The Amazon Rainforest

• The Amazon Rainforest


  Rainforest in South America
• The Water and Carbon Cycles are Important to the Amazon Environment
• Human Activities in the Amazon are Affecting the Water and Carbon Cycles
• Attempts to Limit Human Impacts on the Amazon
• Selective Logging


  1. Only some trees cut, just the oldest ones

  2. This is less damaging to the forest

  3. The canopy is still there and the soil isn't exposed

  4. The forest is able to regenerate, so the impact on the carbon and water cycle is small
• Replanting


  1. New trees are planted to replace the ones that are cut down

  2. It's important that the same types of tree are planted that were cut down, so that the variety of trees is kept for the future and the local carbon and water cycles return to their initial state
• Laws to protect rainforests

  • Laws that ban the use of wood from forests that are not managed sustainably
  • Laws that ban excessive logging
  • Laws that control land use, eg the Brazilian Forest Code says landowners have to keep 50-80% of their land as forest
• Protection


  • Many countries have set up national parks and nature reserves to protect rainforests
  • Within national parks and nature reserves, damaging activities such as logging can be monitored and prevented
• Tropical rainforests contain only about 1 kg/m² of soil
• When forests are cleared and burned, 30-60 per cent of the carbon is lost to the atmosphere
• Unburned vegetation decays and is lost within ten years
• The soil fungi and bacteria that used to recycle the dead vegetation die off
• When forest clearance first occurs, the soils are exposed to the heavy tropical rainfall
• This rapidly washes away the topsoil and attacks the deep weathered layer below
• Most of the soil is washed into rivers before the forest clearance has caused a reduction in the rainfall
• Of the rainfall that is evapotranspired back into the atmosphere, about 48 per cent falls again as rain
• Only about 30 per cent of the rainfall actually reaches the sea
• The rest is caught up in this constant closed system loop
• Between 2000 and 2007, the Brazilian Amazon was deforested at a rate of 19,368 km per year
• During this time, an area of forest larger than Greece was destroyed
• Brazil is the world's fourth largest climate polluter, with 75 per cent of its greenhouse gas emissions attributed to deforestation and land use change
• 59 per cent of this is from loss of forest and burning in the Amazon
• Removal of forest using slash and burn techniques

  1. Reduces the retention of humidity in the soil's top layer down to a depth of one metre

  2. Facilitates sudden evaporation of water previously retained in the forest canopy

  3. Increases albedo (reflectiveness) and temperature

  4. Reduces porosity of soil, causing faster rainfall drainage, erosion and silting of rivers and lakes
• Any moisture that evaporates from deforested areas forms shallow cumulous clouds which usually do not produce rain
• Forests emit salts and organic fibres along with water when they transpire
• These act as condensation nuclei and assist in cloud and rain formation
• Their loss inhibits the formation of cloud and reduces rainfall
• If destroyed, the vast carbon store will be released into the atmosphere
• Differences between tropical rainforest and pasture land

  • Forests absorb approximately 11 per cent more solar radiation
  • The average temperature in the rainforest is approximately 24.1°C; in pastures it is 33°C
  • The daily temperature variation of Amazon forest soils at 20 cm did not exceed 2.8°C, though under pastures it was 8°C
  • The moisture content in the upper one metre of pasture soil is about 15 per cent less than under nearby forest
  • Deeper forest roots can pump more soil moisture to the surface, producing 20-30 per cent more air humidity and consequently 5-20 per cent more precipitation than pastures
• Studies investigating climate change indicate that by the year 2050, temperatures in Amazonia may increase by 2-3°C
• There has been an increase in the frequency and intensity of droughts in Amazonia experienced between the 1970s and 2010s
• There has been a reduction in the Amazon Basin's forest cover, with 27 per cent lost by 2020 and deforestation continuing
• Although much of this is due to deliberate deforestation, some is also occurring as a result of climate change, with trees dying due to their intolerance of higher temperatures and changing seasonality
• A 2009 study estimated that if global temperatures rise 2°C above pre-industrial levels, the Amazon dieback could see 75 per cent of the forest destroyed over the following decades, rising to 85 per cent with a 3°C rise
• Amazonian savannas and grasslands in the upper 5 cm of soil contain only about 1 kg/m² of carbon
• Strategies to reduce the effects of environmental change in Amazonia

  • Creation of national parks and forest reserves
  • Forest biofuel production
  • Reforestation
  • Enrichment of degraded forests using native species
• There are links between what is happening in the Amazon basin and external forces operating at different scales (government policies or the decisions of transnational corporations)