Geoecology: Human Alteration of Tropical and Temperate Biomes Study Notes

Overview of Biome Alteration by Human Activity

Biomes across the globe are being significantly altered by diverse human activities, according to the 2023 Marking Scheme and exam analysis.
The primary activities responsible for these alterations include: * The Felling of Tropical Rainforest (Deforestation). * Intensive Agriculture Practices. * Industrial Development. * Settlement and Clearance of Forests.
Key regions cited for study include the Amazon Rainforest of South America (Tropical Rainforest Biome) and the North American Desert region of California, USA (Hot Desert Biome).
These regions exemplify how high population growth and economic development affect the natural environment.

The Felling of Tropical Rainforests (Deforestation)

The felling of tropical rainforests has permanently altered biomes, specifically in the Amazon Basin, impacting climate, soils, flora, and fauna.
Historical context of forest coverage: * Since the 1800s, global tropical rainforest coverage has plummeted from approximately $2.9\text{ billion hectares}$ to just over $1.5\text{ billion hectares}$ today.
The Amazon Rainforest (Regional Focus): * Deforestation has increased dramatically since the 1970s. * Primary drivers for clearing include timber extraction, cattle ranches, and soya bean plantations. * The Brazilian government authorizes commercial logging for valuable hardwoods such as teak and mahogany. * Logging contributes approximately $3\%$ to Brazil's economy, supporting financial stability. * Illegal logging accounts for approximately $80\%$ of current deforestation in the Amazon, with much of the wood processed into low-cost plywood. * Over $20\%$ of the Amazon rainforest has already been lost. Projections suggest that without replanting, nearly $60\%$ of the biome could be wiped out or severely damaged by the year $2035$ .

Impact on Biodiversity and Pharmaceutical Resources

The rainforest biome is home to over $15,000$ species, many of which are yet to be discovered.
Loss of Habitat: Felling trees destroys natural habitats, forcing animals to lose food sources and shelter, driving species toward extinction.
Pharmaceutical Value: Approximately $25\%$ of all modern medicines originate from rainforest plants. Examples include: * Quinine: Extracted from the bark of the cinchona tree, used as a treatment for malaria. * Curare: Derived from a tropical vine, used as a muscle relaxant and an anesthetic.
Sustainability Issues: * The mahogany tree requires approximately $60\text{ years}$ to reach maturity, yet more than $2,000\text{ trees}$ are felled every $60\text{ seconds}$ . * The Brazilian rosewood is currently nearing extinction due to overexploitation.
Interdependence Examples: The Three-toed sloth is highly vulnerable; it moves slowly and feeds almost entirely on leaves. When trees are removed, the sloth has no habitat or food, leading to possible extinction.

Impact on Soil and Nutrient Cycles

Soil Erosion: Removal of the canopy layer (the protective forest cover) exposes the soil. Without the root systems to bind the soil together, it is easily washed away by heavy rains.
Disruption of Nutrient Cycle: The removal of the foliage layer stops the supply of organic material (humus) to the top layer of soil (the $O\text{ horizon}$ ). Without this constant input, the soil is quickly depleted of nutrients.
Laterisation: * Heavy rainfall leaches nutrients and minerals from the soil's upper layers ( $O$ and $A\text{ horizons}$ ), a process known as laterisation. * Without canopy shade, intense sunlight causes the exposed, leached soil to harden into a solid, infertile layer called laterite, which prevents new plant growth and forest regeneration.
Sheet Erosion: On slopes, heavy rainfall strips away large sections of soil when tree cover is gone, making regrowth nearly impossible.

Impact on Global and Local Climate

Global Warming: Rainforests act as carbon sinks, storing carbon in trees and soil. When felled, this carbon is released as carbon dioxide ( $CO_2$ ), a greenhouse gas.
Water Cycle Disruption: Trees absorb moisture and transpire it back into the atmosphere. Deforestation reduces these levels of transpiration and humidity.
Drought Conditions: Continued deforestation leads to a reduction in rainfall. Some regions within the rainforest biome are already experiencing drought conditions due to these permanent alterations of the climate.

Intensive Agricultural Practices: Cattle Ranching and Slash and Burn

Intensive farming practices include overgrazing and overcropping. * Overgrazing: Excessive grazing of livestock exceeding the land's carrying capacity. * Overcropping: Using the same land for crops repeatedly without a rest (fallow) period, leading to nutrient loss.
Cattle Ranching specifics: * Ranching is the leading cause of deforestation in the Amazon, accounting for $80\%$ of forest loss. * Approximately $450,000\,km^2$ of Amazon forest (an area larger than Germany) has been cleared for pasture. * Brazil is the world's largest beef producer, catering to China, the EU, and the USA.
Slash and Burn: Trees are cut down and burned. The resulting ash provides a short-term nutrient boost, but the practice is wasteful of valuable hardwoods like mahogany, which could be sold internationally.

Intensive Agricultural Practices: Cash Crops and Monoculture

Soya Bean Cultivation: Soya is Brazil's most widely cultivated cash crop, primarily exported to Britain and North America as animal feed. * Advances in genetic modification (GM) have allowed soya to be grown further north into the Amazon, making Brazil the second-largest soya producer globally.
Monoculture: * Growing a single crop repeatedly depletes specific nutrients and reduces biodiversity. * Farmers rely on artificial nitrogen-based fertilizers, which offer little benefit compared to the organic matter tropical soils require.
Pesticides and Pollution: * Monoculture increases vulnerability to pests and diseases, necessitating large amounts of chemical pesticides. * These chemicals contaminate groundwater and rivers when washed away by rainfall, causing long-term environmental damage.

Industrial Activity in the Tropical Rainforest

Hydroelectric Power (HEP): * $60\%$ of Brazil's electricity is derived from HEP. * The Belo Monte Dam flooded over $500\,km^2$ of rainforest and displaced thousands of indigenous people. * Flooded vegetation decomposes and releases methane, a greenhouse gas $25\text{ times}$ more potent than $CO_2$ . * Dams disrupt fish migration, impacting species like the giant otter and Amazon river dolphin.
Mining: * The Amazon is targeted for gold, bauxite, iron ore, and copper. * Over $50,000\,km^2$ has been cleared for mining. * Mercury used in gold mining contaminates rivers and poisons local food chains. * Open-pit mining removes topsoil entirely, preventing regrowth.
Steel and Blast Furnaces: * Blast furnaces in Brazil often use charcoal made from illegally harvested trees. * The steel industry accounts for nearly $8\%$ of global $CO_2$ emissions. * Furnaces release carbon monoxide, sulphur dioxide, and particulate matter.

Early Settlement and Clearance (Temperate Forest Biome)

The following points relate to the impact of early settlement and clearing in the Temperate Forest Biome as highlighted in historical exam requirements (2021, 2012): 1. Historical forest clearance for fuel and building materials. 2. Expansion of agricultural land for early human settlements. 3. Permanent alteration of the European and North American temperate landscapes. 4. Impact on native temperate flora and fauna through habitat fragmentation. 5. Note: The exam requires a focus on both early and modern industrial settlement patterns when discussing the Temperate forest.

Questions & Discussion

Question (Task): Write 5 SRP’s (Significant Relevant Points) on Industrial development causing Acid Rain in Europe. * Note: This specific section was prompted as a student exercise within the transcript following the discussion of blast furnaces and sulphur dioxide emissions.