Deforestation — AQA A-Level Environmental Science

Deforestation represents the long-term or permanent clearance of forest biomes for alternative land uses including pastoral cattle ranching, commercial arable agriculture, mineral extraction, and urban infrastructure. In AQA A-Level Environmental Science, this topic examines how the removal of forest cover directly alters biological diversity, microclimates, and macro-scale biogeochemical systems.

This topic connects foundational units across the specification, including the carbon cycle, the hydrological cycle, soil conservation, and atmospheric systems. Mastering deforestation enables students to critically evaluate sustainable forestry management systems such as selective logging, strip felling, and agroforestry against intensive clear-cutting practices.

• →Hydrological disruptions: Reduced interception and evapotranspiration lead to lower regional humidity, while decreased infiltration accelerates surface runoff and river peak discharge.
• →Carbon sink degradation: Removal of primary autotrophs halts photosynthetic sequestration and turns active sinks into emission sources via biomass burning and microbial decomposition.
• →Pedological consequences: Canopy loss exposes topsoil to rain splash erosion, compaction, nutrient leaching, and gully erosion, resulting in severe degradation of soil fertility.
• →Albedo and microclimatic shifts: Tree clearance increases surface albedo in some biomes while removing microclimatic buffering, causing wider diurnal ground temperature fluctuations.
• →Forest fragmentation and edge effects: Fragmented patches experience altered microclimates, increased windthrow susceptibility, desiccation, and disrupted ecological corridors.

• Identifies reduced leaf litter and dead organic matter inputs as a cause of lower soil humus and fertility
• Explains that loss of tree roots and organic binding weakens soil structure and increases erosion by water or wind
• Describes increased surface run-off and reduced infiltration on exposed, compacted or crusted soil
• Links removal of vegetation cover to greater leaching or nutrient loss where rainfall is high
• Connects soil erosion and nutrient loss to reduced soil fertility and lower agricultural productivity

• 💡Name the mechanism for each soil change rather than listing effects, for example reduced litter fall lowering humus
• 💡Use precise terms such as humus, infiltration, run-off, leaching and soil structure
• 💡Link soil impacts back to the loss of tree cover, roots and shade so the cause and effect chain is clear
• 💡Always specify the exact mechanism of soil erosion: distinguish between rain splash erosion (kinetic impact of drops), sheet wash, rill erosion, and gullying.
• 💡Use accurate terminology when describing water movement; say 'infiltration into the pedosphere' or 'reduced transpirational draw' instead of vague statements like 'water soaking into the ground'.
• 💡When evaluating forestry management strategies, contrast monoculture plantation forestry with selective logging and coppicing using clear operational criteria.

• States that deforestation makes soil more fertile; correct this by explaining that litter inputs fall and nutrients are lost
• Treats soil erosion as caused only by wind; correct this by including water erosion and surface run-off on exposed ground
• Assumes soil damage is immediate and uniform everywhere; correct this by linking the severity to rainfall, slope, soil type and the extent of clearance
• Assuming deforestation always causes regional rainfall to increase because flooding occurs; students must recognise that flooding is driven by rapid surface runoff, whereas regional atmospheric precipitation often decreases due to reduced evapotranspiration.
• Believing that replanting deforested land with commercial plantation monocultures (e.g. pine or eucalyptus) completely restores original ecological services, ignoring deep structural, biodiversity, and soil-nutrient deficits.
• Confusing atmospheric oxygen depletion with greenhouse gas warming; while forests generate oxygen, modern oxygen levels are largely buffered by ocean systems, making carbon flux and greenhouse warming the primary environmental concern.

1. 1Day 1-3: Review carbon and water cycle fluxes, creating annotated systems diagrams that show inputs, outputs, and stores before and after clear-felling.
2. 2Day 4-6: Study soil degradation pathways (splash erosion, compaction, leaching) and microclimate modifications (albedo changes, diurnal temperature ranges).
3. 3Day 7-9: Compare forestry extraction strategies (clear-cutting, selective logging, strip felling, shelterwood systems) using a balanced advantage/disadvantage matrix.
4. 4Day 10-12: Practice 6-mark and 9-mark extended response questions focusing on evaluating conservation and agroforestry practices under timed conditions.

• 📋Data analysis and calculations: Determining percentage change in forest cover over time, calculating biomass carbon loss, or interpreting river catchment hydrographs post-deforestation.
• 📋Comparative short-answer questions: Contrasting soil nutrient levels and infiltration rates between undisturbed primary forests and cleared agricultural pastures.
• 📋Extended evaluation essays (6-9 marks): Critically assessing the efficacy of sustainable forestry management or comparing economic drivers against ecological degradation.