4.10.4Additional lessons
Sustainability in Ecosystems and Agriculture — IB Biology SL Revision Notes & Topical Questions
5 min read 4 parts Lesson 138 of 142
Part 1 of 4Sustainable Harvesting
Sustainability asks whether a practice can continue indefinitely without damaging the resource or the environment.
Definition
- A resource is harvested sustainably when it is replaced as fast as it is taken, so that it does not run out.
Black cherry timber
- Slow-growing hardwood is harvested by selective felling, leaving seed-producing trees and monitoring regrowth.
Alaska pollock
- A fast-growing fish whose fishery has low bycatch, limited seabed damage and close monitoring, and is certified as sustainable.
Regulation
- Quotas, monitoring and closing areas with high bycatch keep catches within what populations can replace.
Clear felling
- Removing all trees at once leaves no seed source and no timber for many years, so it is not sustainable for slow-growing trees.
| Resource | Sustainable practice | Unsustainable practice |
|---|---|---|
| Hardwood | Selective felling and replanting | Clear felling |
| Fish | Quotas and low-impact nets | Overfishing and heavy bycatch |
Part 2 of 4Pressures on Agriculture
Pressures on Agriculture
Soil erosion
- Clearing land removes roots that hold topsoil, so wind and water carry away the most fertile layer.
Leaching and runoff
- Soluble fertiliser washes out of soil into waterways, wasting nutrients and polluting water.
Agrochemicals
- Pesticides, herbicides and fungicides raise yields but can kill non-target species and spread into the environment.
Fertiliser supply
- Synthetic fertiliser is costly and energy-intensive to make, so its price depends on energy costs.
Carbon footprint
- Machinery, transport and fertiliser production use fossil fuels and release carbon dioxide.
Water use
- Irrigation can lower water tables and raise salt levels in soil, reducing future crop yields.
Part 3 of 4Ways to Improve Sustainability
Sustainability in farming means balancing yield with the long-term health of soil, water and wildlife.
1
Plant cover crops between seasons to hold topsoil together and reduce erosion.
2
Apply fertiliser in small amounts, when rain is not expected, or use organic fertilisers to reduce leaching.
3
Use biological control, such as ladybirds that eat aphids, to reduce reliance on pesticides.
4
Develop crop varieties resistant to pests and disease, reducing chemical use.
5
Switch to renewable energy and efficient machinery to cut the carbon footprint of farming.
Part 4 of 4Exam Checklist & Tips
4.10.4 – Key Points for the Exam
- Sustainable Using a resource at a rate that allows it to be replaced.
- Bycatch Unwanted organisms caught accidentally along with the target species.
- Leaching The washing of soluble substances out of soil by water.
- Biological control Using a natural predator or parasite to reduce a pest population.
- Selective felling Harvesting chosen trees only, leaving the rest of the forest standing to regrow.
- Topsoil The nutrient-rich upper layer of soil that is most vulnerable to erosion.
Common Mistakes
- Defining sustainability as using none of a resource; it means using at a rate that can be replaced.
- Confusing leaching with erosion; leaching moves dissolved minerals, erosion moves soil particles.
- Forgetting to link a farming practice to a specific environmental effect.
- Claiming organic fertiliser removes every environmental problem.
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