Soil Conservation / Ecosystem Management / Man’s Impact on the Environment / The Conservation Movement

A) A second element of ecosystem management, one which has come much more to the fore in recent years, is that of maintaining sustained yield from organic resources. This idea was first applied to the maintenance of the breeding stocks of marine animals and to forestry practice. It is also implicit in the principles of soil conservation, the aim of which is to sustain agricultural fertility. Many authorities would maintain that this is by far the most important aspect of ecosystem maintenance, and that in the face of growing pressure on food resources, the protection of wild life for non-productive reasons is a luxury we can ill afford.

B) In summary, there clearly is a need to ensure that environmental management permits the maximum use of biological resources consistent with the maintenance of the greatest diversity of organic life.

C) As applied to organic resources, one aspect of environmental management is the preservation and protection of wild life or of natural habitats from modification and depletion by man. This may be carried out for a combination of ethical, scientific or aesthetic reasons. To this end, nature reserves, wildlife refuges and similar controlled areas have been set up all over the world, designed to protect a particular habitat and its communities. These have not always been entirely successful. A classic example of the lack of understanding of ecological principles occurred with the establishment of National Parks in East Africa: these were designed originally to protect game animals, man being excluded except as a sightseer. But as a result, animals such as elephant, hippo and buffalo, whose populations had formerly been kept in check by hunting, increased to an extent that widespread devastation of their habitat resulted. What has been often overlooked in the past in environmental management is, first, that ecosystems cannot simply be “preserved”, but are dynamic in character, and second, man is an important habitat factor in many cases: the ecological niche occupied by him cannot suddenly be left vacant.

D) The widespread current concern over the status of ecosystems is the product of a movement that has slowly been gathering momentum over the last hundred years or so. Early efforts at the conscious management of biological resources often arose out of economic necessity: the imminent disappearance of the last forests in Britain and central Europe in the eighteenth century prompted landowners to adopt methods designed to save the last remaining forests and to stimulate forest productivity. The conservation movement as such was born in the United States. The ruthless clear-felling of great stands of forest in the western states and the experience of the Kansas dustbowl in the 1930s served to focus attention on the problem. Currently, of course, conservation has become a much wider issue than the maintenance of natural biological systems.

E) Modern environmental management policies attempt to reconcile these apparently conflicting aims – namely, preservation and productivity. Multipurpose schemes are often now attempted. This is most successfully applied to management of forests, which because of their size are often well suited to a variety of uses – for timber, wildlife conservation, water supply and recreation. In Britain, National Reserves are now managed as multiple resource units.

Model: 1 – D

9.6 Read the text “Environmental Factors” through and make the review of it.

ENVIRONMENTAL FACTORS

Factors which have some effect on the life of an organism at some stage in its development are called environmental factors. These can be divided into groups as follows: first, a climatic group, which includes conditions of light, temperature, water availability and wind; second, topographic influences of slope angle, orientation and altitude; third, edaphic(soil) factors, especially pH and fertility; and fourth, biotic controls, such as a competition between species and the effects of grazing.

These groups are themselves interrelated so that it is extremely difficult to isolate the influence of individual factors. For example, topography and climate will influence soil development; and climate and soil will influence the pattern of biotic controls by determining the species which may inhabit a particular place and compete there for survival.

Lightis extremely important environmental factor because it is the vital source of energy for ecosystems and it can also act as a control of functions such as reproduction and migration. Excess light can be a limiting factor in ecosystem development by damaging plant tissues and decreasing productivity.

The influence of light varies with its three main aspects: its quality (that is, wavelength composition), its intensity and its duration (day length).

Temperature is a universally important environmental factor both for its direct effects on organisms and for its indirect effects in modifying other factors such as relative humidity and water availability. Each species has its own minimum, maximum and optimum temperatures for life but the actual limits at any time vary with such things as the age of the individual and water balances in the body. Generally, aquatic plants and animals have narrower tolerance ranges for temperature than those which live on land. This is mainly because there is far more temperature variation in terrestrial ecosystems.

Water availability may often restrict ecosystem development because most organisms need large amounts of water to survive. It not only forms a large percentage of the tissues in plant and animal bodies but it is also essential for transport and cooling. In plants, water provides support and is essential for photosynthesis.

Distributions of plants may largely depend on the effectiveness of precipitation; this will be a function of the kind of precipitation, the type of vegetation present and the rate of evaporation. In many areas fog or dew is important in providing essential moisture for plant growth and thus extending the distribution ranges of species.

In the case of animals, water usually only acts as a limiting factor when it is in short supply. There is a great variation in the amounts of water needed different species but usually cold-blooded animals require less than warm-blooded ones, which use it for heat regulation. Some animals display specific adaptations for survival in arid habitats. Desert animals may avoid the hottest and driest season by becoming inactive – that is, aestivating.

Wind can act as an environmental factor either directly by causing mechanical damage to plants or indirectly by affecting relative humidity and evaporation rates. High wind velocities can cause an appreciable increase in the rate of transpiration and limit plant growth. In very exposed situations such as mountain summits, coasts and open plains vegetation may be dwarfed as a result of wind action.

Topography can influence ecosystem development in three major ways. First, by the direct effects of altitude on temperature. Temperature decreases as altitude increases either at the dry adiabatic lapse rate (10°C/km) or, more usually, at a lower rate than this, approximately 6°C/km. Second, topography can act indirectly, since temperature changes affect relative humidity. The combination of changes in temperature and relative humidity leads to the development of an altitudinal zonation of ecosystems. At a low level, desert merges into pine forests, which are succeeded by fir and spruce, and then by alpine communities at the highest altitude.

The third way in which topography can influence ecosystem development is by local variation in slope orientation and angle. South-facing sides of valleys receive strong incident light (in the northern hemisphere) and are therefore warmer and drier than north-facing slopes which are in the shadow for a lot of the time. This leads to great contrasts in species structure and productivity between sides of valleys. Angle of slope will be a critical factor in soil formation and drainage.

The soil is a vital component of terrestrial ecosystems, particularly in cycling nutrients without which all life would cease. Soil and the rest of the ecosystem are closely related; one will influence the workings of the other. Particular attributes of soils, such as texture, pH, soil climate and organic content operate in a closely interrelated fashion to exert control on rates of decomposition, nutrient cycling and plant distribution and productivity.

Soil texture is very important in determining the soil climate, since it affects aeration, drainage and ease of root penetration.

Biotic factors are the interactions that occur between living things. Biotic factors are usually far more diverse and intricate than other environmental controls because they rely on the activities of a wide variety of organisms.

Most habitats can be occupied by many different types of plants and animals. The success of a particular species will depend on its ability to obtain its requirements for life. Competition arises if the resources of a habitat are insufficient to meet the demands of all the organisms living there. Generally competition is most intense between individuals of the same species or of different species that have similar ecological niches, especially at young stages in the life cycle.

Man is by far the most important biotic factor. He has caused fundamental modifications of ecosystems by fire, hunting and agriculture, man has obliterated large areas of natural systems and caused pollution of both terrestrial and aquatic habitats.

9.7 Read the passage about the ozone layer and answer the questions (1-14) by writing a word or a short phrase. The first one is done for you as an example.

Model: 1 Where is ozone found? the Earth’s stratosphere

2 What does ozone filter out?

3 Where is there a high level of concentration of ozone?

4 What was London known as in the past?

5 What was the major cause of London’s smog?

6 What does sunlight encourage to turn into ozone?

7 Give two examples of crops affected by too much ultra-violet radiation.

8 What are malignant melanomas?

9 Give one of the two vital properties of CFCs.

10 About how long does it take СFСs to break down?

11 When does chlorine become an ozone destroyer?

12 What do the scientists compare with the area of the United States and the height of Mount Everest?

13 Do governments ban CFCs?

14 Is CFC a ‘greenhouse’ gas?

Ozone, spread thinly in the Earth’s stratosphere, about 10 km to 50 km above ground level, is essential to all forms of life. The molecules of ozone at that level ‘filter out’ high energy ultraviolet (UV) radiation from the sun, and in doing so protect plants and animals from harmful UV rays. Many scientists believe that certain forms of life were unable to live on land before the ozone layer had formed. But, nearer the ground, ozone is a problem, and by the sea it may even damage your health. Scientists now believe that the invigorating effect that comes from being near the sea is not caused by ozone in the atmosphere, but instead is a result of ions (electrically charged particles) in the sea air. Similarly, the distinctive smell of the sea probably comes from old fish and rotting seaweed, rather than ozone. But even more serious than the effect of ozone by the sea is its high level of concentration in polluted cities all over the world.

In the past, London was so famous for its smogs that the city was commonly known as ‘the Smoke’. These smogs were thick, smoky fogs which enveloped the city, and they persisted until the early 1960s. Coal-burning fires were the major cause of this health hazard, which was not eradicated until legislation was enacted in the late 1950s, setting up ‘smokeless zones’ and controlling the types of fuel that could be burned. But recently, a new type of smog has hit the headlines – of which one of the constituent parts is ozone. The combination of exhaust gases from cars and factories, still air, warmth and clear sunshine, has resulted in a highly poisonous form of ozone. Sunlight encourages a chemical reaction which changes oxygen in the air to ozone – hence the name ‘photochemical smog’; even small amounts of ozone can irritate people’s eyes, give them headaches and affect their breathing. Higher concentrations can also damage plant tissues, and may have other, more severe, consequences. In short, ozone is best kept at a distance from plants and animals.

So when does ozone become a friend to life on earth? Well … the molecules of ozone ensure that a good deal of UV radiation is prevented from reaching people and plants on Earth (and within 10 km of the earth). This is good news for plants – because crops such as maize, wheat and rice give lower and poorer quality yields if too much UV radiation reaches them.

It is good news for human beings too – high levels of UV radiation can cause malignant melanomas, or skin cancers, some of which may be capable of spreading to other parts of the body if they are not treated at an early stage. Why is it that ozone has become so well-known in the last decade? The answer involves ozone itself, UV radiation, and a family of chemicals called chlorofluorocarbons (or CFCs).

CFCs were first demonstrated by the American inventor Thomas Midgley when he inhaled a lungful of CFCs gas and used it to blow out a candle. This showed two vital properties of CFCs: they do not burn and they are not poisonous. For this reason they became the ideal replacement for ammonia in refrigerators: ammonia is toxic, inflammable, and has an unpleasant smell.

The CFC family of chemicals has many other uses, for example, inside aerosols. Within a can, the CFC is a liquid; when the pressure is released it becomes a gas. Other uses are as cleaning solvents.

In Thomas Midgley’s time, CFCs seemed the answer to many problems. Unfortunately, each time they are used some of the gas escapes into the atmosphere. CFCs are very stable – it takes perhaps 75 years before they break down. They remain in the air and reach high into the atmosphere.

This is where the problems begin. Up in the stratosphere, conditions seem to be perfect for breaking down CFCs and releasing chlorine. This is especially true during the cold winters above the South Pole in Antarctica. In temperatures of below –80°C, atoms of chlorine are formed. When the sun returns in spring, the chlorine becomes an ozone destroyer.

Just one chlorine atom can destroy thousands of ozone molecules.

The scientist Joe Farman, until recently head of the British Antarctic Survey team which has been carrying out research in the Antarctic for the past 20 years, first reported the ‘hole’ above Antarctica in 1985. Experts think that the hole is as big in area as the United States (approximately 9,500,000 sq km) and as deep as the height of Mount Everest (nearly 8,850 m). Every southern summer – early in November – the Antarctic hole breaks up into blobs of ozone-reduced air that drift around in the southern hemisphere.

Why do governments not just ban CFCs? The United States banned their use in aerosols five years ago, since when few countries have followed. Manufacturers have been working to find a replacement for CFCs which will not damage the ozone layer, and which does not have other harmful properties.

Some scientists believe that we should not have been so quick to condemn CFCs. They argue that gases from burning vegetation and wood-rotting fungi do far more damage to the ozone layer.

Even so, the effect of CFCs as a ‘greenhouse’ gas in warming the Earth is significant. The search to replace CFCs continues.

9.8 Read the text “How Are People Affected by a Volcano Eruption?” and answer the questions after it.