Amazon Rainforest Case Study

Question 1

Where is the Amazon Rainforest located? Give some general information

Answer 1

South America (70% in Brazil)
It is 6 million km2 - world's largest rainforest - dominated by tall hardwood evergreen trees

Question 2

What are average temperatures like in the Amazon rainforest?

Answer 2

High - 25-30°C - little seasonal variation in temperature

Question 3

What is precipitation like in the Amazon?

Answer 3

Very high amounts of precipitation (>2000mm annual rainfall) - evenly distributed throughout the year

Question 4

Describe the water cycle in the Amazon rainforest

Answer 4

Very high annual rainfall (>2000mm) - evenly distributed throughout the year
High interception by forest trees - capture 10% of precipitation
High rates of evapotranspiration due to high temps and high density of flora - around half of rainfall is returned to the atmosphere, which contributes to the high humidity
Intercepted rainfall accounts for 25% of evaporation
Rapid runoff due to high and intensive rainfall
Very high mean relative and absolute humidity
Significant water storage in soils and aquifers due to abundant rainfall and deep tropical soils
Vegetation has a crucial role in the water cycle - interception, absorption, storage, transpiration

Question 5

Describe the carbon cycle in the Amazon rainforest

Answer 5

Humid equatorial climate is ideal for plant growth
Very high NPP - av. 2500g/m2/year
Biomass between 400 and 700tonnes/ha - mostly large forest trees (180tonnes/ha above ground, 40tonnes/ha in roots)
Soil carbon stores average between 90 and 200 tonnes/ha
Rapid exchanges of carbon between atmosphere, biosphere and soil compared to other ecosystems
Rapid decomposition of organic matter and quick release of CO2 - high rates of carbon fixation (via photosynthesis)
Leached and acidic soils contain only limited carbon and nutrient stores

Question 6

How does temperature influence the carbon and water cycles in the Amazon?

Answer 6

High temperatures generate high rates of evapotranspiration. Convection is strong, leading to high atmospheric humidity, development of thunderstorm clouds and intense precipitation. Water is cycled continually between the land surface, trees and atmosphere by evaporation, precipitation and transpiration.
High temperatures stimulate primary production and promotes rapid decomposition.

Question 7

What is Net Primary Productivity?

Answer 7

The rate of production of organic compounds in plants from carbon dioxide (carbon fixation) - respiratory losses.

Question 8

How does rock permeability and porosity influence the carbon and water cycles in the Amazon?

Answer 8

Large parts of amazon basin are impermeable crystalline rock - rapid runoff and minimal water storage capacity.
However, some permeable and porous rocks, such as limestone and sandstone, store water and slow runoff. Geology dominated by igneous and metamorphic rocks, with small outcrops of carbonates (e.g. limestone) in western parts of the Amazon basin

Question 9

How does relief affect the water and carbon cycles?

Answer 9

Most of the Amazon basin comprises of extensive lowlands - areas of gentle relief - water moves horizontally across the surface (overland flow) or horizontally through soil (throughflow). In the west, the Andes create steep catchments with rapid runoff. Widespread inundation across extensive floodplains occurs annually, storing water for several months and slowing its movement into rivers.

Question 10

How does vegetation and organic matter in soils affect the water and carbon cycles?

Answer 10

Forest trees are the principle carbon store - approx 100 billion tonnes of carbon in the Amazon rainforest. Absorbs around 2.4 billion tonnes of CO2 a year and releases approximately 1.7 billion tonnes by decomposition. rainforest is a carbon sink of global importance. 60% of rainforest carbon is stored above ground in biomass. Rapid cycles of carbon

Question 11

Deforestation n stuff

Answer 11

Averaged 17,500km2/year between 1970 and 2013
Since 1970 almost 1/5 primary forest destroyed or degraded
In recent year rates of deforestation have slowed
Use of land that was previously rainforest used for subsistence farming and agriculture, e.g. cattle ranching, soya cultivation

Question 12

impacts of deforestation on the water cycle

Answer 12

Devastating floods on Madeira river in 2014 - almost 20m above normal level - vast expanses of floodplains inundated - 60 died, 68,000 evacuated - outbreaks of cholera and leptospirosis
Reduced water storage in trees, soils (which become eroded), permeable rocks (due to more rapid runoff) and in the atmosphere (from evapotranspiration)
Increases runoff by a factor of 27 - half of rain falling onto grassland goes directly into rivers
Disrupted cycle can lead to permanent climate change - no longer trees extracting moisture from soil, intercepting rainfall, transpiring, stabilising forest albedo and ground temperatures
Predicted 20% decline in regional rainfall - forests hundreds of km downwind also affected

Question 13

Impacts of deforestation on the carbon cycle

Answer 13

Deforestation and agriculture exhausts carbon biomass store - biomass of trees represents approximately 60% of all carbon in the ecosystem - croplands and pasture contain only a small amount of carbon compared to forest trees (180 tonnes/ha for above ground forest, 2.7 tonnes/ha for soya cultivation)
Input of organic matter into soils drastically reduced - soils, depleted of carbon and exposed to strong sunlight, support fewer decomposer organisms, thus reducing flow of carbon from soil to the atmosphere
Nutrient stores destroyed - trees are main nutrient store, so nutrients removed from the ecosystem - also nutrients washed away by rainwater (rather than being taken up by tree roots) - nutrient-rich soils no longer protected by trees so are eroded by rapid runoff

Question 14

How has legislation been used as a management strategy in the Amazon rainforest?

Answer 14

Protection through legislation of large expanses of primary forest not yet affected by deforestation - since 1988 Brazilian government has established forest conservation areas that now cover an area 20 times the size of Belgium
As of 2015 44% of the amazon comprises of national parks, wildlife reserves and indigenous reserves where farming is banned

Question 15

How has reforestation been used as a management strategy in the Amazon rainforest?

Answer 15

Projects to reforest areas degraded or destroyed by subsistence farming, cattle ranching, logging and mining. Sponsored by local authorities, NGOs and businesses

• Aim for 1000km2 commercial timber or government owned deforested land
• Plan for 20 million fast growing tropical hardwood seedlings (on 4000 smallholdings) to mature over 25 years
• Financial assistance given to smallholders
• Monoculture, but sustainable - sequesters carbon in trees and soils, reduces CO2 emissions from deforestation, re-establishes carbon and water cycles, reduces runoff and loss of plant nutrients from soil
• Surui people scheme to protect rainforest on tribal lands from illegal logging and to reforest degraded ares - carbon credits scheme

Question 16

How has the improvement of agricultural techniques been used as a management strategy in the Amazon rainforest?

Answer 16

Improving agricultural techniques to make permanent cultivation possible (often farmers over farm land and deplete it of nutrients and healthy soil, so move on to other land
- diversification - rotational cropping and combining livestock and arable operations - integrating crops and livestock could allow fivefold increase in ranching productivity and help slow rates of decomposition