Deforestation

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Deforestation

  1. 1. DEFORESTATION Design by Joe Naumann
  2. 2. Unit XI. Deforestation and the role of forests in the climate system. A. History of forests Earth 4.6 byr Life >3 byr Multicellular Life 600 myr Plants on land 400 myr (green algae) Ferns, etc. 200 - 70 myr Flowering plants 100 myr (Angiosperrms)
  3. 3. Unit XI. Deforestation and the role of forests in the climate system. A. History of forests • First land plants short…..<0.5 m (100 myr) • As competition for light increased, they grew taller. Required support (trunks). • Tall forests for ~300 myr, but dramatic changes in composition. • Only last 100 myr would look familiar. Less than 2% of Earth history.
  4. 4. Unit XI. Deforestation and the role of forests in the climate system. B. Forest types • Boreal Forests (conifers) • Temperate Forests (mixed deciduous hardwoods) • Tropical Rainforests (conifers and hardwoods)
  5. 5. NPP: Net Primary Productivity What is the net annual production of organic matter by a particular ecosystem,usually measured in the amount of Carbon fixed as organic matter. Net means the total fixed minus the total respired. gC/km2/yr is the (net) grams of carbon fixed over each square kilometer in an average year.
  6. 6. Characteristics of Earth’s Forests Forest Type Where? Area (km2) Rainfall Soil NPP gC/km2/yr Biodiv- ersity Boreal Temperate Tropical Rainforest High N Latitudes (50-60 °N) Mid- Latitude (30° - 50°) Low Latitude (0 - 30°) 12 M 12 M 17 M Low 20-50 cm/yr Moderate 50 to 100 cm/yr High 2 to 10 m/yr Immature, but abundant minerals yet to be released Rich, fertile, abundant nutrient reserves Poor, highly leached. Most nutrients recycles 300 M 500 M 1000 M Low High Moderate
  7. 7. Unit XI. Deforestation and the role of forests in the climate system. B. Forest types • Boreal Forests: slow growing, cold, 1/2 year low light, shallow, immature, but mineral-rich soils. Low plant and animal diversity. Capable of sustained harvest, but low yield (slow growth)
  8. 8. Unit XI. Deforestation and the role of forests in the climate system. B. Forest types • Temperature Forests: Mixed deciduous hardwoods and evergreens, fertile soils. Resistent to disturbance: if cleared, rapid recolonization. Sustained yield OK in most regions.
  9. 9. Unit XI. Deforestation and the role of forests in the climate system. B. Forest types • Tropical Rainforest: Closed canopy, high rainfall. Most in Brazil (Amazonia), central West Africa (Congo, Zaire), Indonesia and Madigascar. Also Central America, Angola, Peru, Bolivia, India and scattered outliers.
  10. 10. Percentage area covered by different ecosystems
  11. 11. NPP (gC/m2/yr) for different ecosystems
  12. 12. Percentage net NPP (gC/m2/yr) for different ecosystems 70% 3%
  13. 13. Unit XI. Deforestation and the role of forests in the climate system. B. Forest types • Tropical Rainforest are the lungs of the world. They inhale CO2 and exhale O2 through the process of photosynthesis.
  14. 14. Unit XI. Deforestation and the role of forests in the climate system. B. Forest types • Tropical Rainforest: The risky bit….. Soils: Ancient, little rock, highly leached (high rainfall), and few sources of new nutrients. Almost all nutrients are recycled. Incapable of sustained high harvest.
  15. 15. Unit XI. Deforestation and the role of forests in the climate system. C. Deforestation: why we should be concerned. • Loss of biodiversity • Global warming (burning releases CO2) • Climate impacts
  16. 16. Unit XI. Deforestation and the role of forests in the climate system. D. The role of forests in the climate system.
  17. 17. How a geologist views a tree.…Key variables: Leaf area index Rooting depth Water-holding capacity of the soil.
  18. 18. D. The role of forests in the climate system. Amazonia: Estimated that 50% of the rainfall over the Amazon Basin is recycled water. During a rainfall event, leaves intercept rainwater, and organic-rich soil absorbs rainfall. Leaf evaporation and transpiration returns water vapor to the atmosphere. Two effects: • landward migration of rainfall • water vapor fuels more storms
  19. 19. D. The role of forests in the climate system. Amazonian Paradox: Amazon rainforest requires heavy rainfall to exist, but half the rainfall is itself depedent on the rainforest being present.
  20. 20. D. The role of forests in the climate system. Examples: Two adjacent catchments…. One clear cut, the other left forested. Stream runoff in the deforested catchment was 4 to 10 times the forested catchment. Rainfall similar in the two basins, so difference is decreased evapotranspiration.
  21. 21. Forested Deforested
  22. 22. D. The role of forests in the climate system. Examples: Ivory Coast: Replacement of rainforest by cropland over last 5 deacdes,; runoff increased 8-fold. Areas formerly suitable for cocoa now abandoned due to lower rainfall, less humidity and more extreme summer temperatures. Similar example in India where rice production fell after rainforest removed.
  23. 23. D. The role of forests in the climate system. Examples: Ivory Coast, India Proving cause and effect is difficult, but first principles provides a reasonable mechanism to explain these observations.

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