How to divide the biological community in an area

Biological community refers to the sum of all kinds of organisms that live in a certain natural area and are directly or indirectly related to each other. A biological community, like a population, has a series of basic characteristics, which are not included in the various populations that make up it. That is to say, these characteristics can only be shown at the overall level of the community. The basic characteristics of biological communities include species diversity and growth forms (such as forests, shrubs, grasslands, swamps, etc. ) and structure (spatial structure, time combination and species structure), dominant species (species whose size, quantity or activities determine the characteristics of the community), relative richness (relative proportion of different species in the community) and nutritional structure.

As a general noun, it is synonymous with community. At present, the word biome is only used to emphasize the consideration method of Clements and Shelford (F.E. Clements & V.E. Shelford, 1939). Clements believes that plant communities are not the combination of individuals and species, but the combination of ecological groups represented by growth forms. This new stage of organisms must be based on individual organisms and called compound organisms. Shelford (19 12) once used the term physiological activity type for animals, which is equivalent to the growth type of plants and is called ecological population (mores, plural, mos, singular, with different meanings), and its combination is animal community. In the future, plants and animals will be regarded as the functional life forms of mune, and the unity will be further emphasized. Succession is the development and growth of complex organisms, equivalent to its adult climax community, which is only determined by climate. Some people call this view biological ecology.

The concepts of biological community and ecosystem are different. The latter includes not only the biological community, but also the abiotic environment in which the community is located, and regards them as a whole linked by matter, energy and information. Therefore, the biome is only equivalent to the biological part of the ecosystem.

There are three main types of relationships among various organisms in a biological community: ① Nutritional relationship, that is, the relationship between one species feeding on another species, whether it is the living or dead residue or the product of their life activities. It can also be divided into direct nutritional relationship and indirect nutritional relationship. Bees that collect nectar and dung worms that eat animal feces have direct nutritional relations with the biological species that serve as their food; When two species compete for the same food, there is an indirect nutritional relationship between them. Because the activities of one species will affect the feeding of another species. (2) Environmental relations, the living conditions of one species are changed by the life activities of another species. Plants play a particularly important role in this respect. Shrubbery, grass, ground cover and all animals under the canopy are in relatively uniform temperature, high air humidity and low light conditions. Plants also affect other living things around them with various secretions (gas and liquid). One species can also provide shelter for another species, for example, parasitism or nesting in animals, epiphytes on branches and so on. (3) The cloth-helping relationship refers to the participation of one species in the distribution of another species, and animals play a major role in this respect. They can carry seeds, spores and pollen of plants to help them spread.

The relationship between nutrition and environment is the most significant in biological communities, and it is the basis of the existence of biological communities. It is these two relationships that bring together organisms of different species and combine them into relatively stable communities of different scales.

Edit the category division of this paragraph.

According to the climatic conditions, the division is mainly the life zone, that is, the biological community units within the division range of tundra, summer green forest, tropical rain forest and savanna. F.E. Elements (1916) put forward this term, and then it refers to the general biological community, emphasizing the morphological structure related to the biological habitat and developing towards the climax. However, after V.E.Shelford( 1932), it is mostly confined to the biostratigraphy of large animals and plants corresponding to the strata, while Clements and Shelford( 1939) and so on. According to the climax of plants, the appearance characteristics of the community are put forward, and the two are combined to be named according to the units determined by the influencing species of animals, such as Stipa-Antilo capra community. But now, the idea of taking it as the basic unit of community almost does not exist, but taking climate zoning as the type of biological community and applying it to the division of types. As for the relationship between animals and plants, there is no special consideration, but there is a strong tendency to discuss species composition, life form or life form composition and community appearance.

Species The biological communities on the earth are first divided into two categories: terrestrial colonies and aquatic communities. Although their basic laws are similar, they are essentially different. These differences are basically caused by different environments. The structure of aquatic community is simpler than that of terrestrial community. In water, the soil under the water is different from that on land. The relationship between plants and benthos and water and soil is mainly mechanical. The environmental factors experienced by aquatic community organisms are very different from those experienced by terrestrial organisms. When studying terrestrial colonies, we should first study the precipitation and temperature of the environment, while when studying aquatic communities, light, dissolved oxygen and suspended nutrients are more important.

The difference of surrounding environment also determines that the species that make up terrestrial and aquatic communities are very different. Lower plants are dominant in aquatic communities, especially algae. In terrestrial biota, higher flowering plants are dominant. There are many kinds of animals in aquatic communities, but higher arthropods and higher vertebrates are only secondary; On the contrary, insects (higher arthropods), especially birds and mammals, play a major role in terrestrial biota.

There are a series of transitional forms between typical aquatic communities and terrestrial colonies. For example, the biome of swamp, the submerged area of flooded plain terrace and the biome of coastal part affected by high tide and low tide.

The distribution of animals and plants is controlled by many factors, but from the global or the whole continent, the most important factor is global climate. The largest and most recognizable part of the global biota restricted by climate is the biota. The biota is divided according to the dominant top vegetation. The environmental conditions (climate and soil) of similar biota distributed in different continents are basically similar. So they have the same appearance. The annual average temperature and precipitation are considered to be the main factors that determine the appearance. Based on these two factors, the approximate boundary between the main appearance types is expressed. As R.H. Whitaker himself pointed out, this model has some limitations, and it can't fully express: ① the influence of temperature and precipitation in different seasons; Significant contrast between maritime climate and continental climate; (2) the influence of fire on grass-dominated communities in many areas; ③ The influence of soil differences; (4) Continuous gradual change between groups.

The main biota in the world are: ① Terrestrial biota: tropical rain forest, tropical seasonal forest and monsoon forest, subtropical evergreen forest, temperate deciduous broad-leaved forest, Taijialin or northern coniferous forest, spiny forest, subtropical shrub, tropical savanna, temperate grassland, tundra, desert, polar-alpine desert. ② Land-water transitional biota: inland swamp (including acid swamp and common swamp) and coastal swamp (salt swamp, including tropical and subtropical mangrove). ③ Aquatic biota: still fresh water (lakes and ponds), flowing fresh water (rivers), estuaries, offshore, ocean or deep sea.

Edit the spatial distribution of this paragraph.

An area is always composed of many habitats, which are interrelated along the environmental gradient (formed with the change of height, soil characteristics, surface water conditions, etc.). ). Although sometimes this gradient may be interrupted by some kind of obstacle. But in most cases, a continuous gradient is formed. Every habitat may develop a climax natural community suitable for it. Along a continuous environmental gradient, the characteristics of one community usually change smoothly to those of other communities. If the community is sampled regularly along the environmental gradient (spline) and the species and quantity of plants are counted, the fluctuation of population distribution along the gradient can be observed. According to the richness of plant species, population curves are mostly symmetrical bell-shaped. Curves usually overlap each other by a large part, but form a sudden break where one species repels another.

When observing the distribution of population along a belt or the change of plant growth pattern along a climate gradient, we usually see the continuous change of community, that is, it appears as a continuum. This is the principle of community continuity. According to this principle, along the continuous environmental gradient, natural communities generally change with each other gradually, instead of suddenly giving way to the combination of other species with clear boundaries. Of course, many exceptions to this principle can also be observed in nature. For example, the abrupt change of topography (cliff), the abrupt change of rock properties (acid granite or sand shale becomes alkaline limestone), the complete change of water conditions (water body moves to the shore), the forest edge between forest and grassland (caused by fire) and so on. In these cases, one community suddenly gave way to another.

Sharp community transition (such as forest edge between forest and grassland) is called ecological ecotone. There is often a "boundary effect" here, that is, the species diversity in the ecotone is particularly high: there are both species appearing at the edge of the forest itself and species from two adjacent communities.

Edit the community structure of this section.

Include spatial structure, time combination and species structure.

Plants with different life forms (trees, shrubs and herbs) live together in space structure, and their vegetative organs are arranged at different heights (or different depths in water), thus forming stratification. Stratification increases the number of organisms that can be accommodated per unit area, enables them to make full use of environmental conditions in more ways, and greatly weakens the competition intensity between them; In addition, multi-level communities are more productive than single-level communities.

Stratification is most obvious in temperate forests, for example, temperate deciduous broad-leaved forest can be clearly divided into four layers: trees, shrubs, herbs and lichens (ground cover). The hierarchical structure of tropical forests is the most complex, and some levels may be the most developed, especially the arbor layer, where giant trees, ordinary trees and small trees of various heights are densely packed together, while the shrub layer and herb layer are often not very developed. Herb communities are equilayered, although there are fewer layers (usually only herb layers and ground cover layers).

The community not only has layers on the ground, but also has root distribution underground. Underground stratification and aboveground stratification of communities generally correspond; Tree roots extend into the deepest soil, shrub roots are shallow, herbaceous roots are mostly concentrated in the surface soil, and moss roots are directly distributed on the surface.

The vertical stratification of biological communities is closely related to light conditions, and the plants in each layer adapt to the light level of that layer and reduce the light intensity of the lower layer. The decline of light intensity is the most obvious phenomenon in the forest. The tallest tree has plenty of light. On average, the light reaching the lower tree is only 10 ~ 50% of the total light of the upper tree, 5 ~ 10% of the shrub layer and 1 ~ 5% of the herb layer. With the change of light intensity, the temperature and air humidity also change.

Each layer of plants and the microclimate it restricts create a certain environment for the unique animals living in it, so animals are also stratified in species, different species appear at different levels, and even the same male and female individuals are distributed at different levels. For example, in the forest, three groups of birds can be distinguished: those who feed in the tree crown, those who live near the ground, and those who live in shrubs and bush leaves.

Due to the accumulation of litter and the transformation of soil by plants, woodland has also created a special animal habitat environment. The higher floors (grasslands and undergrowth) are occupied by insects, birds, mammals and other plants-eating animals. Insects, ticks, spiders and a large number of microorganisms live in litter, decomposed plant residues, mosses, lichens and fungi. On the surface of the soil, the roots of plants are dense, and bacteria, fungi, insects, ticks and worms all live here. Sometimes there are burrowing animals at a certain depth in the soil.

Of course, there are also some alien creatures that are not fixed on a certain layer. Such as vines, epiphytes and animals that move freely from one layer to another. It is difficult for them to rank; This situation is common in tropical rain forests with extremely complex structures.

Because lower organisms are developed in the environment formed by the shade of higher plants, there is a close interaction and interdependence between species at different levels of biological communities. The upper plants in the community reproduce vigorously, and the density of the lower plants will decrease accordingly; However, if the upper plants become sparse for some reason, the light and heat conditions of the lower plants are improved, the mineral nutrients in the soil are increased due to the enhanced release, and the development of the lower plants will be strengthened. The flourishing growth of the lower layer is also beneficial to animal residents. This is especially true in forest communities, where sparse tree layers will lead to a large number of shrubs or light-loving herbs. The complete closure of the tree layer sometimes even inhibits the most shade-tolerant herbs and mosses.

Biological communities have not only vertical structural differentiation, but also horizontal structural differentiation. The horizontal heterogeneity of the community is characterized by patches; In different patches, plant species, quantitative proportion, canopy density, productivity and other properties are different. For example, in a grassland area, Stipa densiflora is the most dominant species, but it does not constitute a continuous vegetation, but is distributed at a certain distance (30 ~ 40 cm) from each other. The space between each species of Stipa is occupied by different smaller grasses and dicotyledonous weeds, and mixed with bulbs. But some of these plants also appear in the interior of Stipa bungeana. Therefore, there is a gap between Stipa and a few other plants, and they are obviously different in appearance, quantity and quality. But compared with the whole plant community (Stipa grassland), their differences are inferior, not obvious and unstable. Similar differences can be observed in the composition and quantitative proportion of plant species in forests, in dark places and bright places. This kind of horizontal inconsistency within the community is called the mosaic of the community. In some cases, this inconsistency is caused by the difference of community environment, such as the difference of light intensity affecting the distribution of plant species or the small fluctuation of the surface; In some cases, it is caused by a plant cluster formed by the underground stems of the same parent; In other cases, they may be caused by the interaction between species, such as the formation of spotted parasitic plants where the roots of host species appear. Animal activities are sometimes the cause of heterogeneity. Plants are usually not randomly distributed in the horizontal space of the community, but in clusters or clusters. Many animal populations, whether terrestrial colonies or aquatic communities, also have the nature of cluster distribution. In contrast, regular distribution is less common. The distribution of shrubs, songbirds and some other animals in some deserts is an example of this regular distribution.

The biological species that form a community in time often show "differentiation" in time, that is, "complementarity" in time. For example, species with different temperatures and water needs are combined in temperate zones: some grow in cold seasons (spring and autumn) and some appear in hot seasons (summer). For example, in deciduous broad-leaved forest, some herbs bloom before trees shed their leaves in spring, while others bloom in late spring, summer or autumn. With the alternation of leaf emergence and flowering of different plants, the related insect species also change in turn: some appear in early spring and some in summer. The different responses of birds to seasons are manifested in the seasonal migration of migratory birds. Creatures also show behavioral rhythms related to daily time: some animals move during the day; Others are active at dusk; Others move at night and hide in some hidden place during the day. The flowers of most plant species bloom during the day, which is consistent with the activities of pollinators; Some plants bloom at night and are pollinated by nocturnal animals. Many zooplankton will move to the surface of the water at night and sink to the depth to stay away from the bright light during the day, but different species have different vertical movement patterns and ranges, and the complex rhythm of tides controls the activities of many coastal organisms. Native creatures also have species that move vertically day and night.

Species structure Each specific biological community has a certain species composition. However, the number of species in different biological communities varies greatly. For example, in the biological communities of tropical forests, there are tens of thousands of plant species, 6.5438+million invertebrate species and thousands of vertebrate species, among which the relationship between populations is very complicated.

There are far fewer species in tundra and desert communities. According to the data of the Soviet scholar ба Tikhomirov, there are 39 species of higher plants 139, 670 species of lower plants, about 1000 species of animals and 2,500 species of microorganisms in the tundra community of Termel Peninsula in northern Siberia. Accordingly. The biomass and productivity of these biomes are also much smaller than those of tropical forests.

The complexity of organisms in biological communities is expressed by the concept of species diversity. Diversity is related to the number of biological species in a certain area and the uniformity of individual distribution among species. For example, both communities contain 5 species and 65,438+000 individuals. In one community, these 65,438+000 individuals are evenly distributed in all five species, that is, there are 20 individuals per 65,438+0 species, while in another community, 80 individuals belong to 65,438+0 species, and the remaining 20 individuals are allocated to the other four species. In this kind of community,

In temperate and polar regions, only a few species are common, while the individuals of most other species are rare and their species diversity is very low; In tropical areas, individuals are evenly distributed among all species, and two adjacent trees rarely belong to the same species (tropical rain forest), so species diversity is relatively high. The species diversity of the community depends on the evolution time, environmental stability and favorable ecological conditions. The tropics are the oldest and the environment is the most stable since its formation. The high temperature and rainy climate is most conducive to the growth of organisms, and the species diversity of biological communities is the largest. In the harsh tundra environment, the situation is just the opposite, so the species diversity is low.

Each plant plays a different role in the community. Often some species appear in the form of a large number of individuals, that is, large populations; Other species appear in the form of a few individuals, that is, small populations. The appearance of the community is determined by the plant species with many individuals and large volume (large biomass). For example, the overall appearance of most forest and grassland communities depends on one or several plant species. For example, most of the oak forests in Shandong Peninsula of China rely on Quercus acutissima, the pine forests at the southern foot of Yanshan Mountain rely on Pinus tabulaeformis, and Stipa grandis or Stipa krylovii in Ximeng, central and eastern Inner Mongolia Plateau. In a forest composed of dozens or even hundreds of plants, often only one or two trees provide 90% of the wood. These species with a large number of individuals and biomass in the community are called dominant species and occupy a dominant position in the biological community. There is often more than one dominant species, and the most dominant species is called constructive species. Usually, terrestrial biological communities are named according to the species of constructive plants, such as deciduous broad-leaved forest, Stipa grassland and sphagnum swamp. The constructive species are the founders of the community and create conditions for the life of other species in the community. For example, spruce has formed a dense dark coniferous forest in the coniferous forest belt. Under its crown, only plants that adapt to strong shading conditions, high air humidity and acidic calcareous soil can survive; Corresponding to these factors, unique animal dwellers have also formed in spruce forest. Therefore, in this case, spruce has played a powerful role in establishing species.

The constructive species in pine forest is pine, but it is weaker than spruce, because pine forest has sparse trunk, loose crown and light transmission, and the composition of animal and plant species is far more diverse than spruce forest. You can even see plants that can survive in the environment outside the forest in the pine forest.

In the biological communities in temperate and cold regions, the constructive species are more obvious; Whether it is forest community, shrub community, herb community or moss community, it is possible to determine the constructive species (sometimes more than one). Subtropical and tropical biota, especially tropical biota, have no obvious dominant species, so it is difficult to determine the constructive species. In addition to the dominant species, the species that are not dominant in individual number and biomass but are still widely distributed are common species; The number of individuals is very small, and only the occasional species is the occasional species.

Most biological species in the biological community are related to dominant species and constructive species to some extent, and they form a species complex within the biological community, which is called synbiotic group. Synbiotics are also structural units in biological communities. For example, a dominant plant, its related epiphytes, parasites, parasites, and insects and mammals that feed on it form a synbiotic group.

Many biological species living in a community are selected in the process of long-term evolution and can coexist in this environment. They each occupy a unique niche and play a unique role in transforming environmental conditions and utilizing environmental resources. The combination of the specific habitat occupied by each species in the community and the unique functions it performs is called niche. Therefore, the higher the species diversity of a biological community, the higher the degree of niche differentiation.

Edit the community features of this section.

It can be described from three aspects: productivity, organic matter decomposition and nutrient cycle.

Green plants in productivity communities produce organic matter from inorganic substances through photosynthesis, which is the most important function of biological communities. In the process of photosynthesis, the total amount of organic matter produced by plants in a period of time is called total primary productivity, which is usually expressed in grams per meter for 2 years or kilocalories per meter for 2 years. But in order to survive, plants need to breathe, and breathing consumes part of the organic matter produced by photosynthesis, and the rest is used for accumulation (growth); The amount of organic matter left by plants after breathing for a period of time is called net primary productivity. For example, in forests, 60-75% of the total output may be breathed by plants, and the remaining 40-25% is the net output. In aquatic communities, less than half of the total output is breathed by plants. Net primary production will gradually accumulate and increase with the progress of time, and the amount accumulated to any observation time is plant biomass. Biomass is expressed in grams per square meter or kilograms per hectare.

Ecology is more concerned with the productivity of the community, that is, the output per unit time. For terrestrial or underwater communities, the biomass per unit area is calculated, while for phytoplankton and soil communities, it is determined by the unit volume. Therefore, biological productivity is the output of square meter area (or cubic meter volume) per unit time, which is often expressed in grams of carbon or grams of dry organic matter.

Biological productivity should not be confused with biomass. For example, phytoplankton may produce as much organic matter per unit area a year as high-productivity forests, but the biomass of the former is only 1% of the latter, because most of it is consumed by heterotrophs. In terms of productivity, the annual growth of meadow grassland biomass is much greater than that of coniferous forest. According to the data of the Soviet Union, in the case that the biomass of plants in the middle meadow grassland is 23 tons per hectare, their annual output reaches 10 tons per hectare, while in the coniferous forest, the annual growth is only 6 tons per hectare when the biomass of plants is 200 tons per hectare. Small mammals have higher growth and reproduction speed than large mammals and provide higher yield under the same biomass.

Consumers who consume primary products have also formed their own biomass. The organic matter they produce in a period of time is called secondary production, that is, production in heterotrophs. The speed at which consumers produce and output is called the second productive force.

The primary productivity of different communities on the earth is very different. According to the primary productivity, R.H. Whitaker divides the terrestrial biota into four categories (see table 1).

The biomass of green plants is partly decomposed by decomposers in the form of litter, partly carried out of the community by wind, water or other power, and partly passed along the food chain. The rest accumulated in the community in the form of organic matter.

Decomposition of organic matter In many communities, the net primary production obtained by animals from living plant tissues is much smaller than that used by decomposers such as bacteria and fungi after the death of plant tissues. In the forest, animals can't eat 10% of leaf tissue and 1% of living wood tissue, and most of them fall to the ground to form a litter layer covering the soil surface, which is used by various soil organisms. These soil organisms include scavengers that feed on dead plant tissues and dead animal tissues, bacteria and fungi that decompose organic matter, and animals that feed on these organisms. Although animals contribute to the destruction of garbage, bacteria and fungi play the most important role in reducing dead organic matter into inorganic final products.

The biomass of decomposers is very small compared with consumers and even smaller compared with producers. However, the activities of decomposers with small biomass are very important in community function. The remains of all dead creatures in the community are destroyed by decomposers. If there is no decomposition activity of decomposers, the dead residues of organisms will continue to accumulate, just like peat in acid swamps. Not only the productivity of the community may be limited because nutrients are locked in dead tissues, but also the whole community will cease to exist.

Producers in nutrient cycling communities absorb inorganic nutrients from soil or water, such as nitrogen, phosphorus, sulfur, calcium, potassium, magnesium and other elements, and use these elements to synthesize some organic compounds, form protoplasm, and keep cells performing functions. Consumer animals get these elements from edible plants or other animals. When decomposers decompose animal and plant wastes and dead residues, they release nutrients and return them to the environment, which are then absorbed by plants. This is the nutrient cycle, or the biological cycle of matter. For example, in a forest, a certain nutrient is absorbed from the soil to the roots and transported upward to the leaves through the conductive tissue of the tree. At this time, it may be eaten by leaf-eating cockroaches, and then used by cockroach-eating birds. Until the birds die, they are decomposed and released into the soil, and then reabsorbed by plant roots. Many nutrients return to the soil from forest trees in a short way-they decompose when plant tissues fall to the litter layer, or fall from the plant surface to the soil under the action of rain.

Different communities have different amounts of nutrients and the speed of circulation. In some communities, a large part of certain elements remain in plant tissues, and only a small part is free in soil and water. For example, the amount of phosphate dissolved in water is only a small part compared with that in plankton cells and particles. In tropical forests, most nutrients are preserved in plant tissues, and nutrients released by rainwater infiltration into soil and litter decomposition are quickly re-absorbed. However, when the forest is cut down or burned, a lot of nutrients will be lost due to erosion and the downward movement of nutrients in soil moisture. In the open ocean, with the sinking of plankton cells and organic particles, nutrients are also brought to the depths, so there are few nutrients in bright surface water for photosynthesis, so the productivity is very low.

Edit community succession in this section.

The biological community is always in constant change, including diurnal change, seasonal change and interannual fluctuation, but these changes and fluctuations have not caused changes in the nature of the community, and some of its characteristics are still maintained. But sometimes there is another phenomenon in nature: one community develops into another completely different community, which is called community succession or ecological succession. For example, the abandoned farmland near Beijing mainly grows annual weeds in the first year, and then after a series of changes, it finally forms deciduous broad-leaved forest. Each stage in the succession process is called continuous community. Succession finally reached a relatively stable community, called climax community.

In most cases, the dominant component in the process of biological community succession is plants, and animals and microorganisms only change with the changes of plants. The basic reason for the evolution of plants is that the earliest plants settled in a place, through the accumulation and decomposition of their residues, added organic matter to the soil, changed the properties of the soil (including fertility), changed the surrounding microclimate through shading, and some even added some organic compounds to the soil through the secretion of roots, thus changing the environment in the community and creating conditions for the invasion of other species. When this change accumulates to a certain extent, it will be unfavorable to the survival and reproduction of the original plant itself, so succession will occur. Of course, changes in external factors can also induce succession.

Some successions can be completed in a relatively short time, for example, after a forest fire, a series of rapidly changing communities appear in the burned area, and finally a stable primitive type is restored. But sometimes the succession is very slow, even taking hundreds or thousands of years to complete. According to the research of Soviet scholars, Betula platyphylla, Populus davidiana and Alnus cremastogyne first appeared in abandoned farmland in Taiga spruce forest area, because the seeds of these trees were easily carried away by the wind and began to germinate when they landed on soft grass soil. These are the so-called pioneer species. The strongest of them settled in abandoned land or cultivated land, where they consolidated and gradually changed the environment. After 30-50 years, birch crowns are closely connected, forming new conditions. The new conditions are suitable for spruce growth, but not for birch itself, so the mixed forest is gradually formed. However, this kind of mixed forest does not exist for a long time, because the birch trees that like light can't stand shading and can't regenerate under the crown of spruce. About 80 ~ 120 years after the first batch of birch seedlings appeared, a stable spruce forest was formed.

There are two types of succession: succession from primitive inanimate places (such as sand dunes, the rock surface after volcanic lava condensation, the ground exposed by glacier retreat, and the collapse and slump of hillsides). ) is called primary succession. In the case of primary succession, the speed of community change is generally not large, and the successive series of communities keep a long time interval, while the biological community sometimes takes hundreds of years or even longer to reach its climax. If a community develops in a place where a living thing once existed, then this succession is called secondary succession. Mature soil and abundant biological propagules are usually preserved in this area, so the formation of climax community through secondary succession is much faster than that of primary succession. Under modern conditions, secondary succession can be seen everywhere, often after fire, flood, grassland reclamation, forest logging, swamp drainage and so on.