Sustainable Yield (HL) (DP IB Environmental Systems & Societies (ESS))
Revision Note
Sustainable Yield
Sustainable yield refers to the rate at which a resource can be harvested or used without compromising the ability of the system to regenerate or replenish that resource for future use
It ensures:
The long-term sustainability of resources by not over-exploiting them
The resource remains available for future generations by allowing natural regeneration
Maximum sustainable yield (MSY)
Maximum sustainable yields (MSYs) are the highest rates of net primary productivity (NPP) or net secondary productivity (NSP) that can be harvested from a system without depleting it
In agricultural, aquacultural or silvicultural systems (farming, fish farming or forestry), MSY is the highest amount of biomass (i.e. crops, livestock, seafood or trees) that can be sustainably harvested over time without degrading the soil, water or wider ecosystem
Sustainable yields and trophic levels
Sustainable yields are generally higher for organisms at lower trophic levels
These are the organisms closer to the base of the food chain, like plants or herbivores)
This is because less energy is lost from the system at lower trophic levels, making them more efficient for resource production
Energy is lost as heat during the transfer between trophic levels
This makes higher trophic levels (like carnivores) less efficient for resource use
Plant-based foods at lower trophic levels are the most energy-efficient and sustainable for human consumption
They require much fewer resources (e.g. land, water, and energy) to produce compared to animals at higher trophic levels
For example, growing crops like wheat or rice for direct human consumption is more sustainable than raising livestock for meat
This means that sustainability in food production is much easier to achieve when humans consume from lower trophic levels (ideally from the first tropic level, known as producers)
Growing crops for direct human consumption (plants) is more sustainable than raising livestock, which requires plants to be grown as feed
Exam Tip
Remember that sustainable yield is about maintaining the balance between resource use and regeneration, ideally, so that human food production can continue to feed human populations indefinitely.
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