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.
Part 1 of 3
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.
Part 2 of 3
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.
Part 3 of 3
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 Climate change can make a historical reference condition harder to sustain.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.