IB Environmental systems and societies 1.2F Resilience of a System Notes

Resilience is a system's capacity to absorb shocks and bounce back

1. Resilience applies to both ecological and social systems, letting them adapt, survive, and keep functioning despite external shocks.
2. Resistance is the ability to withstand a disturbance without significant change.
3. Recovery is the speed and completeness with which a system returns to its original state after a disturbance.

Several factors set how resilient a system is

1. Adaptability is the capacity to reorganize or adjust processes to cope with new conditions.
2. Redundancy means several species or components perform similar roles, so function continues if one fails.
3. Feedback control uses negative feedback loops to restore balance after a disturbance.
4. Storage size buffers change, since larger stores of energy, matter, or biomass slow the rate of change.

Ecological and social resilience share the same logic

Resilience matters because it keeps systems stable and sustainable

1. Stability: resilient systems hold equilibrium and stay away from tipping points.
   1. Tipping points themselves are covered in 1.2C, so treat this only as the threshold resilience protects.
2. Adaptation: they can adjust to new conditions such as climate change or economic shifts.
3. Sustainability: resilience supports long-term survival and function.

Diversity builds resilience through redundancy

1. Biodiversity raises resilience because many species perform similar ecological functions.
   1. When one species declines, another can take over its role, such as pollination or nutrient cycling.
2. Diverse ecosystems spread risk because not all species respond to a given stress in the same way.

Storage size and stability

1. Storage is the quantity of energy, matter, or biomass held in a system component such as trees, soil, or water.
2. Large storages act as buffers, slowing the rate of change and giving stability against disturbances.
3. Small storages respond fast to inputs or losses, so the system is less stable.

Diversity and storage combine

A prairie shows both factors at work

Case study

North American Prairie Systems

• Native tallgrass prairies once stretched across central North America.
  • Deep, organic-rich soils stored large amounts of nutrients.
  • High species diversity and strong negative feedbacks stabilised the system.
  • Periodic fires cleared litter while plants regrew from underground meristems.
• Replacing prairie with monoculture wheat farming cut diversity and resilience.
  • Low diversity raised vulnerability to pests and diseases.
  • Loss of root biomass shrank soil nutrient storage, and fertilisers only masked the weaker long-term stability.

How humans reduce resilience

1. Humans cut resilience by reducing biodiversity, altering storages, and pushing change faster than natural recovery.
2. As diversity or storages fall, ecosystems grow more vulnerable to disturbance and slower to recover.

Deforestation

1. Deforestation removes carbon and nutrient storages held in biomass and soil.
2. It cuts photosynthesis, primary productivity, and carbon sequestration capacity.
3. Thin tropical soils then lose nutrients fast through erosion and leaching, slowing recovery and raising drought risk.

Conversion to Monocultures

Why monocultures lose resilience

1. Single-crop systems replace diverse ecosystems, cutting genetic and species diversity.
2. Lower diversity raises vulnerability to pests and diseases.
3. Reliance on fertilisers and pesticides leaves resilience low and dependent on human management.

Dam Construction

1. Dams alter water storages and flow regimes.
2. Downstream ecosystems receive less water, harming wetlands and aquatic biodiversity.
3. The result is lower system resilience and possible habitat loss or species displacement.

Overfishing

1. Overfishing depletes fish populations faster than they can recover.
2. It disrupts food webs and nutrient cycling.
3. It strips a major biological storage of energy and biomass from aquatic ecosystems.

Invasive Species

1. Invasive species outcompete natives and reduce biodiversity.
2. They simplify food webs, leaving ecosystems less adaptable to change.
3. This raises the chance of ecosystem collapse after a disturbance.

Tie every human impact back to storage and diversity