implic of defores & farming practices on carbon cycle lows?

• Deforestation is second only to burning of fossil fuels as a source of greenhouse gas emissions
• Amazon is absorbing less than half as much CO2 than it did 20 years ago
• Rising temperature causes parts of the Amazon to dry out


  Desiccated trees absorb less CO2, are more susceptible to wildfires
• Researchers found 75% of the forest has lost its because of both climate change and deforestation
• This means trees will take longer to recover after droughts / fires / deforestation
• Amazon Rainforest stores up to 120 billion tonnes of carbon (equivalent to 12 years of global emissions at current rates)
• If cleared by fire, most of the carbon will be released as CO2 into the atmosphere


  Leading to enhanced greenhouse effect globally
• Parts of the Amazon are already a larger carbon sources than carbon sinks due to wildfires and slash-and-burn deforestation
• Slash-and-burn agriculture


  Forest trees are felled and those not used as timber are left to dry for a few months, then burnt. The land is planted with crops e.g. bananas, palms, maize, rice. After a year or two, productivity of the soil declines and the farmers move onto another part of the rainforest to clear for short-term agricultural land.
• Clearings were left idle for 20-100 years for the forest to recover and again provide fertile land (decomposition of leaf litter resumes) and timber
• If the clearing cycle becomes shorter e.g. 5-8 years

  The rainforest is unable to recover and is replaced by tough grasses
• The amount of carbon stored in biomass is drastically reduced
• Cattle ranching vs soy production


  • Carbon stored as biomass in grass is much less than in trees (180 tonnes / ha)
  • Grazed pastures can sequester more carbon than soy production (2.7 tonnes / ha) because manure from the cattle can be decomposed to humus in the soil carbon store
  • When soy is harvested periodically, soil is disturbed, releasing more CO2 from the soil into atmosphere
• Soy production causes more disturbance to the carbon cycle of tropical rainforest