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L6 - Summary Questions
1. How is population growth rate calculated?
2. Differentiate between immigration and emigration.
3. List four factors affecting growth rate.
4. Which is the main factor that reduces fertility rate?
5. List four effects of urbanisation.
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Lecture 7
Land and Human Populations
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In the beginning:
• There were natural ecosystems
• The land was covered with forests
• There were many
species
• There was no waste
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…Watersheds were forested
- Watersheds are also called drainage basins
or catchment areas
- They are areas of land that drain into
bodies of surface water
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Functions of Watersheds- Forested watersheds act as giant sponges increasing infiltration
- They release water slowly moderating flooding and
maintaining stream flows in dry periods
- They control soil erosion improving water quality
- They are habitats for many species
- They regulate rainfall on a small scale
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Rainfall Impact and Trees
Trees break the impact of rainfall on the soil thus reducing soil erosion.
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Then came man:
• Man requires food, shelter and clothing
– Animals are hunted or reared for food and
clothing
– Forests are cleared for crops and housing
solutions
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Early impact was minimal:
• Population levels were low
• Activities were for survival
• There was respect for nature
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Jamaica Population Growth
0
500000
1000000
1500000
2000000
2500000
3000000
Year
Po
pu
lati
on
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Competing uses for land:
• Agriculture (37%)
• Forests (31%; 3,402 km2)
• Housing and
Industry (5%)
• Mixed Use (27%)
• Total Area (10,964 km2)
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Competing uses for land cont’d:
• Bauxite
• Roads
• Waste Disposal
• Burial Ground
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Land Use Issues
Agriculture
- crops grown on ~11% of
Earth’s land
- 37% of Jamaica is agricultural land (1998)
Housing
- 1/5 of people in the
world have inadequate
housing
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Road Construction
- the most serious impact, especially in LDCs, is the chain of events it starts
- roads make forests more accessible to farming, logging, cattle ranching, pests, diseases & biotic pollution
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Waste Disposal
- landfills take up space
- deprive future generations of valuable resources
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Jamaican Watersheds
- >1/3 have deteriorated
Causes of Jamaican Watershed Destruction
1. Unsuitable hillside agricultural practices
2. Illegal settlements on hillside lands
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Causes of Jamaican Watershed Destruction cont’d
3. Deforestation due to illegal removal of trees for fuelwood, charcoal production, yam sticks and lumber
4. Forest fires caused by individuals
5. Unapproved quarrying and sand mining
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Effects of Watershed Destruction
1. Massive soil loss through soil erosion
2. Siltation of drains and rivers
3. Destructive flooding downstream
4. Water pollution
5. Reduced water availability and quality
6. Loss of habitat for flora and fauna
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Agriculture
- the growing of crops & the tending of livestock for subsistence, sale, or exchange
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Three Main Types of Agriculture
1. Subsistence
2. Industrialised
3. Sustainable
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Subsistence Agriculture
- production for family sustenance
- still practiced in many parts of the world
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Subsistence Agriculture cont’d
Features of Low Input / Subsistence Agriculture:
• Human Labour
• Slash and Burn
• Shifting Cultivation
• Fallow Periods
• Animal Manure
• Mixed Cropping
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Impact of Slash & Burn Cultivation
- also called Shifting Cultivation
- plots abandoned after 2-5 years due to loss of soil fertility
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Innovations:
• The diesel engine
• Motor vehicles
• Medicines
• Pesticides
• Fertilizers
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These led to:
• The Industrial revolution
• The Green Revolution
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Industrialised Agriculture
- also called modern or advanced agriculture
- one crop or animal for sale
- use large amounts of :
a) fossil fuel energy
b) water
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Industrialised agriculture has a greater impact on the environment than any other human activity
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Industrialised Agriculture cont’d
Features of High Input/Conventional Agriculture:
• Mechanisation
• Monocropping
• Synthetic Pesticides
• Synthetic Fertilizers
• Genetic Engineering
• Irrigation
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Mechanisation
- causes land degradation through soil compaction
- exacerbates
soil erosion
- causes decline in
soil fertility
- erosion damage causes decreased water quality
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Soil Erosion
- movement of soil components, especially surface litter and topsoil, from one place to another, usually by exposure to wind or flowing water
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Soil Erosion cont’d
Soil Erosion is caused by:
• Farming
• Logging
• Building
• Overgrazing
• Four-wheeling
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Soil Erosion cont’d
The 3 Main Effects of Soil Erosion are:
1. Loss of topsoil
2. Reduced productivity
3. Surface water pollution
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Monocropping:
- also called monoculture
- cultivation of a single crop, usually on a large
area of land
- simplifies ecosystems reducing biodiversity
- encourages the build up of pests thus increasing
the use of pesticides
- depletes the soil of nutrients
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Use of Pesticides
Pesticide
- any chemical designed to kill or inhibit the growth of an organism that people consider undesirable
- fast-breeding insect species undergo natural selection and develop genetic resistance to chemical pesticides
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Effects of Pesticide Use
- harmful to applications, consumers and the environment
- pollution of rivers & streams from pesticide runoff
- Pesticides linked to cancers and low sperm count
- persistent pesticides adhere to sediment and become bioaccumulated and biomagnified
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Use of Fertilisers
Fertilisers
- substances that add plant nutrients to soil and improves its ability to grow crops
2 Main Types of Fertilisers:
- Organic Fertiliser
- Commercial Inorganic Fertiliser
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Commercial Inorganic Fertiliser
- commercially prepared mixtures of plant nutrients applied to the soil to restore fertility and increase crop yields
- supply only 2 or 3 of the 20+ nutrients needed by plants
- leads to soil compaction
- water pollution
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Disruption of Habitat
- over-fertilization of rivers caused by runoff of nitrates and phosphates
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EFFECTS OF EUTROPHICATION
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Genetic Engineering
- splices genes and recombines sequences of existing DNA molecules to produce DNA with new genetic characteristics
- transfers traits from one species to another to make new genetic combinations
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Irrigation- The application of water to crops
- Types- Natural/Rainfall- Flood irrigation- Overhead/sprinkler- Drip irrigation (most efficient- 90%)
- Flood irrigation is wasteful and causes salinisation and waterlogging
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Salinisation Due to Irrigation
Salinisation:- accumulation of salts in soil
that can eventually make the soil unable to support plant
growth
- lowers crop growth and yields
- kills crop plants & ruins the land
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Other Impacts of Agriculture on the Environment
Overgrazing
- destruction of vegetation when too many grazing animals feed too long & exceed the carrying capacity of a rangeland area
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Other Impacts of Agriculture on the Environment
Desertification
- process whereby agricultural productivity of land falls by 10%
- conversion of rangeland to desert-like land
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Sustainable Agriculture
- Crops grown in harmony with the environment
- Health of humans and livestock important
- Environment important
- Workers important
- eg. Organic agriculture, biodynamic agriculture
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Sustainable Agriculture Cont’d
Includes the use of:
- Companion cropping/mixed farming
- Soil conservation
- Addition of organic matter
- Use of alternatives to pesticides
- Social justice
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Soil Conservation Methods
- methods used to:
◦ reduce soil erosion
◦ prevent depletion of soil nutrients
◦ restore nutrients
- most methods involve keeping the soil covered with vegetation
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Soil Conservation Methods cont’d
Major Methods Include:
1. Conservation tillage
2. Contour farming, Terracing, Strip cropping, &
Alley cropping
3. Gully reclamation & Windbreaks
4. Land-Use Classification & Control
5. Maintaining & Restoring soil fertility
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Soil Conservation Methods cont’d
1. Conservation Tillage- crop cultivation with little or no soil disturbance
▪ Minimum Tillage
▪ No-till Farming
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Soil Conservation Methods cont’d
2. Contour Farming, Terracing, Strip Cropping & Alley Cropping
- used mainly on sloping land which is more prone to erosion
▪ Contour Farming- used on gently sloping land
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Soil Conservation Methods cont’d
2. Contour Farming, Terracing, Strip Cropping & Alley Cropping cont’d
▪ Terracing- used on steeper slopes
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Soil Conservation Methods cont’d
2. Contour Farming, Terracing, Strip Cropping & Alley Cropping cont’d
▪ Alley Cropping (Agroforestry)- planting crops with rows of trees on each
side
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Soil Conservation Methods cont’d
3. Gully Reclamation & Windbreaks
▪ Gully Reclamation
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Soil Conservation Methods cont’d
3. Gully Reclamation & Windbreaks cont’d
▪ Windbreaks (Shelterbelts)- row of trees planted to block wind flow
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Soil Conservation Methods cont’d
4. Land Use Classification System
- describes different categories of land that are suitable and unsuitable for cultivation
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Soil Conservation Methods cont’d
5. Maintaining & Restoring Soil Fertility
Involves the use of:
1. organic fertilizers
2. crop rotation
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Alternatives to Pesticides
1. Cultivation Practices
- mow weeds
- rotate crops
- plant rows of hedges or trees
2. Resistant Varieties
- genetically resistant to certain pest insects, fungi and diseases
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Alternatives to Pesticides cont’d
3. Natural Enemies (Biological Control)
- predators, parasites & pathogens
can be encouraged or imported to regulate
pest populations
4. Birth Control (Reproductive Controls)
- males are lab-raised and
sterilised, then released to mate
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Alternatives to Pesticides cont’d
5. Insect Sex Attractants (Pheromones)
- when a female is ready to mate she releases a pheromone (chemical
sex attractant)
6. Insect Hormones
- hormones: chemicals produced by an organism to control its
growth & development
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Alternatives to Pesticides cont’d
7. Zapping Foods With Radiation
- gamma irradiation of foods is
used to kill insects & prevent them
from reproducing
8. Biopesticides
- plant & microbe toxins are
synthesised for mass production
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Alternatives to Pesticides cont’d
9. Quarantine
- restriction of the importation of exotic
plant and animal material that
might harbour pests
10. Integrated Pest Management (IPM)
- biological and cultivation techniques
are used first, then biopesticides
when necessary
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Organic Fertiliser
Organic Fertiliser
- organic materials, such as animal manure, applied as a source of plant nutrients
3 Basic Types of Organic Fertiliser
- Animal Manure
- Green Manure
- Compost
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Organic Fertiliser cont’d
Animal Manure
- dung and urine of farm animals
- improves soil structure
- stimulates beneficial bacteria and fungi
Green Manure
- freshly-cut or still-growing vegetation that is ploughed into the soil
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Organic Fertiliser cont’d
Compost
- partially decomposed organic plant and animal
matter
- made up of animal manure, topsoil, kitchen
scraps
- rich, natural fertilizer
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Other Solutions to Land Pollution• sustaining existing forests and national parks
• restoring damaged areas
• support efforts to protect, expand, mend
Jamaica’s national park system
• support efforts to protect large areas of remaining
undeveloped lands
• reduce or eliminate the input of pollutants or
waste
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Legislations
The Watersheds Protection Act
- law governing watersheds in Jamaica
- administered by NEPA
- reduces soil erosion
- ensures proper land use
- maintain optimum levels of groundwater
- promote regular flows in waterways
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Other Legislation Relevant to Land Pollution
• Forest Act
• Rural Agricultural Development Act
• Water Resources Act
• Town and Country Planning Act
• Land Development and Utilisation Act
• Country Fires Act
• The Mining Act
• Wildlife Protection Act
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L7- Summary Questions
1. What are the effects of mechanisation?
2. What is the name given to measures used to reduce soil erosion?
3. What is the difference between bioaccumulation and biomagnification?
4. Which type of irrigation is the most efficient?
5. List four alternatives to pesticide use.