2020-10-10
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Forests
Forest can be found in all regions of the world. As a rule, forests dominated by deciduous or broadleaf forests are more species-rich than forests dominated by conifer or needleleaf forests. Forests sometimes contain many tree species within a small area (as in tropical rain and temperate deciduous forests), or relatively few species over large areas. Forests function as carbon dioxide sinks, animal habitats, hydrologic flow modulators and soil conservers. Trees provide food, medicine, shelter and warmth. They also support biodiversity.
According to FAO assessments carried out at approximately ten-year intervals since 1948, the total estimated global forest area in 2000 was nearly 4 billion hectares, of which 95 percent was natural forest and 5 percent was forest plantations.
About 47 percent of the world's forests occur in the tropical zone, 9 percent in the subtropics, 11 percent in the temperate zone and 33 percent in the boreal zone.
The world's natural forests continue to be lost or converted to other land uses at a very high rate. During the 1990s, the total loss of existing natural forests was 16 million hectares per year, of which 15 million hectares occurred in the tropics. This means that 4.2 percent of the natural forest area that existed in 1990 was lost by 2000. For the tropics, the loss of existing natural forest was 7.8 percent.
There are three major types of forests, classified according to latitude: tropical forests, temperate forests and boreal forests (taiga).
Tropical forests
Tropical forests are characterized by the greatest diversity of species. They occur near the equator, within the area bounded by latitudes 23.5 degrees N and 23.5 degrees S. One of the major characteristics of tropical forests is their distinct seasonality: winter is absent, and only two seasons are present (rainy and dry). The length of daylight is 12 hours and varies little. Temperature is on average 20-25° C and varies little throughout the year: the average temperatures of the three warmest and three coldest months do not differ by more than 5 degrees. Flora is highly diverse: one square kilometer may contain as many as 100 different tree species. Trees are 25-35 m tall, mostly evergreen, with large dark green leaves. Fauna includes numerous birds, bats, small mammals, and insects.
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More than one half of tropical forests have already been destroyed.
Temperate forest
Temperate forests occur in eastern North America, north eastern Asia, and western and central Europe. Well-defined seasons with a distinct winter characterize these forests. Moderate climate and a growing season of 140-200 days during 4-6 frost-free months distinguish temperate forests.
Unlike tropical forests, temperate forests have two layers of vegetation. The tallest trees are 15-30 meters high and shrubs and smaller trees are 5-10 meters high. This is why the soil receives more light than in tropical forests and the undergrowth is rich: ferns, mosses and lichens, especially in very rainy areas.
The main trees living in temperate forests are beeches, sycamores, oaks, aspens, walnut trees, lime trees, chestnut trees, birches, elms and tulip trees in America.
Boreal forest (taiga)
Boreal forests, or taiga, represent the largest forest biome. Boreal forests occur between 50 and 60 degrees north latitudes and can be found in the broad belt of Eurasia and North America: two-thirds in Siberia with the rest in Scandinavia, Alaska, and Canada. In Europe boreal forests can be found in Norway, Sweden, Finland, and Russia. Seasons are divided into short, moist, and moderately warm summers and long, cold, and dry winters. The length of the growing season in boreal forests is 130 days. The dominant tree species are coniferous trees: firs, spruces and pines. These tree species are better adapted to severe conditions than deciduous trees due to the following reasons:
1. needle like leaves reduce surface area through which water can be lost, especially in winter,
2. conical shape promotes shedding of snow and prevents loss of branches,
3. dark colour of needle like leaves helps the foliage absorb maximum heat from the sun and begin photosynthesis as early as possible.
11. выпишите из текста:
a) 4 словосочетания с модальными глаголами
b) 5 прилагательных в сравнительной и превосходной степени сравнения
c) глаголы «to be» и «to have». Определите их видо-временную форму.
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12. переведите словосочетания с существительными в роли определения. Обратите внимание, что в английском языке определяемое слово в словосочетаниях с существительными в роли определения стоит на последнем месте. Таким образом, перевод на русский язык нужно начинать с него: car make - марка машины, bus stop – остановка автобуса.
Phone number, lecture hall location, record book cover, hostel room number, part time work, correspondence department, first-year student, group mate, the University park, the University lecture halls, needleleaf forests, tree species, tree species list, carbon dioxide sinks, animal habitat, soil conservers, forest plantations, forest area, forest biome, oak tree, birch tree catkin.
13. Подготовьте вопросы и ответы на них по своей части текста:
