Ecology: the Biology of Interactions. 3.04. Classification of Biomes
A biome is a large type of biogeocoenosis characterized by a similar type of vegetation and occupying certain regions of the planet. Biomes are regulated by macroclimate and, first of all, by precipitation and temperature...
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3.03. Examples of Ecosystems
D. Shabanov, M. Kravchenko. Ecology: Biology of Interactions Section 3. Biogeocenology and Ecology of Communities
3.05. Ecological Balance
3.04. Classification of Biomes What kinds of biogeocenoses are there? Everyone knows that a biogeocenosis where trees are the predominant producers is called a forest. Biogeocenoses located in arid climates, where grasses dominate, are called steppes in Eurasia, prairies in North America, pampas in South America, and veld in South Africa. To understand the diversity of biogeocenoses, a classification is needed. There are quite a few such classifications, and here we will use one that is likely most frequently applied in the international scientific community. The unit of this classification is the biome. A biome is a large type of biogeocenosis characterized by a similar vegetation type and occupying specific regions of the planet. Biomes are regulated by macroclimate, primarily by precipitation and temperature (Fig. 3.4.1). Fig. 3.4.1. Distribution of some terrestrial biomes depending on precipitation and temperature Biomes have a certain integrity. For example, between the zones of deciduous forests and steppes lies the forest-steppe zone, where forest and steppe biomes "meet." Under the existing climate, both types of biogeocenoses can be stable in the forest-steppe zone. Forests require more water than steppes, but forest soil retains it more effectively than steppe soil. Where a forest already exists, enough moisture is retained in the soil for the forest to survive. Where a steppe is located, there is insufficient water for forest development. If humidity or temperature changes, the boundary between forest and steppe gradually shifts. Arid forests are replaced by steppes, and humid steppes become overgrown with forests. However, a wide strip remains where the two types of ecosystems alternate in a mosaic pattern. Riparian areas, ravines, and lowlands become forested, while sandy areas and sun-warmed slopes become steppe-like. The characteristic vegetation type depends on the soil and climate, influences them, and determines almost the entire composition of the community that develops in a particular place. How can the relationships between different types of communities be represented? There are two main methods: ordination (i.e., arranging in a specific space in a specific order) and classification (i.e., dividing into separate groups—classes or taxa). Ordination emphasizes the continuity of changes in properties, while classification emphasizes the discreteness of breaks. An example of community ordination is shown in Fig. 3.4.1; an example of a multi-level hierarchical classification of biomes is given below. The main biomes on Earth are as follows. Terrestrial Biomes Tundra. A biome of cold, humid climate characterized by negative average annual temperatures, precipitation of about 200-300 mm per year, and, most often, the presence of permafrost. Arctic tundra, located at high latitudes, and alpine tundra, located in high mountains, are distinguished. Vegetation consists of low-growing perennials: lichens, mosses, grasses, and shrubs. Taiga. A forest biome of cold climate with long, snowy winters and precipitation exceeding evaporation. The main forest-forming species are conifers, with low species diversity of trees (1-2 dominant species). Deciduous Forest. A forest of the temperate zone. It develops in regions with moderately warm summers and relatively mild winters with frosts. Characterized by uniform precipitation distribution, absence of droughts, and precipitation exceeding evaporation. In autumn, as daylight shortens, leaves fall. Deciduous forests are relatively species-rich and characterized by a complex vertical structure (presence of several layers). Steppe. An area of grassland vegetation in the semi-arid zone of the temperate climate. The most numerous grasses are feather grasses and sedges, many of which form dense sod. Potential evaporation exceeds precipitation. Characterized by soils rich in organic matter—chernozems. Synonyms include prairie, pampas, veld. Savanna. Tropical grassland and tree communities that develop in areas with a distinct alternation of dry and wet seasons. Individual trees or clusters of shrubs are scattered among open grassy areas. Desert. A rather diverse group of biomes located in areas with extremely arid climates or, in the case of arctic or alpine deserts, extremely low temperatures. Sandy, rocky, clay, salt, ice, and other deserts are known. Typically (except for ice deserts, which develop in very cold conditions), either the average annual precipitation is less than 25 mm, or conditions ensure very rapid evaporation of moisture. Chaparral. Sclerophyllous shrublands in the Mediterranean climate with mild, rainy winters and dry summers. Characterized by significant accumulation of dry wood, leading to periodic fires. Seasonal Tropical Forest. Found in regions with hot climates and high rainfall, where precipitation is unevenly distributed throughout the year, with a dry season. Extremely species-rich. Evergreen Rainforest. The richest biome, located in regions with high rainfall (>2000 mm) and almost constant temperature (around 26°C). These forests contain 4/5 of all plant species on Earth, with tree vegetation predominating. Freshwater Biomes Lentic (standing) waters. Puddles, oxbow lakes, natural and artificial ponds, lakes, and reservoirs. Life conditions are determined primarily by depth (and light penetration) and the amount of biogens. Exchange of biogens and gases between the surface and depth is often difficult. Lotic (flowing) waters. Streams, brooks, and rivers. Conditions depend heavily on the flow rate. Capable of transporting significant amounts of water and other inorganic and organic substances, closely linked to surrounding terrestrial systems. Wetlands. Water bodies with a high amount of organic matter, the decomposition of which is slowed down due to a lack of oxygen in the water; predominantly characteristic of temperate and moderately cold climates. Marine Biomes Pelagic Zone. Open ocean and marine depths far from the coast. Producers (primarily phytoplankton) are concentrated in a relatively thin surface layer of water where light penetrates. Continuous sinking of biogens from the surface to the depths is characteristic. Continental Shelf. The coastal zone of seas and oceans, reaching a depth of approximately 200 m. Rich in species and diverse marine communities. The most diverse aquatic ecosystems are found in coral reefs, which also belong to the continental shelf. "Hotspots" of biodiversity are also characteristic of great depths—for example, at the sites of volcanic gas vents in seawater ("black smokers" and other phenomena). Upwelling Zones. Relatively small areas of the ocean where deep, biogen-rich waters rise to the surface. They have an exceptional impact on the productivity of the entire ocean. Estuaries. Zones of mixing of river and sea waters, formed in seas opposite the mouths of large rivers. Characterized by a significant amount of organic matter carried by rivers into the sea and constant fluctuations in salinity. Additional Materials: Educational Model: Distribution of Biomes on Earth
3.03. Examples of Ecosystems
D. Shabanov, M. Kravchenko. Ecology: Biology of Interactions Section 3. Biogeocenology and Ecology of Communities
3.05. Ecological Balance