CASE STUDY | Tropical Rainforest - Amazon

Question 1

Describe the rates of flow in the carbon cycle in the Amazon

Answer 1

• Amazon’s humid climate creates ideal conditions for plant growth
• Net primary productivity (NPP) is high, averages 2500g/m^2/year
• Biomass between 400-700 tonnes/ha

Question 2

Describe the carbon stores in the Amazon

Answer 2

• Amazon rainforest is a major store is a major global reservoir of stored carbon, absorbing 2.4 billion tonnes a year
• 220 tonnes C/ha stored by large forest trees, typically store around 180 tonnes C/ha above ground, further 40 tonnes C/ha in their roots
• Soil carbon stores average between 90-200 tonnes/ha

Question 3

Describe the fluxes in the carbon cycle in the Amazon

Answer 3

• Compared to other forest ecosystems, exchanges of carbon between the atmosphere, biosphere and soil are rapid
• Warm, humid conditions ensure speedy decomposition of dead organic matter and the quick release of CO2
• Rates of carbon fixation through photosynthesis are high
• The Amazon’s leached and acidic soils contain only limited carbon and nutrient stores, the fact that such poor soils support a biome with the highest NPP and biomass of all terrestrial ecosystems emphasises the speed with which organic matter is broken down, mineralised and recycled

Question 4

Describe the inputs to the water cycle in the Amazon

Answer 4

• high average annual rainfall (more than 2000mm)
• rainfall fairly evenly distributed through the year, though most areas experience at least one drier period
• high intensity, convectional rainfall

Question 5

Describe the processes within the water cycle in the Amazon

Answer 5

• interception by forest trees is around 10% of precipitation
• 25% of evaporated water comes from intercepted rainfall
• there is rapid run off as a result of high rainfall, intensive rainfall events and well-drained soils
• depending on the seasonal distribution of rainfall, river discharge may peak in one or two months of the year

Question 6

Describe the outputs from the water cycle in the Amazon

Answer 6

• between 50-60% of precipitation in the Amazon is recycled by evapotranspiration
• extensive evaporation as a result of high temperatures, large number of clouds formed

Question 7

Describe the stores within the water cycle in the Amazon

Answer 7

Atmosphere
- high temperatures allow the atmosphere to hold large amounts of moisture, absolute and relative humidity is high
Soil / groundwater
- abundant rainfall and deep tropical soils leads to significant water storage in soils and aquifers

Question 8

What are the three main physical factors that impact the carbon cycle?

Answer 8

Vegetation
Organic matter in soils
Temperature

Question 9

How does vegetation impact the carbon cycle?

Answer 9

• Forest trees dominate the biomass of the Amazon basin and are the principal carbon store
• In total approximately 100 billion tonnes of carbon is stored in the Amazon rainforest
• Absorbing around 2.4 billion tonnes of CO2 a year and releasing 1.7 billion tonnes through decomposition, the rainforest is a carbon sink of global importance
• 60% of rainforest carbon is stored in the above ground biomass of tree stems, branches and leaves, the remainder is below ground, mainly as roots and soil organic matter

Question 10

How does organic matter in soils impact the carbon cycle?

Answer 10

• Leaf litter and other dead organic matter accumulates temporarily at the soil surface and
  within rainforest soils
• High temperatures and humid conditions promote rapid decomposition of organic litter by bacteria, fungi and other soil organisms
• Decomposition releases nutrients to the soil for immediate take-up by tree root systems, and emits CO2 which is returned to the atmosphere.

Question 11

How does temperature impact the carbon cycle?

Answer 11

• High temperatures and intense sunlight stimulate primary production
• Net primary production (NPP) averages about 2500 grams/m2/year, Amazonia alone accounts for 15–25% of all NPP in terrestrial ecosystems
• Also contributes toward higher rates of decomposition, high temperatures and humid conditions promote rapid decomposition of organic litter by bacteria, fungi and other soil organisms

Question 12

What are the three main physical factors impacting the water cycle?

Answer 12

Geology
Relief
Temperature

Question 13

How does geology impact the water cycle?

Answer 13

• Impermeable catchments (such as the impermeable, crystalline rocks that comprise large parts of the Amazon Basin) have minimal water storage capacity resulting in rapid run-off
• Permeable and porous rocks (such as limestone and sandstone) store rainwater and slow run-off

Question 14

How does relief impact the water cycle?

Answer 14

• Most of the Amazon Basin comprises extensive lowlands, in areas of gentle relief water moves across the surface (overland flow), or horizontally through the soil (throughflow) to streams or rivers
• In the west, the Andes create steep catchments with rapid run-off
• Widespread inundation across extensive floodplains (such as the Pantanal) occurs annually, storing water for several months and slowing its movement into rivers

Question 15

How does temperature impact the water cycle?

Answer 15

• High temperatures throughout the year result in high rates of evapotranspiration
• Convection is strong, leading to high atmospheric humidity and the development of thunderstorm clouds and intense precipitation

Question 16

What is the main human process impacting the carbon and water cycles in the Amazon?

Answer 16

Deforestation

Question 17

How does deforestation in the Amazon impact the carbon cycle?

Answer 17

• Present day deforestation most severe in the tropical rainforest
• In primary rainforest, unaffected by human activity, the biomass of trees represents around 60% of all carbon in the ecosystem, above ground carbon biomass in the rainforest is approximately 180 tonnes/ha−1, most of the remaining carbon is found in the soil as roots and dead organic material
• Deforestation exhausts the carbon biomass store, croplands and pasture only contain a small amount of carbon compared to forest trees
• Biomass of grasslands in areas of former rainforest is 16.2 tonnes/ha-1 and for soya cultivation it is just 2.7 tonnes/ha-1
• Deforestation drastically reduces inputs of organic material to the soil, soils depleted of carbon and exposed to strong sunlight, support fewer decomposer organisms, thus reducing the flow of carbon from the soil to the atmosphere

Question 18

What are the two main strategies to manage tropical rainforests to positively impact the water and carbon cycles?

Answer 18

Afforestation
Improved agricultural techniques

Question 19

Instances of afforestation in the Amazon

Answer 19

• Brazil is committed to restoring 120,000km^2 of rainforest by 2030
• Since 1998, Brazilian government has established ‘Amazon Regional Protected Areas’ which now cover an area 20x size of Belgium
• Parica Project in Rondonia, aims to develop a 1000km^2 commercial timber plantation on government-owned, deforested land, plan is for 20 million fast growing tropical hardwood seedlings planted on 4000 smallholdings to mature over a period of 25 years - although this project is a monoculture and cannot replicate biodiversity, it is sustainable
• UN REDD afforestation scheme, since its inception has helped over 50 countries with monitoring and afforestation targets

Question 20

Instances of improved agricultural techniques in the Amazon

Answer 20

• Diversification, soil fertility can be maintained through rotational cropping and combining livestock and arable operations, integrating crops and livestock could allow for a fivefold increase in ranching productivity and help slow rates of deforestation, as farming is the leading cause of deforestation in Amazonia
• Human engineered soils, or dark soils, are being investigated, these are made up of charcoal, waste and human manure, and attract microorganisms and fungi that allow the soils to maintain their long term fertility, idea launched by discoveries that as late as the sixteenth century, the Amazon supported high population densities, proving that the Amazon’s natural resources have not always been too poor to support permanent civilisation