SL and HL: Subtopic 1.2 Systems: Humans reduce ecological resilience mainly by decreasing biodiversity and the size of important storages. This weakens stabilizing feedback mechanisms, making ecosystems less able to resist disturbance and avoid tipping points.
The Mechanism
Resilience is a system's tendency to avoid tipping points and maintain stability. Diverse ecosystems may contain species with overlapping functions, allowing compensation when one is lost.
Large storages, such as forest biomass, soil organic matter and groundwater, buffer change. Human activities reduce these storages or remove them faster than natural flows replace them.
| Human activity | How resilience is reduced |
|---|---|
| Deforestation | Reduces biomass, carbon storage and habitat diversity; increases drought and erosion risk. |
| Overharvesting | Shrinks populations and genetic diversity, limiting recovery from disease or environmental change. |
| Pollution | Removes sensitive species and simplifies food webs, leaving fewer alternative pathways. |
| Soil degradation | Reduces nutrient, water and organic-matter storages, weakening productivity and recovery. |
| Climate change | Adds repeated disturbances and may strengthen positive feedback loops. |
A negative feedback loop counteracts change and helps maintain stable equilibrium. If human pressure damages this stabilizing mechanism, positive feedback can amplify disturbance until a small additional change causes a major shift in equilibrium.
For example, Amazon deforestation and fires reduce forest biomass and moisture recycling. Reduced rainfall can cause further tree death, reinforcing drying and increasing the risk of transition to a drier ecosystem. This threatens environmental justice for forest-dependent Indigenous communities.
A common misconception is that resilience means an ecosystem never changes. Resilient systems can change, but they maintain stability and avoid crossing a tipping point.
Exam Technique
For an explain question, present a causal chain: human activity reduces diversity or storage; negative feedback weakens; disturbance is amplified; and tipping-point risk rises. Support a higher-mark response with a named example and an accurate systems or feedback-loop diagram.