Лекция: Vegetation
An increase in CO2, may he expected to enhance global plant growth up to a saturation value of possibly around 1,000 ppmv, when a saturation limit may be reached. However, deforestation could decrease the biosphere's capacity to act as a carbon sink. A sustained increase of only 1°C can cause considerable change in tree growth, regeneration and species extent. Species migrate only slowly but, eventually, extensive forested areas may change to new vegetation types, and it has been estimated that 33 per cent of the present forest area could be affected, with as high as 65 per cent of the boreal zone being subject to change. Alpine tree lines appear to be quite resistant to climatic fluctuations. However, surveys of plant species on peaks in the European Alps indicate an upward migration of alpine plants by 1-4 m per decade during this century.
Tropical forests are likely to be affected more by human deforestation than by climate change. However, decreases of soil moisture are particularly destructive in hydrologically marginal areas. In the Amazon, climatic predictions support the idea of increased convection, and therefore of rainfall, in its western equatorial portion, where present rainfall is most abundant. Because of the particularly high temperature rises predicted for the high northern latitudes, boreal forests are expected to be strongly affected by their advance northwards into tundra regions. This may produce the positive feedback effect of further regional warming because of the lower albedo of forests during the snow season. Climate change over the next 100 years may be expected to exert the least changes on temperate forests.
Wetlands at present cover 4-6 per cent of the land surface, having been reduced by human activities by more than half during the past century. Climate change will affect wetlands mainly by altering their hydrological regimes. Although general predictions are difficult to make, it is believed that eastern China, the USA and southern Europe will suffer a natural decline in the area of wetlands during the next century, decreasing the methane flux to the atmosphere.
Drier regions may be expected to be more profoundly affected than wet ones. Rangelands (including grasslands, shrublands, savannas, hot and cold deserts, and tundra) occupy 51 per cent of the terrestrial land surface, contain 36 per cent of the world's total carbon in their biomass and support half the world's livestock. The lower-latitude rangelands are most at risk both because an increase in CO2 (increasing the carbon/nitrogen ratio) will decrease the nutrient value of forage and because the increasing frequency of extreme events will cause environmental degradation. Most deserts are likely to become better and not significantly wetter, increases in rainfall being generally associated with increased storm intensity. Greater wind speeds and evaporation may be expected to increase wind erosion, capillary rise and salinization of soils. Central Australia is one of thefew places where desert conditions may improve.
It is obvious from the foregoing that a major effect of climate change involving global warming is that desiccation and soil erosion will increase in currently semi-arid regions, rangelands and savannas adjacent to the world's deserts. This will increase the current rate of desertification, which is proceeding at six million hectares per year partly dueto high rainfall variability and partly to unsuitable human agricultural activities such as overgrazing and over-intensive cultivation.
Упражнение 2.
Прочитайте следующие слова и определите их соответствия в русском языке:
regeneration, type, extensive, migration, idea, tundra, regional, season, human, hydrological, regime, natural, biomass, risk, degradation, intensity, erosion, salinization, effect, hectare, agricultural, cultivation.
Упражнение 3.
Заполните таблицу, образовав недостающие части речи.
| v. | n. | adj. | adv. |
| suggest relate | increase response | particularly |
Упражнение 4.
В правой колонке найдите русские эквиваленты следующих английских словосочетаний из текста Vegetation:
| 1. saturation value 2. considerable changes 3. climatic fluctuation 4. more then half 5. mainly 6. environmental degradation 7. semi-arid region 8. current rate 9. temperate forests 10. however 11. because of | a. полузасушливый регион b. главным образом c. современная скорость d. уровень насыщения e. значительные изменения f. леса умеренной зоны g. из-за h. деградация окружающей среды i. однако j. колебания климата k. более половины |
Упражнение 5.
Составьте 5 вопросов к первому абзацу текста Vegetation.
Упражнение 6.
(Парная работа) Ответьте на вопросы в упражнении 6.
Упражнение 7.
Найдите подлежащее в каждом предложении второго абзаца текста Vegetation.
Упражнение 8.
Вставьте соответствующий предлог и подберите определение к каждому слову: upon off from in out for on over.
| 1. carry … 2 depend … 3. go … 4. look … 5. result … 6. give 7. take 8. get | a. зависеть от b. продолжать c. быть следствием e. преодолевать f. искать g. взлетать h. уступать i. выполнять |
Упражнение 9. Прочитайте текст и найдите ответы на следующие вопросы (Контрольное время 7 минут):
1. Каковы два основных способа воздействия вырубки мировых лесов на климат Земли?
2. К каким изменениям в составе атмосферы привело бы уничтожение тропических лесов?
3. Каким образом вырубка тропических лесов сказалась бы на сезонном характере осадков, уровне грунтовых вод, поверхностном стоке?
4. Может ли уничтожение лесов привести к деградации почвенного покрова и изменению температурного режима?