FUNDAMENTALS OF PHYTOCOENOLOGY AND PLANT GEOGRAPHY - T. P. Larkina - 2017

CHAPTER 1. FUNDAMENTALS OF PHYTOCOENOLOGY

1.3. Biotic Relations in Phytocoenoses

A plant's life within a phytocoenosis depends not only on abiotic conditions, but also on The Nature of its interactions with other co-inhabitants. Depending on the competitive strength of species—that is, a species' ability to secure a particular position within the phytocoenosis—L. G. Ramensky proposed dividing dominant species into: a) violents (from Latin *violentus* — vehement); b) patients (from Latin *patiens* — patient); and c) explerents (from Latin *explere* — to fill/complete). Violents are the most robust species capable of forming communities or persistently invading them. L. G. Ramensky figuratively referred to them as the "lions of the plant world." Typical violents include English oak, as well as weeds such as creeping couch grass and common lady's mantle. Patients are plants that win the Struggle for Existence through sheer endurance (the "camels of the plant world"). These include many dominants inhabiting extreme environments, such as glassworts, succulent species, and others. Explerents are plants that possess very low competitive power in the struggle for existence within a phytocoenosis, yet are capable of rapidly seizing vacant territory, albeit for a short duration. L. G. Ramensky figuratively called them the "jackals of the plant world." Many weeds belong to explerents.

Plants living in proximity influence one another by competing for existence ("a place in the sun," soil moisture, nutrients, etc.), but they may also assist neighbors without harming themselves. Biotic relations in nature can be divided into four groups:

1) relations in which both interacting species derive mutual benefit (++), such as Symbiosis. Symbiotic relationships are widespread in the plant and fungal kingdoms, manifesting as various types of mycorrhiza and the existence of the lichen phylum, which is exceptionally adapted to extreme environmental conditions;

2) relations in which one component benefits while the other provides this benefit without incurring any harm (+0), such as commensalism. Examples of commensalism include plants that settle on the trunks or branches of other plants, causing them no harm while securing a habitat for themselves. This is how orchids and certain ferns live;

3) relations in which one component gains a tangible benefit while the other experiences severe suppression, potentially even leading to its death (+ -), such as parasitism. Parasites in plant communities can include both flowering plants (dodder, toothwort) and an extensive group of Fungi (rusts, smuts, etc.⁾;

4) relations in which both components experience severe suppression (- -), such as competition. Competition in plant communities is the most widespread type of all biotic relations, and it manifests more severely the more similar the vital needs of the plants are.

1.4. Agrophytocoenology

Agrophytocoenology is the science of human-created plant communities—agrophytocoenoses (cultivated phytocoenoses)—their Structure, dynamics, biotic relations among co-inhabitants, and ways to enhance the stability and productivity of valuable crop yields.

Agrophytocoenosis is a human-created and regularly maintained community characterized by relatively low ecological reliability, but high yield (productivity) of one or several plant species (varieties). Because an agrophytocoenosis is formed upon a natural foundation of numerous environmental components (solar energy, Water, soil, soil fauna consumers), it cannot be considered a purely artificial object. Even The Role of weed producers is not always negative in such phytocoenoses, and they occupy their own nature-assigned place within them.

At a certain stage of agricultural development, a branch of geobotany inevitably emerged to focus on the comprehensive study and Selection of Cultivated plants as potential co-inhabitants in artificially created phytocoenoses.

Mixed cropping is widely practiced to ensure the efficient use of arable land and to increase crop yields. Artificial hayfields and pastures are sown with grass mixtures comprising four, five, or more plant species. Forest planting and reforestation work, as well as the creation of parks and recreational zones, also apply the principles of agrophytocoenology.

Agrophytocoenoses are always created with consideration for all environmental factors (climate, soil, slope exposure, etc.) of their intended Location. The selection of species and varieties of future co-inhabitants is equally important. This is preceded by a detailed study of their biology: biometric and phenological features, mutual compatibility, degree of ecological valence, and the like.

While The Study of natural phytocoenoses provided by nature is typically dominated by a descriptive approach, the creation of agrophytocoenoses offers researchers vast opportunities for theoretical and practical scientific inquiry. This involves employing a vast array of Methods from geobotany, plant physiology, soil microbiology, crop production, silviculture, meadow management, etc., all aimed at increasing the quantity and quality of agricultural yields.

1.5. Phytoindication of Plant Lands

Both individual plant species and entire plant communities are closely linked to the full complex of environmental conditions. The composition of a plant community can provide an exhaustive characterization of a habitat—its soil type, moisture levels, groundwater depth, Temperature regime, and more. Plants can serve as indicators (markers) of habitat environmental conditions. Academician V. Komarov wrote: "We must ensure that Changes in the plant cover allow us to judge the soil without error." Another prominent geobotanist, L. G. Ramensky, developed special scales by which the water supply of a habitat can be assessed using the plants inhabiting the phytocoenoses. The water supply scale has 10 steps: desert, desert-steppe, dry-steppe, mid-steppe, humid-steppe, dry and fresh meadow and forest, damp-meadow, marsh-meadow, and riparian.

Phytoindication is widely applied both at the Initial Stages of agricultural land development and on areas already cultivated by humans. Indicational geobotany (indicational phytocoenology) makes it possible to provide an ecological assessment of a habitat using individual plant species or plant communities. Those species, phytocoenoses, or ecological series of communities used as indicators of specific environmental conditions (soil characteristics, moisture, etc.) are called indicators, while the Components of the geographical environment determined by means of these indicators are called indication objects or indicands.

The directions of indication can vary, for example, soil indication (pedoindication), rock indication (lithoindication), indication of the depth and thickness of groundwater strata (hydroindication), and so on.

Indicators are divided into Direct and Indirect. Direct indicators are those directly linked to the indication object (indicand) and thus incapable of existing in nature without it. For instance, halophyte communities are direct indicators of saline soils. Many stenobiotic species and communities (having a very narrow ecological range) also serve as direct indicators. Indirect indicators are those linked to the indication object not directly, but through some intermediate link in the chain of environmental conditions. Thus, the steppe plant *Leymus giganteus*—a pioneer of sandy soils—acts as an indirect indicator of local accumulations of fresh infiltration water beneath the sands; it has no direct connection to this water, but it indicates conditions under which free infiltration of atmospheric precipitation and its accumulation under the sand are possible.

1.6. Succession and Dynamics of Phytocoenoses

Any phytocoenosis is subject to constant change over time because, like any ecosystem, it exists in a state of internal dynamic equilibrium. It is customary to distinguish between diurnal, seasonal, multi-annual, and age-related Variability in phytocoenoses.

Diurnal variability usually depends on physiological causes and is associated with the processes of Photosynthesis, Transpiration, and Plant Mineral Nutrition. It is known that grasses are divided by flowering time into morning, daytime, midday, etc., while many plants bloom exclusively during the day or in the evening.

Seasonal variability in phytocoenoses is determined by the change of seasons, which establishes a seasonal rhythm of vegetative processes. Seasonal variability is most clearly manifested in the shift of aspects (appearance, physiognomy) of phytocoenoses. For example, more than ten aspect shifts can be observed in steppes during a single growing season. In meadow communities, parameters such as vertical layering are highly dynamic.

Year-to-year variability—fluctuation (from Latin fluctuatio, meaning wavering)—depends on many causes. The decisive factors in this process are external, primarily climatic. For example, in wet years, moisture-loving plants will gain a developmental advantage within the same community, whereas drought-resistant plants will thrive in dry years. Abnormal winter freezes can temporarily disrupt the stable equilibrium of forest ecosystems. As a rule, year-to-year shifts do not lead to a fundamental restructuring or the replacement of one phytocoenosis by another.

Age-related variability is particularly pronounced in forest communities. A forest changes as it ages. All the vital processes occurring in a young forest, as well as its outward appearance, sharply distinguish it from an old-growth forest: the understory, shrub layer, herbaceous cover, and moss layer all change. A shift in illumination can, for instance, reduce the Abundance of sun-loving plants and give rise to shade-tolerant species.

Succession (from Latin successio, meaning succession or inheritance). Most phytocoenoses are subject to long-term, unidirectional changes that fundamentally alter all their key parameters (species composition, abundance, layering, etc.). This inevitably results in the replacement of one phytocoenosis by another, a process known as succession.

Successions lead to the formation or restoration of a stable, resilient phytocoenosis, but they can also result in its degradation—disintegration, instability, and even complete destruction. For many phytocoenoses, the expected sequence of stages is known, ranging from the initial phase to the most balanced and stable one. Such a balanced, stable community is called a climax community (from Greek klimax, meaning ladder or step). Successions are inextricably linked to biotic, abiotic, and ever-increasing anthropogenic factors.

1.7. Phytocoenosis and the Environment

The plant and its environment constitute a dialectical unity. When interacting with its environment, a phytocoenosis is capable of creating its own internal microenvironment, known as the phytoclimate. A closer look at phytocoenoses reveals how one forest type differs from another, how a lowland meadow differs from an upland one, and how a raised bog differs from a fen. The relationship between the environment and the phytocoenosis is multifaceted: every ecological factor influences the phytocoenosis, while the phytocoenosis, in turn, can modify environmental factors such as humidity, temperature, illumination, and so forth.

Any phytocoenosis exerts a significant influence on soil and air humidity. This is particularly evident in forest communities, where the humidity of the soil surface beneath the tree canopy is almost always higher than in open areas free of timber stands, whereas deeper in the soil the opposite is true. This is because forest soil surfaces feature A large accumulation of organic debris capable of absorbing and retaining moisture, while the canopies of all forest tiers reduce surface evaporation. Forest tree canopies intercept precipitation. The older and denser the forest, the less atmospheric precipitation reaches the ground. This also depends on the forest type: moisture from conifer needles is retained as droplets, whereas on deciduous trees it flows down freely and rapidly.

Phytocoenoses affect ambient temperature. Forest tree canopies block the sun's rays, meaning the forest always offers coolness during the heat. A dense grassy meadow cover also impedes the penetration of sunlight to the soil surface; consequently, the temperature of unvegetated soil surfaces is always higher.

Illumination intensity within a phytocoenosis is determined by all its structural parameters, with the biological traits of the upper-tier plants being the primary governing factor. Illumination beneath a deciduous canopy is generally lower than under a coniferous one. The impact of a phytocoenosis on light levels also depends on the season. In spring, the lower tiers of deciduous forests receive considerably more light than they do in summer.

Wind speed in flat terrain is always greater in the upper atmospheric layers than near the ground. Forests and artificial windbreaks reduce wind force. Wind energy continuously diminishes as one moves deeper into the forest. In the lower tier of a forest phytocoenosis, wind force and speed are always lower than in the upper tier.

Vegetation, particularly forest cover, regulates the water regime of the area it occupies. This dependence is especially pronounced in mountainous and hilly landscapes. Uncontrolled deforestation on slopes leads to ravine formation and intensifies erosion, thereby harming the surrounding environment and the national economy. Improper use of meadows and pastures, even on gentle slopes, likewise leads to subsequent soil erosion and the destruction of their vegetative cover.

It is well known that soil-forming processes depend on parent rocks, topography, climate, and living organisms—Bacteria, fungi, Algae, Lichens, higher plants, and Representatives of the animal kingdom. The accumulation of organic matter in the soil is a critical factor in pedogenesis. For instance, annual plant litterfall amounts to 400 kilograms per hectare in the tundra, up to ten tons in the steppe, and up to 200 tons in a tropical rainforest. Consequently, soil humus accumulation, chemical and particle-size composition, fertility, moisture retention capacity, and thermal regime will vary accordingly. The prolonged accumulation of organic matter and changing soil properties will inevitably alter not only the core parameters of the phytocoenosis but also impact the entire biogeocoenosis.

1.8. Classification of Phytocoenoses

A vast diversity of phytocoenoses exists in nature; many share a high degree of similarity in composition and the quantitative ratio of co-dwelling organisms, yet they may differ across a range of features.

For example, in pine forests sharing the same dominant species (Scots pine), the shrubs and herbaceous undergrowth may be represented by different species. To classify phytocoenoses in geobotany, specific taxonomic units are established, numbering six in total.

1. The smallest taxonomic unit is the association. All phytocoenoses similar in floristic composition, dominants, subdominants, layering, habitat conditions, and other features belong to the same association. An association is named after its designated dominant and subdominant plants. In Russian naming conventions, for example, the first word (a noun) denotes the genus of the association's dominant species, while the second word (an adjective) is derived from the genus of the subdominant plant—for example, bereznyak snytyevy (goutweed-birch forest). In Latin names, the suffix -etum (without a connecting suffix) is appended to the genus of the dominant, and -osum to that of the subdominant. For instance, an association featuring an oak forest with an undeveloped understory and a herbaceous layer dominated by goutweed is designated as oak-goutweed forest (Quercetum aegopodiosum).

2. Associations are grouped into association groups. Examples include Norway spruce forest with green mosses, and Norway spruce forest mixed with broadleaved tree species.

Academician V. N. Sukachev classifies all Russian spruce forests into the following most typical association groups:

1. Green-moss spruce forests (spruce-hylocomium forests). The first canopy tier is dominated by spruce, with a ground layer of green mosses. The understory is either absent or represented by isolated shrubs. The herb-dwarf shrub layer contains lingonberry, bilberry, wood sorrel (oxalis), one-flower wintergreen (Maianthemum bifolium), and other typical woodland flora. Depending on which species predominates (dominates) in this layer, distinctions are made between oxalis spruce forests (occupying richer, well-drained soils); lingonberry spruce forests (confined to drier, nutrient-poor soils); and bilberry spruce forests (growing on wetter, poorly aerated soils).

2. Long-moss spruce forests. The tree canopy consists of spruce mixed with birch. The ground layer forms a carpet of Polytrichum moss (Hair-cap moss), which serves as an indicator of excessive moisture and poor soil drainage. The herbaceous cover is poorer in both species richness and individual count compared to green-moss spruce forests. The role of spruce as an edificator plant is somewhat suppressed here, and the NEGATIVE IMPACT OF hair-cap moss on its regeneration becomes apparent.

3. Sphagnum spruce forests. These forests are confined to low-lying habitats with poorly drained soils. The accumulation of excess moisture encourages the proliferation of sphagnum mosses. Spruce exerts no significant influence on the environment or companion plants, and its growth is stunted. As the sphagnum expands and peat accumulates, spruce gradually yields ground to pine, often accompanied by birch. Certain typical spruce associates gradually drop out of the herb layer.

4. Bog-herbaceous spruce forests. On relatively fertile, waterlogged soils with flowing water, a tall and lush herbaceous cover develops beneath the spruce canopy. Over time, birch becomes admixed into the tree layer. The understory is well developed. The density of the moss cover varies, but it does not form a dense, dominant carpet.

5. Complex spruce forests. These feature a complex vertical structure. Broadleaved species may occur alongside spruce in the tree stand, sometimes even forming a sub-canopy tier. The understory is well expressed. The herbaceous layer contains numerous broadleaved forest species. Mosses do not form a continuous cover. Complex spruce forests are restricted to rich, well-drained soils, frequently overlying limestone bedrock.

Russian pine forests are likewise structurally heterogeneous. V. N. Sukachev distinguishes 6 association groups for pine forests, 5 of which are analogous to those of spruce.

1. Green-moss pine forests. Soils are nutrient-poor but well drained. The tree canopy is represented by spruce-free pine, occasionally mixed with birch. The understory, if present, is sparse. The ground is carpeted with green mosses. Based on the COMPOSITION OF THE herb-dwarf shrub layer, distinctions are made between lingonberry pine forests on poorer, drier soils (Fig. 8); oxalis pine forests associated with richer soils; and bilberry pine forests on wetter soils (Fig. 9).

2. Long-moss pine forests (Pineta dolichomoso-sphagnosa). Pine forests growing on poorly drained and waterlogged soils. Hair-moss (Polytrichum commune) establishes and spreads in the ground cover, leading to a decline in pine growth.

3. Sphagnum pine forests. Waterlogged forests dominated by sphagnum moss. Pine growth is stunted.

4. Herb-bog pine forests. Soils have a slightly elevated nutrient content and are adequately moist, with no stagnant water. The understory is sparse or absent; the herbaceous layer is dense, and the moss layer does not form a continuous carpet.

5. Mixed (complex) pine forests. On relatively fertile soils, broadleaved species are present alongside pine in the tree canopy; the understory is well-developed. The herbaceous layer exhibits high species diversity, while the moss layer is weakly developed (Fig. 10).

6. Lichen pine forests (Fig. 11). These forests are typically found on nutrient-poor, dry, sandy soils. The tree layer is represented by pine; the understory is either absent or contains occasional shrubs, while the herbaceous cover is sparse, low-growing, and species-poor.

The soil is covered with lichens (Cladonia, Iceland moss Cetraria islandica).

3. Formation — a higher taxonomic unit. It unites groups of associations that share common edifiers (or a single edifier). Consequently, all groups of spruce forest associations formed by Norway spruce, or pine forest associations formed by Scots pine, belong to the same formation.

4. Formations are grouped into formation groups. These include all spruce forests or all pine forests. By a similar principle, all oak forests or all birch forests are classified into the same formation groups.

5. Formation classes — the next higher taxonomic rank, which divides, for example, all forests into: a) coniferous forests; b) deciduous forests. A formation Class comprises formation groups whose edifiers have taxonomically closely related plant species.

6. Vegetation type (the highest taxon) in a broad sense refers to a assemblage of formations that are similar both in structure and habitus, as well as ecologically. It should be noted that there is no universal consensus on the definition of this taxon. The most widespread and straightforward is the concept proposed by M. Brockmann-Jerosch and E. Rübel in the early 20th century. They envisioned the distribution of vegetation types on an "ideal continent" influenced by only two primary ecological factors: temperature and moisture. Based on this concept, they distinguished four main vegetation types: 1) Woody type. Dominated by trees, i.e., the woody or forest vegetation type; 2) Herbaceous type. Dominated by grasses — the herbaceous vegetation type; 3) Desert type. The desert vegetation type; 4) Vagrant (floating) type. This peculiar vegetation type consists of organisms that are not attached to a substrate (such as a waterbody bottom) and either float freely in the water or move freely through the atmosphere above the soil.

In practice, Russian researchers more commonly use A. P. Ilyinsky's Classification, which is based on differences in life forms, physiognomy, and consequently, the taxonomic composition of edifiers, taking into account the geographical location of plant communities. This classification includes a total of 17 vegetation types, of which the most widespread in Russia are the following:

1. Temperate summer-green forests. The trees in these forests shed their foliage not during a hot, dry period (like evergreen savanna forests), but rather during the cold winter season (Fig. 5).

2. Coniferous evergreen forests. They grow in moderately cold and cold climates (Fig. 12).

3. Meadows. This is mesophytic herbaceous vegetation, frequently dominated by grasses (humid and mesophytic graminoids) (Fig. 13).

4. Steppes. Primarily composed of xerophytic grasses (Fig. 7).

5. Wetland and peatland vegetation — formations of hygrophilous bryophytes and flowering plants. These habitats are characterized by excessive moisture (Fig. 14).

6. Tundra. Cold desert vegetation (Fig. 15).

7. Marine and aquatic vegetation, as well as other unattached plant communities lacking a substrate.

Currently, other systems of vegetation classification have been developed for practical economic Applications, such as the classification of forage lands, forest type classifications, and others.