Ecosystems under stress: resilience and restoration
Connect disturbance, feedback and the limits of ecological management.
A-level study: check your qualification and chosen options below.
Disturbance and resilience
An ecosystem may recover from a disturbance without returning every population or process to its previous state. Distinguish resistance during a disturbance from resilience after it. The chosen outcome and period affect any judgement.
Repeated disturbance can leave insufficient recovery time. A food-web change can also affect the conditions for recovery. Treat a threshold as a hypothesis supported by evidence, rather than a dramatic label for every observed decline.
Worked example
Fictional cover falls from 60% to 30% after a disturbance and recovers to 45% five years later. Half the initial loss has been regained: (45 − 30)/(60 − 30) = 50%. Cover alone does not establish recovered diversity or function.
Common mistake: A recovery in one indicator is not proof that an ecosystem has fully recovered.
Coral stress at interacting scales
Coral reefs face pressures that can act at different scales. Thermal stress can cause bleaching; local pollution and sediment can affect conditions and recovery. Reducing a local pressure may help without eliminating a wider climatic pressure.
Bleaching is not identical to immediate mortality. Compare the severity and duration of exposure with observed recovery. A source describing one reef or event should not be generalised automatically to every reef.
Worked example
Fictional Sites A and B lose 20 and 8 percentage points of coral cover after a hot season. Site A also has poorer water quality. The contrast supports further investigation, but differences in heat exposure, species and prior condition prevent a simple causal attribution.
Common mistake: A correlation between local pollution and decline does not isolate its effect from thermal stress.
Restoration and the reference condition
A restoration project should state the condition it aims to establish and the evidence of success. Survival of planted organisms is one outcome; recruitment, functioning and durability are others. Climate change can make a historical reference condition harder to sustain.
Evaluate the spatial reach of a project and who maintains it. A successful small site may not demonstrate affordable restoration at landscape scale. Compare restoration with preventing further degradation and recognise that each addresses a different stage of the problem.
Worked example
A fictional project plants 1,000 fragments and reports 700 surviving after a year. Survival is 70%, but this does not mean that 70% of the reef is restored. Area, recruitment, biodiversity and later survival need separate measures.
Common mistake: A survival percentage cannot be treated as a percentage of an ecosystem restored.
Try a different resource
Scatter plots
Six locations were observed once. Several unmeasured factors could influence the number of trees.
Scroll the diagram sideways to see the full resource.
| Distance (km) | Trees within 50 m |
|---|---|
| 1 | 21 |
| 2 | 12 |
| 3 | 3 |
| 4 | 3 |
| 5 | 12 |
| 6 | 21 |
Resource description
1 km: 21 trees; 2 km: 12 trees; 3 km: 3 trees; 4 km: 3 trees; 5 km: 12 trees; 6 km: 21 trees
Write an explanation
Check your answer
- Connect local and global pressures.
- Specify the indicator, baseline and period used to judge success.
- Compare prevention, recovery and restoration.
- Support a conditional judgement with a taught ecosystem and sourced evidence.
Practise and review a written answer
Read further
Course links
Next topics
Ecosystems: energy, nutrients and disturbance · Carbon cycles: stocks, fluxes and changing feedbacks
Selected teaching for this option. Detailed named landscapes, field evidence and the full specification still need study with your teacher.