Tropical Rainforests

• Tropical Rainforests


  • Hot and Wet All Year Round
• Plants in Tropical Rainforests

  • Most trees are evergreen to take advantage of continual growing season
  • Many trees are really tall, canopy cover is dense, little light reaches forest floor
  • Lots of epiphytes (plants that grow on other plants)
• Soil in Tropical Rainforests

  • Not very fertile as heavy rainfall washes nutrients away
  • Surface nutrients from decayed leaf fall, but this layer is very thin as decomposition is fast
• Many indigenous people have adapted to life in the rainforests, making a living by hunting, fishing, gathering nuts and berries, and growing vegetables in small garden plots
• Biodiversity


  Variety of organisms living in a particular area, both plants and animals
• Rainforests have extremely high biodiversity, containing around 50% of the world's plant, animal and insect species, and may contain around half of all life on Earth
• Rainforests are stable and productive environments because their climate is constant - it's hot and wet all the time. Plants and animals don't have to cope with changing conditions and there is always plenty to eat
• Many organisms have evolved to depend on just a few other species for survival - they are specific to a particular habitat and food source. Many species are also only found in a small area
• Deforestation and uncontrolled development of the rainforest are likely to lead to the extinction of many species and the loss of biodiversity. The number of threatened species in Brazil increased from 628 in 2008 to 1182 in 2014
• The warm and wet climate helps fungi and bacteria on the forest floor to decompose dead plant material rapidly


  This makes the surface soil high in nutrients, meaning plants can grow easily
• Plants pass on their nutrients when eaten by animals


  The dense vegetation provides lots of food, so animal populations are high. When the animals die, their nutrients are transferred back to the soil, making it richer and encouraging lots of vegetation
• Many plant and animal species have formed symbiotic relationships where they each depend on the other for survival


  For example, the agouti (a rodent) is one of the only animals that can crack open the hard seed pod of the Brazil nut tree to eat the nut inside. The agouti also bury the nuts, which can sprout into new seedlings. If the agouti became extinct, Brazil nut tree numbers would decline and so could the populations of all the other animals that depend on Brazil nut trees for food or shelter
• Cecropia trees have hollow stems and produce an energy-rich foodstuff at the base of their leaves


  This makes the trees an ideal home for Azteca ants, who rely on the trees for food and shelter. The ants fight off other insects that try to feed on the tree and attack lianas that compete with the Cecropia for sunlight. Without the Azteca ants, Cecropias would be much more vulnerable to predators
• Cutting down trees (deforestation)


  Can contribute to climate change
• Reducing tree cover


  May increase the risk of drought, affecting the plants and animals that live in the rainforest ecosystem
• Fewer trees


  Soil has less protection from heavy rainfall, the few nutrients present would wash away more easily and plants would struggle to grow
• Plant Adaptations in Tropical Rainforests

  • Trees compete for sunlight by growing tall
  • Plants have thick, waxy leaves with pointed drip tips to channel rainwater and repel it
  • Climbing plants like lianas use tree trunks to reach sunlight
  • Trees have smooth, thin bark as no need to protect from cold
  • Large, stable buttress roots support tall tree trunks
  • Plants drop leaves gradually throughout year to go on growing
• Animal Adaptations in Tropical Rainforests

  • Many animals spend entire lives high up in the canopy, with strong limbs to move around quickly
  • Some birds have short, pointed wings to manoeuvre between dense trees
  • Some animals have suction cups to help them climb
  • Some animals have flaps of skin to help them glide between trees
  • Some animals are camouflaged to hide from predators
  • Some animals are adapted to low light levels on the rainforest floor
  • Many animals are nocturnal to save energy in the heat
• The Amazon is the largest rainforest on Earth, covering an area of around 8 million km2 across parts of several countries
• Almost 18 million hectares of Amazon forest were lost between 2001 and 2012, an average of 14 million hectares per year
• Since 2012, deforestation in the Amazon has been increasing, with 2021 having the highest rates since 2006
• It's estimated that around 40% of the Amazon will have been deforested by 2050 if the current rate of deforestation is not reduced
• Causes of Deforestation in the Amazon Rainforest (2000-2005)

  • Commercial Farming (65-70%)
  • Subsistence Farming (20-25%)
  • Commercial Logging (5-10%)
  • Mineral Extraction (1-2%)
  • Energy Development (1-2%)
  • Other (2-3%)
• 95% of deforestation in the Amazon is due to just 50% of the causes
• Deforestation in the Amazon

  Trees absorb CO2 from the atmosphere, so deforestation causes some of this CO2 to be released, contributing to global warming
• Up to 25% of Brazil's CO2 emissions come from deforestation
• Brazil is losing up to 100 tonnes of topsoil per hectare per year due to deforestation and soil erosion
• Deforestation in the Amazon

  • Environmental and Economic Impacts
• Deforestation


  Causes climate change by releasing CO2 stored in trees
• Deforestation


  Leads to soil erosion and reduced soil fertility
• Brazil is losing up to 100 tonnes of topsoil per hectare each year due to soil erosion
• Deforestation


  Reduces the attractiveness of the area to tourists
• Deforestation has brought wealth to many Amazonian countries through economic development and industries like farming, mining, and logging
• The global rate of deforestation is very high, averaging 22 million hectares per year from 2007 to 2017
• Brazil and Indonesia accounted for almost half of global deforestation from 2001 to 2014
• Efforts to reduce deforestation rates have had mixed results, with some countries like Costa Rica increasing forest cover, while others like Brazil under Bolsonaro saw rapid increases in deforestation
• In 2023, President Lula of Brazil pledged to work towards net-zero deforestation in the Amazon by 2030
• Tropical Rainforests


  • Very Valuable to People and the Environment
• Many products, including rubber, coffee, chocolate and medicines, are sourced from the rainforest
• Protecting rainforests may reduce the greenhouse effect by reducing CO2 emissions and allowing the trees to continue absorbing CO2