Sustainable Yield (HL) (DP IB Environmental Systems & Societies (ESS))

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