tropical rainforests

• Tropical Rainforests are Hot and Wet All Year Round
• Climate


  1. The climate is the same all year round-there are no definite seasons

  2. The temperature is generally between 20-28C and only varies by a few degrees over the year

  3. Rainfall is very high, around 2000 mm per year. It rains every day
• Plants


  • Most trees are evergreen to help them take advantage of the continual growing season
  • Many trees are really tall and the vegetation cover is dense-very little light reaches the forest floor
  • There are lots of epiphytes (plants that grow on other living plants and take nutrients and moisture from the air, e.g. orchids and ferns
• Soil


  The soil isn't very fertile as heavy rain washes nutrients away. There are surface nutrients due to decayed leaf fall, but this layer is very thin as decay is fast in the warm, moist conditions
• People

  • Many indigenous people have adapted to life in the rainforests. They make a living by hunting and fishing, gathering nuts and berries, and growing vegetables in small garden plats
• Rainforests Have Very High Biodiversity
• Animals

  • Rainforest ecosystems are believed to contain more animal species than any other ecosystem. Gorillas, jaguars, anacondas, tree frogs, sloths and howler monkeys are all found here, and there are also many species of insects and birds
• Biodiversity


  • Biodiversity is the variety of organisms living in a particular area-both plants and animals
  • Rainforests have extremely high biodiversity-they contain 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 (see p.26) 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
• Rainforests are Interdependent Ecosystems
• Interdependence


  1. 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

  2. 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. This is a key part of the nutrient cycle (see p.20)

  3. Many plant and animal species have formed symbiotic relationships (where they each depend on the other for survival)
• Symbiotic relationships


  • Agouti (a rodent) are one of the only animals that can crack open the hard seed pod of the Brazil nut to eat the nut inside. Sometimes, the agouti bury the nuts- these 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. People who sell Brazil nuts to make a living could also be affected.
  • 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. Without Cecropia trees, the Azteca ants could struggle to survive. The ants fight off other insects that try to feed on the tree. They also attack lianas, which compete with the Cecropia for sunlight by winding vines around their stems. Without the Azteca ants, Cecropias would be much more vulnerable to predators
• But Humans are Interfering with these Ecosystems
• Changes to one part of the rainforest ecosystem

  Can have knock-on effects on the whole ecosystem
• 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


  The soil would have less protection from heavy rainfall, the few nutrients present would wash away more easily and plants would struggle to grow
• Tropical Rainforests - Adaptations
• Plants


  • Trees compete for sunlight by growing tall
  • Plants have thick wax leaves with pointed drip-tips. These channel rainwater to the point, encouraging runoff so the weight of the water doesn't damage the plant. The leaves' waxy coating also helps to repel the rain
  • Climbing plants, such as lianas, use tree trunks to reach sunlight
  • Many trees have smooth, thin barks as there's no need to protect the trunk from cold temperatures. The smooth surface also helps water to run off easily
  • Large, stable buttress roots support the tall trees' trunks
  • Plants drop their leaves gradually throughout the year, meaning they can go on growing all year round
• Layers of plants


  • Emergent trees only have branches at their crown, where the most light is available
  • Some undercanopy plants have large leaves to absorb as much sunlight as possible
• Animals


  • Many animals spend their entire lives high up in the canopy. They have strong limbs so that they can move around their habitat quickly and easily, e.g. howler monkeys
  • Some birds have short pointed wings so that they can easily manoeuvre between the dense tangle of trees, eg, the harpy eagle
  • Suction cups help some animals climb, eg, tree frogs
  • Others have flaps of skin that help them glide between trees, eg, flying squirrels
  • Some animals are camouflaged, eg leaf-tailed geckos look like leaves so they can hide from predators
  • Some animals are adapted to the low light levels on the rainforest floor, eg. anteaters have a sharp sense of smell so they can detect predators without seeing them
  • Many animals are nocturnal, eg, sloths. They feed at night when it's cooler -this helps them to save energy
  • Many animals can swim, e-g jaguars. This helps them cross river channels
• Deforestation is the removal of trees from forests. It's happening in many tropical rainforests, like the Amazon
• The Amazon Has Experienced Large-Scale Deforestation
• The Amazon


  The largest rainforest on Earth-it covers an area of around 6 million km, including parts of Brazil, Peru, Colombia, Venezuela, Ecuador, Bolivia, Guyana, Suriname and French Guiana
• Almost 18 million hectares of forest were lost between 2001 and 2012 -an average of 1.4 million hectares were lost per year in this period
• It's estimated that almost 30% of the Amazon will have been deforested by 2030 if the current rate of deforestation is not reduced
• Reasons for deforestation in the Amazon

  • Commercial Farming
  • Subsistence Farming
  • Commercial Logging
  • Mineral Extraction
  • Energy Development
  • Population Growth
  • Road Building
• Commercial Farming


  • Cattle ranching is the main cause of deforestation in the Amazon-in Brazil, there are around 200 million cattle on about 450 000 km² of pasture
  • Soy is another commercially farmed crop - up to 250.000 km² of former forest has been used for its production. Rice, corn and sugar cane are also grown
• Subsistence Farming


  • Forest is cleared by small-scale farmers who need land to grow food for themselves and their families. Many indigenous people are subsistence farmers
• Commercial Logging


  • The Amazon is full of valuable hardwood such as mahogany, which makes logging extremely tempting to both legal and illegal businesses
• Mineral Extraction

  • Gold, iron ore and copper are mined and exported to help boost countries' development. Explosives are sometimes used to clear earth, and deep pits have to be dug to reach the mineral deposits
• Energy Development


  • Building hydroelectric dams floods large areas of forest. The construction of the Balbina Dam (near Manaus, Brazil) flooded 2400 km² of rainforest
• Population Growth


  • Population growth and migration to the area is putting pressure on the Amazon rainforest, especially as the Brazilian government offers land in the rainforest to poor people from overcrowded cities, e.g. many farmers have been settled along the Trans-Amazonian Highway
• Road Building


  • The 4000 km Trans-Amazonian Highway connects the Brazilian coast to Peru, Colombia and Ecuador, through the Amazon. New roads built for logging have opened up areas that were previously too hard to get to, destroying and threatening more of the forest
• Deforestation in the Amazon has Environmental and Economic Impacts
• Trees remove CO2 from the atmosphere

  The Amazon stores around 140 billion tonnes of carbon. Deforestation releases some of this as CO2 which causes global warming
• Up to 25% of Brazil's CO2 emissions come from deforestation
• Soil erosion


  Brazil is losing up to 100 tonnes of topsoil per hectare each year. With less tree canopy to intercept rainfall and fewer tree roots to absorb it, more water reaches the soil. This reduces soil fertility as nutrients in the soil are washed away. Commercial and subsistence farmers are then forced to find new areas to farm, leading to further deforestation
• Economic development, farming in particular, has brought wealth to many Amazonian countries
• Economic impacts

  • Brazil exported almost $600 million of beef in March 2018
  • The mining industry creates jobs for lots of people, eg, the Buenaventura mining company in Peru employs over 8000 people
  • Logging contributes a huge amount to Brazil's economy, but it can destroy resources that countries depend on, eg, timber, and reduce the attractiveness of the area to tourists
  • Local Brazilian rubber tappers who extract natural rubber from rubber trees have lost their livelihoods as trees have been cut down
• The global rate of deforestation is very high. From 2007 to 2017, an average of 22 million hectares of forest were lost each year