Case Study - Tropical Rainforests

Location:

between Tropic of Cancer and Capricorn - 23.5° North and South of Equator, covers 40% of S. American continent, largest tropical rainforest on Earth.

Climate:

hot, humid, wet, avg. temps. 21°c - 30°c, up to 2500mm of rain a year

Vegetation:

Rich biodiversity (estimated 390 billion individual trees) - 4 layers in rainforest: Shrub layer - dark, floor is covered in thick blanket of dead/decaying roots and leaves (humus), limited growth of vegetation, often flooding/ Under Canopy - shady and cooler, often vines take root in the ground and climb up trees to reach sunlight/ Canopy - continuous layer of treetops that is more sheltered, trees between 20-40m tall, habitat for most wildlife (jaguar, sloth)/ Emergent Layer - tallest trees, up to 60m, can trap more sunlight.

Drip Flow

Flow of rainwater from plant leaves to the ground after it has been intercepted

Transpiration

process of water loss from plants through the stomata

Soils:

Made of decomposed organic matter, poor in nutrients, (nutrient store of biomass is huge), heavy rain causes leaching of nutrients from soil, and trees suck up any nutrients from roots

Rainforest System

Open system - receives inputs of water and carbon from outside the system

Positive feedback loop

Increased transpiration - more precipitation - increases plant productivity - amplifies transpiration further

Human influences - Cattle ranching:

Most significant cause of deforestation - lack of vegetation causes transpiration rates to decrease, (less water is intercepted - so can also lead to increased flooding->{2009 flooding near Manaus led to more than 376,000 people left homeless}- and less is returned to atmosphere so impacts climate - decreases humidity), reduction in precipitation rates, negative impact on tree growth (also affect carbon cycle).

Secondary impacts of Human influences:

Dry soils and vegetation are more prone to wildfires, (or could be intentional wildfire), fires release soot particles which impact cloud and raindrop characteristics, further inhibits rainfall.

Carbon Store

around 80-120 billion tonnes of carbon

Statistics for deforestation

11,088km² of rainforest was destroyed between Aug 2019 - July 2020, at current rates it's predicted the Amazon will collapse by 2064

Causes of deforestation

Cattle ranching/ Road expansion (proposed project to improve trans-Amazonian Highway is predicted to cause 561,000 hectares of forest loss), large-scale agriculture, logging, HEP (75% of Brazil's electricity comes from this)

Impacts of deforestation - on soil:

Soil erosion - soil becomes dry so precipitation, (due to less interception often increases) washes away topsoil, leaches nutrients, less vegetation grows, and carbon contained in soil will be transferred to rivers

Impacts of deforestation - photosynthesis

(less trees), less photosynthesis, less carbon and water taken in from atmosphere, less oxygen reproduced as well, loss of carbon sink, - more carbon in air - global warming - climate change

Potential negative feedback loop

More carbon in atmosphere & warmer temps - could lead to more plant growth - they could then take in carbon - {doesn't work - although some research showed that carbon fertilisation explains 70% of the greening effect - but current studies show that increased carbon levels aren't enough to increase plant growth as other factors e.g. nitrogen are needed, and plants may also die faster