Olga Morozova

Vegetation is the totality of vegetation communities and also accompanying groups of plants occurring in the various regions of the Earth. In contrast to flora, vegetation is characterized not only by the species composition, but by the abundance and the combination of species and of various life forms of plants, and by their spatial structure and dynamics. Vegetation is a most important component of the biosphere that is closely related with climate, hydrology, soils, relief, and animal life.

The zonal pattern of vegetation distribution is greatly predetermined by climate. Vegetation zonality, for example, in the great plains of Russia such as the Russian Plain and the West-Siberian Lowland is reflected in the change in the great ecological and physiognomic categories of vegetation. Zonality is most evident in the plains. In the mountains, zonality appears as the altitudinal belts. Terrestrial vegetation is represented by several types, which characterize the great biomes.

High-latitude islands of the Arctic are situated in the polar desert zone. Vegetation there is composed mainly of soil algae, liverworts, and mosses. The coastal part of the Kola Peninsula, the northern part of the Russian Plain, the Yamal Peninsula, the Taimyr Peninsula, the Northern Yakutiya and the Chukotka Peninsula are occupied with tundra vegetation. This type is also well developed above the forest belt in the Khibiny Mountains, in the Ural, and in the mountains of Northeastern Russia. Poly-dominant communities are formed in the tundra by vegetation groups, with dwarf shrubs, sedge grasses, lichens, and mosses dominating.

Boreal vegetation occupies a considerable part of Russia. Dark coniferous forests composed of spruce (Picea abies, P. obovata), fir (Abies sibirica), and Siberian pine (Pinus sibirica) are typical in the western taiga zone, which is affected by the humid Atlantic air mass. In East Siberia, where climate continentality is greater, they become the light coniferous forests (larch or Larix sp.). North of the boreal zone of Russia, open woodlands occur: in European Russia, birch (Betula tortuosa), spruce, and pine; in Siberia, larch and spruce; and in East Russia, larch open woodlands. Great areas, especially in West Siberia, are occupied by flat frost mound oligotrophic bogs.

To the south, open woodlands give way to the northern taiga. Communities of spruce and pine compose the European part of this zone. Communities situated in West Siberia are composed mainly of spruce and Siberian pine. Siberian larch dominates in the eastern part of the zone. Communities of the middle taiga in European Russia are represented mainly by spruce and spruce/pine forests; in West Siberia, spruce/Siberian pine forests dominate, in some places with fir admixture; in Central and East Siberia, spruce/larch and larch forests prevail. A considerable part of the Ob'-Irtysh interfluve area is occupied by secondary aspen/birch forests. Communities of the southern taiga are composed of spruce. Watersheds are covered with pine-sphagnum, oligotrophic sphagnum, and mesotrophic/eutrophic bogs. Larch and Siberian pine larch forests are typical for the mountains situated in a continental area of Siberia.

The southern taiga zone is represented by mixed broad-leaved/coniferous forests, which are distinguished by the rich floristic composition and complicated structure of tree layers. Forests occupying a western part of the zone, i.e., the marshy woodlands, are represented mainly by pine/broad-leaved communities. In West Siberia, southern taiga gives way to birch hemiboreal forests with rich grass cover.

Broad-leaved forests (nemoral vegetation type) are represented in European Russia and in the Far East. Their small patches, composed mainly of lime tree, occur in the mountains of South Siberia (Altay, Kuzteskiy Alatau). Mountain forests in the Altay Mountains and in West Syan, which are composed of firs, tall grasses, and nemoral species but lack taiga shrubs and mosses, belong to this type. Oak, lime, and hornbeam (in the western areas) are the major species that found the communities of broad-leaved forests in European Russia. Oak forests are abundant along the valleys of the rivers and ravines in the northern steppe zone.

Meadow steppes and steppe meadows are typical for the northern steppe zone in European Russia and in West Siberia. Droughty bunchgrass communities represent true steppes. They stretch to the east of the Southern Ural and further to the southern Zaural'iye (areas located southward from the Ural Mountains). Dry "true" steppes are located in the mountain basins in Central Siberia (Minusinskaya, Eniseisko-Chulymskaya etc.), Transbaikalia, Tuva, Southern Altay, and in the Prikhankayskaya Plain. Deserted steppes appear in Kazakhstan, Tuva, south-eastern Altay, and in European Russia, where they occupy comparatively small areas on the Yergueni Upland.

The Caspian Lowland is occupied by desert communities (psammophyte and halophyte deserts of wormwoods, dwarf shrubs, and shrubs) and also by littoral vegetation (pioneer communities of coastal halophytes).

The high-mountain vegetation type presented by the alpine communities occurs in the Karpaty, the Caucasus, the Ural, and South Siberia.

Human activity has greatly affected the formation and development of vegetation over the last five to seven years in Russia. This fact is taken into account, when mapping current vegetation. Spontaneous vegetation consists of communities formed without human impact (some tundra, forest, and steppe communities). Serial vegetation is reflected the stages of natural succession. Anthropogenic vegetation includes secondary meadows and synanthropic vegetation.

Vegetation zones and belts

A vegetation zone is a lateral change of vegetation that follows the alteration of the climate hydrothermal regime. Vegetation zones naturally change from north to south and with the distance from the ocean.

The plains of European Russia, West Siberia, and Central Siberia illustrate vegetation zones. Russia presents the whole spectrum of vegetation zones, including polar deserts; Arctic and sub-Arctic tundra; forest-tundra; northern, middle, and southern taiga; coniferous and broad-leaved forests; broad-leaved forests; meadow; true and dry steppes; semi-deserts; and deserts.

Zonal vegetation occupies well-drained flat interfluves covered by loamy sands or loam. Intrazonal and exclave vegetation communities occur within a zone. Intrazonal vegetation is represented by the meadow vegetation of floodplains; vegetation of the bogs, rocks, taluses; and coniferous forests on sandy soils, etc. Exclave vegetation is zone specific, but could also be met in other zones, e.g., broad-leaved forests located at the ravine slopes in the steppes, steppe patches occupying south-facing slopes in the boreal zone, etc.
A vegetation belt is a relatively wide and monotonous vegetation strip in the mountains. It may be a single vegetation type or may alternate several vegetation types.

In the mountains, vegetation belts change with the increase in absolute height. Vegetation that is typical for the geographic zone where the mountain system is located dominates only in the foothills and in a low part of the slopes. Upwards, the vegetation transforms into that corresponding to a more northern zone. Desert, semi-desert, steppe, forest-steppe, and forest belts are distinguished in the mountains like the zones in the plains. As one moves upward, the forest belt gives way to sub-Alpine meadows and shrubs, which in turn change into Alpine meadows, and grass and moss lichen heathlands.

The climate of a geographic zone affects the altitudinal zonation. At the same heights of 400-800 meters (m) above sea level, slopes of the Northwestern Altay, which are turned to the south, are covered by steppe vegetation, while slopes of the more continental Southeastern Altay are covered by semi-desert vegetation and slopes of the Dzhungarskiy Alatau bear desert vegetation. As continentality increases, vegetation belts shift up. For example, the forest belt occupying the Northwestern Altay at the height interval between 1,200-1,600 m above the sea level is located between 1,600 and 2,000 m in the Eastern Altay.
The belts stretch symmetrically at various slopes in the mountains with a humid climate, especially in the north. For example, the forests composed of larch (Larix daurica) cover the mountain slopes of all aspects in East Siberia. The belts are located asymmetrically in the regions with dry and moderately humid climate that is typical for the southern mountains in moderate climate zone. For example, the northern slopes of the Tien Shan are often covered with coniferous forests, while the same height interval of the southern slopes is occupied by steppe.

Width of a vegetation belt by absolute height can be various and depends, on the one hand, on the value of climatic gradients, and on the other hand, on ecological requirements of the vegetation. For example, a belt of elfin wood, which requires snow cover, is located at the very edge of the forest zone and has a width of only 50-70 m, while a belt of larch forest located below occupies a range of 1,000-1,500 m.
Boundaries between the belts are often fuzzy. They become more distinct under dry continental conditions. Every vegetation belt is represented by phytocoenotic patchwork. Some of the phytocoenosises can occur in several belts (grass bogs, vegetation of solonchaks, etc.).

Climate inversions cause corresponding inversions of vegetation cover. Apart from this, the lack of some belts is a typical phenomenon for many mountain systems. Inversions and lack of some vegetation belts greatly complicate altitudinal zonation.

Communities

Paleogeographic variant of a community is a type of community that is reconstructed on the basis of paleogeographic, paleozoologic, and paleobotanic data.
The vegetation paleocommunity (paleophytocoenosis) is reconstructed from the pollen spectrum, and analysis of the plant micro-remains with the use of carpologic reconstruction. (Carpology involves identification by the fruits and seeds.) Paleocommunities vary by structure and composition, depending on the period for which reconstruction is made.
Paleoecologic reconstruction has shown that either coniferous-broad-leaved, or broad-leaved forests, which had a composition significantly different from the current one, dominated in the interglacial periods on most of Russia, to the north of the steppe area. In Northeastern Russia (the Chukotka Peninsula, the Kolyma Valley), vegetation similar to the current one (i.e., larch open woodlands with Siberian dwarf pine) has been reconstructed for the same period.

In the epoch of great Pleistocene glaciations, the combinations of tundra, forest, and steppe vegetation groups occupied vast areas to the south of the glacial shield with a part of wormwood-grasses communities. The periglacial forest-steppe zone, where larch, pine, and birch prevailed in some places, stretched to the south of this area of mixed vegetation. Forests with some broad-leaved tree species remained on the uplands (Srednerusskaya, Privolzhskaya, Pridneprovskaya, Zhiguli etc.). Vegetation that covered the Caucasus and the Southern Ural was analogous to the current one (foothills, steppes, and mountains were covered with coniferous-broad-leaved and broad-leaved forests). In Siberia, the areas located to the south of the glaciation shield were occupied by mixed (periglacial) vegetation. To the south of this zone stretched tundra and forest-tundra. South Siberia was occupied by periglacial forest-steppe (a combination of cryoarid steppes and larch forests). Paleocommunities located in the extreme northeast of Russia were represented by tundra with a part of steppe species.
Primary and secondary vegetation communities are the communities developing spontaneously, without a significant human impact. Populations of all plants are presented here by an entire age spectrum corresponding to their biological special features. These communities are characterized by a micro-mosaic structure of the layers.

The primary forest communities could be considered to be broad-leaved-Siberian pine and fir-spruce forests of various ages in the Far East, fir-cedar forests in the mountains of South Siberia, pine-larch forests in Siberia, and spruce forests and pine forests of various ages in the European North. Primary communities are characterized by a considerable age cycle. The lifetime of one generation of the trees of broad-leaved-cedar forests in the Far East makes up 300-400 years; in the European spruce forests, it is 270 years. Polar deserts, tundra, mountain areas occupied by Siberian dwarf pine, Siberian pine-larch, and larch forests are also primary communities.

Secondary vegetation communities are the communities that are formed at the site of the primary ones under the effect of exogenous factors. Secondary communities occupy most of European Russia. Primary vegetation has been nearly eliminated as a result of a strong, long-term, man-induced effect. A considerable part of the forests in European Russia is secondary, since they arose as a result of cutting. Steppes, meadow communities, and forest-steppes are also secondary communities.

Architecture

Architecture is a totality of the descriptions of an organism's form and growth.

Architecture is used to describe the growth of plants, production processes in the communities, and vegetation classification, and to construct the evolution processes. For example, the form of trees and the structure of the tree layer is used in some forest classification, where the main forest types are the following: spruce-like forests (Peceids forest), the forests with hanging branches, dense crowns, and short needles, and oak-like forests (Quercids forest), the forests with horizontal branches, usually open crowns and long needles. Among the broad-leaved forests, oak-like ones (Quercid forests, including Quercid robur, Q.petraea, Q.pubescense, Alnus glutinosa, and A. incana), can be distinguished on the structural basis of the overstorey, as can Fagid forests (Fagus, Quercus rubra, Ulmus populus, Fraxinus) and lime-like or Tilid forests (Tilia, costanea, Betula).

 

PHYTOMASS

Above-ground living phytomass

Above-ground phytomass is a total amount of living organic matter of the plants accumulated to the present moment. It is expressed in units of dry matter or carbon per unit area. Phytomass structure includes both the perennial (stems, branches, lignified sprouts of dwarf sub-shrubs, long-term needles and leaves) and the annual (annual leaves and needles, flowers, fruits, assimilating sprouts etc.) above-ground parts of a plant. A ratio (in percent) between these two parts can help describe particular vegetation communities of various natural zones.
Least reserves of above-ground phytomass (about 1 ton per hectare (t/ha) are typical for Arctic tundra and desert communities (of saltwort and wormwood, saltwort, solonetz, etc.). A preponderance of the lower plants, such as mosses and lichens in tundra, lichens and algae in semi-deserts and deserts, is typical for these coenosises. The reserve of above-ground phytomass in the deserts of ephemeral plants, saltwort and wormwood, desert steppes, and dry solonetz steppes is within 1-2 t/ha in each. The communities of dry and moderately dry steppes, solonetz steppes, and meadow steppes possess considerably higher phytomass reserve (5-6 t/ha).
Phytomass reserves increase from the meadow steppes in European Russia to that in Western and Middle Siberia. Increase of climate continentality and aridity, rise of soil salinity, and mineralization of groundwaters are followed by greater growth of the roots. So, their part in phytomass structure also increases. Phytomass in moss-lichen, dwarf shrub, and shrub tundra has the same values as it has in the steppe communities.
Reserves of above-ground phytomass increase in open woodlands and closed forests up to 20-40 t/ha. The greatest phytomass is accumulated in the forest communities. However, lignified above-ground organs make up most of their phytomass. Phytomass reserves increase from the northern taiga to the southern one from 110 to 230 t/ha. In the sub-zones of mixed coniferous/broad-leaved forests and broad-leaved forests, phytomass reserves increase to 230-310 t/ha. In West Siberia, phytomass reserve increases gradually and does not reach the maximum typical for the Russian Plain, because of the bogging. Sub-zones of mixed coniferous/broad-leaved forests and broad-leaved forests are replaced in Siberia by aspen-birch forests with a reserve of above-ground phytomass of about 150 t/ha.
Phytomass of terrestrial ecosystems make up 81.8 Pg of dry matter (DM), including 59.47 Pg DM accounted for by above-ground phytomass. Area of the lands with vegetation cover is assessed to be 1,630x106 ha. Phytomass reserve of the coniferous forests make up 75.3% of the total phytomass of all forest ecosystems of Russia; larch forests account for 33.6%; pine forests for 16.7%; spruce forests for 14.3%; cedar forests for 8.1%; and fir forests for 2.5%. Small-leaved forests (mainly birch and aspen) contain 18.7% of the total phytomass reserve. Hardwood forests (oak, beech, etc.) account for only 3.4%.

Above-ground phytomass (dead)

Dead above-ground phytomass is the amount of organic matter that is contained in all annually dying-off parts of the plants in the above-ground part of the community, in the organisms or their parts that die off in the course of aging or natural thinning, and also in forest litter, peat soil horizon, steppe litter, etc. Annual litter fall is the organic matter that is contained in the parts of the trees and shrubs that fall off, i.e., in the leaves (needles), flowers, paleas, fruits, seeds, small shoots, etc.
It does not include dead above-ground material (e.g., standing dry trees, dry branches of live trees, stumps) or on-ground material (downed wood, windbreak, etc.). These parts compose coarse woody debris. Coarse woody debris in terrestrial ecosystems of Russia makes up 9,909.7x1012 t DM. Of this value, 55% accrues to the forests of the middle taiga, 15% to the northern taiga, and 17% to the southern taiga.
The amount of above-ground dead phytomass increases from the northern limit of the forest range to the southern one (3.5-10.9 t/ha per year). Leaves (needles) prevail in the dead above-ground phytomass of all forest types, and make up about 60%-78% of its total amount. The rest is composed of branches (12%-15%), bark (1%-14%), and fruits (1%-17%). The amount of dead above-ground phytomass of lower layers (grasses, shrubs, and mosses, etc.) depends on the degree of their development and fluctuates from 0 (in forests where ground vegetation is lacking) to 2 t/ha. Usually this value makes up not more than 10% of the total amount of dead above-ground phytomass.
Litter is long-term deposits of plant residues of various mineralization at the soil surface. Litter is most developed in the dwarf shrub tundra, where its amount makes up 83.5 t/ha. Pine forests of the southern taiga and spruce forests of the middle taiga contain 45 t/ha of litter each, spruce forests of the southern and northern taiga - 35 and 30 t/ha, respectively, and broad-leaved forests contain 15 t/ha of litter. The amount of steppe litter is rather great in the northern sub-zones of the steppe (6.2 t/ha); however, it sharply decreases southward.

Below-ground phytomass (living)

Below-ground phytomass is the total amount of live organic matter of the plants that has been accumulated to the moment in the below-ground part of a community (roots, rhizomes, tubers, bulbs).
Below-ground phytomass in terrestrial ecosystems of Russia makes up 22.33 Pg DM. The portion of below-ground parts in the phytomass structure varies depending on bioclimatic zones. The part played by roots and other subterranean organs is especially great in the desert communities, where they make up 75%-95% of total phytomass. It is 65%-90% in communities of droughty and moderately droughty steppes, solonetz steppes, meadow steppes, and meadows. In the tundra zone, roots and other subterranean organs account for between 85%-90%, but they rarely exceed 10% in moss bogs because of the prevalence of rootless plants (mosses). The portion of roots in open woodlands and closed forests is decreased by up to 22%-25%. The part of subterranean organs in forest communities makes up 21%-29% of total phytomass. Absolute amounts of phytomass of subterranean organs in the deciduous forests are similar in all climatic belts and make up 82-96 t/ha. Amount of the roots in the moderate coniferous forests is noticeably less and makes up 20-60 t/ha.

Below-ground phytomass (dead)

Below-ground dead phytomass is the total amount of organic matter that is contained in dead below-ground organs of the plants (roots, rhizomes, tubers, bulbs).
Dead below-ground phytomass in terrestrial ecosystems of Russia makes up 19,648.8x1012 t DM, of which 47% are accounted for by middle taiga, 27% by tundra communities, and 17% and 10% by the northern and southern taiga, respectively.
Dead below-ground organs make up about 60%-70% of total below-ground phytomass. This value increases eastward. The portion of dead below-ground organs in mountain tundra and in bogs does not exceed 70%, in meadows of the forest zone and meadow steppes in European Russia, it makes up about 50%. This value in true and dry steppes of European Russia and West Siberia is about 35%, in steppes of Middle Siberia, it increases up to 50%-60% and in steppes of Transbaikalia - up to 70%-75%. The portion of dead below-ground organs in semi-deserts is 50%-60%. The portion shrinks in the arid areas southward (25%-30%) and in psammophyte communities (10%).

Gross production by natural vegetation communities

Gross production is the total phytomass increase over a unit of time per unit of area, including a certain amount of organic material used for transpiration and growth, and also the amount of dead phytomass and organic material consumed by heterotrophs. In other words, it is the total amount of organic material produced by the autotrophic organisms in the course of total or real photosynthesis. The synonyms are total photosynthesis, total assimilation, and assimilated energy.
Annual phytomass produced in the course of photosynthesis increases from the northern latitudes to the moderate ones; it then starts to decrease toward the desert zone and again increases toward the humid subtropics.
Gross production is a sum of net primary production and the amount of organic material used for transpiration. Transpiration expenditures depend on temperature conditions. As temperature increases, the amount of organic material used for transpiration grows. Transpiration expenditures are different for different plant species. The ratio between the masses of photosynthesizing and nonphotosynthesizing organs is also of great importance. Algae have the most photosynthesizing tissue per total biomass; trees have the least (about 1%-2% in deciduous trees and 4%-5% in coniferous trees). Grasses occupy an intermediate place in this range. Transpiration expenditures (percentage of the total production) vary from 30%-40% (communities of plankton algae) to 70%-80% (tropical rainforests). Temperate forests use 50%-60% of the total production for transpiration.

Net primary production

Net primary production (NPP) is the amount of phytomass produced by a community over a unit of time per unit of area, including the organic material consumed by heterotrophs and the amount of organic material excreted by roots and above-ground parts of the plants, and minus a certain amount of organic material used for transpiration and growth. This is the amount of organic material produced by autotrophic organisms in the course of visible or apparent photosynthesis. This value does not include a certain amount of organic material used by the producers for transpiration and growth. The energy that was contained in this part of the organic material was released in the form of heat, so it does not belong to this biogeocoenosis. Methods for determining NPP can be direct (field measurement of production) or indirect (laboratory measurement of CO2 fluxes, studying the wood growth by the annual rings, etc.). Synonyms for this concept are: visible or apparent photosysnthesis and net assimilation.
Minimum NPP (less than 1 t/ha per year) is typical for the Arctic tundra. It is slightly higher (1.0-2.5 t/ha per year) in moss/lichen, dwarf shrub, and shrub tundra and also in various saltwort deserts. The NPP of forest-tundra, light coniferous forests in the northern taiga (and dark coniferous forests in West Siberia), and of moss bogs in the taiga makes up from 2.5 to 4.0 t/ha per year. In spruce forests of the northern taiga within the Russian Plain and cedar/fir middle taiga forests of West Siberia, NPP is higher and makes up from 4.0 to 6.0 t/ha per year. Increase in NPP up to 6.0-8.0 t/ha per year is observed in the forests of the middle taiga in European Russia and of the southern taiga in West Siberia. A greater amount of organic matter (8.0-10.0 t/ha per year) is produced by the forests in the southern taiga and by sub-taiga forests of aspen and birch in West Siberia. The same amount of NPP is typical for droughty and moderately droughty steppes in European Russia. The area with the greatest NPP (10.0-15.0 t/ha per year) within the Russian plain and West Siberia stretches as a strip gradually converging from the west to the east and it covers the ranges of broad-leaved forests, meadow steppes, and steppe solonetz meadows. Maximal annual NPP (15.0-30.0 t/ha per year and more) is typical for the humid sub-tropic forests and some grass bogs and long-flooded areas in the floodplains and deltas of the southern rivers (plavni), which are covered with reed, reed mace, and sedge grasses.

Forest growth models

Forest growth models are the models describing the state and development of forest communities. The models have been developed for the following purposes:
(1) description of the plant growth; (2) description of population stochastic processes, e.g., self-thinning of standing trees; (3) description of the physiological processes; and (4) description of the dynamics of forest communities.
Growth of the individual plants and general course of development is most usually described by the parameters of biomass. The following formula is used for the growth description of individual plants:

where M(t) is a plant biomass at a point in time t and l is the linear dimensions of a plant (height, diameter, etc.). Growth of forest communities can be expressed through a ratio of biomass to net annual production (coefficient of biomass accumulation). This coefficient increases from 1.0, where the community is annual; to 2-4 where it is meadow; to 4-7 where it is shrub; to 10 where it is young forest, and to 25-35, where it is mature forest.
Growth dynamics can sometimes be simulated with the use of climatic parameters (temperature, precipitation). For example, H. Lieth (1975) used the following formula for calculation:

F = 3000 min*{(1 + exp*(1.315-0.119T)) - 1(1 - exp*(-0.00064P))} ,

where F is annual production (in grams per cubic centimeters per year), T is air temperature, and P is precipitation [in millimeters(mm) per year].
Photosynthesis intensity and respiration are also described in the models. The following formula is used for photosynthesis intensity:

where k is the maximal value of photosynthesis, a is the initial slope of the photosynthesis curve, and En is the intensity of photosynthetic active radiation (380-710 mm).
When describing respiration it is possible to distinguish proper growth respiration and respiration maintaining a total system. When the photosynthesis process dominates over the respiration ones, NPP is produced. This is typical for intensively developing "young" ecosystems.
"Gap models" are used to develop the "spatial models." In gap models, the growth of every tree is described by differential equation and regeneration and die-off (by probabilistic parameters). The model JABOWA of D. Botkin et al. (1972) was one of the first such models. The growth of every tree is described there by the following equation:

where D is a diameter, H is a height, l is a leaf index, Dm is a maximal diameter, Hm is a maximal height, r is a parameter of wind velocity,and f(*deviation) is a function of optimal growth deviation due to competition. The model was used for studying forests' response to climate change in the north of the USA and for development of long-term forecasts.
Change of communities and "models of forest development" are described by the theory of Markov's chains and matrices of Markov's probabilities. They are useful for describing changes in heterogenous objects undergoing certain successions, e.g., successions of different-age forest plantations. The model includes vegetation growth, regeneration, and die-off. Standing trees are divided into classes by age and size. Matrices of probabilities describe transition from one class to another.
The "model of neutrality" - where succession is considered as a process of change in populations with the various life cycles and various strategies - uses the population approach for describing dynamics of the communities. Most often this model is used to describe the formation of species composition.
The model of dynamics of a whole community usually includes the following blocks: photosynthetic, growth, hydrometeorological, and soil. The concept of competitive interactions is in the basis for this model. Strength of a competitive pressure increases as biomass of adjacent specimens grows, and it decreases proportionally to remoteness from the adjacent specimens. Modeling is based on the selective use of a resource, when reduction of a reserve of one species provokes growth and development of another. Most models consider only functional dependence among the various parameters of a community. Scientists of the Institute of Forest of the Russian Academy of Sciences have proposed an imitation model of a multi-species, different-age community that includes a volume structure of a community at every stage of modeling. The following propositions are in the basis for the model: (1) modeled area of a community is subdivided into three-dimensional cells of finite size; (2) biological properties of the arboreal specimens change in time discretely in correspondence with the ontogenesis periodization; (3) time series of the states of every cell forms a closed loop; and (4) transition of every cell from one state to another is predetermined by a current state of the cell and state of the adjacent cells. The model has been developed on the basis of encapsulated programming. This circumstance makes it possible to change, to develop, and to exclude various blocks.
Growth models are commonly used to plan forestry activities and to forecast vegetation response to climate change.

References

Botkin D.B., J.F. Janka, and J.R. Walles. 1972. The rational limitation and assumptions of a northeast forest growth simulator. JBM Journal of Research Development 16:101-116.

Leith H. 1975. Modeling of primary production of the globe. Ecology 2:12-13. [In Russian]