The plague that's killing trees
1. A strange sickness influences the growth of tree throughout vast areas of American forests. Scientists fear it being the start of a widespread environmental disaster. From mountain peaks of New England to foothills in the Deep South, some species of trees p.re being deformed and some have stopped growing at all. The trees are losing their vitality and resistance to insects and diseases. Beech trees are producing abnormally brittle wood (xpy ). Spruce and fir branches are growing vertically instead of horizontally. Acid rain and air pollution are supposed to be the causes of such disaster. Acidity breaks down the waxy coating on leaves. Roots are damaged. The loss of green color (chlorosis) points to nutrient deficiency in the soil.
2. Scientists agree that when coal, oil and other fuels are burnt, the emissions are converted in the atmosphere into particles that return to the earth in the form of highly acidic rain ( ), snow or fog. There is certainly a close link between acid rain and the devastation (pa) of forests. Gaseous pollutants such as nitrogen oxides, sulfur dioxide and airborne microscopic particles of metals pollute the atmosphere and influence the plant growth.
3. It was estimated that biomass the combined weight of tree trunk, limbs and branches in Vermont dropped for eight species of trees. The most dramatic change is in the red spruce (a ). More alarming is the 25% decline in biomass of the commercially valuable sugar maples and beeches. Commercial foresters report no change in timber production.
4. But scientists are discovering shortages to come in many areas. Timber economy is growing slower than ever. Pitch-pine growth is already at a standstill, hardwoods ( ), such as: yellow birch, black oak, sugar maple and hickory ( - ) are also affected. Even tolerant trees are losing growth. According to the results of an Oak Ridge National Laboratory study of 34 species in 15 states in the eastern half of the nation hidden damage is occuring.
II 2 - :
What pollutes the atmosphere and influences the plant growth?
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The importance of forests
1. The significance of forests is not restricted to timber use. They are an important geographical and ecological factor. They protect the soil and water resources better than the most excellent artificial measures. Forests prevent soil erosion, retain surface waters, making them clean and still, and contribute to an increase in ground waters. In this respect, watershed forests are a kind of reservoir for useful moisture. Just the fact that forests regulate the flow of rivers, prevent their pollution and their being clogged by silt, prevent floods or reduce them in size, makes them extremely valuable.
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2. The forest is a powerful accumulator of the solar energy, it has a considerable influence on the formation of the climate, gas exchange in the atmosphere, and therefore it creates the living conditions for the people. Photosynthesis is the start of this circulation.
3. The forest, being the greatest biological composition in the world, assisting in air purification against dust and enriching it with oxygen, is an important regulator of the gas balance in nature. It is necessary to provide people with optimal oxygen rate in the amount of 400 kg per capita annually. For this purpose it is necessary to have 0.1-0.3 ha of forest per capita. It is known that one big tree while consuming carbon dioxide, is producing as much oxygen as one person needs a day for respiration. Under the conditions of the industrial city the energy of. photosynthesis is ten times decreased being affected by air pollution. It means that one person needs 10 trees instead of one.
4. The ability of the forest to clean the atmosphere from different mechanical substances, the majority of which is dust, involving insoluble and soluble components, is getting higher and higher importance nowadays. Forests are preserving their dust protective ability even when they are leafless. Therefore forests and plantations of trees in cities are extremely necessary, and they are irreplaceable from the social and hygienic points of view.
5. The sanitary and hygienic importance of forest is manifested by their antimicrobe, sterilizing effect on the environment. The first and the most important property of forests is the ability to enrich the atmosphere with ionizing oxygen and phytoncidal substances. Five-seven hour stay in the forest leads to the increase of the tone, improvement of the functions of the higher nervous activity, 1030% increase of the minute respiration volume. Thus, the forest is a powerful air filter of antimicrobic, sterilizing properties, ionizing effect on the air and the total sanitary effect on environment.
II 3- :
Why does one person need 10 trees instead of one in the industrial city?
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