The Amazon Rainforest

• Context

  The largest rainforest on Earth at 6 million km squared;

  70% is in Brazil (rest are in Peru, Ecuador, Venezuela, Colombia, Bolivia and Guyana)

  Dominated by evergreen hardwood trees.

  Average annual temperatures between 25 and 30 degrees with little to no seasonal variation.

  High average annual rainfall at >2000 mm with no dry season.
• The Amazon’s precipitation

  High annual rainfall at >2000 mm.

  No notable seasonal variation.

  High-intensity and conventional rainfall.
• The Amazon’s interception

  Intercepts 10% of all precipitation.

  Intercepted rainfall accounts for 25% of all evaporation.
• The Amazon’s evapotranspiration

  High rates of evaporation and transpiration due to high temperatures, moisture and dense vegetation.

  High evapotranspiration-precipitation feedback loop that sustains high rainfall totals.

  50% of all precipitation is returned to the atmosphere.

  Moisture lost in transpiration is derived from the soil via tree roots.

  Most evaporation is from intercepted moisture from leaf surfaces.
• The Amazon’s run-off


  Rapid run-off related to high precipitation, intense rainfall events and well-drained soils.

  Depending on seasonal distribution of precipitation, river discharge may peak in one or two months of the year.
• The Amazon’s atmosphere (water)

  High temperatures allow the atmosphere to store large amounts of moisture.

  Absolute humidity is high.

  Relative humidity is also high.
• The Amazon’s soil/groundwater (water)

  Abundant rainfall and deep tropical soils leads to significant water storage in soils and aquifers.
• The Amazon’s vegetation (water)

  Rainforest trees play crucial role in the water cycle, absorbing and stowing water from the soil and releasing it through transpiration.
• The Amazon’s soil/peat (carbon)


  Leached and acidic soil.

  Stoes 90 to 200 tonnes/ha.

  Contains limited carbon and nutrient stores.

  Poor soils support a biome with the highest NPP and biomass of all terrestrial ecosystems.
• NPP: Net Primary Productivity (NPP) is the amount of energy that is transferred from the environment to the biomass.
• The Amazon’s vegetation (carbon)

  NPP is high, at 2500 grams/m squared a year.

  Biomass at 400 to 700 tonnes/ha.

  Large forest trees typically store around 180 tonnes C/ha above ground, with a further 40 tonnes C/ha in their roots.
• Exchange between carbon stores are rapid; the humid conditions allow for faster decomposition, and carbon fixation through photosynthesis is high.
• Physical factor; Geology (water)

  Large partes of the Amazon Basin are made up of impermeable crystalline rocks.

  Impermeable catchments have minimal storage capacity resulting in rapid run-off.

  Permeable and porous rocks such as limestone and sandstone store rainwater and slow run-off.

  Surface runoff causes flooding of channel storage.
• Physical factor; Relief/Slopes (water)

  Most of the Amazon Basin comprises extensive lowlands.

  Gentle relief allows overland flow and throughflow to steams and rivers.

  In the west the Andes create steep catchments with rapid run-off.

  Widespread inundation across extensive floodplains occur annually, which store water for several months and slows it movement into rivers.
• Physical factor; Temperature (water)

  Average annual temperatures between 25 and 30 degrees with little to no seasonal variation; this causes high rates of evapotranspiration.

  Convection is strong, leading to high atmospheric humidity, the development of thunderstorm clouds and intense precipitation.

  Water is cycled continually between the land surface, forest trees and the atmosphere by evaporation, transpiration and precipitation.
• Physical factor; vegetation (carbon)

  The forest trees dominate the biomass carbon store in the Amazon, and is the principal carbon store.

  60% of rainforest carbon is stored in the above ground biomass of tree stems, branches and leaves, with the remainder being below ground as roots and soil organic matter.
• Physical factor; geology (carbon)

  Dominated by ancient igneous and metamorphic rock, which do not store carbon.

  Small outcrops of limestone near the Andes.

  Significant regional carbon store in the context of the slow carbon cycle.
• Accounts for 25% of all NPP in terrestrial ecosystems.
• Photosynthesis connects the rainforest to the atmosphere carbon stores.