Whether a resource is renewable has almost nothing to do with what it is made of. It depends on a race between two speeds: how fast we take it, and how fast nature puts it back. Win that race and a forest lasts forever. Lose it and the same forest behaves exactly like a lump of coal.
📘 What you need to know
Renewable natural capital is replaced at a rate equal to or faster than it is used.
Non-renewable natural capital is replaced more slowly than it is used, or not at all on human timescales.
Renewable capital includes living systems (forests, wetlands, reefs) and non-living systems (groundwater, the ozone layer).
Fossil fuels, uranium and mineral ores are non-renewable; once used, they must be recycled or done without.
Soil is the borderline case — renewable if treated well, non-renewable once eroded or built over.
Use is sustainable when it stays within the rate of replacement.
Unsustainable use examples: deforestation, overfishing and over-extraction of groundwater.
The definition is about speed, not substance
The test that decides everything
Renewable: rate of replacement ≥ rate of use
Non-renewable: rate of replacement < rate of use
This is why you cannot just memorise a list. A tuna population is renewable when boats take a small share of it each year, and effectively non-renewable when the fleet takes more than the fish can breed back. The label follows the behaviour.
Reading a log scale: the gap between coal and a fish stock is not a few times bigger. It is roughly a hundred million times.
Renewable natural capital
Living systems
Forests, wetlands, coral reefs and grasslands regenerate themselves, because they capture solar energy and use photosynthesis to turn it into new biomass. That is the engine that refills the stock.
Forests supply fuelwood and timber, and grow back through seed dispersal and natural growth, so new trees replace the harvested ones.
Wetlands keep water clean, control floods and shelter huge numbers of species. They rebuild themselves through sedimentation and nutrient cycling, and can recover after droughts or after damage from mining and construction.
Non-living systems
Groundwater is recharged by rainfall soaking into the ground, so an aquifer can supply fresh water indefinitely if withdrawal stays within the recharge rate.
The ozone layer repairs itself. Cut emissions of ozone-depleting substances and stratospheric ozone slowly climbs back — which is exactly what has been happening since those chemicals were phased out.
The ozone layer is a lovely example to keep in your pocket, because it shows renewable capital recovering in real life once humans stopped overloading it. It answers “can damage be reversed?” with a yes, and a condition attached.
Non-renewable natural capital
These resources are either irreplaceable, or replaced only over geological timescales — periods so long that, for planning purposes, the stock is simply fixed.
Resource
Why it counts as non-renewable
Fossil fuels (coal, oil, natural gas)
Formed over millions of years from the remains of living things. Once extracted and burned, they cannot be replaced within human timescales
Uranium
Not a fossil fuel, but reserves are finite and are not replenished on any useful timescale
Minerals and metals
Elements dug out of the crust. Rare earths and lithium have finite reserves; once gold and silver reserves are gone, supply has to come from recycling and existing stockpiles
Degraded soil
Renewable in principle, but non-renewable in practice once it is lost faster than it forms
Soil deserves its own sentence in your notes. Soil is renewable to a degree, because new soil forms from weathered rock and decaying material. But excessive tilling and deforestation strip it away far faster than that, and urbanisation buries it under concrete, which removes its ability to regenerate at all. Soil is the clearest case of a renewable resource being pushed into the non-renewable box by the way we treat it.
Sustainable yield: how much can you take?
If a stock regrows, there is a harvest you can take year after year without shrinking it. That harvest is the sustainable yield, and it is just the amount the stock grows by.
Sustainable yield
sustainable yield = growth of the stock in a year
= (stock at the end of the year) − (stock at the start)
Everything about resource management follows from comparing your harvest with that number. Take less and the stock grows. Take exactly it and the stock holds steady. Take more and you are into the capital, and each year there is less left to grow.
The difference between the green line and the red line is one extra tonne caught for every two that were safe. Small overshoots are not small.
Look at how quickly the red line falls once it starts. Overexploitation is not a gentle slope, because a smaller stock also breeds more slowly — you lose the harvest and the ability to regrow it at the same time. That feedback is the reason collapsed fisheries so often fail to bounce back even after fishing stops.
Sustainable use in practice
🧩 Three worked examples of sustainable management
Forest management — selective logging rather than clear felling, replanting after harvest, and protecting biodiversity so the ecosystem keeps functioning. The forest keeps supplying timber, other forest products, and its ecosystem services.
Fisheries management — setting catch limits, closing the season while fish are breeding, and creating marine protected areas where no fishing happens at all, so stocks can rebuild and spill over into fished areas.
Renewable energy — using solar, wind and hydroelectric power reduces reliance on fossil fuels, so the energy supply draws on a flow rather than a fixed stock.
And what unsustainable use looks like
Unsustainable use
What is happening
Consequences
Deforestation
Logging and clearance for farmland or infrastructure remove trees faster than they regrow
Habitat loss, soil erosion and desertification, and climate change as stored carbon is released
Overfishing
Catches exceed the rate at which fish reproduce
Depleted stocks, disrupted marine ecosystems, and lost livelihoods in fishing communities
Over-extraction of water
Groundwater is pumped out faster than rainfall recharges the aquifer
Freshwater depletion, saltwater intrusion into coastal aquifers, and long-term water scarcity
Notice the pattern. All three follow the same sentence: the rate of use is greater than the rate of replacement. If you can write that line and then explain the specific consequences, you can answer almost any question in this section.
Worked examples
WE 1
Calculate a sustainable yield
An unharvested woodland holds 12 000 tonnes of timber. One year later it holds 12 900 tonnes. Calculate the sustainable yield, and state what happens if 1 200 tonnes are harvested each year. (3 marks)
Step 1: find the yearly growth12 900 − 12 000 = 900 tonnes per yearStep 2: that growth is the sustainable yield
Harvesting 900 tonnes a year leaves the stock unchanged at 12 000 tonnes.
Step 3: compare with the proposed harvest1 200 − 900 = 300 tonnes taken from the capital each year, so the woodland shrinks and next year’s growth will be smaller still.
Sustainable yield = 900 t per year; 1 200 t per year is unsustainablealways show the subtraction, and always give the unit — tonnes per year, not tonnes
WE 2
Explain why soil can be either renewable or non-renewable
Explain why soil may be classified as renewable natural capital in one location and non-renewable in another. (3 marks)
Point 1: the rule being applied
A resource is renewable if it is replaced at least as fast as it is used, so the classification depends on rates, not on the material.
Point 2: when soil is renewable
Under careful farming, new soil forms from weathering and decomposition fast enough to replace what is lost, so fertility is maintained.
Point 3: when it is not
Excessive tilling and deforestation cause erosion far faster than soil forms, and urbanisation buries it permanently, removing its ability to regenerate.
Same resource, two classifications, decided by how it is managedthis “it depends on the rate” idea is the single most useful sentence in the whole topic
WE 3
Suggest strategies for a declining fishery
A coastal fishery has seen catches fall for ten years. Suggest three strategies to make the fishery sustainable, and explain how each works. (3 marks)
Strategy 1: catch limits
Cap the annual catch below the stock’s growth rate, so the population can rebuild.
Strategy 2: closed seasons
Ban fishing during the breeding season so adults can spawn before they are caught.
Strategy 3: marine protected areas
Close part of the sea to fishing entirely; the protected population grows and young fish spread into the fished areas.
Bring the rate of use back below the rate of replacement“suggest” wants a strategy plus a mechanism — a bare list of three names is one mark, not three
💡 Exam tips
Define renewable and non-renewable using rates. Compare the rate of use with the rate of replacement.
Split renewable capital into living (forests, wetlands) and non-living (groundwater, ozone) systems.
Use soil as your example whenever a question asks whether the categories are clear-cut.
For a calculation, sustainable yield is simply the annual growth of the stock. Show the subtraction.
Learn three sustainable strategies and three unsustainable practices, each with its consequences.
When asked about consequences, give environmental and social ones — lost stocks and lost livelihoods.
⚠ Common mix-ups
Saying renewable means unlimited. Renewable resources run out easily if used too fast.
Calling every biological resource renewable. An overfished stock is being mined, not harvested.
Forgetting ozone and groundwater. Renewable capital is not only living things.
Treating soil as obviously renewable. Examiners like this one precisely because it is not obvious.
Confusing the stock with the yield. The yield is the growth, not the total amount there.
Assuming a collapsed stock recovers once you stop. A small population also breeds slowly, so recovery can take decades or never happen.
Up next: Resource Security and the Choices Behind It. Sustainability tells you what a society should do. The last page in this section deals with why different societies, facing the same facts, choose completely different things.
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