etc.

In the last column of the form - “General remarks for the entire phytocenosis” it is advisable to make a conclusion about the phytocenosis being studied, note its specificity, the main features of the species composition and structure. Thus, for derived forest cenoses, it is important to indicate how great the degree of disturbance is and how it manifests itself, and whether there is a tendency to restore the native species. When describing meadow phytocenoses, it should be noted

feeding advantages of grass stand and the influence of human economic activity. When finishing the description of swamp communities, it is necessary to emphasize what type of swamp this phytocenosis belongs to.

Tundra vegetation. The tundra is distributed mainly in the northern hemisphere. It occupies large areas on the northern edge of the continents of Eurasia and North America, and is also found on the Antarctic islands of the southern hemisphere. In the USSR, the area occupied by tundra is 14.7% of the entire territory of the country.

The ecological conditions of the tundra are extremely unique and cause the appearance of a certain adaptability of plants.

In arctic and subarctic climates, a characteristic feature of the tundra is the absence woody vegetation. Of the existing environmental factors, the thermal and chemical characteristics of tundra soils are of greatest importance, explaining the reasons for its treelessness. Many hypotheses have been put forward on the issue of treeless tundras. One of the main reasons should be considered the phenomenon of “physiological dryness”, which is created in supercooled thawed soil when tree roots, due to low temperatures, cannot “use” soil water (B.N. Gorodkov). According to some scientists, the ecological conditions for the germination of tree seeds in the tundra are deteriorating due to climate change (V.B. Sochava).

The flora of the tundra is distinguished by a certain originality. Its species composition is poor and numbers no more than 500 species of higher plants. In the process of adaptation to living conditions in the tundra, certain phytocenoses were formed. A particularly important role in them is played by green mosses and lichens, as well as perennial plants adapted for development in conditions of a short growing season.

The herbaceous vegetation of the tundra is low-growing (5-15 cm), forms many shoots, due to which it often takes a semi-oval shape in the form of “pillows” (for example, semolina, saxifrage plants). Due to the abundance of light in the summer, tundra plants have large and bright flowers (poppy, forget-me-not, gum, etc.).

Also common in the tundra are shrub plants with a characteristic woody stem and dull leathery leaves that have a waxy coating and pubescence (blueberry, cranberry, bearberry, dreadberry, etc.).

Among the shrubs common in the tundra, only dwarf birch and different kinds Iv. These low-growing shrubs have small, pubescent leaves, reclining trunks, often hidden in the moss cover. Among the coniferous shrubs, juniper is found at the southern border of the tundra, and dwarf cedar is found in Eastern Siberia.

Distributed across three continents, the tundras do not remain homogeneous. Within their boundaries, from north to south, one can outline a natural change in certain types of tundra(formations).

Arctic tundra is common on the coast of the North Arctic Ocean. Its vegetation cover is characterized by sparseness (coverage area no more than 60%). Of the shrubs, only the Dread is found here. Herbaceous species are represented by sedge, cotton grass, polar poppy, etc. The moss cover is formed by polytrichous and green mosses. Lichens are characterized by scale forms. Areas not occupied by vegetation are rocky placers, areas complicated by stone polygons and polygons.

Moss-lichen tundra is characterized by a complex vegetation cover. On clay soils, a moss cover of green mosses is developed. The upper tier of this formation includes willows, blueberries, and dreadas; of herbs - sedge, arctic bluegrass.

Lichen associations are common on sandy soils. The following geographical pattern can be outlined in their distribution. In the western Arctic (up to the Yenisei River), in the presence of deep snow cover Resin tundras are widespread (lichen predominates - moss), which provide valuable pastures for reindeer herding. In the eastern part of the Taimyr Peninsula, in conditions of little snow in winter, bushy lichens (Allectoria, Cetraria) are common.

Moss-lichen tundras are characterized by significant swampiness (up to 30%). The swamps are predominantly lowland moss and sedge with a characteristic hilly topography (Fig. 64).

Shrub tundra is a formation that replaces the moss-lichen tundra to the south. In the western sector of the Arctic

shrubs are represented by dwarf birch (erniki). East of the river Lena is dominated by various types of willows and alders. The wide development of shrub plants is characteristic. Very large areas (up to 50%) are occupied by swamps.

In the south, the tundra is limited by forest-tundra. In this subzone there is an alternation of open forest and tundra areas. Thus, in the European and North American forest-tundra, birch and spruce woodlands are common, in the Asian forest - larch. In the forest-tundra, trees are far apart from each other, their height is no more than 6-8 m, have thin curved trunks. The ground cover is dominated by lichens, green mosses and grasses (Fig. 65).

Forest-tundra should be considered as a transition zone to the forest zone. Its border is very tortuous. On flat interfluves, the tundra moves south. On the contrary, along river valleys and mountain slopes of southern exposure, the forest moves north. The sparseness of the forest-tundra tree stand is a consequence of unfavorable climatic conditions associated with low rainfall.

It should be noted that the boundary between tundra and forest does not remain constant and is subject to certain dynamics. Facts such as the overgrowing of the tundra of the Far Northeast and North America with larch forest, the overgrowing of spotted and polygonal areas of the Arctic tundra indicate that the forest boundary tends to shift in a northerly direction.

Taiga vegetation.This type of vegetation is widespread in the area temperate climate northern hemisphere - Eurasia and North America. Within the USSR, taiga occupies more than 11 million hectares. km 2.

Vegetation of the taiga type is mesophilic and is represented by such life forms as coniferous trees, shrubs, grasses, etc. This type of phytocenosis is distinguished by its complex structure and great diversity. Further characteristics coniferous forests will be given using the example of the taiga of the USSR.

Forest classification is carried out taking into account forest-forming species, i.e. those tree species that predominate in the forest. On this basis coniferous forests are divided into dark coniferous(spruce, fir, cedar) and light coniferous(pine, larch).

The distribution of coniferous forests is largely determined by the distribution area of ​​their forest-forming species (see Fig. 62). At the same time, in order to make the characteristics of forests more specific and show all the diversity, they use the concept of types of forest. Forest types are distinguished on the basis of the general physiognomic characteristics of the phytocenosis, its floristic composition and habitat conditions. In taxonomic meaning, the forest type approaches the concept of association.

Let us consider a brief description of the main formations of coniferous forests.

Spruce forests. This formation is most common among dark coniferous forests of the European part of the USSR and Western Siberia. The forest-forming species is spruce. In the USSR, spruce has up to 10 species, of which the most common are common spruce (European part of the USSR) and Siberian spruce (northeast of the European part of the USSR and Western Siberia).

Spruce is one of the shade-tolerant species, therefore spruce forests differ in density and shade. The undergrowth in the spruce forest does not develop widely. In the undergrowth there are shrubs: buckthorn, honeysuckle, juniper. The herbaceous cover is characterized by shrubs (lingonberries and blueberries), ferns, mosses, wood sorrel, wintergreen, etc. Green mosses and bearded lichen are abundant in the spruce forest.

Spruce forests form a large number of associations. Currently, to identify them, as well as determine patterns of distribution, ecological series method, developed by acad. V. N. Sukachev. Ecological series make it possible to identify the sequence of arrangement of plant associations in connection with changes in environmental conditions (Fig. 66).

If we consider the change in types of spruce forest depending on environmental conditions, the following pattern can be outlined. Optimal growing conditions (point ABOUT) corresponds to the association spruce-sorrel forest. With increasing dryness and decreasing soil fertility (a number of A) association is replaced spruce-lingonberry. In conditions of increased dryness it grows spruce-lichen forest. In moist areas with signs of stagnation

waterlogging (number IN) develops spruce-blueberry. A typical spruce forest association is spruce forest, which grows in low areas of excessive moisture. In swampy conditions it is replaced by sphagnum spruce forest- an association where spruce is heavily oppressed, and sphagnum moss forms a continuous cover (the final member of the series IN). Under conditions of flow humidification (row D) an association is formed along the stream valleys marsh-grass spruce forest(stream) with developed undergrowth. The association is also peculiar oak spruce forest, which is confined to the most fertile soils of the forest zone (a number WITH). Spruce usually contains an admixture of broad-leaved species (oak, linden), hazel in the undergrowth, and a cover where oak broad-grass predominates is also developed.

The given spruce forest associations do not exhaust all the diversity. The considered ecological series show how the composition of associations changes with changes in environmental conditions and position in the relief (Fig. 67). Thus, ecological series can be considered as one of the methods for studying plant associations with frequent changes in space.

A certain pattern is emerging in the distribution of dark coniferous forests on the territory of the USSR. Within the European part of the USSR, spruce forests predominate, which occupy wide and flat watersheds. In the West Siberian Lowland, forests of this type gravitate toward river valleys, as areas that are more drained. In southern Siberia they are found in the mountains, where the participation of fir and cedar increases (Tian Shan).

Fir forests are similar in characteristics to spruce forests. Their predominant associations belong to the “greenwashers” group.

Fir forests have a more limited distribution. They avoid both dry and wet places. Mixed fir forests with an admixture of Siberian spruce and cedar are often found (West Siberian Lowland, Ural, Altai, Sayan Mountains, etc.).

Larch forests occupy a large area in the USSR. The distribution area of ​​larch is in Eastern Siberia (north of 48° N), where Dahurian larch is widespread. This species, having a shallow root system, is well adapted to growing in conditions of a sharply continental climate on swampy soils with close permafrost. Siberian larch is common in the mountains of southern Siberia.

A characteristic feature of larch forests is that they form pure stands of trees. Since the density of crowns in the forest is small, the larch forest has a park-like appearance. In the upper tier, larch reaches 30-35 m height. The ground cover is dominated by pine grasses and shrubs (reed grass, lingonberries), and in some places sphagnum mosses. Larch forests have a large supply valuable wood industrial importance, and are also valuable hunting grounds.

Pine forests. This is the most widespread type of coniferous forest in the temperate zone. The main forest-forming species is Scots pine. Other types of pine (Crimean, Pitsunda, etc.) have a very limited range.

Compared to other tree species, pine has a large ecological range. It is most widespread on sandy plains and river terraces. At the same time, it forms peculiar associations in peat bogs. Pine forests penetrate into the forest-steppe zone and are found in the mountains.

Pine forests, like larch forests, often have pure stands of one or two-tier structure. The grass cover in them is poor and is mainly characterized by the predominance of shrubs (heather, blueberries, lingonberries, etc.). In pine forests of dry habitats, a cover of lichens or green mosses is developed (Fig. 68, 1).

The main associations of a pine forest and the patterns of their change can be expressed by a system of ecological series, similar to spruce forests, which include associations of certain environmental conditions (lichen pine forest, green moss pine forest, sphagnum pine forest, etc.).

In terms of the composition of their associations, cedar forests are close to pine forests. Their distribution area is confined to the northeast of the European part of the USSR and Western Siberia. Cedar forests, like pine forests, are found in sphagnum bogs. In the mountains of Siberia there are cedar forests of a mixed type - cedar-larch (Altai, Sayan, etc.).

The geographical patterns of distribution of coniferous (taiga) forests in the northern hemisphere are quite complex. Distributed in the temperate climate zone, coniferous forests vary noticeably in composition both from north to south and from west to east.

Currently, geobotanists divide taiga-type forests into three groups of formations: northern taiga, middle and southern taiga, which are characterized by the predominance of certain forest types. Geographically, they represent wide stripes (subzones), which are clearly visible on the plains (Russian Plain, West Siberian Lowland). Thus, the northern taiga of the European part of the USSR, located south of the forest-tundra, is distinguished by the dominance of species of Siberian origin (spruce, cedar, larch). The predominant forest type here is a green moss spruce forest. The middle taiga is characterized by spruce (spruce-blueberry) and spruce-fir forests; southern taiga - spruce forests with an admixture of broad-leaved species (oak, elm, linden, maple). The northern and middle taiga are very swampy, and sphagnum pine forests are common in the raised bogs.

The taiga in the Asian part of the USSR retains the same division. Its distinctive feature is the large swampiness of forests (up to 50%).

In the northern taiga of the West Siberian Lowland (the southern border coincides with the latitudinal segment of the Ob River), pine, spruce-larch, and pine forests are common. East of the river In the Yenisei region, larch forests predominate in the area of ​​permafrost development.

The middle taiga in Western Siberia is characterized by the dominance of dark coniferous fir-spruce forests (“urmans”) and cedar forests. In Central Siberia and Yakutia they are replaced by larch-pine forests (Dahurian larch).

The southern taiga is characterized by a predominance of pine and birch forests, and in lower areas - spruce-fir (Western Siberia), cedar-fir (Central Siberia) and larch open forests (Transbaikalia). A special variety is represented by swampy larch forests “Mari”, widespread in Central and Eastern Siberia and the southern regions of Transbaikalia. The forests consist of Daurian larch, have an undergrowth of birch (birch) and a continuous sphagnum cover. This type of forest is confined to river valleys, where peat-bog soils are formed.

Coniferous forests Western Europe do not form marked subzones and grow only in the mountains (Alps, Pyrenees, Carpathians, etc.). Besides Scots pine and spruce there are European larch and fir, which form a special forest belt.

Coniferous forests in North America occupy large areas (Labrador, Alaska, the mountains of the Pacific coast, the Atlantic plains). Unlike European coniferous forests of the American type, there is a wide variety of species of pine, spruce, fir, and larch. Specific species are also found in forests, especially on the west coast of the mainland, such as Douglas fir, tsuga, thuja, in the Sierra Nevada mountains - gigantic sequoia(mammoth tree). The named tree species are distinguished by their gigantic height (up to 80-100 m). The main reason for the species richness of the American taiga is the favorable conditions for species migration during the Ice Age.

Summer green deciduous forests. Deciduous forests in temperate latitudes become widespread in marine climates. In Eurasia, these forests are typical of Western Europe, the south of the Russian Plain, the Caucasus and the Carpathians. Further to the east they are replaced by coniferous forests. The habitat of deciduous forests is represented in the Far East of the USSR, in eastern China and in Japanese islands. Deciduous forests are found in Northern and South America(Patagonia).

Deciduous forests are divided into broad-leaved and small-leaved.

The broad-leaved forest-forming species are oak, beech, linden, maple, elm and ash. These forests have a well-developed crown, and the upper layer in them is usually composed of one forest-forming species. Since the forests are shady, the undergrowth and grass cover are poorly expressed. The predominant herbaceous species are ephemeroids, which develop intensively in spring and autumn. Typical formations deciduous forests are the following.

Beech forests greatest distribution have in Western Europe. Near the northern border of their range, they are distributed on the plains, in southern Europe - in the mountains, where they form a forest belt. Within the USSR, beech forests are found in western Ukraine, Moldova, as well as in the Carpathians, Crimea and the Caucasus, where they form a special belt.

The beech forests of Europe are of the same type. The forest-forming species in them is beech. Due to the large shade, undergrowth and summer grasses are usually absent. In the mountains, beech's companions are fir and yew.

Beech forests in North America (eastern USA, Canada) differ from European ones. The forests have a wide variety of species, but are dominated by American beech and sugar maple. Vines made from wild grapes are characteristic.

Oak forests are the more common type of broadleaf forest. In the USSR, oak forests are common in the European part, where they form a subzone of broad-leaved forests. In oak groves, the main forest-forming species is pedunculate oak, to which maple, ash, linden, and elm are mixed. The oak groves are multi-tiered. They contain an undergrowth of hazel and euonymus. The grass cover includes plants - oak forest broad grass (sniffle, lungwort, hoofed grass etc.), the aspect of ephemeroids with subsnow development is also characteristic in spring (see Fig. 68, 1, 2). Compared to beech forests, oak forests have a wider range and are found in other subzones, for example, forest-steppe, where they form gulley forests. The forest-forming species in the oak forests of Western Europe are holm and downy oak, which are combined with evergreen rhododendron and yew (Ireland). In North America, oak forests are common in the continental west bordering the prairies. Unlike European ones, there is a large presence of broad-leaved species: several types of oak, maple, walnut, plane tree, etc. Oak forests are also characterized by lianas.

Small-leaved forests (birch, aspen, alder) Along with conifers and broad-leaved trees, they are especially widespread. By origin these forests are secondary which became widespread after the cutting down of broad-leaved coniferous forests. However, examples of primary birch forests are known in the West Siberian forest-steppe (pegs) and in Kamchatka.

There is also a mixed type of forests - coniferous-broad-leaved, in which small-leaved species occupy a significant place. These forests are mainly distributed on the border of coniferous and broad-leaved forests. Depending on the change in environmental conditions, there is an alternation of different types of coniferous and broad-leaved forests: oak forests are confined to the slopes of the southern exposure of river valleys, and are common on terraces pine forests, on flattened watersheds there are spruce forests. Mixed forests are especially typical for the European part of the USSR, where they form an entire subzone.

Steppe vegetation.Steppes are a herbaceous type of xerophytic vegetation with a closed grass stand, developing in a temperate climate with a lack of summer precipitation. The steppes occupy the largest areas in the USSR, stretching across a wide strip in the European and Asian parts. Steppe areas (Pashto) found within the Danube Lowland. In North America, steppes are called prairies.

Vast expanses of steppes (pampas) in subtropical parts of South America, Africa and Australia.

We will consider the main features of steppe vegetation using the example of the steppes of the USSR. In terms of physiognomic characteristics, steppe vegetation differs sharply from other herbaceous types (for example, meadows, swamps), since it expresses xerophytic features. To withstand summer droughts, plants have developed adaptations such as a waxy coating on the leaves, their pubescence, and in some cases, reduction of the leaf blade. All above-ground vegetative parts of plants have a dull green tint, which creates a certain steppe background.

Steppe vegetation is characterized by the predominance of special floristic groups. Are being widely developed turf grasses, having narrow rolled leaves and turf deep in the soil (feather grass, fescue, tonkonog). Also presented sedge, legumes, forbs, ephemerals.

The most distinctive feature of the steppe is its dynamism. The flora of the steppe consists of plants that do not coincide in their phenological phases. Therefore, the appearance of the steppe and its color background changes in different periods. Thus, in early spring, the appearance of the steppe is determined by the flowering of yellow tulips, blue hyacinths, golden goose onions and white crocuses. The silvery color of steph in May is due to feather grass. June marks the flowering of tumbleweed plants. The golden-green background of the steppe in July is associated with the flowering of feather grass. In August, wormwood and steppe asters begin to bloom.

During the entire flowering period in the steppe, there are up to 12 colorful phases (Streletskaya steppe). The noted change in aspects in the steppe should be considered as the adaptation of vegetation to certain environmental conditions.

V.V. Alekhine divided the steppes of the USSR into types: northern (meadow) steppes and southern steppes located on the border with semi-deserts.

The northern steppes are characterized by the development of colorful forbs. The participation of feather grasses is insignificant (common and angustifolia feather grass). The predominant cereals are loose turf (brome, wild oats, bentgrass, etc.). The maximum species richness was noted when the number of species per 1 m 2 reaches 80, and their number is up to 2000. Steppe phytocenoses have a complex layering.

The southern steppes are distinguished by the predominance of feather grasses, forming the aspect: feather feather grass (fescue) and feather grass “tyrsa”. There are very few forbs in the grass cover. Only the phase of spring ephemeroids (tulips) is clearly expressed and the number of tumbleweed plants is increased. In the southern steppes, the grass cover is very sparse and is generally characterized by low species richness compared to the northern steppes: by 1 m 2 area there are no more than 12 species.

The northern and southern steppes in the European part of the USSR are completely plowed. The remaining virgin areas have been declared nature reserves.

The Siberian steppes have many common features with the European ones. However, in conditions of a peculiar rugged topography (Barabinskaya steppe), they are combined with grass swamps and salt marshes. In the steppes of Western Siberia, feather grasses are prevalent. Near the border of the birch forest-steppe there are forest and swamp species, as well as saltwort plants.

The North American prairies are close in floristic composition to the European steppes. Three types of grasses are dominant in the American prairies: feather grass, wheatgrass and grama (the latter is not found in the European steppes). A feature of the prairies is the distribution of deep-rooting species, whose roots go to a depth of 1.6-2 m. At the same time, cereals are distinguished by their high height (80-120 cm).

The types of steppes in North America are extremely diverse. The tallgrass prairies of the Great Plains are close to the “northern” type steppes. Cereal formations are dominated by grasses such as bearded grass, Indian grass, feather grass, and wheatgrass. In spring there is an abundance of flowering herbs.

In the drier conditions of the Prairie Plateau, short-grass steppes are common, where dense-grass grasses (gram grass, endemic buffalo grass) predominate.

The “Pampas” of South America occupy vast plains in the south and east of the mainland (Argentina, Uruguay). The vegetation has all the features of xerophytes and is characterized by clearly defined changing aspects. The main elements of the steppes are perennial grasses of the genus feather grass, bearded grass, and millet. A variety of herbs.

Desert vegetation. The desert type of vegetation is characterized by a predominance of subshrubs and shrubs. The factors determining the development of deserts are essentially climatic, since they are formed in an arid climate with a high moisture deficit in extratropical and tropical regions of the globe (deserts of the USSR, central Asia, the Sahara, Colorado, South America, Australia, etc.) - Unfavorable in Deserts also have edaphic conditions: the soils are depleted in humus and saline, groundwater is located at great depths. Compared to steppe vegetation, desert vegetation is characterized by a sharp increase in drought-resistant species. In the process of plants adapting to unfavorable climate conditions, a number of life forms. Among them, the plants most adapted to tolerate dryness are xerophytes, having a developed taproot and superficial lateral roots, a rigid stem, and reduced leaves. The most typical representatives are subshrub plants, such as camel thorn, black and white saxaul, etc. (Fig. 69).

The other predominant life form is ephemeroids. These tuberous and bulbous perennial plants finish

growing season for 1-2 months before the onset of the dry period (bluegrass, tulips, onions). At this time, the deserts are covered with a continuous carpet of flowering plants.

A number of desert plants have the ability to accumulate water reserves in the hairs covering the leaves (for example, the kokpek subshrub) or in the tissues of the leaves and stem (plants succulents). The latter are very characteristic of many deserts around the world. Their main representatives are cacti, euphorbia, etc. The amount of water they accumulate can be 96% of their weight. The named life forms form a complex complex with saltwort plants.

According to the nature of environmental conditions and, first of all, according to the precipitation regime, the nature of the substrate, the deserts of the globe can be divided into a number of types: clayey, sandy, rocky, saline. Let us consider their main features using the example of the deserts of the USSR.

The deserts of Central Asia occupy more than 2 million hectares. km 2(10% of the area). By climatic conditions they can be divided into northern and southern.

Northern deserts are formed under conditions of a temperate continental climate with an even distribution of precipitation throughout the year. These are predominantly clay deserts (Ustyurt, Bet-Pak-Dala, etc.).

A common feature of their vegetation cover is the predominance of xerophyte shrubs in combination with saltworts. Depending on the soil, a number of typical phytocenoses are formed. The most common are wormwood deserts (clayey ones), which are characterized by the predominance of various types of wormwood and saltwort. The vegetation cover is monotonous and very sparse (cover does not exceed 40%).

In areas with highly saline soil, saltwort deserts are widespread, represented by a group of associations dominated by the low subshrub Kokpek and the cushion-shaped subshrub Biyurgun.

The named types of deserts do not occupy large areas. In conditions of complex microrelief, depending on the degree of soil salinity, they form complexes. For example, at the bottom of basins and saucer-shaped depressions there is a kokpek desert, on their slopes - a solyanka desert, and in higher areas - wormwood deserts (Fig. 70). This complexity of vegetation cover is reflected in the legends of geobotanical maps.

Climatically, the southern deserts are quite different in temperature regime and pronounced spring-autumn maximum precipitation. This explains their significant difference and the wide variety of types.

Clay deserts of the southern variant are formed on piedmont loess plains (Kopet-Dag, Pamir-Alai, Tien Shan). Their vegetation cover is mesophytic in nature. In spring, a continuous turf of grass forms, which can be compared to a meadow. The most typical plants are bulbous ephemera: sedge, bulbous bluegrass, which form a dense, albeit low (20 cm) turf. Projective coverage reaches 80-100%. In spring, the ephemeral desert is used as pasture. In summer, all ephemerals die off and the soil surface becomes very dry.

Sandy deserts (Karakum, Kyzylkum, Muyunkum, Balkhash sands, etc.) have the greatest diversity of plant associations. There is a wide variety of life forms here, including ephemerals, shrubs and trees.

This is largely explained by the properties of the sands, which create favorable water regime(permeability, poor capillarity, ability to condense moisture). In the sandy desert at a depth of 100-150 cm There is a constant moisture horizon, which in spring is supplemented by a “hanging horizon.” Among the unfavorable environmental factors on sands is their mobility. Plants, as an adaptation for growing on moving sands, form deep-reaching adventitious roots.

The distribution of plant associations depends on the degree of sand fixation. Tall grass dominates on mobile dunes and dune chains Celine(up to 1 m), juzgun, sand acacia- low trees (up to 6 feet) with a characteristic “weeping” shape (Fig. 71).

In areas where ridged and hummocky sands develop, gnarled bushes are widespread white saxaul(up to 2-3 m). Its distinctive feature is the summer shedding of branches. Other shrubs include juzgun and tree-like solyanka. Under the canopy of white saxaul, a grass cover of ephemerals and ephemeroids develops.

Saline deserts are usually confined to river terraces (Amu Darya, Ili, etc. rivers), sea coasts and deep depressions where highly saline soils are developed. They are characterized by a peculiar solyanka (halophytic) vegetation, among which succulent plants predominate. The most typical plants are: sarsazan – semi-shrub with a fleshy stem (sparse thickets of sarsazan occupy large areas on the coast of the Caspian Sea), succulent solyanka(tamarix) - plants whose leaves are covered with a salt crust, and sulfur wormwood.

On slightly saline soils, associations are common black saxaul- leafless tree-like solyanka, reaching a height of 5-9 m. Dense thickets of black saxaul are common in the Balkhash region, in the lower reaches of the Amu Darya, etc. Saxaul is a good fuel, which is slightly inferior in calorific value to some types of coal.

The desert type of vegetation on the globe occupies significant areas. In Eurasia, outside the USSR, there are vast deserts that form under subtropical and tropical climate(Tar, Registan, Rub El-Khali, Syrian, Gobi Desert, Alashan, etc.). These are predominantly mountainous deserts, which are characterized by the development of thorny cushion-shaped shrubs (astragalus), succulents, and wormwood.

Large areas (up to 40%) are occupied by desert in Africa (Sahara, Kalahari, etc.). The vegetation of the Sahara approaches to some extent the deserts of Central Asia. In sandy areas, shrubs (camel thorn, acacia) and grasses (related to seline) are common. Significant areas are also occupied by rocky desert (“gammada”), which is characterized by lichens that form a continuous crust on the stones and rare subshrubs. Deserts South Africa characterized by the dominance of succulents, which are distinguished by an abundance of species: aloe, euphorbia (Karoo desert).

In the sandy Kalahari Desert, cereals predominate, and acacia is the dominant tree species.

The Namib Desert (the Orange River basin) is most distinctive, where special forms of succulents dominate, which look like stones - "plant-stones" A very peculiar endemic relict plant Velvichia(obviously a representative of the Mesozoic flora). The lifespan of Velvichia is more than 100 years. Its woody stem is up to 1.5 in diameter m rises to a height of no more than 20 cm(Fig. 72).

The deserts of North America are unique: along with the indicated types (saltwort, black wormwood, etc.)

spreading creosote bush desert (Colorado plateau, California coast). Mexican highland deserts at altitudes 1000-2250 m above sea level are the center of education cactus flora. This area contains up to 500 species of cacti, Opuntia, agaves, and tree-like yuccas (Fig. 73). Giant cacti in the desert are combined with thorny bushes (mimosa, creosote bush, etc.). The vegetation cover of the Mexican desert is very sparse.

The deserts of South America and Central Australia are saline plains and plateaus, abundant in sand and salt marshes. The plant background in them is formed by halophytic shrubs, succulents and herbs. Specifically Australian are shrub deserts with a predominance acacia and shrubby eucalyptus trees Vast sandy spaces are occupied by the formation of hard and prickly grasses (spinifex), growing on loose sand and stones (Western Australia).

Subtropical shrub-woody vegetation.Moistureny sub rainforests typical for areas of subtropical climate. This type of forest is common in eastern Asia, Central and South America and other areas and is represented by evergreen trees and shrubs. The dominant species in hard-leaved forests are laurel, plane tree, oak, boxwood. Ferns and mosses are abundant, often growing as epiphytes. The forests of Florida, Chile and Patagonia are dominated by evergreen beech.

A variety of this formation are evergreen hard-leaved forests and shrubs, typical for the countries

The Mediterranean, as well as California, southwestern Australia, South Africa (Cape Region), South America (Patagonia). The life forms of hard-leaved forests are very unique. Plants have xerophilic adaptations: hard leaves twig-like stems covered with resinous secretions. The dominant species in Mediterranean forests are stone And cork oak. The forests have an undergrowth of evergreen shrubs, such as myrtle And heather.

IN Southern Europe, North Africa and the countries of Asia Minor, groves of pine pine and Lebanese cedar begin to dominate in evergreen forests.

Hard-leaved forests of the subtropical zone are everywhere combined with thickets of various tall shrubs, which in the Mediterranean are called maquis. The maquis formation is characterized by strawberry tree, myrtle, and tree-like heather. In thickets of low evergreen shrubs called gariga, Shrubby oak, thyme, rosemary, gorse, etc. predominate (southern France). In North Africa and southern Spain, the gariga is represented by a dwarf palm. The hard-leaved eucalyptus forests of southern Australia are very distinctive, with evergreen undergrowth and bush thickets (scrab) of various types of acacias, bushy eucalyptus, etc.

Moist tropical (rain) forests. This type of forest formations becomes widespread in the equatorial climate zone. Forests occupy vast areas in Africa (the Congo and Niger river basins), Central and South America (the Amazon river basin) and southeast Asia. Tropical rainforests stand out among all other forest formations with a wide variety of species. The trees are dominated by tree ferns, different types of ficus palm trees(coconut, oilseed, wine) rubber plants(Hevea brasiliensis).

The structure of tropical forests is the most complex. The number of tiers in them reaches 4-5. Tall trees (up to 60 m and above), with characteristic plank-shaped roots. The shade of the forest is maximum and only 1/150 of the incoming light reaches the soil surface. It should also be noted that there is less diversity in the types of grass cover, where spore-bearing plants predominate: ferns, mosses. Another characteristic feature tropical forests are abundant lianas and epiphytes(Fig. 74). The distribution of such life forms is explained by the large shade of the tropical forest. The most common: palm vines (up to 300 m), vines from the family Philodendron, pepper, vanilla, etc. Epiphytes are herbaceous species from the fern and orchid families, as well as mosses and algae.

A very characteristic formation of tropical rainforests is mangrove vegetation, widespread in the tidal zone of bays and lagoons of the northern and east coast South America, West Africa, Hindustan, etc. Mangrove vegetation consists of thickets of evergreen shrubs. The participation of trees in them is small. In terms of species, this formation is extremely monotonous (rhizophora and some palm species predominate). This is explained by the specific environmental conditions, since the crowns of trees rise out of the water during high tide, and during low tide the trunks, stilted and breathing roots are exposed. This root system is a kind of adaptation for transmitting oxygen during coastal flooding. Mangrove plants also have features characteristic of halophytic plants (Fig. 75).

In the region of the equatorial monsoon climate, a special type of deciduous (winter-green) tropical rainforests develops (Indochina, Hindustan, Sunda Islands). The forests are similar to tropical ones, but during periods of drought the trees shed their leaves. These forests differ in the nature of the tree stand. Included mixed forests Forest-forming species are valuable tree species (sandalwood, rosewood), bamboo, palm trees. There are many flowering shrubs and herbs in the forests. Also characteristic are lianas and epiphytes that lose their foliage during dry periods.

With increasing dryness in the tropical zone, winter-green tropical rainforests are replaced by dry xerophilous forests and thorny bushes. This formation occupies large areas in Africa (Rhodesia, Angola, Somalia),

Argentina, northern Australia. Xerophilous forests are stunted and sparse. They are dominated by leafless trees and shrubs such as acacia, palms, intertwined with vines. The undergrowth is dominated by thorny bushes. The xerophilous forests of Brazil are unique "caatinga" with many specific species: cacti, including tree-like ones, trees from the bombasaceae family, which have swollen barrel-shaped trunks with a diameter of several meters (Fig. 76). The distribution of these formations can be seen on the map of the world's vegetation.

This is a woody-herbaceous type of vegetation that is transitional from tropical forests to deserts tropical zone. Savannas are widespread in southern and central Africa (Niger and Upper Nile river basins), South America (Brazil, Orinoco River basin) and Australia.

In conditions of severe aridity of the tropical climate, evergreen trees in savannas have hard, pubescent leaves that are shed during the dry season. Another feature is the umbrella shape of the crown as an adaptation from strong winds. Trees in the savanna are scattered in small groups. The main representatives are umbrella-shaped acacia And baobab - giant tree reaching a height of up to 25 m and having a diameter of up to 9 m(can reach an age of 5000 years) (Fig. 77). In Australian savannas, trees are dominated by eucalyptus trees, in the savannas of South America, “llanos” are varieties of palm trees. The grass cover of savannas is dominated by tall xerophytic, rigid-stemmed grasses (such as bearded grass).

Swamp vegetation. Swamps develop in different climatic zones - from equatorial to subarctic. They are especially characteristic of the forest zone of temperate climates.

Swamps are characterized by hygrophilic plants growing in conditions of excessive moisture and experiencing the influence of “physiological dryness”. When plants die, peat accumulates.

Modern classification of swamps is based on the identification types(formations) by the following signs: 1) position in the relief, 2) moisture and nutrition conditions, 3) prevailing plant associations.

The most common type is lowland swamps. They form on the bottoms of valleys of streams, ravines, gullies and are characteristic of all natural zones. The moistening of the swamps is associated with the close occurrence of mineralized groundwater. The grass cover of lowland bogs is dominated by green mosses, various sedges and grasses. In older bogs, birch, alder and willows appear. This type of bog is characterized by weak peat (the thickness of the peat layer does not exceed 1-1.5 m).

A variety of grass and hypno-grass swamps are tall-grass swamps with thickets of reeds, reeds, cattails, widespread in floodplains and lake basins in the forest, forest-steppe and steppe subzones of the European part of the USSR, Siberia and the Far East.

Raised bogs have specific features. They form on flat watersheds and occupy vast areas of the forest zone (for example, the West Siberian and Pechora lowlands, Polesie). Moistening of raised bogs is associated exclusively with precipitation and in conditions of flattened terrain

becomes excessively stagnant. The surface of the bog acquires a convex profile due to the uneven growth of peat. The excess of the central part of the swamp over the periphery reaches 3-4 m. During the development of the swamp, a complex microrelief is formed on its surface, represented by a combination of small ridges and depressions (see Fig. 82).

The ecological conditions of the raised bog are very unique. Plants adapt to growing in an environment depleted in mineral nutrition, especially nitrogen compounds. Common in high bogs sphagnum mosses and associated marsh species: cotton grass, wild rosemary, Cassandra, heather, cranberry etc. The peculiarity of their life forms is that they have adventitious roots and a moving growth point. The vegetation of the raised bog (Fig. 78) is also adapted to tolerate “physiological dryness”.

The shrub plants of the raised bog have narrow leathery leaves with a waxy coating and a woody stem. Sedges, cotton grass, etc., having narrow, hard leaves, also acquired a specific appearance. The most common tree species found in raised bogs is pine And birch, less commonly cedar and larch. The trees in the swamp are severely depressed and stunted.

The named plant dominants for raised bogs (trees, shrubs, mosses, etc.) form certain associations, depending on environmental conditions. The following pattern emerges in their distribution: in the central part of the raised bog, pine-sphagnum association, towards the periphery of the flywheel in places where the ridge-hollow complex develops, it is replaced by pine-shrub, on the edge of the swamp

is spreading pine-cotton grass association (the nature of the distribution of associations in the raised bog and their location in plan, see Fig. 79).

Raised bogs have a large practical significance. Their peat layer often reaches a thickness of 6-10 m. Peat is used as a fuel raw material, fertilizer and for the production of a number of chemicals.

Raised bogs are common in North America (mainly in the northeast). Here the swamps are similar in nature to European ones, but larch predominates among the tree species. In South America, sphagnum bogs are found in the Andes and on the island of Tierra del Fuego.

Transitional swamps are mixed in nature and form on terraces or concave slopes of interfluves. The vegetation cover of such bogs combines the features of lowland and raised bogs and is characterized by a predominant distribution sphagnum-cotton grass-sedge associations.

The process of development of wetlands is very complex. The death and accumulation of plant debris in the swamp is essentially related to its water regime, since the growth of the peat layer reduces the influx of groundwater. This, in turn, entails a change in ecology and corresponding marsh associations. The types of swamps mentioned above can be considered as certain stages this development. Lowland sedge-grass bogs of ground moisture are replaced by transitional sphagnum-sedge bogs of mixed nutrition. Raised bogs of exclusively atmospheric nutrition represent the final stage of bog development, at which the tendency for peat to grow in height appears.

The outlined diagram gives the most general idea of ​​the development of swamps. At the same time, the reasons causing waterlogging are extremely diverse. During the development of spruce and pine formations, waterlogging is facilitated by the development of moss cover from cuckoo flax and sphagnum. Forest burnt areas and clearings often become swamped. And finally, swamps arise on the site of lakes and river oxbows, which are populated by wetland vegetation. Let's look at this process in general terms.

Lake waterlogging most often occurs through overgrowth. With gentle banks and a gradual increase in depth, aquatic vegetation is located in the form belts V next sequence: 1) in the deepest places a belt of green algae stands out (at depths above 6 m); 2) a belt of flowering plants immersed in water (hornwort, pondweed); 3) a belt of broad-leaved pondweeds with wide floating leaves and inflorescences on the surface of the water (at a depth of 4- 5 m); 4) belt of water lilies at a depth of 2-3 m(water lily); 5) belt of reeds up to 2 m(reed, reed, horsetail); 6) belt of large sedges at a depth of up to 0.7 m; 7) belt of small sedges (Fig. 80).

Each of the marked belts is not durable and is replaced by the neighboring one - less deep-sea. This is explained by the fact that deposited plant residues contribute to the shallowing of the reservoir. This is how associations consistently shift from the periphery to the center. Its last stage is the transformation of the lake into sedge bog.

Of all the listed marsh associations, the most widespread on the globe are reed swamps with a predominance of high reed thickets (up to 6-10 m). In African tropical swamps along the banks of rivers and lakes there are thickets of papyrus, reeds and reeds; in Indian swamps there are thickets of bamboo.

Meadow vegetation.Meadows are a herbaceous type of mesophilic vegetation that grows in conditions of moderate moisture in various natural zones of the globe (tundra, forest zone, tropical, etc.).

Based on their location, meadows can be divided into floodplain (flood) and watershed (dry) meadows. Floodplain meadows are of greatest interest as a type of plant formation. Their vegetation is formed on fertile soils under the influence of a long-term flood regime and the deposition of loose river sediments.

Floodplain meadows are characterized by a number of floristic features: predominance loose turf cereals(timothy grass, fescue, bluegrass, awnless bromegrass), legumes(clover, alfalfa, mouse peas) and forbs(meadow geranium, meadow cornflower, common cornflower and a number of others). The grassland of the meadows is of high quality and represents valuable hayfields!

On the floodplains of large rivers, which are distinguished by complex microrelief and varying moisture levels, a variety of environmental conditions are created. When crossing the floodplain from the river bed towards the slope, a complex ecological series.

In the elevated riverbed part of the floodplain, composed of sandy alluvium, the driest conditions are created. Here, the sparse grass cover is dominated by long-rhizome grasses (creeping wheatgrass, awnless brome); there are also some steppe species.

The central part of the floodplain is composed of clayey alluvium and has a high groundwater table. Loose turf grasses, legumes and flowering herbs with a closed herbage dominate here.

The character of the meadow changes dramatically in the near-terrace part of the floodplain. This low area of ​​the floodplain at the foot of the slope turns out to be the most moist due to the stagnation of hollow waters and the release of springs. The near-terrace floodplain is often forested. The indigenous type of forest is alder with an undergrowth of black currant.

In wet meadows, turf grasses (for example, pike) and sedges predominate.

In the forest zone there are also dry meadows that form on watersheds. Unlike floodplains, dry lands are of secondary origin, as they arise on the site of cut down or burned forests. Therefore, in their herbage, in addition to purely meadow mesophytes, there are elements of forest herbs and a well-developed moss cover. The productivity of such meadows is low.

In the steppe zone, watershed meadows form in depressions (estuaries, valleys, floods, etc.).

The vegetation of meadows is influenced by the type of vegetation (steppe, desert, etc.) among which it is formed. So, on the floodplain of the river. On the Oka River, which crosses the subzone of broad-leaved forests, there are steppe species; on the floodplain of the river. Teberdy - subalpine species. On the floodplains of the steppe rivers Sal and Manych, saltwort plants, characteristic of semi-deserts, predominate.

Alpine vegetation represents a special type of high-mountain low-grass meadows that are located above the upper border of the forest. Altitude position alpine meadows fluctuates depending on geographical latitude mountains, slope exposure, degree of continental climate. For example, in the Alps and the western Caucasus, alpine meadows are located at altitudes of 2200-3000 m above sea level.

Alpine vegetation is similar to tundra vegetation in a number of ways: the predominance of perennial shrubs, cushion plants, etc. All this is an adaptation of alpine vegetation to the conditions of a short growing season with sharp temperature contrasts during the day. Under conditions of high light intensity, alpine plants acquire a short, squat shape and brightly colored flowers.

Alpine vegetation is divided into two altitudinal zones: the lower - subalpine, the upper - alpine meadows.

Subalpine meadows are most widespread in the mountains of Central Asia and the Caucasus. Their vegetation is distinguished by its extraordinary diversity and brightness. The grass cover is dominated by grasses and flowering herbs (geraniums, scabiosa, bluebells, alpine poppies, forget-me-nots, anemones, asters and many others). This type of herbal phytocenosis is characterized by complex tiers and high species richness. The subalpine meadows of the western Caucasus are characterized by the development tall grass, reaching a height of up to 2 m and more (bellflower, hogweed, elecampane, columbine). There are also thickets of Caucasian rhododendron, juniper, and willow.

Alpine meadows give way to subalpine ones at altitudes above 3000 m. The grass cover of the Tien Shan meadows is dominated by mesophytic plants. Its important element is turf sedges(cobresia) with a very large and bright flower. The size and brightness of the colors of the flowers are a characteristic feature of alpine vegetation. Flowering herbs are similar to the subalpine zone, but in appearance the vegetation of alpine meadows is distinguished by low grass stand. The leaves of herbs are arranged in the form of a rosette, often without a stem (chickweed, forget-me-nots, buttercups, alpine poppies and many others). There are many bulbous plants in the alpine meadow: tulips, hyacinths, mountain lilies etc. The alpine meadows of the Alps are distinguished by the nature of their vegetation by the abundance of species of tundra flora (for example, dryad); there are endemic species, such as edelweiss, primrose.

- Source-

Bogomolov, L.A. General Geography / L.A. Bogomolov [and others]. – M.: Nedra, 1971.- 232 p.

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Development of views on the nature of phytocenosis

At the dawn of the development of geobotany, the idea of ​​a phytocenosis as a really existing discrete unit of vegetation cover took shape, which at that time seemed quite appropriate, since the identification of individual phytocenoses significantly facilitated the task of studying vegetation as a whole. However, at the beginning of the 20th century, a diametrically opposite point of view was expressed, according to which the vegetation cover seemed continuous, and its division into individual elements- phytocenoses - artificial. The absence of sharp boundaries between plant communities and the presence of transition zones between them contributed to the emergence of the doctrine of continuity of vegetation cover, based on individualistic concept:

• Each type of plant is individual in its requirements for conditions. external environment and has characteristic environmental amplitudes for each environmental factor
• Environmental factors change gradually, both in space and time
• The transition from one combination of cenopopulations to another occurs continuously: some species gradually decrease their abundance and disappear, others appear and increase.

Extreme supporters of the concept of continuity of vegetation cover considered not a phytocenosis, due to its artificiality, but an individual plant as an object of study of geobotany. Extreme supporters of the idea of ​​discreteness postulated a clear distinction and delineation of individual phytocenoses.

Based on the synthesis of both concepts, the idea of ​​a combination of both discreteness and continuity in the nature of vegetation was put forward. This was presented as one of the manifestations of inconsistency inherent in the material world as a whole. According to this idea, the vegetation cover has the property of continuity, but it is not absolute, but relative. At the same time, it also has the property of discreteness, but this is not absolute, but relative. These properties are organically combined, not excluding, but complementing each other.

Formation of phytocenosis

Primary free area of ​​the earth's surface after a volcanic eruption

The formation of phytocenoses can be considered both in a dynamic aspect (change of communities) and in terms of their formation on free areas of the earth's surface.

Distinguish primarily vacant areas, which in the past were not populated by plants and do not contain their rudiments. Phytocenoses can form on them only when diaspores are introduced from the outside. Such areas include rocky outcrops, fresh river and sea sediments, the exposed bottom of reservoirs, areas freed from glaciers, lava fields, etc. In general, they occupy insignificant areas on Earth.

Secondary vacant areas are formed in places where vegetation previously existed, but was destroyed due to the influence of some unfavorable factor. Examples include burnt areas, scree, unseeded arable land, areas of phytocenoses eaten away by pests or livestock. In most cases, soil and diasporas are preserved on them, and the formation of phytocenoses occurs much faster than in initially free areas.

The formation of a phytocenosis is a continuous process, but can be conditionally divided into stages:

1. Pioneer group- coenopopulations are small in number, there are no relationships between them
2. Group-thicket community- coenopopulations are distributed in clumps in which interaction between plants occurs
3. Diffuse community- coenopopulations mix, a system of interspecific interactions is developed

1. Migration- introduction of diasporas
2. Ecesis- consolidation of the first settlers
3. Aggregation- formation of groups of offspring around mother plants
4. Invasion- mixing of coenopopulations
5. Competition- development of competitive relations due to a sharp increase in crowd density
6. Stabilization- formation of a sustainable closed community

E.P. Prokopiev, summing up the various division schemes of the process of formation of a phytocenosis, proposes to distinguish three stages in it:

1. Receipt of primordia into a free area. The species composition of the emerging phytocenosis will depend on the species composition of plants in the surrounding area and the nature of the distribution of their diaspores, and the main role will be played by the rudiments of allochoric species, mainly anemochores.
2. Ecotopic (abiotic) selection. Not all diasporas that land on a free plot will take root on it: some will not germinate, and some of those that have sprouted will die in their young state due to an unfavorable combination of abiotic factors. Established plants will be pioneers for this territory.
3. Phytocenotic selection. Due to the reproduction and settlement of pioneer species throughout the site, they will begin to influence each other and change the ecotope, forming a biotope (habitat). The primary abiotic environment of the ecotope turns into a secondary biotic - phytoenvironment. Under the influence of the phytoenvironment and the mutual influence of plants, some pioneer species that are not adapted to it fall out. This may occur, for example, due to shading or allelopathy. At the same time, new species, already adapted to the given phytoenvironment, are established on the site.

Factors of phytocenosis organization

Factors in the organization of a plant community can be divided into four groups: characteristics of the environment (ecotope), the relationship between plants, the influence of heterotrophic components (animals, fungi, bacteria) on vegetation and disturbances. These groups of factors determine the combination and characteristics of cenopopulations of species in a phytocenosis.

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

• climatic (light, heat, water regimes, etc.)
• edaphic (particle-size and chemical composition, humidity, porosity, water regime and other properties of soils and soils)
• topographic (relief characteristics)

Plant relationships are divided into contact And mediated : transabiotic- through abiotic environmental factors and transbiotic- through third organisms.

Violations, both anthropogenic and natural origin can completely transform the phytocenosis. This occurs during fires, felling, livestock grazing, recreational load, etc. In these cases, derivative phytocenoses are formed, which gradually change towards the restoration of the original one if the impact of the disturbing agent has ceased. If the impact is long-term (for example, during recreation), communities are formed that are adapted to existence at a given level of stress. Human activity has led to the formation of phytocenoses that did not previously exist in nature (for example, communities on toxic industrial waste dumps).

Interactions of organisms in phytocenoses

The presence of a system of relationships between plants is one of the main signs of the existing phytocenosis. Studying them, due to the large overlap and strong influence of abiotic factors, is a difficult task and can be implemented either in the form of an experiment, during which the relationships of two specific species are studied, or by isolating such relationships from a complex of others using methods of mathematical analysis.

Direct (contact) mutual influences

In ecological terms, the relationship between epiphytes and phorophytes is usually represented by commensalism, but elements of competition may also appear:

• epiphytes partially intercept light and moisture from phorophytes
• by retaining moisture, they contribute to the decay of the phorophyte
• By shading the phorophyte, epiphytes reduce its effective photosynthetic surface
• growing profusely, can cause deformation or breakage of phorophytes

Transabiotic interactions

The influence of plants on each other, mediated by abiotic environmental factors. They arise due to the overlap of phytogenic fields of neighboring plants. Divided into competition And allelopathy.

Competition develops either due to the initial limitation of habitat resources, or as a result of a decrease in their share per plant due to overpopulation. Competition leads to a decrease in resource consumption by the plant and, as a consequence, a decrease in the rate of growth and storage of substances, and this, in turn, leads to a decrease in the quantity and quality of diaspores. Distinguish inside- And interspecific competition.

Intraspecific competition affects fertility and mortality rates in a coenopopulation, determining the tendency to maintain its numbers at a certain level, when both values ​​balance each other. This number is called maximum density and depends on the amount of habitat resources. Intraspecific competition is asymmetrical - it affects different individuals differently. The total phytomass of the cenopopulation remains constant in a fairly large range of density values, while the average mass of one plant begins to steadily decrease when thickened - law of constant harvest(C=dw, where C is the yield, d is the coenopopulation density and w is the average weight of one plant).

Interspecific competition is also widespread in nature, since the vast majority of phytocenoses (except for some agrocenoses) are multispecies. The multi-species composition is ensured by the fact that each species has an ecological niche characteristic only of it, which it occupies in the community. Moreover, the niche that a species could occupy in the absence of interspecific competition is fundamental, tapers to size implemented. In a phytocenosis, differentiation of ecological niches occurs due to:

• different plant heights
• different depths of penetration of the root system
• contagious distribution of individuals in the population (in separate groups/spots)
• different periods of growing season, flowering and fruiting
• unequal efficiency of plants' use of habitat resources

With weak overlap of ecological niches, coexistence of two cenopopulations can be observed, while with strong overlap, the more competitive species displaces the less competitive species from the habitat. The coexistence of two highly competitive species is also possible due to the dynamism of the environment, when one species or another gains a temporary advantage.

Allelopathy- the influence of plants on each other and on other organisms through the release of active metabolites into the environment both during the life of the plant and during the decomposition of its remains. Allelopathic activity of one type or another is determined by a certain set of chemical substances of different nature, the qualitative and quantitative composition of which significantly depends on external conditions. Allelopathically active substances are secreted both by above-ground organs (mainly leaves) and underground, mainly in three ways:

• active secretion through glands or hydathodes
• washout by precipitation
• excretion through decomposition of litter by microorganisms

The sum of secretions of various plants in a phytocenosis is its biochemical environment. Since the composition of secretions is not constant, we can talk about the existence of an allelopathic regime of phytocenosis, along with water, air, etc.

Transbiotic interactions

Influence of phytocenosis on the environment

Structure of phytocenosis

Depending on the specifics of the research in the concept of “biocenosis structure”, V.V. Masing identifies three directions that he developed for phytocenoses.

1. Structure, as a synonym for composition (specific, 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 high-quality and quantitative analysis composition.

2. Structure, as a synonym for structure (spatial, or morphostructure). In any phytocenosis, plants are characterized by a certain affinity to ecological niches and occupy a certain space. This also applies to other components of the biogeocenosis. Between the parts of the spatial division (tiers, sinusia, microgroupings, etc.) you can quite easily and accurately draw boundaries, you can plot them on the plan, calculate the area, and then, for example, calculate resources useful plants or animal feed resources. Only on the basis of data on the morphostructure can one objectively determine the points at which certain experiments were performed. When describing and diagnosing communities, the spatial heterogeneity of cenoses is always studied.

3. Structure, as a synonym for sets of connections between elements (functional). The basis for understanding structure in this sense is the study of relationships between species, primarily the study of direct connections - the biotic connex. This is the study of chains and nutrition cycles that ensure the circulation of substances and reveal the mechanism of trophic (between animals and plants) or topical (between plants - competition for nutrients in the soil, for light in the above-ground sphere, mutual assistance).

All three aspects of the structure 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, that is, life activity and production plant mass, and the latter, in turn, largely determines the morphology of cenoses. And all of these aspects reflect the environmental conditions in which the biogeocenosis is formed.

The phytocenosis consists of a number of structural elements. There are horizontal and vertical structure of phytocenosis. The vertical structure is represented by tiers, distinguished 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, understory layer, etc. The number of layers may vary. The evolution of phytocenoses is moving in the direction of increasing the number of tiers, as this leads to a weakening of competition between species. Therefore, in the older temperate forests 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, somewhat different from the environment in the inter-canopy space), terrain heterogeneities (which cause changes in groundwater levels, different exposures), and the species characteristics of some plants (reproducing vegetatively and forming monospecies “spots” , changes in the environment of one species and the response of other species to this, allelopathic effects on surrounding plants), animal activities (for example, the formation of patches of ruderal vegetation on rodents).

Naturally repeating spots (mosaics) in a phytocenosis, differing in the composition of species or their quantitative ratio, are called microgroups, and such a phytocenosis is mosaic.

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

Dynamics of phytocenoses

dynamic processes: reversible (daily, seasonal, fluctuations) and irreversible (succession, evolution of communities, disturbances of communities). Fluctuations are year-to-year changes associated with unequal conditions for the existence of plants in different years. the composition does not change, the size and age composition of the population may change. Succession is a gradual change in phytocenoses that is irreversible and directional. caused by internal or external reasons in relation to phytocenoses, reasons. primary and secondary successions are distinguished. Primary successions begin on lifeless substrates, while secondary successions begin on substrates on which the vegetation has been disturbed.

Classification of phytocenoses

When classifying phytocenoses, similar communities are combined into groups - classification units.

The lowest unit of classification is association (a set of homogeneous phytocenoses that have more or less the same appearance, similar floristic composition and the same dominant species across tiers). The names of the associations are given by listing the Russian names of the dominant plants of each tier of the phytocenosis, starting from the uppermost tier (Scots pine + Norway spruce - lingonberry + blueberry - pleurocium moss) or the Latin generic and species names of the dominants (Pinus sylvestris + Picea abies - Vaccinium vitis-idaea + Vaccinium myrtillus - Pleurozium schreberi) with the addition of suffixes to the base

In forest phytocenoses, all the features of plant communities are most clearly expressed, which is probably due to the very long history of their evolutionary formation. This allows us, based even on the consideration of one example, to say what a phytocenosis is.

Phytocenosis(from the gr. phyton - plant and koinos - general) - a stable system of autotrophic and heterotrophic organisms (biota) co-existing on a certain area of ​​the earth's surface and the phytocenotic environment created by them and their predecessors (including soil and phytoclimate), a system characterized by a specific structure and complex relationships of components (cenobionts) both among themselves and and with the phytocenotic environment, which is productive and participates in the circulation of substances.

This definition excludes the possibility of classifying various unstable temporary systems or forms of coexistence of organisms as phytocenoses, which, as a rule, are only the initial (procenoses) or intermediate (ancenoses) stages of the formation of stable communities. Such unstable forms are the vast majority of cultural cenoses created by man, the existence of which is supported by man himself (agrocenoses) and which, when his tutelage ceases, embark on a long path of restoration of phytocenoses. For the same reason, so-called heterotrophic phytocenoses cannot be classified as phytocenoses (biocenoses) (Rabotnov, 1976). If these important divisions are not made, then the vegetation cover may appear to the geobotanist as something completely chaotic, difficult to delimit and map. S.I. Korzhinsky had this point of view (1888, see also section 1.1), as G.F. Morozov (1904) wrote that “only a set of sustainable plantings can and should be called a forest.”

The presence of a phytoenvironment in phytocenoses (Reverdatto, 1935; Bykov, 1953), or, better said, a phytocenotic environment (Lavrenko, 1959), is recognized by most geobotanists (social - according to Pachosky, 1921; biologically modified - according to Sukachev, 1928; endogenous - according to Gounot, 1956; internal - according to Yaroshenko, 1961), however, as a rule, it does not appear in definitions of phytocenosis. If we add to this that autotrophic, like many heterotrophic components in phytocenoses, for example fungi, draw all nutrients, including carbon and oxygen, from the resources of the internal environment of communities, that many relationships of coenobionts with each other occur through this environment, and this environment itself not only inseparable from the phytocenosis, but also quickly degrades or even disappears after its destruction, it will become clear that the phytocenosis cannot be considered only a collection of organisms.

Life exists on different conditions of its organization - cell, organism, population, species and biocenosis, each of them has its own characteristics. One of the features of the last level of life - biocenosis - is its biocenotic environment.

For geobotanists, all this is quite clear; it is not without reason that many of them, while studying the vegetation cover, simultaneously study the soils underneath it or do this in collaboration with soil scientists. Without such a study, many features of phytocenoses, in particular environmental ones, are especially difficult to understand and explain.

When considering and defining phytocenosis, we include in it not only autotrophic, but also heterotrophic organisms, and not only heterotrophic plants, but also animals. Of course, a geobotanist is not a zoologist, but without taking into account the activities of a number of animals, especially phytophages, it is impossible to understand many aspects of the autoregulation of communities and their stability. And almost no serious geobotanist ignores pests of forests, meadows and pastures. Some geobotanists (Gams, 1918; Du-Rietz, 1930, 1965) in this regard prefer to use the term “biocenosis” rather than “phytocenosis.”

The share of participation of the animal population in phytocenoses usually does not exceed 0.1% by biomass. Comprehensive studies of phytocenoses (stationary) usually take place under the auspices of geobotanists. In all this lies the depth and attractiveness of geobotanical research.

Having accepted phytocenoses as terrestrial biocenoses, we, of course, will focus on their floristic composition and phytocenotic environment, and only in necessary cases will we turn to the biota as a whole.

Geobotany

Topic 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 cultivated plants). Phytocenology is one of the biological sciences that studies living matter at the coenotic level, i.e. at the level of communities of organisms (slide 4-5).

The task of phytocenology includes the study of plant communities from different points of view (composition and structure of communities, their dynamics, productivity, changes under the influence of human activity, relationships with the environment, etc.). Great importance is also given to the classification of phytocenoses. Classification is a necessary basis for studying vegetation cover and for compiling maps of vegetation in various territories. The study of phytocenoses is usually carried out by their detailed description using a specially developed technique. At the same time, quantitative methods are widely used to take into account various characteristics of the phytocenosis (for example, the share of participation of individual plant species in the community).

Phytocenology is not only a descriptive science; it also uses experimental methods. The object of the experiment is plant communities. By influencing the phytocenosis in a certain way (for example, applying fertilizers to a meadow), the response of vegetation to this influence is revealed. The relationships between individual plant species in a phytocenosis, etc. are also studied experimentally.

Phytocenology is of great economic importance. Data from this science are necessary for the rational use of natural vegetation (forests, meadows, pastures, etc.) and for planning economic activities in agriculture and forestry. Phytocenology is directly related to land management, nature conservation, reclamation work, etc. Phytocenological 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 ( USA).

Phytocenosis and its features

According to the generally accepted definition of V.N. Sukacheva, phytocenosis (or plant community) should be called any collection 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 occurs only when they are more or less close, touching their aboveground or underground organs. A collection of individual plants that do not influence each other cannot be called a phytocenosis.

The forms of influence of some plants on others are varied. However, not all of these forms have the same importance in the life of plant communities. In most cases, the leading role is played by transabiotic relationships, primarily shading and root competition for moisture and nutrients in the soil. Competition for nitrogenous nutrients, of which many soils contain little, is often particularly intense.

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 a forest are very different in appearance from single trees that grow 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 herbaceous phytocenoses, for example in meadows. Here the plants are smaller in size than when growing alone, they bloom and bear fruit less profusely, and some do not bloom at all. In phytocenoses of any type, plants interact with each other and this affects their appearance and vital condition.

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 sets 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 a collection of plants that creates its own special environment (phytoenvironment) can be called a phytocenosis. Every phytocenosis, to one degree or another, transforms the environment in which it develops. The phytoenvironment differs significantly from the ecological conditions in an open space devoid of plants (light, temperature, humidity, etc. change).