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Our Impact on the Ecosystem (part 1): Deforestation & Overfishing

Students will learn about the <br>- effects of deforestation and overfishing

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Our Impact on the Ecosystem (part 1): Deforestation & Overfishing

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  1. Our Impact on the Ecosystem Chapter 22 Content • Effects of Man on the Ecosystem • Conservation (Environmental Biotechnology)

  2. Ecosystem

  3. Balance in the ecosystem

  4. How do we affect the ecosystem? ◼ Natural resources are resources supplied by nature that are used by humans ◼ Air, water, soil, wildlife and forests are renewable resources (i.e. they can be replaced in the ecosystem by natural cycles as long as humans do not overuse them) ◼ On the other hand, fossil fuels take millions of years to form naturally ◼ They cannot be replaced once they are used, hence they are called non-renewable natural resources

  5. How do we affect the ecosystem? Human activity Agriculture Industry Uses natural resources leading to 1. Deforestation 2. Over-fishing 3. Pollution

  6. 1) Deforestation

  7. Deforestation Definition: The removal of forests by cutting and burning to provide land for agricultural purposes, residential or industrial building sites, roads, etc., or by harvesting the trees for building materials or fuel.

  8. Deforestation

  9. Reasons for deforestation 1. Urban development 2. Cultivation 3. Grazing 4. Timber 5. Fibres

  10. Damaging effects of deforestation Soil erosion i) Flooding ii) iii) Desertification iv) Climate changes

  11. i) Soil erosion

  12. Soil erosion

  13. Importance of plants ◼ Leaf canopy → protects soil from impact of rain ◼ Roots → hold soil + water (water released gradually to soil below and nearby streams and lakes)

  14. Removal of plants ◼ Soil exposure to direct force of the rain ◼ Without a shelter belt, water runoff become intense ◼ Topsoil (fertile layer) washed away (esp. on slopes) ◼ Severe in tropical areas (due to high rainfall)

  15. Sheet erosion ◼ The removal of a fairly uniform layer of soil from the land surface by raindrop splash and/or runoff.

  16. Gully erosion ◼ Removal of layers of soil due to heavy rainfall, thus creating small channels which eventually widen and deepen as more soil is removed, forming gullies

  17. Gully erosion

  18. ii) Flooding

  19. Why do floods occur? ◼ With trees removed, rainwater is not retained and released slowly ◼ Blockage of water flow in rivers/streams due to silting (eroded soil) ◼ Water levels rise rapidly and flows inland Silting

  20. iii) Desertification

  21. Desertification Definition: Destruction of land leading to desert-like conditions What leads to desertification? 1) Hardening of soil (due to water evaporation caused by the heating of soil by the sun) → Plant life not supported → Animal life is not supported → Land becomes barren → habitats are lost and many species of organisms become extinct 2) Overgrazing by animals - because plants cannot regenerate fast enough

  22. Result of desertification ◼ Loss of habitats ◼ Extinction of species of organisms ◼ Loss of potential medicinal resources which may be useful in treating diseases ◼ Upsetting O2and CO2balances

  23. iv) Climate changes

  24. How does deforestation result in climatic changes? → with forests, rainwater is retained and absorbed by roots of trees → water lost during transpiration → relative humidity of air around forests high → water vapour condenses + precipitates as rain → However when trees are cleared the area becomes dry & warm → annual rainfall decreases

  25. What have we learnt so far? ◼ Deforestation - definition - reasons for deforestation - damaging effects of deforestation (i) soil erosion (ii) flooding (iii) desertification (iv) climatic changes

  26. 2) Over-fishing

  27. How do uncontrolled fishing practices harm the ecosystem? i) Humans catch fish for food. As the human populations increases, so does the demand for fish. Some species of fish have been caught in such large numbers that their populations have decreased drastically (over-fished) ii) Indiscriminate fishing (i.e. do not distinguish between the targeted catch and immature organisms or unwanted species e.g. gigantic drift nets trap almost everything in their path. Marine life e.g. sharks, turtles, dolphins are unintentionally caught. Though dumped back into the sea, they often die

  28. How do uncontrolled fishing practices harm the ecosystem? iii) Some methods of fishing destroy the seabed and marine habitat - shrimp/prawn trawlers drag large fishing nets along the bottom of the sea. Many unwanted species are trapped in the process - scallop dredges scrape the seabed, destroying coral reefs and organisms that live on the seabed - In cyanide fishing, cyanide (a poison) is squirted in the water around coral reefs. The cyanide stuns reef fish and makes them unable to swim properly. Fishermen then capture the fish for sale as pets. Explosives (e.g. dynamite) are also used to stun and catch reef fish. Both cyanide and explosives kill corals and many other reef organisms

  29. Destructive fishing methods Trawling Dredging 1. 2. Dredging Trawling

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