What types of trees are found in temperate latitudes. Mixed and deciduous forests. Scale in ecology

16.06.2019

Temperate forests are forests found in temperate regions such as eastern North America, western and central Europe, and Northeast Asia. Temperate forests are found at latitudes between approximately 25° and 50° in both hemispheres. They have a temperate climate and a growing season that lasts 140 to 200 days a year. Precipitation in temperate forests tends to be evenly distributed throughout the year. The temperate forest canopy is primarily composed of broadleaf trees. In the polar regions temperate forests replace .

Temperate forests first appeared about 65 million years ago, during the beginning cenozoic era. At that time, global temperatures dropped and forests sprang up in more temperate regions above the equator. In these regions, the temperature was not only cooler, but also showed seasonal fluctuations. Plants evolved and adapted to climate change.

Today, in temperate forests that are closer to the tropics (where the climate has not changed so much), trees and other plant species are more reminiscent of vegetation from. Temperate evergreen forests can be found in these regions. In areas where climate change has been more intense, deciduous trees have evolved (they shed their leaves each year when the weather turns cold as an adaptation, allowing the trees to withstand seasonal temperature fluctuations in these regions).

Main characteristics of temperate forests

The following are the main characteristics of temperate forests:

grow in temperate regions (at latitudes between about 25°-50° in both hemispheres);
experiences distinct seasons, with a growing season that lasts 140 to 200 days;
the forest canopy consists mainly of deciduous trees.

Classification of temperate forests

Temperate forests are divided into the following habitats:

Temperate deciduous forests - grow in eastern North America, Central Europe and parts of Asia. They are characterized by temperature fluctuations from -30° to +30° C throughout the year. They receive about 750-1500 mm of precipitation per year. Vegetation deciduous forests includes a variety of broad-leaved tree species (eg oak, beech, maple, hickory, etc.) as well as various shrubs, perennial grasses, mosses and mushrooms. Temperate deciduous forests are found in mid-latitudes, between the polar regions and the tropics.
Temperate evergreen forests - consist mainly of evergreen trees that renew their foliage throughout the year. Temperate evergreen forests are found in eastern North America and the basin mediterranean sea. They also include subtropical broadleaf evergreen forests in the Southeastern United States, southern China, and eastern Brazil.

Some of the animals that inhabit temperate forests include:

The Eastern Chipmunk (Tamias striatus) is a species of chipmunk that lives in the deciduous forests of eastern North America. Oriental chipmunks are small rodents with red-brown fur adorned with dark, light and brown stripes that run along the back of the animal.
The white-tailed deer (Odocoileus virginianus) is a species of deer that inhabits deciduous forests in eastern North America. White-tailed deer have a brown coat and a tail that is white on the back.
The American black bear (Ursus americanus) is one of three species of bears that live in North America, the other two and . Of these species, black bears are the smallest and timid.
Robin (Erithacus rebecula) is a small bird from the flycatcher family (muscicapidae). The range of robin habitat is quite extensive and includes: Northwest Africa from Morocco to eastern Tunisia and the Mediterranean coast, as well as most Eurasian continent.

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Deciduous forests are located along the southern edge of the forest zone.

Among deciduous species, broad-leaved species are distinguished, which have large leaves(oak, maple, ash, beech, elm, elm, etc.), and small-leaved (birch, aspen). The former are relatively shade-tolerant, so their plantations are shady. The latter need a significant amount of light, and the forests of them are light. Obviously, in connection with such an attitude towards light, broad-leaved species in the struggle against small-leaved species gain the upper hand and form the most stable phytocenoses.

Of the broad-leaved forests, oak forests, or oak forests, are the most widespread in the USSR. They are floristically richer than coniferous forests, almost always contain impurities of ash, linden, maple, elm, elm, and in the west - beech and hornbeam; in the second tier there are wild apple trees and maples, the undergrowth usually consists of hazel or forest hazel. Since oak forests belong to ancient phytocenoses that developed back in the Tertiary, they develop in a mild climate and on rich soils, they have a complex structure: they usually have two tree tiers, two shrubs, and the grass cover also breaks up into three or four tiers. The grass cover includes grasses with wide leaf blades, the same sedges, various dicotyledons, etc. When they die, all these plants form a thick dead layer that interferes with the development of a moss carpet, which, as a rule, is absent in oak forests.

In the spring, while the oak leaves have not yet unfolded, numerous oak ephemerals develop, forming a colorful carpet of yellow anemone, purple corydalis, azure snowdrops, pink toothbrush, etc. Snowdrops appear right from under the snow.

In the first half of summer, linden blossoms, and the herbaceous vegetation becomes poorer; this impoverishment progressively increases until autumn, when the grass dries up, although some spring species bloom a second time. Plants that bloom in spring before the forest is shaded have mostly yellow or pink-violet corollas, while those that bloom already in the shade of oak crowns have white corollas.

Oak forests of Eurasia are characteristic of the continental climate. In more favorable conditions, they are replaced by beech forests, and in a mild Mediterranean-Atlantic climate by chestnut forests. AT Western Europe and in the Caucasus leading role beech forests play, in Middle-earth they are joined by walnut forests.

Deciduous forests in North America are very diverse. In the area of the Appalachian Mountains (34-40°N), the lowest vertical zone is represented by a belt of chestnut forests, which are distinguished by a wide variety of species. The oak distribution area, gravitating towards the Great Lakes region, is characterized by plantations of red oak (Quercus rubra), black oak (Q. velutina), white oak (Q. alba), hickory (Hicoria ovata), etc. forests of Nyssa aquatica and swamp cypress Taxodium distichum grow in water areas; in places less flooded, in addition to these species, ash and poplar also grow, and in even drier places - Caribbean pine, oak, ash, hickory, red maple, etc.

Between the areas occupied by deciduous forests and the taiga zone, there are often mixed forests where conifers and hardwoods meet.

compact array of trees and shrubs. More than a third of the land surface is covered with forests or suitable for their development. However, the areas occupied by forests are unevenly distributed between the continents and even within each of them. For example, forest cover covers almost half of South America, about a third of Europe and the US, and much of Africa and Asia; in Australia, on the contrary, there are few of them, and some major countries, such as Egypt, are generally treeless. Forests are completely absent in Antarctica and Greenland, but low trees grow in the extreme south of the latter.

Although the most characteristic feature of a forest is the presence of trees and shrubs, it is not just woody vegetation, but a complex community (or ecosystem) consisting of closely related elements. Like all ecosystems, the forest is formed by a combination of living organisms (biota) and the inanimate (abiotic) environment of their habitat. The forest biota includes, in addition to trees and shrubs, other plants (grasses, mosses, fungi, algae, and lichens), as well as vertebrates and invertebrates, and bacteria. The abiotic component is represented by air, soil and water. All these components are alive and inanimate nature are closely interconnected due to the passage of energy flow through the ecosystem and the circulation of oxygen and other substances in it. For example, sunlight is used by plants for photosynthesis, the process of making organic nutrients from water and carbon dioxide. Since this is characteristic only of green plants, all animals must eat either these plants or other animals, which in turn eat plants. Thus, plants directly or indirectly provide food for all other organisms. As a by-product of photosynthesis, oxygen is released into the air, replenishing its reserves in the atmosphere. Bacteria and other organisms involved in the decomposition of organic matter play a vital role in forest ecosystems Oh. They turn complex chemical compounds, which make up metabolic wastes and the remains of plants and animals, into simple ones that can be reused by organisms ( see also ECOLOGY).

In most forests, several tiers are distinguished, formed by the foliage of plants. different heights. The topmost, consisting of the crowns of the most tall trees, is called the first tier or forest canopy. In some areas, especially in the tropics, individual giant trees rise significantly above the canopy. If there are other relatively closed tree tiers under it, they are called the second, third, etc. Shrubs, tall grasses (in some types of forest) and stunted trees form the undergrowth. The herbaceous layer consists of subshrubs and grasses. Mosses, lichens and creeping plant species form a surface, or ground, layer.

Organic matter, consisting of fallen leaves, twigs, flowers, fruits, bark and other plant remains, as well as feces and animal carcasses, shells of pupae and larvae, etc., forms forest floor on the soil surface. In most forests, the litter is the most densely populated layer. Often there are several million living organisms per square meter, from protozoa and bacteria to mice and other small mammals.

The edge of the forest is a transitional strip between it and the adjacent type of vegetation. It is characteristic that within the limits of the edge the trees are covered with foliage almost to the very ground, and many shrubs and herbs common here are rare or not found at all in the forest and in neighboring open plant communities. Some bird species, often thought of as forest birds, actually live mainly on forest edges, which are also an important habitat type for mammals.

Geography forest resources the globe . M., 1960
Forests of the USSR, tt. 15. M., 19661970
Walter G. Vegetation of the globe, tt. 13. M., 19691975
Bukshtynov A.D., Groshev B.I., Krylov G.V. The woods. M., 1981

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FOREST, compact array of trees and shrubs. More than a third of the land surface is covered with forests or suitable for their development. However, the areas occupied by forests are unevenly distributed between the continents and even within each of them. For example, forest cover covers almost half of South America, about a third of Europe and the US, and much of Africa and Asia; in Australia, on the contrary, there are few of them, and some large countries, such as Egypt, are generally treeless. Forests are completely absent in Antarctica and Greenland, but low trees grow in the extreme south of the latter.

Although the most characteristic feature of a forest is the presence of trees and shrubs, it is not just woody vegetation, but a complex community (or ecosystem) consisting of closely related elements. Like all ecosystems, the forest is formed by a combination of living organisms (biota) and the inanimate (abiotic) environment of their habitat. The forest biota includes, in addition to trees and shrubs, other plants (grasses, mosses, fungi, algae, and lichens), as well as vertebrates and invertebrates, and bacteria. The abiotic component is represented by air, soil and water. All these components of animate and inanimate nature are closely interconnected due to the passage of energy flow through the ecosystem and the circulation of oxygen and other substances in it. For example, sunlight is used by plants for photosynthesis, the process of making organic nutrients from water and carbon dioxide. Since this is characteristic only of green plants, all animals must eat either these plants or other animals, which in turn eat plants. Thus, plants directly or indirectly provide food for all other organisms. As a by-product of photosynthesis, oxygen is released into the air, replenishing its reserves in the atmosphere. Bacteria and other organisms involved in the decomposition of organic matter play a vital role in forest ecosystems. They convert the complex chemical compounds that make up metabolic waste and the remains of plants and animals into simple ones that can be reused by organisms.

In most forests, several tiers are distinguished, formed by foliage of plants of different heights. The uppermost, consisting of the crowns of the tallest trees, is called the first tier or forest canopy. In some areas, especially in the tropics, individual giant trees rise significantly above the canopy. If there are other relatively closed tree tiers under it, they are called the second, third, etc. Shrubs, tall grasses (in some types of forest) and stunted trees form the undergrowth. The herbaceous layer consists of subshrubs and grasses. Mosses, lichens and creeping plant species form a surface, or ground, layer.

Organic matter, consisting of fallen leaves, twigs, flowers, fruits, bark and other plant remains, as well as feces and animal carcasses, shells of pupae and larvae, etc., forms forest litter on the soil surface. In most forests, the litter is the most densely populated layer. Often there are several million living organisms per square meter - from protozoa and bacteria to mice and other small mammals.

Forest classifications.

There are many types of forests and many ways to classify them. For example, they can be classified by geographical distribution (eastern, tropical, etc.) or by position in the relief (plains, floodplains, etc.). They can also be grouped according to the seasonal aspect. Thus, forests are considered evergreen if living foliage is preserved on trees. all year round. In a deciduous forest, the leaves fall with the onset of the cold or dry season, and the trees remain bare for several weeks or months each year. Some forests, such as the oak forests of the southwestern United States, are formed by trees shedding old leaves and forming new ones within two to three spring weeks. Such communities can be called semi-deciduous or semi-evergreen.

Sometimes the basis for the classification of forests are characteristics the tree species that form them, and the forests are respectively divided into coniferous, broad-leaved, mixed, etc. A combination of morphological and seasonal characteristics is also possible in the classification (for example, evergreen coniferous or broad-leaved deciduous forests). In another case, the names of forest-forming species are used (oak-brown or red-oak-white-oak-holokary forests, etc.).

For some purposes, especially commercial ones, it is useful to classify forests according to the relative age of the trees. For example, stands of the same age consist of trees of approximately the same age, while stands of different ages consist of trees of a wide age range.

There are also sparse (light) or closed forests. In the first case, tree crowns, as a rule, do not touch or overlap, and the canopy is discontinuous. In a closed forest, it is more or less continuous and is formed by intertwining or overlapping tree crowns.

Another descriptive classification is based on the degree of forest disturbance, mainly as a result of human activities. For example, in a virgin (primary) forest, mainly mature or old (overmature) trees grow, and the rest of the vegetation is not artificially changed. On clearings, conflagrations and abandoned fields, secondary, or derivative, forests develop.

FACTORS AFFECTING FOREST GROWTH

It is believed that the distribution of forests is determined mainly regional peculiarities climate, i.e. mainly by temperatures and precipitation, and at a more local level by microclimate. Soils, fires, animals and non-woody vegetation play an important role in creating microclimatic conditions.

Climate and relief.

In general, forests are common in regions where the annual rainfall is at least 250-380 mm, and the duration of the frost-free period is at least 14-16 weeks. Moisture conditions depend on the temperature and the nature of the relief. For example, in the Tucson region (Arizona, USA) there is a desert, and only rarely scattered low trees and saguaro cacti (giant carnegia) grow on the watersheds, and in the west of Colorado, in the national monument of the same name, the slopes of the valleys and hilltops are covered with sparse forests from juniper and cedar pine. Differences in the vegetation of these areas are explained by climatic conditions: despite the same amount of precipitation (approx. 280 mm per year), relative humidity lower in Arizona because due to more high temperatures more water lost through evaporation and transpiration.

Low temperatures also make water inaccessible to plants (so-called physiological dryness). Under such conditions, cold deserts are formed. The absence of trees in the polar regions and high mountains is explained by the short growing season and the inaccessibility of frozen water for plants.

The impact of local climatic conditions is most noticeable in latitudinally extending valleys or on the slopes of mountain ranges of the same orientation. In the Northern Hemisphere, the slopes of the northern exposure are not illuminated by direct sunbeams. As a result, they are colder than the southern ones, they have less evaporation and do not change temperatures so quickly and abruptly. Rock weathering is also weaker here, and these slopes are usually steeper. In the semiarid regions, forests can grow on them, while in the southern regions adjacent to them, only shrubs or herbaceous vegetation. In humid areas, both slopes are usually covered with forest, but beech, maple, hemlock and other moisture-loving tree species grow on the northern ones, and oak, hazel and other trees that can tolerate long periods of low soil moisture on the southern ones.

Soils.

Humidity and chemical composition Soils are the main conditions that determine the distribution of trees. As mentioned above, humidity depends on the amount of precipitation and topography. In addition, it is affected by the structure of the soil, i.e. the size of its constituent particles, the degree of their aggregation, or sticking together, and the amount of organic matter present. In general, the larger the particles, the less they are aggregated, the lower the content of organic matter and the water-holding capacity of the soil.

On soils with a high content of certain chemicals, forests and even individual trees usually do not grow at all. A striking example– soils formed on serpentinites – rocks consisting of magnesium silicate with an admixture of iron. Serpentine moors are small, prominent patches of herbaceous vegetation scattered among the forests of Pennsylvania, Maryland, California, several other states, and Canada. Soil salinization is much more widespread, excluding the possibility of growth of almost all tree species. It is observed along the shores of the seas and in deserts.

Some properties of soils, mainly their chemistry, affect the composition of tree species that settle on them. This is especially noticeable in places where alkaline soils formed on limestones closely coexist with acidic soils formed on sandstones, gneisses and shales. For example, in the eastern United States, sugar maple, beech, and basswood are common in calcareous soils, while oak and hazel often dominate in acid soils. In the southwestern United States, limestone soils are treeless, although forests grow nearby on soils formed on other rocks.

Fires.

Few trees can survive fires that recur annually or at intervals of several years, and most species do not tolerate fire at all. Thus, frequent fires usually do not allow the development of the forest and lead to the spread of other types of vegetation, in particular herbaceous. For example, a significant part of the prairies in the United States and Canada, probably for this reason, remained treeless. On almost every continent, areas devoid of trees due to frequent fires cover areas from a few hectares to thousands of square kilometers.

Within forest regions, fires can have a profound effect on forest composition. For example, in the western United States, lodgepole pine and Douglas pine (Menzies' pseudosuga) are commonly found in in large numbers either after strong fires, or in areas that often burn out. Under similar conditions, in the northeast of the United States, Banks pine grows, and in the southeast - pine and bog pine. In the absence of fires, these species are eventually replaced by other tree species. Forestry is now using the method of planned burning, which favors the growth of fire-resistant tree species with valuable wood.

Animals

have a significant impact on both distribution and composition of forests. For example, rabbits in Great Britain and other countries not only leave huge areas treeless, but also deprive them of shrub cover. It is possible that bison are partly responsible for the deforestation of the prairies of the Midwest of North America. Even small mammals, such as mice, can interfere with the reforestation of burnt areas and abandoned agricultural land by eating seeds and nibbling tree shoots. And yet, of all living beings, the most powerful influence on forests is exerted by a person who cuts down and burns them, poisons them with pesticides until they are completely destroyed, and then plows up or builds up the vacant lands. Livestock grazing also hinders reforestation in clear cut areas.

Other factors.

Few studies have focused on the role of shrubs, herbaceous plants, lichens and mosses in crowding out forests or slowing their recovery. However, in forest regions, areas covered with shrubs sometimes remain treeless for more than 30 years. Even a herbage of grasses or other plants, such as goldenrod or asters, can prevent many tree species from settling. Over the past few years, it has been experimentally shown that many of these plants release chemical compounds that inhibit the germination of tree seeds.

FOREST HISTORY

The age of the Earth is 4.5–6.6 billion years. Primitive life forms probably arose very early in our planet's history, since fossils plant cells were found in rocks older than 3.1 billion years. The oldest organisms known to us are blue-green algae and bacteria, fossils of which have been found in Africa. Tree plants, and thus the first forests, are relatively recent, and their history spans less than 10% of the Earth's lifetime. Although it would seem that trees are evolutionarily more progressive than flowering grasses, fossil remains indicate that the latter descended from tall tree-like ancestors, and not vice versa.

The oldest land plants are known from the Upper Silurian deposits of Australia, ca. 395 million years. Vegetation, consisting of low shrub forms, spread widely on land in the Early Devonian, ca. 370 million years ago. The first trees were giant horsetails and club mosses, reaching a height of more than 7.5 m. These trees in the Late Devonian formed low-growing forests with an undergrowth of primitive ferns and other small plants.

During the Carboniferous period, which began approximately 345 million years ago, dense forests of giant horsetails, club mosses and tree-like ferns up to 30 m or more high grew on vast areas of land. Apparently, they were confined to waterlogged lowlands, where dead leaves and fallen trunks did not decompose, but accumulated in the form of peat. Subsequently, the peat was covered with silty and sandy deposits. As they accumulate, peat under conditions high pressure gradually transformed into coal. It often contains numerous plant fossils. An important evolutionary event in carboniferous period was the appearance of primitive gymnosperms - seed ferns and cordaites.

The Permian period began c. 280 million years ago with a sharp transformation. The climate became more and more arid, and the face of the planet changed under the influence of powerful glaciation of the Southern Hemisphere, mountain building and catastrophic redistribution of land and sea. During this period, giant horsetails, club mosses and tree ferns died out, they were replaced by primitive cycads and conifers. The appearance of the forests of the Earth began to change, and this process continued during the Mesozoic era, which began ca. 225 million years ago. In the Triassic and Jurassic periods, cycads and conifers were the main forest-forming species. A lot of ginkgos appeared. One of the species - ginkgo biloba - is still in vivo found in Eastern China and planted as an ornamental tree in cities Southern Europe, East Asia and North America. Sequoias also grew in abundance, now limited to California and southern Oregon, and during the Triassic and Jurassic they were found in much of North America, Europe, Central Asia, and even Greenland. were most widely distributed coniferous forests from species similar to modern araucaria. The petrified trunks of coniferous trees have been preserved in national park Petrified Forest (in translation - stone forest) in Arizona and some other parts of the world.

The oldest known angiosperms, or flowering plants, are palms, the remains of which have been found in Triassic deposits in Colorado. Next, Jurassic period characterized by an increase in the diversity of flowering plants. The role of conifers and other gymnosperms decreased, and gradually over Cretaceous(135-65 million years ago), flowering plants became dominant, mostly trees and shrubs. They were represented by the ancestors of such modern species as ficus, magnolia, holly, oak, sassafras, willow and maple. During the Cretaceous and Paleogene, metasequoia, the "deciduous" conifer tree, now growing only in the interior of China. The wide development of forests of this composition in North America, in Greenland and in most of the Arctic indicates that a mild climate prevailed on Earth.

The Paleocene period, which began ca. 65 million years ago, was characterized by warm humid climate. Under such conditions, the flora was distinguished by species diversity and abounded in angiosperms. Almost everywhere in the Northern Hemisphere, forests were distributed, similar in composition to modern forests tropics and temperate zone. The most northern of the main types of flora then existing, the arcto-tertiary, included deciduous trees and other plants very similar to those currently growing in eastern North America and Asia. The second type of flora - tertiary neotropical - was confined to more low latitudes and was represented by evergreen broad-leaved species related to modern species growing in the tropics and subtropics.

In the Neogene climatic conditions, apparently became more diverse, and there was a shift in flora types towards the equator. Forest areas were shrinking, and grass communities were spreading over ever larger areas. The third type of flora - madrotetian - was apparently formed on the basis of the above two in connection with the progressive aridization of the climate in the west of North America. This flora is characterized by small-leaved trees and shrubs, close to those now growing in the southwestern United States and Mexico.

The arctotertiary flora has spread circumpolarly in the northern regions of the globe. Forests throughout this territory were marked by a striking similarity. They were dominated by broad-leaved species (elm, chestnut, maple), as well as alder and metasequoia. In the Late Cenozoic, many trees that are now characteristic of the eastern regions of the United States with wet summers disappeared in the west of North America as a result of mountain building processes and climate changes that took place there. Conifers, which played a minor role in the Arcto-Tertiary flora, became dominant in the western forests.

The final period of the Cenozoic era, called the Quaternary, began c. 1.8 million years ago and continues to this day. It was characterized by the alternation of extensive continental glaciations and warm interglacial epochs, similar to the modern one. Despite the short duration Quaternary period(only 0.5% of the history of our planet), it is with him that the evolution of man, who has become the dominant species on Earth, is associated. In Europe, the composition of forests has become simpler, as many tree species have died out, and the area of forests themselves has been significantly reduced everywhere. Huge areas of land were repeatedly covered with powerful ice sheets, and then freed from ice. Even now, 10,000 years after the end of the last glaciation, the forests of the Northern Hemisphere are still adapting to the climate changes that have occurred since then.

FORESTS OF THE GLOBE

By the nature of the forest cover, three large latitudinal zones can be distinguished: boreal, or northern, coniferous forests (taiga); temperate forests; tropical and sub rainforest. In each of these zones, there are several types of forests.

Zone of boreal (taiga) forests

Zone boreal forests- the most northern. It extends from 72° 52º N. in Asia (which is much north of the Arctic Circle) to about 45 ° N.L. in the central part of this continent and in the west of North America. There is no similar zone in the Southern Hemisphere.

The taiga forests are characterized by evergreen conifers, mainly different types spruces, firs and pines. Deciduous deciduous trees are also often found, for example different kinds birch, alder and poplar. In Siberia, larch dominates, shedding needles for the winter.

Temperate forest zone.

Such forests are common in North and South America, Asia, Africa, New Zealand and Australia. They are represented by summer-green (deciduous), broad-leaved, coniferous, evergreen, mixed (rain), hard-leaved (sclerophilous) and other less common types of forests.

Summergreen forests are common in eastern North America, the British Isles, mainland Europe, East Asia and Japan, as well as in the extreme southwest of South America. Usually they consist of only one tree layer, although in some areas a second one is also expressed. Shrub undergrowth is developed in some places, usually not having a continuous distribution. There are few tree vines here, and as a rule, only mosses, liverworts and lichens are represented from epiphytes. Herbaceous plants play an important role blooming in spring when the trees are bare. Most trees also bloom in the spring, before the leaves come out.

Coniferous forests of temperate latitudes are distributed mainly in the west and southeast of North America and in Eurasia. The most characteristic of them are various types of pines, but other conifers are also common in the west of North America.

Evergreen mixed (rain) forests of temperate latitudes are found where there is a lot of precipitation, and temperatures rarely fall below 0 ° C. Such communities are found in the southwest of North America, the southeast of the United States, southern Japan, Korea, China, Australia, New Zealand and the extreme south of Africa. Oaks, magnolias and notophaguses dominate here, to which conifers are mixed. Of the epiphytes, lichens and mosses are most characteristic, densely covering the lower parts of tree trunks.

Hard-leaved (sclerophyllous) forests are common in areas with dry, hot summers and cooler, wetter winters, dominated by evergreen trees and shrubs with small, leathery leaves. Trees are usually stunted with twisted trunks. Sparse forests of this type are typical for the Mediterranean and Black Sea regions, where evergreen oaks and pines predominate. Forests of the Mediterranean type, but with a different species composition, are also found in the extreme south of Africa, in Australia, Mexico, central regions Chile and the southwestern United States.

Tropical and subtropical forest zone.

This zone is the leader in species diversity of tree species. For example, at least 2,500 tree species grow in the Amazon basin alone. It is believed that there are about the same number on the Malay Peninsula. As a rule, the trees of this zone are thin-barked with thick leathery leaves covered with a wax coating. Usually the leaves fall off at the same time and are quickly replaced by new ones, so the plants are never naked. Although some species drop all foliage at once, in different species this leaf fall occurs at different times and is not associated with any specific seasonal phenomenon. In tropical rainforests, caulifloria is extremely widespread, i.e. the development of flowers and fruits directly on the trunk and branches of trees.

Savanna forests are common in tropical regions with a distinct dry season and less annual rainfall than in the dense forest belt. It is characterized by trees from the legume family, usually with a flat umbrella-shaped crown, shedding foliage in the dry season. As a rule, they are far apart from each other, except in places where groundwater is near the surface. The grass cover is almost continuous and is formed mainly by grasses. Usually the height of the trees is less than 18 m, and often no more than 3–4.5 m, and therefore, during the wet season, grasses can rise above the tree layer. Savannah forests cover most of Cuba and other Caribbean islands, many parts of Brazil, northern Argentina, Eastern and Central Africa and some areas of India, China and Australia.

In those tropical regions where precipitation is even less and the dry season is longer, communities of xerophilous thorny trees and shrubs are widely developed. They are common in South America, the Caribbean, Mexico and Central America, northern Africa and Australia. Tree species here are deciduous or with leaves in the form of scales. Leafless shrubs with green stems are also characteristic. Many species are covered with spines, and the stems or roots of plants are often swollen and composed of water-storing tissues.

Typical savannas are common in the tropics and subtropics. These are "park" communities in which individual deciduous or evergreen trees or their groups are scattered among a dense carpet of high grasses. Savannahs are found in hot climates with quite large quantity precipitation (more than 2000 mm per year), relatively evenly falling during the wet season lasting from 4 to 6.5 months. Huge areas can be flooded during the rainy season. Acacias and other legume trees are most common in savannahs, but palm trees are also common.

The roots of most tree species here reach the usually shallow water table, so the trees are only short of moisture during exceptionally dry periods. Their trunks are mostly low and often twisted, and the crowns are located at a height of 3–6 m. Savanna grasses up to 4.5 m high sometimes rise above the trees.

FOREST MANAGEMENT AND FOREST PROTECTION

The science that studies forests is called forest science. One of its main applied industries is forestry, which develops methods for reforesting, utilizing and reforesting clear cuts, burnt areas and otherwise disturbed forest areas. It is also dealing with the problem of creating forests in formerly treeless areas. Forestry requires knowledge of the properties of tree species and their genetics in order to breed hybrids or select natural lines with special traits, such as increased resistance to insect or disease attack and high growth rates. The direction called dendrology is associated with the classification of trees. Another area of forestry is the ecology of tree species.

Dendrometry, or forest inventory, is the establishment of quantitative parameters of forests: timber reserves, height and quality of trees and stands. Such data are needed to evaluate forests for commercial purposes, as well as to study their development and determine the effectiveness of various methods of their use and cultivation.

Forest inventory - a system of measures for breeding and purposeful use forests based on knowledge in the field of forestry, socio-economic information and business experience. The first attempts at rational forest management were aimed at improving hunting conditions and the renewal of game animals. In the 18th century, forest management work began in Germany in order to increase wood production. Although in the United States already in 1817 protected plantations appeared to provide ship timber for the navy, but only at the end of the 19th century. showed interest in forest management. Initially, two goals were pursued: water protection and logging. Later, the concept of multi-purpose use of forest areas was formed: for wood production, reproduction wildlife, protection of water and soil resources, recreation, scientific research, satisfaction of aesthetic and other needs. Usually one of these functions predominates, but there are also multi-purpose forests.

Another important area of modern forestry is the protection of forests. Every year, forests are severely affected by insect and disease infestations, fires and adverse weather events such as hurricanes, droughts and heavy snowfalls with gusty winds, resulting in icing of trunks and branches. A person can also apply great harm irrational logging, grazing in unsuitable for this purpose forest lands, the destruction of predators that control the number of pests, and direct deforestation.

Protection of wildlife resources.

Many species of game animals are part of forest ecosystems and are often found in forest lands and where forests alternate with open landscapes. In addition, many species of fish abound in dense, cool waters in forested watersheds. Beaver, mink, elk, bear, fox, deer, turkey, partridge and other large and small game animals inhabit mainly forests. Some species prefer old forests, others prefer young communities with dense undergrowth and undergrowth, and still others live where forests alternate or border on treeless areas. One of the objectives of the rational use of forests is to create the most favorable conditions for the habitat of a certain species of animals or to ensure the greatest species diversity fauna.

Protection of waters and soils.

Forests in general are very effective in regulating surface runoff and conserve water in the soil. Everyone who has taken shelter from the rain under the trees knows that their crowns intercept and retain part of the precipitation. Most of the rest of the water is absorbed by the soil rather than running down the surface into rivers and lakes. Therefore, soil erosion is poorly developed in forested areas. Although part of the absorbed moisture again comes to the surface from the springs, this does not happen immediately, but after a few days or weeks, and is not accompanied by sharp floods. Another part of the infiltrated moisture enters deeper aquifers and replenishes groundwater.

Fighting forest fires and their prevention.

Fires damage or destroy valuable timber and adversely affect reforestation. Depriving the soil of vegetation cover, they lead to a serious and long-term deterioration of the condition of watersheds, reduce the recreational and scientific value of landscapes. At the same time, wild animals suffer or die, houses and other buildings burn down, people die.

Of all the events that cause economic damage to forests, forest fires are the most controllable, as most of them are caused by humans.

To prevent forest fires, mass propaganda (posters, thematic exhibitions, special environmental programs) and compliance with laws restricting the use of fire in forests are important. Reducing the risk of fire is equally important. To do this, flammable shrubs are removed along the roads. To reduce the risk of fire from lightning strikes, deadwood is cut down. Inside the forests, fire-fighting clearings are laid, dividing the forest into sections, within which the fire is easier to localize and extinguish.

When a forest fire starts, first of all, it is necessary to accurately and quickly detect its source. During periods of special fire danger, for example, during a drought, air patrols are additionally active. When a fire is spotted, firefighters are alerted to its location and extent. Dispatchers quickly form and dispatch fire brigades, often assisted by volunteers. While the fire is being fought, observers on towers and in the air transmit by radio information about the speed and direction of its spread, which helps to quickly extinguish the fire.

Control of pests and diseases.

The cost of wood loss due to insect damage and disease outweighs the damage caused to forests by all other factors, including fires.

AT normal conditions the number of insect pests and disease-causing organisms (pathogens) in forests is relatively low. They thin out dense young stands and kill weak or damaged trees. Nevertheless, from time to time the number of such insects or pathogens increases dramatically, which leads to the death of trees over large areas. The complete extermination of all harmful species is economically unprofitable and biologically unreasonable. Therefore, the task of protecting forests is to prevent outbreaks of their numbers and reduce losses in cases where such outbreaks do occur.

Research is needed to develop methods for protecting forests from damage. They include determining the species of forest pests, studying their life cycle, food or host species, and natural enemies. These works make it possible to develop new lines or hybrids of tree species that combine resistance to diseases and pests with useful economic properties.

To reduce the populations of forest pests such as gypsy moth, spruce budworm and moth, aerial spraying of insecticides was widely used in the past. However, this destroys not only the pests against which it is used, but also beneficial insects. Insecticides are also deadly to birds, mammals, and other animals, so such measures are usually resorted to only when all other measures have failed.

Herbicides are used to kill intermediate hosts of disease-causing organisms or infected trees in order to limit the spread of the disease. Direct treatment of plants with pesticides is usually advisable only in nurseries and artificial plantations. Most pathogen killers are applied to the soil or applied at the seedling stage before planting.

A number of preventive measures are applied to avoid or reduce the damage caused by pests or diseases. Particularly susceptible to disease, weak or infected trees are removed at periodic sanitary cuttings. Intermediate hosts of pathogens are destroyed by herbicides. Measures are being taken to protect and increase the number of natural enemies of insect pests.

FOREST CLEARING

The destruction of forests on earth is happening at an alarming rate. In the mid-1990s, according to the World Resources Institute, tropical forests alone were disappearing at a rate of 16-20 million hectares per year, i.e. 0.6 hectares per second, mainly to meet the needs of a growing population for agricultural land and timber. AT temperate zone Northern hemisphere forests are heavily affected by air pollution industrial enterprises, and the vast forests of Siberia (taiga) are under the threat of large-scale deforestation.

Deforestation is a serious global environmental problem. Forests in the process of photosynthesis absorb a huge amount of carbon dioxide, so their destruction can lead to an increase in its concentration in the atmosphere, which, as many scientists believe, will increase in the 21st century. will contribute global warming in connection with the so-called. greenhouse effect. Moreover, the now widespread burning of tropical rainforests in developing countries leads to an increase in carbon dioxide in the atmosphere. The rainforests are still home to most of the planet's animal, plant and microbial species, the diversity of which is constantly declining. Some of them are used or will be used in the future in medicine and agriculture.

Literature:

Geography of the world's forest resources. M., 1960
Forests of the USSR, tt. 1–5. M., 1966–1970
Walter G. Vegetation of the globe, tt. 1–3. M., 1969–1975
Bukshtynov A.D., Groshev B.I., Krylov G.V. The woods. M., 1981

Broad-leaved forests are common in areas where the natural landscape is characterized by an optimal ratio of heat and moisture. The geographic map of the Earth captures significant areas of their natural growth in the temperate zone of Europe, Manchuria, the Far East, Japan, eastern China, and North America. Small areas are occupied by deciduous forests in Central Asia, in southern South America. In Russia, broad-leaved forests replace mixed ones and occupy a territory in the form of a triangle, the base of which is located at the western border of the state, and the top rests on Ural mountains. In Western Siberia, a narrow strip of birch and aspen forests separates the taiga from the forest-steppe.

Characteristics of the natural zone of broad-leaved forests.

The necessary conditions for the development of these forest ecosystems include the complex interaction of relief, soil, climate, and water. The temperate climate is characterized by warm, long summers and mild winters. The annual amount of precipitation, evenly distributed throughout the year, is somewhat higher than evaporation, which significantly reduces the level of waterlogging of soils. The main tree species of broad-leaved forests are oak, linden, elm, maple, ash, beech, and hornbeam. Most of these forests are multi-layered systems: high tree layer, undergrowth, shrub, several herbaceous of varying heights. The ground layer is formed by mosses and lichens. There are also forests in which high and dense crowns of trees exclude undergrowth, grassy cover. The soil in them is densely covered with a layer of old leaves. Decaying, organic residues form humus, contribute to the formation of stable organo-mineral compounds, since the leaves are rich in ash, calcium, potassium, and silicon. In smaller quantities they contain magnesium, aluminum, phosphorus, manganese, iron, sodium, chlorine.

Wide leaf blades are not adapted to the adverse conditions of the cold period of the year, therefore they fall off. Falling leaves, thick bark of trunks and branches, resinous, dense scaly buds - all this is a defense against excessive winter evaporation. Stable snow cover during the thawing period, it strikes the soil due to active leaching. Broad-leaved forests are characterized by sod-podzolic, gray, brown forest soil, less often there are varieties of chernozem.