Tropical Rainforest

• Amazon rainforest


  Occupies area of 70% in Brazil but extends over Peru, Ecuador, Venezuela, Colombia, Guyana, Bolivia
• Amazon rainforest is in South America and occupies an area of 5.5 million km²
• Rainforest


  • No seasonality
  • Found at Equator
  • High average annual temperatures
  • Significant cloud cover
  • High annual rainfall
  • Evenly distributed throughout year
  • Convectional rainfall at high intensity
  • High humidity
  • Year round growing season
  • Around 12 hours daylight
• Rainforest water cycle


  1. Intense heating during day

  2. Convection

  3. Warm, moist air forced to rise

  4. Storms clouds form

  5. Precipitation high average annual rainfall
• Interception by trees is high at 10%, accounting for 20-30% of all evaporation
• Around half of incoming rainfall is returned to atmosphere by evapotranspiration
• Soil and groundwater store large amounts of moisture due to high rainfall and deep tropical soils
• Trees play a crucial role in the water cycle, absorbing, storing and releasing water through transpiration
• A single large rainforest tree can pump 1000 litres of water into the atmosphere per year and release 100 gallons of water per day, contributing to humidity
• Every day the Amazon rainforest releases 30 billion tonnes of moisture into the atmosphere, which is then used to create clouds that help keep the Amazon cool
• Trees can reduce surface temperatures by 1-10°C through increased evaporation
• Global wind patterns influence the volume of water coming from the Atlantic to the Amazon Basin
• The Amazon Basin recycles water around the countries, reducing flooding of regions through interception and cooling the temperature of regions
• Carbon cycle in rainforest

  • Major global reservoir of stored carbon
  • Net primary productivity is high
  • Large forest trees store 180 tonnes of carbon above ground and 40 tonnes in roots
  • Between 14-40 kg carbon per square metre
• Carbon cycle in rainforest

  1. Photosynthesis high rate

  2. Respiration high rate due to high temperatures

  3. Decomposition extremely high due to high temperatures and humid conditions
• The Amazon rainforest sequesters 2.4 billion tonnes of carbon per year
• When destroyed or degraded, the rainforest has huge potential to be a source of carbon emissions, with 30-60% of carbon lost to the atmosphere
• Physical factors affecting water cycle

  • Gentle relief allows water to move across surface and through soil
  • Steep catchments in Andes with rapid runoff
  • Widespread inundation across flood plains
  • Impermeable catchments have minimal water storage capacity
• Physical factors affecting carbon cycle

  • High temperatures all year round lead to increased rates of photosynthesis and decomposition
  • Warmer air has greater ability to store carbon
• Rainforests have 10x more leaf area than temperate forests, leading to more litter and organic matter in soils
• Rainforest soils are dominated by ancient igneous and metamorphic rocks, with carbonates largely absent, leading to poor soil quality
• Madeira drainage basin


  • Largest tributary in Amazon, accounting for 15% of total discharge
  • Since 1970, almost 50% of primary forest has been destroyed or degraded
• Impacts of deforestation


  1. Less trees means less evapotranspiration and precipitation

  2. Reduced water storage in trees, soils and permeable rock leads to increased runoff and flooding

  3. Reduced cloud cover and increased temperatures due to less evaporative cooling
• The 2014 floods in Madeira were caused by deforestation on the lower slopes of the Andes, resulting in massive reduction in water storage and accelerated runoff
• Deforestation


  • Reduces evapotranspiration
  • Reduces rainfall
  • Increases likelihood of droughts and wildfires
• Deforestation reduces the Amazon's ability to absorb and store carbon, converting it into a source of carbon emissions
• Forest fires produce 3 times more carbon than the Amazon absorbs
• Deforestation dramatically reduces inputs of organic material to soils, depleting them of carbon and reducing decomposer organisms
• Deforestation destroys the main store of plant nutrients in the forest trees, with nutrients then washed out of the exposed soils
• Strategies to manage tropical rainforests

  • Protection through legislation and establishing conservation areas
  • Reforestation and afforestation projects
  • Improving agricultural techniques to make them more sustainable
• Reforestation projects


  • Rondônia project to develop 1000 km² of commercial timber plantations
  • Scheme to plant 20 million native tree seedlings on 4000 smallholdings
• Indigenous Surui people participate in a scheme to protect primary rainforest on their tribal lands and reforest degraded areas
• The REDD scheme provides payments to the Surui people for protecting the rainforest and abandoning logging
• Reforestation increases soil organic matter and moisture, and improves infiltration to reduce runoff
• Improved agricultural techniques


  • Maintaining soil fertility through rotational cropping and integrating crops and livestock
  • Using human-engineered 'dark soils' made from charcoal, waste and manure to allow intensive and permanent cultivation
• Arctic tundra


  • Occupies 8 million km² in northern Canada, Alaska and Siberia
  • Extends from the boreal edge of coniferous forest to the Arctic Ocean
  • Defined by the 10°C July isotherm