Tropical rainforests (TRF)
Physical characteristics:
Climate:
o Warm and wet
o Around 26°C, little variation
o >2500mm rainfall, large rivers, e.g. the Amazon and the Congo rivers
Vegetation:
o Rich vegetation
o 30-45m tall trees
Soils:
o Thin and poor, lots of vegetation due to rapid nutrient recycling.
o Nutrients locked up in:
Biomass (living vegetation and animals)
Litter (dead wood and leaves, animal remains)
Interdependence of TRF ecosystem components
Main components: climate (rain and sunlight), soil, vegetation (trees and plants) and animals. All
components interact to create an interdependence. Native people can also be part of and live in
harmony with the ecosystem. Human activity can also upset ecosystem’s balance.
Biodiversity
TRF has highest biodiversity in the world- 2/3 of world’s plant species found in TRF, and ½ of world’s
animal species.
Human exploitation: reducing biodiversity- endangered + extinct species, decline in ecosystem
productivity
Adaptations to TRF environment
Plants:
Poor soils:
o Rapid nutrient cycling
o Intensity + absorption of sunlight, photosynthesis
o Warm, humid climate- ideal for plant growth
o Ability for plants to adapt (competition)
Heat and humidity
o Waxy leaves + flexible stems, allow water to run off and allow leaves to move with
sun
o Circulating water (water cycle) as cooling system
o Passing water to soil or returning it to atmosphere
o Leaves cope with large amounts of water falling on them
Sunlight competition
o Most sunlight received by tops of tall trees, shade on forest floor so least sunlight
received near ground
o Less photosynthesis near bottom of forest, different ways to access food + nutrients:
Parasitic plants use other plants for food and water, or gain access from the
soil
General
, o Dark green leaves with lots of chlorophyll
o Only grow branches above main canopy to preserve energy
o Wide leaves to absorb more sunlight
o Very tall plants
Animals:
Food competition
o Many animals, a lot of competition- specialised animals only eat off a certain
plant/animal that few others eat, e.g. parrots + toucans have big strong beaks to
break open nuts
o Some symbiotic relations between plants + animals- trees create fruit eaten by
animals for seed dispersal
Camouflage
o Escape predators, help catch prey
o Poisonous animals use bright colours to warn other animals (arrow frogs)
Deforestation
Long history, most damage done in last century. 62 countries have TRF, little records kept of original
extent, but UN Food and Agriculture organisation think ½ of world’s TRF has been cleared.
Fluctuation of deforestation rates. Greatest rates in Brazil.
At least 20% of Amazon rainforest cleared since 1970 (761 000km2, roughly UK size)
Rate of reduction shows protective measures, e.g. Mexico. Only the rate has decreased, and
deforestation continues. Global rates:
- 1 hectare/second
- 31 million hectares/year
Brazil:
Brazilian rainforest lowland basin drained by Amazon river. Most clearance south of Amazon, where
TRF most accessible by main Brazilian cities (Rio de Janeiro, Sao Paulo, Brasilia).
Rainforest has been inhabited and used by indigenous tribes for centuries to:
- Harvest fruits/nuts
- Cut wood for fuel
- Use timber for housing
- Medicinal purposes
- Slash and burn (little lasting damage)
- Small-scale subsistence farming
Shifting cultivation- forest left to regenerate after one piece of land has been exhausted.
Human activity does not always lead to deforestation, but it can lead to forest degradation, where
the forest ecosystem is changed negatively and resource supply declines.
Causes of deforestation in Brazil
TRF of Brazil (5th largest country, largest TRF area) is being exploited in two ways:
1) By using resources, e.g. timber, water, minerals
Physical characteristics:
Climate:
o Warm and wet
o Around 26°C, little variation
o >2500mm rainfall, large rivers, e.g. the Amazon and the Congo rivers
Vegetation:
o Rich vegetation
o 30-45m tall trees
Soils:
o Thin and poor, lots of vegetation due to rapid nutrient recycling.
o Nutrients locked up in:
Biomass (living vegetation and animals)
Litter (dead wood and leaves, animal remains)
Interdependence of TRF ecosystem components
Main components: climate (rain and sunlight), soil, vegetation (trees and plants) and animals. All
components interact to create an interdependence. Native people can also be part of and live in
harmony with the ecosystem. Human activity can also upset ecosystem’s balance.
Biodiversity
TRF has highest biodiversity in the world- 2/3 of world’s plant species found in TRF, and ½ of world’s
animal species.
Human exploitation: reducing biodiversity- endangered + extinct species, decline in ecosystem
productivity
Adaptations to TRF environment
Plants:
Poor soils:
o Rapid nutrient cycling
o Intensity + absorption of sunlight, photosynthesis
o Warm, humid climate- ideal for plant growth
o Ability for plants to adapt (competition)
Heat and humidity
o Waxy leaves + flexible stems, allow water to run off and allow leaves to move with
sun
o Circulating water (water cycle) as cooling system
o Passing water to soil or returning it to atmosphere
o Leaves cope with large amounts of water falling on them
Sunlight competition
o Most sunlight received by tops of tall trees, shade on forest floor so least sunlight
received near ground
o Less photosynthesis near bottom of forest, different ways to access food + nutrients:
Parasitic plants use other plants for food and water, or gain access from the
soil
General
, o Dark green leaves with lots of chlorophyll
o Only grow branches above main canopy to preserve energy
o Wide leaves to absorb more sunlight
o Very tall plants
Animals:
Food competition
o Many animals, a lot of competition- specialised animals only eat off a certain
plant/animal that few others eat, e.g. parrots + toucans have big strong beaks to
break open nuts
o Some symbiotic relations between plants + animals- trees create fruit eaten by
animals for seed dispersal
Camouflage
o Escape predators, help catch prey
o Poisonous animals use bright colours to warn other animals (arrow frogs)
Deforestation
Long history, most damage done in last century. 62 countries have TRF, little records kept of original
extent, but UN Food and Agriculture organisation think ½ of world’s TRF has been cleared.
Fluctuation of deforestation rates. Greatest rates in Brazil.
At least 20% of Amazon rainforest cleared since 1970 (761 000km2, roughly UK size)
Rate of reduction shows protective measures, e.g. Mexico. Only the rate has decreased, and
deforestation continues. Global rates:
- 1 hectare/second
- 31 million hectares/year
Brazil:
Brazilian rainforest lowland basin drained by Amazon river. Most clearance south of Amazon, where
TRF most accessible by main Brazilian cities (Rio de Janeiro, Sao Paulo, Brasilia).
Rainforest has been inhabited and used by indigenous tribes for centuries to:
- Harvest fruits/nuts
- Cut wood for fuel
- Use timber for housing
- Medicinal purposes
- Slash and burn (little lasting damage)
- Small-scale subsistence farming
Shifting cultivation- forest left to regenerate after one piece of land has been exhausted.
Human activity does not always lead to deforestation, but it can lead to forest degradation, where
the forest ecosystem is changed negatively and resource supply declines.
Causes of deforestation in Brazil
TRF of Brazil (5th largest country, largest TRF area) is being exploited in two ways:
1) By using resources, e.g. timber, water, minerals
