The Amazon Rainforest

Introduction: World’s largest tropical forest- hot wet and vegetation dense

  • Home to ½ of world’s plant and animal species
  • Home to endangered species such as Amazonian manatee
  • Caught the public’s attention in 1980s when a series of news reports said that an area of rainforest the size of Belgium was being cut down and subsequently burnt every year.


Role in Water Cycle:

  • 1/5th Earth’s freshwater stored in Amazon
  • Very wet- lots of evaporation over Atlantic Ocean and wet air is blown towards Amazon= high rain
    • Moisture contributes to the formation of rain clouds, which release the water back onto the rainforest. In the Amazon, 50-80% of moisture remains in ecosystem’s water cycle
    • Rainfall across the whole basin is approximately 2300 mm annually
  • Warm temperature- evaporation is high so increases precipitation
  • Dense canopy: high interception = less water flow
    • 50% of rainfall never reach ground, its intercepted by forest and re-evaporated = rain

Role in Carbon Cycle:

  • 35% of World’s CO2 emissions is absorbed in the Amazon Rainforest- carbon sink
  • More CO2 = More productive= Vegetation absorbs more CO2 for photosynthesis- increases biomass
  • However- as trees are growing more quickly also dying younger
    • Dead Amazonian trees emit 1.9 billion tons of carbon to the atmosphere each year.
  • Thus we may not be able to rely on Amazon as an effective carbon sink


Human activities and the cycles:

Deforestation for timber or farming: 7.3 million hectares forest is lost annually

  • 75% of Brazils GHG emissions due to deforestation and land use change
  • Effects on Water Cycle:
    • Flooding: No tree canopy to intercept rainfall so more water reaches the ground- saturation = water moves to rivers via surface runoff-
    • Drought: Deeper forest roots=pump more soil moisture to surface=20% more air humidity = 20% more precipitation
  • Effects on Carbon Cycle:
    • No roots to hold soil= heavy rainfall washes away nutrient-rich top layer of soil= Carbon transferred to hydrosphere
    • No leaf litter, no humus formed, soil cannot support new growth, limits CO2 absorbed
    • Forest absorbs 11% more solar radiation than pasture land

Climate Change

  • Drought due to decreased rainfall E.G 2005-2010 droughts: release a 5 billion metric tons of carbon dioxide once the trees that are killed by the new drought rot.
  • Plants adapted to moist conditions so many die- could also lead to forest fires
  • A 4° C increase in temperature, would see 85%of the forest die in the next 100 years
  • 75% of Brazils energy from reservoirs which are lowest since 2005



  • Selective logging: loggers choose only wood that is highly valued, such as mahogany. Clear-cutting is not selective- Forest structure maintained and canopy still present = regenerate
  • Replanting: UN Conference in Lima: Peru plans to restore 3.2 million hectares of forest by 2020
    • BUT has to ensure the same type of tree planted = variety of trees kept same
  • Environmental Law: ban use of unsustainable wood, excessive logging and control land use:
    • Brazilian Forest Code: landowners to keep 50-80% of their land forest BUT
  • Protection: Many countries have set up nation parks and nature reserves
    • Tumucumaque National Park by World Bank- World largest tropical forest park
    • Remote and difficult to acess so no poaching BUT some small scale mines
    • No indigenous tribes in the park so will not have to meet needs of local people.
    • BUT WWF is providing US$1 million just to mark out area and prepare the plan