Topic 4: Sustaining Ecosystems

• The Nutrient Cycle

  • Forest floor is hot and damp so dead leaves decompose quickly, releasing nutrients into the soil
  • As organic material decays and is recycled so quickly by plants and trees, there are few nutrients in the soil- so trees have their roots very close to the surfaces
  • Greatest store of nutrients is in the biomass
• The Water Cycle

  • Rainforests produce their own rainfall
  • rainforest heats up in the morning, water evaporates and forms clouds to make rainfall for the next day (convectional rainfall)
  • Water lost through pores in the leaves and evaporates (evapotranspiration)
  • Roots of plants take up some moisture, but most is evaporated from the canopy layer which also intercepts most rainfall
• Climate

  • Hot and wet
  • Reliable input of rainfall (over 2000mom per year)
  • Daily temperatures average between 26 and 28 degrees
  • Climate can vary on a smaller scale (different levels or rainforest) called microclimate
• Soil profile

  • soils in tropical rainforests are called latosols
  • Soils are shallow and lack minerals
  • Fertility sustained by rapid replacement of nutrients from dead leaves
  • Humus (decomposed layer) is very thin
  • Minerals such as calcium and magnesium leached quickly due to heavy rainfall
  • Top layers of soil are red due to high concentrations of aluminium oxide and iron oxide
  • Rapid chemical weathering, particularly of the original rock (parent rock) on which the soil has formed
• Indigenous peoples

  • Tropical rainforests are home to 50 million indigenous peoples
  • They depend on their surroundings for food, shelter and medicines
  • Indigenous farmers have practised a sustainable system called shifting cultivation
  • have small agricultural gardens which have been cleared of trees and burnt-ash released adds minerals to soil, making it more fertile
• Interdependence in the rainforest ecosystem

  Each part of the ecosystem relies in every other part for survival so any small changes in human activity ot the environment can have dramatic effects in the ecosystem. Eg: the soil relies on the forest cover to intercept rainfall to prevent severe leaching of minerals
• Goods provided by tropical rainforests

  • Fruits and vegetables
  • Nuts
  • Oils
  • Flavourings
  • Fibres
  • Wood
  • Gums and resin: eg chewing gum, gold ball coating, paint products
  • Rubber: eg car tyres
  • Medicines
• Services of the rainforests

  • Trees reduce flood risk as the leaves intercept and slow down rainwater
  • Maintain some of the world’s most fragile soils, protecting from erosion
  • Habitat for diverse flora and fauna
  • Absorb carbon dioxide, store the carbon (carbon sink) and give out oxygen
  • maintain water cycle, pumping moisture to provide defence against drought, forest fires, extreme weather
• Human exploitation of tropical rainforests

  • Logging
  • Agriculture
  • Palm oil plantations
  • Tourism
  • Dam building and hydroelectric power
  • Road construction
• Human causes of deforestation

  • Hydropower
  • Agriculture
  • Road building
  • Mining
  • Logging
  • Settlements