Lesson Notes By Weeks and Term v5 - Grade 12

Lesson Video

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Performance objectives

• Explain human impacts on the environment with SA examples.
• Describe causes & consequences of deforestation.
• Discuss the impact & control of alien invasive species.
• Outline sources & consequences of pollution.
• Explain sustainable development.

Lesson summary

The human impact on the environment is one of the most crucial topics in Life Sciences today, especially in South Africa. Our country, with its rich biodiversity and unique environmental challenges, faces significant consequences from unsustainable practices. This section of the course examines how human activities affect ecosystems, biodiversity, and resources. Understanding these impacts is vital for every South African citizen as it directly influences our access to clean water, food security, economic stability, and the health of our environment for future generations.

Lesson notes

2.1 Deforestation: Deforestation is the clearing of forests for other land uses, such as agriculture, urbanization, and mining. In South Africa, historical and ongoing deforestation is driven by several factors.

Causes: Agriculture: Expansion of agricultural land for crops (e.g., maize, sugarcane) and livestock grazing. The clearing of indigenous forests to create space for farmlands.

Urbanization: Growth of cities and towns requires land for housing, infrastructure, and industrial development.

Mining: Clearing forests to access mineral resources like coal, platinum, and gold.

Fuelwood: In many rural areas, wood is a primary source of energy for cooking and heating, leading to unsustainable harvesting of trees.

Consequences: Loss of Biodiversity: Forests are habitats for a vast array of plant and animal species. Deforestation leads to habitat loss and species extinction.

Example: The endangered Knysna elephant population is threatened by habitat loss due to deforestation.

Soil Erosion: Tree roots hold soil in place. Without trees, soil is easily eroded by wind and water, leading to land degradation and reduced agricultural productivity.

Climate Change: Trees absorb carbon dioxide from the atmosphere. Deforestation releases stored carbon dioxide, contributing to global warming. Deforestation also reduces the planet's capacity to absorb further CO

2. Water Cycle Disruption: Forests play a role in regulating the water cycle. Deforestation can lead to altered rainfall patterns and increased flooding.

Economic Impacts: Deforestation can negatively impact tourism, forestry industries and subsistence farmers who rely on forest products.

Worked example

A farmer clears 5 hectares of indigenous forest to plant maize. The forest contained an estimated 100 tons of carbon per hectare. Calculate the amount of carbon released into the atmosphere.

Solution:

Total carbon in the cleared forest: 5 hectares 100 tons/hectare = 500 tons of carbon.

This means 500 tons of carbon will be released into the atmosphere as carbon dioxide as the vegetation decomposes or is burned.

2.2 Alien Invasive Species:

Alien invasive species are plants and animals that are introduced to an area outside their natural range and cause harm to the environment, economy, or human health. South Africa is particularly vulnerable due to its diverse ecosystems and global trade links.

Examples:

Plants: Australian wattles (Acacia species), Eucalyptus trees, Water hyacinth.

Animals: European starling, Feral cats, Carp (fish).

Impacts:

Competition with Native Species: Alien plants compete with native plants for resources like water, nutrients, and sunlight.

Example: Australian wattles outcompete indigenous fynbos plants.

Habitat Alteration: Some invasive species alter habitats, making them unsuitable for native species.

Example: Water hyacinth chokes waterways, reducing oxygen levels and harming aquatic life.

Economic Costs: Controlling and managing invasive species is expensive. They can also damage agricultural crops and infrastructure.

Disease Transmission: Some invasive animals can carry diseases that affect native species or humans.

Reduced Water Availability: Invasive plants like Eucalyptus trees consume large amounts of water, reducing water availability in already water-stressed regions.

Control Strategies:

Prevention: Preventing the introduction of new invasive species is the most effective strategy. This includes strict border controls and quarantine measures.

Early Detection and Rapid Response: Identifying and eradicating new invasions early on can prevent them from spreading.

Mechanical Control: Physically removing invasive plants or trapping invasive animals.

Chemical Control: Using herbicides or pesticides to kill invasive species. This method must be used cautiously to avoid harming non-target organisms.

Biological Control: Introducing natural enemies (e.g., insects, fungi) of the invasive species. This method requires careful research to ensure that the biological control agent does not become invasive itself.

Integrated Control: Using a combination of different control methods.

Worked

Example: