Human Impact on the Environment

Question 1

Ecosystem

Answer 1

Living (biotic) organisms and non-living (abiotic) organisms.

Question 2

Biotic factors

Answer 2

All living organisms.

Question 3

Biodiversity

Answer 3

The variety of plant and animal species in the ecosystem. it is important to maintain a stable ecosystem.

Question 4

World population

Answer 4

The constant increase in world population has a detrimental effect on the environment. It leads to greater demand for food, energy, medicine, housing and manufactured goods and places added pressure on natural resources. The balance in the ecosystem is disrupted.

Question 5

Biotic and Abiotic Factors

Answer 5

The interaction between biotic and abiotic factors and components helps to keep the ecosystem in equilibrium.

Question 6

Biome

Answer 6

Any area within a specific climate in which specific organisms live. The variety of organisms in an ecosystem is called biodiversity.

Question 7

Atmospheric and Climate Change

Answer 7

The atmosphere is composed of layers of air where each layer has its own temperature patterns. Some gases that surround the earth, like oxygen, hydrogen, carbon dioxide, water vapour and nitrogen, are necessary to sustain life on this planet. The atmosphere is important because it filters solar energy as it shines through the gas layers, reducing the harmful effects of ultraviolet light.

The gas layers go through natural, cyclic temperature increases and decreases, which takes hundreds of years to complete. Changes in the earth’s orbit, together with changes in the sun’s intensity, affect the amount of solar energy that reaches the earth’s surface. Climates change in response, depending on whether more solar energy is released out of the atmosphere during the cycle.

Climate change affects weather and rainfall patterns, which in turn affect the survival of the plant and animal species in a specific region. Geometric human population growth, industrialisation and high levels of pollution are having a direct impact on the atmosphere and have increased the rate at which climate change is taking place.

Question 8

Consequences of Atmospheric and Climate Change include:

Answer 8

• Periods of unusually warmer weather
• Extremes in temperature, which will lead to drought, changes in agricultural patterns and food shortages
• Polar warming and melting of polar ice-caps and glaciers
• Changes in low and high air pressure zones, result in cyclones and hurricanes
• Severe rain and thunderstorms, will cause floods
• Longer droughts and dry periods that lead to desertification
• Changes in plant and animal distribution and population
• Increased environmental degradation and natural disasters
• Increased loss of biodiversity

Question 9

Factors that cause and contribute towards atmospheric and climate change:

Answer 9

Carbon dioxide emissions, deforestation, greenhouse effect, global warming methane emissions and ozone depletion.

Question 10

Carbon Dioxide Emissions

Answer 10

Carbon dioxide is a colourless, odourless, incombustible gas. Atmospheric levels of CO2 have increased by 40% over 150 years due to human impact and industrialisation. South Africa relies mostly on fossil fuels like coal and liquid fuel used to produce more than 90% of the country’s energy.

Most energy is generated from coal-burning power stations. The remaining energy need is supplied by nuclear power and renewable energy sources like solar, wind and hydropower. Almost half of the energy produced nationally is consumed by the mining and industrial sectors, which releases millions of tons of CO2 to produce their goods. The energy and carbon intensive economic activities of industry in South Africa make use of the largest CO2 emitter in African and 12th globally.

Question 11

South African Carbon Tax

Answer 11

The South African government has recently commited to reducing CO2 emissions by 43% by 2020 to comply with the Kyoto Protocol. The National Treasury is enforcing the carbon tax on all South Africans:

• Fuel taxes on all petrol and diesel purchases
• Carbon emissions tax on purchases of all new passenger vehicles
• Tax exemptions on income earned with reduced carbon emission
• Accelerated depreciation allowances from investments in biofuels and renewable energy, less tax is paid.

Question 12

Carbon Tax

Answer 12

Carbon tax provides incentives to reduce CO2 emissions and is far more effective than legislation and regulations. Companies and industry are fined if they don’t comply with stipulated levels. Enterprises are rewarded for compliance and tax exemption is increased proportionate to the reduction of emissions. The South African government is implementing improved energy efficiency measures, increasing the use of renewable, non-fossil-fuel-based energy and investing in carbon-friendly technologies to meet 2020 targets.

Question 13

The need to reduce the carbon footprint

Answer 13

Carbon footprint is the measurement of the total amount of carbon dioxide and methane emissions from a defined population, system or activity. The carbon footprint originates from the ecological footprint, which is the measurement of human demand on the earth’s ecosystems. The carbon footprint is measured in units of tonnes and has to parts to the measurement.

Question 14

Primary Carbon Footprint

Answer 14

A measure of the indirect CO2 emissions released by the combustion of fossil fuels and includes domestic energy consumption and transportation.

Question 15

Secondary Carbon Footprint

Answer 15

This is a measure of the indirect CO2 emissions from the whole lifecycle of the products that we use, from manufacturing and transport to the final breakdown.

Question 16

Deforestation

Answer 16

In a well-managed forest, trees are cut down in strips. New indigenous trees are planted and allowed time to grow back. However, this doesn’t always happen and results in deforestation of large portions of the natural forests. Deforestation affects the water cycle in the region. The soil is unprotected and dried out by the sun. Heavy equatorial rains wash the topsoil away and soil erosion results. Rainforest canopies absorb carbon dioxide and produce much of the oxygen and nutrients needed by consumers. When deforestation occurs, more carbon dioxide is present in the atmosphere, allowing heat through the atmosphere. This contributes to the greenhouse effect and global warming, which have a direct impact on climate change.

Question 17

Greenhouse effect and Global Warming as a cause of Desertification, Drought and Floods

Answer 17

The atmosphere acts like a glass box around the earth allowing heat and light from the sun to enter. The atmosphere reduces the amount of heat that is radiated as infrared energy from the earth’s surface. This is called the greenhouse effect. Its a natural process, essential to keep the earth from cooling too much.

Oxygen and nitrogen absorb very little of the infrared radiation. Gases like water vapor, CO2, methane, CFCs, O3 and nitrogen oxide absorb most of the infrared radiation. The concentration of these gases increases in the atmosphere because of pollution, so the greenhouse effect will increase. The increased absorption of the infrared radiation increases the earth’s temperature, causing global warming.

Question 18

Desertification

Answer 18

The complete destruction of a region because of global warming, droughts and deforestation. Droughts reduce the carrying capacity of the land so crops yield is reduced or destroyed, livestock starve and die and this leads to famine. Soil erosion takes place and dust bowls result in further corroding the region. Floods wash the remaining fertile soil away leaving behind an arid wasteland.

Question 19

Methane Emissions (CH4)

Answer 19

Methane is one of the three main greenhouse gases besides water vapor and CO2. It contributes 14% of world global warming. Methane is mainly released as a by-product if decay and is produced under anaerobic conditions. Methane emissions are released from agriculture, energy fugitive emissions (pumps, pipes, storage tanks and valves), waste deposits like landfills, fuel emissions and the mining industry.

Question 20

Ozone Depletion

Answer 20

Ultraviolet radiation in sunlight splits oxygen gas molecules into separate oxygen atoms. These atoms recombine into a molecule that consists of three oxygen atoms (O3) and forms ozone molecules. Ozone is found in the lower atmosphere where it forms a shield in the stratosphere about 25 km above the Earth’s surface. The ozone absorbs and filters out harmful ultraviolet rays from the sun. CFCs collect in the atmosphere when they are released and react with the ozone by reducing the concentration of the ozone layer.

High levels of ultraviolet light can cause skin cancer and cataracts. Plant growth is affected and marine plankton is damaged. The destruction of marine plankton will have a direct impact on the survival of many higher organisms,whales and penguins.

Question 21

Availability of Water

Answer 21

Water resources are under much pressure in SA because of ongoing development, increasing water pollution, wetland destruction, invasive plants and the effects of global warming. We rely on water supply from rivers, since we don’t have a high rainfall. Factors that have an impact on water availability are: construction of dams in catchment areas, destruction of wetlands, poor farming practices, droughts and floods, poor farming practices, exotic plantations, boreholes and aquifers, water wastage and cost of water.

Question 22

Construction of Dams

Answer 22

The population is increasing geometrically but the water available to us for use remains the same. This led to plans to increase storage capacity by building of new dams and water transfer schemes to try to meet future needs. Dams are a man made barrier constructed to collect and retain water in a catchment area. Water is collected from rivers and underground streams and released through floodgates. This means that water flow can be managed and evenly distributed to designated regions as they require it, especially during dry seasons.

Question 23

Destruction of Wetlands

Answer 23

A wetland is an area were much of the land is saturated with water down to a depth of 50 cm for a period of more than two weeks of the year. A wetland is a region of land that is transitional between terrestrial and aquatic systems. The water table is near the surface, resulting in land that is periodically submerged by shallow water. Wetlands have their own watery ecosystems, ranging from marshes, floodplains and coastal lakes through estuaries and mangroves. The presence of water affects the characteristics of the soil and therefore the vegetation and animal life that have adapted to survive in this balanced ecosystem. The plant roots must be able to function in an anaerobic situation for extended periods of time.

Question 24

Wetlands

Answer 24

Wetlands are classified according to biological, physical and chemical factors, with land size and depth of water allowing further classification. Wetlands are important because they:

• Act as a water purification system
• Store water during rainy season for release during dry season
• Control erosion by preventing soil from storm-water-run-off
• Recharge groundwater and raise the water table
• Regulate floodwater and streams
• Provide a unique habitat for plants and animals
• Used for recreational purposes

Question 25

Poor Farming Practices

Answer 25

SA has a dual-agricultural economy, with well-developed commercial farming systems and subsistence-based farming in rural areas. The availability of water directly effects crop production and type of farming because rainfall is unevenly distributed. Where rainfall is low, irrigation systems are used but these are costly. Poor farming practices lead to overgrazing, widespread burning of veld areas to make place for crop farming, not rotating crops, ploughing crop furrows at right angles to the slope or water drainage flow.

Question 26

The impact on water availability:

Answer 26

• Lack of crop rotation decreases soil fertility as the minerals in the soil are not replaced and often there is no money to buy artificial fertilisers.
• The soil becomes infertile and unsuitable healthy plant growth.
• Plants will stop growing and soil erosion takes place.
• When the soil is covered by indigenous plants or crops, the roots hold the soil in place.
• Rain soaks into the soil and plant roots absorb the water.
• Over-use by farm animals that eat vegetation and trample the soil is a problem.
• Bush fires destroy vegetation.
• Exposure of the soil to sun, wind and rain results in soil erosion.
• The rate of soil erosion is increased as the rain washes the soil away.
• Eroded soil is carried into rivers and may cause the rivers to split up.
• During heavy rainstorms, the rivers cannot carry the water away which results in floods.

Question 27

Droughts and Floods

Answer 27

A drought results where there is a lack of rain in an area. The lack of rain can be due to climate change, ozone depletion and a disrupted water cycle due to desertification.
Short, intense droughts lasting a few months, impact subsistence farmers very badly because they don’t have access to expensive irrigation system. This can result in the loss of an entire crop of herd. Droughts that continue for many months or years will severely damage ecosystems and agricultural lands.

Question 28

Exotic Plantations and Depletion of the Water Table:

Answer 28

Exotic plants of pine and blue gum species are not indigenous and don’t grow naturally in South Africa. When these trees are planted on a large scale for economic purposes, they draw high amounts of water from the soil and lower the water table

Question 29

Boreholes and Aquifers

Answer 29

A borehole is a narrow shaft that is drilled into the ground, to access ground water from an aquifer. A vertical pipe and fine screen are installed to prevent the sides of the borehole from caving in and stops sand and sediment from getting into the water. A pump is used to move the water to the surface.

Question 30

Cost of Water

Answer 30

Many municipalities are implementing a payment progression system. The first 5.5 kilolitres are free, after that, usage is divided into brackets where the more you use, the more you pay per litre. Water is becoming increasingly expensive, but if we don’t conserve water, no amount of money will be able to purchase it in the future.

Question 31

Quality of Water

Answer 31

Approximately 70% of the earth’s surface is covered by water, 97% is salt water and the other 3% is fresh water. Fresh water is a renewable source. About 60% of fresh water is frozen in glaciers and polar ice caps. The quality of water is also a major concern. Water as a resource is worthless unless the quality of the water is drinkable. Aquatic plant and animal life are influenced by the quality of the water.
Pollution levels, pH value, chloride and oxygen content of the water directly influence survival. High and low pH values and a high chlorine content causes the death of aquatic plants and animals. Oxygen content can be affected by bacterial growth in polluted water, resulting in death of aquatic animals and plant life, as there is not enough oxygen remaining in the water. Without good quality water, life as we know it will cease to exist.

Question 32

Factors that affect water quality:

Answer 32

• Use of water for domestic use
• Industry
• Agriculture and mining regarding pollution
• Disease
• Eutrophication and algal bloom
• Effects of mining
• Thermal pollution
• Need for water purification and recycling
• Alien water species invasions

Question 33

Domestic use of water and pollution:

Answer 33

Water we use in our homes for drinking, food preparation, cooking, washing our bodies, dishes and clothes, also in our gardens and swimming pools. We need about 50 litres of water per person per day. All our domestic water is of a drinkable quality.

Question 34

Sewage:

Answer 34

The diluted wastes or effluent that contains urine, faeces, bacteria, washing detergents and various other wastes from kitchens and bathrooms in our homes. Sewage must be treated so it can be recycled into the environment. Treated sewage solids can be used as organic fertiliser to improve the air content and fertility of soil. Treated sewage reduces the spread of diseases. Algae growth on water remains normal and aquatic plant and animal life will continue. Agencies monitor raw effluent levels in dams, rivers and the sea around our coastline. When effluent levels exceed legal allowance, investigations are put in place and the culprits are brought to task and fined or closed.

Question 35

Diseases, algal bloom and eutrophication: Waterborne Diseases

Answer 35

When in treated sewage is emptied into rivers and water basses because of unhygienic conditions, it causes diseases like typhoid, dysentery, poliomyelitis and cholera. These diseases are transmitted by disease-causing bacteria when people drink contaminated water or use it for washing or cooking.

Question 36

Diseases, algal bloom and eutrophication: Saprophytic Bacteria

Answer 36

These bacteria break down the effluent, resulting in an increase in the bacteria population. Bacteria respire and absorb large amount of oxygen from the water and increase nitrate levels of the water. This results in oxygen deficiencies from other organisms, which eventually die.

Question 37

Diseases, algal bloom and eutrophication: Algal Bloom

Answer 37

Algal bloom is the unchecked growth of algae as a result of increased levels of nitrates from the saprophytic bacteria. A thick green mass forms and covers the water surface. This prevents light needed for photosynthesis from reaching plants living lower down. The plants eventually die, as they are unable to photosynthesise and produce food. Animals that feed on the plants die when the food web is destroyed.

Question 38

Diseases, algal bloom and eutrophication: Eutrophication

Answer 38

This is a process whereby a body of water acquires a higher than normal concentration of nitrates and phosphates. The nitrate increase promotes an increase in the number of phytoplankton and algae, resulting in algal bloom. The algae die and decompose and decrease the oxygen levels in water. The lack of oxygen results in the death of aquatic plants and animals. The water becomes a cloudy green, brown or red smelly mass of rotting water that holds no value for aquatic plant and animal life. Eutrophication has a serious impact on the quality of drinking water.

Question 39

Eutrophication may be caused by:

Answer 39

• Climate change due to global warming - higher temperatures increase algal and bacterial activity.
• Natural processes, like seasonally flooded floodplains.
• Run-off from cattle, sheep, pig and horse farms where manure contains nitrates, phosphates and ammonia.
• Illegal release of partially or untreated human sewage and washing detergents into streams, rivers and seas increases the nitrate and phosphate content.
• Fertilisers used on crops are leached into the underground water table and streams and washed away during heavy rainstorms into rivers and lakes, increasing the nitrate and phosphate content of the water.
• Silting up of rivers and lakes because of soil erosion, preventing the natural flow of water.

Question 40

Industrial use of water and pollution:

Answer 40

Water is used in processes like fabricating, washing, cooling, dilution, precision cutting and as a solvent in some cases, moving and transporting. The production process for food, paper, chemicals, fuel and gas, metal objects and machines, engines, rubber components and even slaughtering and cleaning all use water.
Hydroelectric dams use the force of water flowing downhill, to drive a turbine connected to a generator, to generate electrical power. Factories and industries are required by law to ensure that the water is released from their premises has been treated and will not impact the environment. In many cases, factories pump waste products from industrial sites into rivers, lakes and the sea. Chemicals that are released like cyanide, mercury, lead and copper are non-biodegradable. When a substance is non-biodegradable it takes thousands of years to be broken down into a harmless state.
The waste and toxins accumulate to a point where it interferes with the ecosystems and food webs. The plants and animals become toxic when high levels of concentration are reached. The toxins spread through the food chain and when people catch and eat the fish, they become ill.
Factories produce tons of solid and semi-solid chemical waste each year. The easiest method of disposing of chemical waste is to dump it. However, government legislation requires that this waste be buried in very specific areas in airtight, lead-proof containers. Factories don’t always comply with the legislation because its expensive. When factories dump chemical waste illegally and don’t follow procedures, they disrupt the ecological balance. The underground water drains into rivers and the seas effecting aquatic animals and plants. Non-biodegradable, lethal chemicals gradually accumulate in plant and animal tissue and cause death.

Question 41

Agricultural use of water:

Answer 41

In SA many regions have their own unique climate and rainfall. Where the rainfall is very low, sheep farming is preferred to crop farming. Water is obtained from underground streams and pumped up through boreholes. Areas that have fertile, arable land but low rainfall use irrigation systems where water is supplied from boreholes or dams and lakes. The over-use of artificial fertilisers, insecticides and fungicides causes water pollution. These products leach into the water table and are washed into underground water streams, rivers, lakes and seas. Insecticides and fungicides are poisonous to aquatic plants and animals and can cause death. The increase in nitrates and phosphates results in eutrophication.
The mining industry has significant impact on the quality of water in SA. In the Limpopo River Basin, mining for coal, gold and semi-precious metals has resulted in acid mine drainage (AMD). This is when metal-rich, acidic water drains from a chemical reaction between water and rocks containing sulphur bearing minerals. Mines are by law expected to filter and clean this water before releasing it into the environment.
The major problem arises when the surface and drain water drains through the mine dumps that contain chemicals like arsenic and sulphur, salts and metals like mercury. These contaminants and chemicals dissolve in the water and lower the pH to acidic. Surface mining causes a further decrease in the quality of the environmental water because of AMD, toxic trace elements, high content of dissolved solids and increased sediment loads in drained water. The water leaches into the underground water, contaminating the aquifers and then to streams and rivers. The lowering of the water pH kills aquatic life. AMD water is unfit for human and animal consumption causing serious illnesses like cancer, failure of organs and body systems and birth defects.
Open-cut coal mining uses water from surface and underground water supplies, to wash the mined coal and settle coal dust. This water cannot be returned to the water source because its contaminated with chemicals, coal dust and is often acidic. Aquifers that lie below mining operations become contaminated by the infiltration of poor-quality mine water run-off. Aquifers may drain into nearby groundwater dams and streams causing further contamination and water pollution.

Question 42

Thermal pollution:

Answer 42

Thermal pollution is when hot water from factories and power stations is pumped into rivers and streams. The increase in temperature kills the plant and animal life. Fish are cold-blooded (ectothermic) and cannot tolerate extreme changes of environmental temperature. The shock of thermal increase causes death, which results in eutrophication. Laws are in place to ensure that industry purifies and cools effluent water before it is pumped into the rivers, streams and the sea. When factories are found to ignore these laws, they are given large fines. Sometimes it is cheaper for the factory to pay the fines when they are caught, than to purify ad cool the effluent wastes which are dumped into the rivers. Stricter laws are being formulated, which will result in the closure of factories that pollute the environment.

Question 43

Water recycling:

Answer 43

Fresh clean water is called white water and sewage water that contains human waste is called black water. During the sewage treatment process, solids are removed, and the remaining water is purified by multiple filtration processes before it is released into natural, surface water like rivers. Water that has been used for washing laundry, dishes and bathing or showering is called grey water. Normal household drainage systems channel everything into the sewage system. Grey water is drained through a sand filter, cooled and stored in an underground tank. The filter removes any possible solids and clarifies the water. An electrical pump is attached to the tank, to pump the water to where it will be used. It is advised to change to environmentally friendly soaps and dishwashing liquid and phosphate-free washing powders and fabric softeners.

Question 44

Advantages of recycling grey water:

Answer 44

• Cost saving because less white water is used. Recycled water can be piped into toilet cisterns tanks to be used for flushing. Grey water is used in under floor heating systems and outdoor requirements like watering the garden.
• Reduced energy is required because of the reduced amount of freshwater that is extracted from rivers and aquifers and pumped to your home. Reduced amounts of wastewater mean a reduction in the energy and chemicals needed to treat and purify the black water.
• Recycled water that is used in the garden is purified in the upper most biologically active region of the soil. Excess water seeps into natural surface and ground water, the quality of the water is maintained as the levels are recharged.
• Increased plant growth because water is available all year round. Plants om the garden flourish during dry seasons without affecting underground and surface water reserves, which are needed for agriculture.

Question 45

Water Purification:

Answer 45

This is the process of removing undesirable chemicals, minerals, solid particles and biological organisms from water that is pumped from a natural water source, so it is acceptable for human consumption. The purification process must adhere to strict standards to produce drinkable water that is odourless, colourless, pure and clean. Water is tested for compliance prior to supplying to municipalities.

Question 46

Alien Water Plants:

Answer 46

In recent years the common water hyacinth plant has become a major problem in local water bodies. Heavy rainwaters in the Witwatersrand area caused flooding of the Crocodile, Hennops and Jukskei rivers. These rivers flow into Hartebeespoort dam, carrying a significant amount if water hyacinth and rubbish into the dam. Although water hyacinth is an alien species, it has certain advantages. The plant floats with root systems that dangle free in the water absorbing phosphates. This deprives algae of a food source and provides a natural habitat where algae-eating zooplankton and indigenous fish can breed and grow. They provide natural habitats for many of the bird species in the area.

The disadvantage is that the population spreads rapidly with vegetative structures called stolons, each growing into new daughter plants. Sexual reproduction produces purple flowers that each disperse about 5 000 seeds. Water hyacinth reproduces mainly by vegetative methods. As an alien plant species, it has no natural enemies to control replication. The plants draw much oxygen from the water and the surface coverage prevents sunlight from entering the water. Aquatic plants do not receive enough light for photosynthesis, so they die, and eutrophication can follow. When water hyacinth plants die, they drop to the bottom of the dam and decay, causing a marshy wetland.

Question 47

Food Security:

Answer 47

Global warming and climate change have a direct impact on food supply and agriculture. Food insecurity results in famine and disease. Many countries, are expected to become hotter and drier, leading to changes in agricultural production and biodiversity distribution. Changes in rainfall affect food production and may cause an increase in diseases.

Question 48

Factors that affect food security:

Answer 48

• Exponential growth of the world population
• Droughts and floods
• Poor farming practices
• Alien plant invasions
• Loss of wild varieties
• Genetically engineered food
• Food wastage

The more people we have on the planet, the greater the need is for food, water, shelter and space. Eventually, the earth’s carrying capacity will be reached and environmental resistance will set in at a far greater rate than at present. Pollution, lack of respect for and abuse of natural resources and the environment will result in food insecurity, famine and an increase in the mortality rate.

Question 49

Human exponential population growth:

Answer 49

As the human population increases so does the demand for food, energy, space and other resources will increase. There will be a massive increase in pollution, wastes, gas emissions and destruction of the environment. Sustainable living and survival are only possible if population numbers and demand for resources are kept within the earth’s carrying capacity.

Question 50

Droughts and floods due to climate change:

Answer 50

Droughts are a period of high temperatures and lack of sufficient rainfall. Droughts affect the environment directly and will have an agricultural, economic and social impact on the people of that region. Increased rainfall at inappropriate times could result in floods, which have a direct impact on growth of plants in agricultural lands, natural river drainage and human infrastructure.

Question 51

Poor Farming Practices: Monoculture

Answer 51

Monoculture is the cultivation of the same crop type on the same piece of ground each year to meet increasing food demands. The disadvantage is that they disturb the natural balance in the food chain because the natural vegetation is cleared to make place for the field of crops.

Question 52

Poor Farming Practices: Pest Control

Answer 52

Pest control is essential as there is often a boom of pest, insect and plant parasite populations, which spread easily and quickly through the crop because the natural enemies were destroyed when the natural vegetation was cleared away. The pests have no predators and the populations grow geometrically. Farmers have no alternative other than to use pesticides and insecticides that destroy the pests but also cause damage and kill other useful organisms in the food chain.

Question 53

Poor Farming Practices: Fertilizers

Answer 53

Fertilizers must be added to the soil as continuous monoculture farming and lack of crop rotation causes a lack of minerals in the soil. The soil slowly becomes infertile and unsuitable for healthy plant growth resulting in soil erosion as plants stop growing. Where overgrazing takes place when farmers keep more livestock than an area can carry. This results in the destruction of the area and a decrease in the carrying capacity. Environmental resistance will follow with a shortage of food. The animals starve and eventually die, unless they are moved to another area. The lack of plant cover will result in the loss of topsoil and soil erosion takes place, unless the area is given time to regain plant cover and replace natural minerals and fertility to the soil.

Question 54

Alien Plants and Reduction of Agricultural Land:

Answer 54

Alien plants do not grow naturally in South Africa. Alien plants have no natural enemies or a means to keep their growth rate in check, so they grow out of control, threatening indigenous plants life and decreasing biological diversity as they take over natural growing areas.

Question 55

The Impact of Alien Plants on Agricultural Land:

Answer 55

• Invade potentially productive agricultural land and contaminate monocultures
• Reduce grazing areas for livestock, resulting in a lack of food; some alien plants are poisonous to eat, resulting in death of livestock.
• Reduce the capacity of indigenous plants to reproduce