Think of a forest as money in a bank. The trees are the savings. The timber you can cut each year without shrinking the forest is the interest. Spend only the interest and you can keep going forever; start spending the savings and the whole thing eventually runs out. That one comparison unlocks nearly everything in this sub-topic.
📘 What you need to know
Natural resources are the sources of energy and raw materials society uses and consumes.
Natural capital is the stock of natural resources available on Earth.
It comes in three forms: renewable resources, non-renewable resources, and ecosystem services.
Natural income is the flow of goods and services that natural capital produces.
Income is sustainable only when the rate of use is less than or equal to the rate of replacement.
Non-renewable resources can generate wealth once, so they cannot give sustainable natural income.
Ecosystem services fall into four groups: supporting, regulating, provisioning and cultural.
What natural capital actually is
Natural resources are anything that comes from nature and can be used to benefit humans. That is a very wide net, and it is meant to be:
Sunlight — drives photosynthesis, and gives us solar energy.
Air — oxygen to breathe, and wind for energy.
Water — drinking, irrigation, hydroelectric power.
Land — soils, farming, construction, wildlife habitat.
Rocks — minerals and construction materials.
Ecosystems — forests, wetlands, coral reefs.
Living things — plants for food and medicine, animals for food and clothing.
In environmental science we call this whole stock natural capital. It splits three ways. Renewable capital replenishes naturally, such as forests and fish populations. Non-renewable capital is finite and cannot be replaced, such as coal, oil, gold and iron ore. And ecosystem services are the benefits ecosystems provide that keep human life and economies working, such as crop pollination, water purification and carbon sequestration.
Natural income: the flow, not the stock
Natural income is the flow of goods and services produced by natural capital. Goods are the tangible things: fish harvested from oceans and rivers, timber taken from forests for building and paper. Services are the processes that keep working in the background: forests absorbing carbon dioxide and regulating climate, wetlands soaking up excess rainfall, mangroves buffering coastlines against storm surges.
The relationship in one line
natural capital = the stock → natural income = the flow it produces
Mineral deposits sit in the capital box but produce nothing in the income box. That asymmetry is the whole reason non-renewables cannot be managed sustainably.
Sustainable natural income
Managed carefully, natural capital keeps producing indefinitely. Take timber as the standard example, and follow the chain:
Trees are cut for timber, but forests are also replanted or left to recover.
The rate of new tree growth is greater than the rate at which timber is taken.
So timber production becomes a sustainable source of income that can keep being sold and used.
In that example the forests are the natural capital and the timber is the natural income. Now compare fossil fuels. They can generate enormous wealth, but they can only be used once and cannot be managed sustainably. So even though they count as natural capital, they cannot produce sustainable natural income.
The bank analogy is worth writing into your answers. Natural capital is the money in the account; natural income is the interest you can live off, but only if the capital is looked after. Spend the capital and the interest disappears with it.
Ecosystem services
Ecosystem services are the benefits ecosystems provide that support life and human well-being. They fall into four groups, and knowing which group a service belongs to is a common short-answer question.
Provisioning services have market prices, so they get counted. Supporting and regulating services usually do not, so they are the ones that get destroyed first.
Service
What it does
Examples
Supporting
The essential ecological processes that make life possible at all
Primary productivity through photosynthesis, soil formation, nutrient cycling such as the carbon and nitrogen cycles
Regulating
The processes that shape and stabilise ecosystems
Climate regulation, flood regulation, water and air quality regulation, erosion control, disease and pest control
Provisioning
The goods humans take out of ecosystems
Food, fibres, fuel, fresh water, timber
Cultural
What people get from interacting with nature in culturally valuable ways
Recreation and tourism, education, health benefits, sense of place and national identity, employment
Regulating services in more detail
Service
How it works
Example
Water replenishment
Water in aquifers, rivers and lakes is naturally topped up, providing drinking water and supporting agriculture and industry
Mountain watersheds, where snowmelt and rainfall recharge rivers and groundwater
Flood and erosion protection
Ecosystems absorb excess rainfall and hold soil in place
Coastal mangroves in Southeast Asia protect shorelines and support fisheries; forest root networks stabilise hillsides
Pollution mitigation
Ecosystems filter pollutants out of water and soil
Reed bed buffer zones strip nutrients and pollutants from water; saltmarshes absorb pollution
Carbon sequestration
Atmospheric carbon dioxide is captured and stored, reducing greenhouse gases
Tropical rainforests such as the Amazon act as major carbon sinks; so do seagrass meadows
Four ways of looking at nature
Calling nature “capital” is itself a value judgement, and ESS wants you to notice that.
Economic value. Framing nature as capital highlights its financial worth, which encourages investment in preserving and using it sustainably, and helps policymakers and businesses see the financial benefit of healthy ecosystems.
Sustainable management. Talking about capital and income naturally leads to managing the stock, so societies are more likely to invest in conservation and keep a continuous flow of clean water, air and fertile soil.
Anthropocentrism. Taken to an extreme, it implies nature exists purely for human use, which can justify over-exploitation and degradation.
Intrinsic value. Critics argue this reduces nature’s inherent worth — the value ecosystems and species have regardless of any use to humans.
The examiner’s angle. The natural capital framing is a tool, not a truth. It makes conservation persuasive to economists, and at the same time risks implying that anything without a price tag has no worth. Saying both sides of that in an essay is exactly the kind of evaluation ESS rewards.
WORKED EXAMPLE
Distinguish between natural capital and natural income, using an example. [3]
Define both, then contrast them with one shared exampleNatural capital is the stock of natural resources available, whereas natural income is the flow of goods and services that stock produces.For a forest: the forest itself is the natural capital, and the timber harvested from it each year is the natural income.Stock versus flow — and income is sustainable only if use does not exceed regrowthUsing the same example for both halves makes the contrast obvious and saves you words.
WORKED EXAMPLE
Explain why non-renewable resources cannot provide sustainable natural income. [3]
Start from the definition of sustainableSustainable natural income requires the rate of use to be no greater than the rate of replacement.Fossil fuels and minerals formed over millions of years, so their replacement rate on human timescales is effectively zero.Any extraction therefore reduces the stock permanently, and once used they cannot be used again.They generate wealth once, so they are capital that yields no sustainable income“Geological timescales” is the phrase to use. It signals precision in one word.
💡 Exam tip
Learn capital = stock, income = flow. Almost every question here tests that one distinction.
Use the bank analogy explicitly. Examiners recognise it and it makes your reasoning obvious.
Know the four ecosystem service categories and one example of each.
Include the sustainability condition: use at or below the replacement rate.
For any “perspectives” question, mention both the economic argument for the framing and the intrinsic-value objection to it.
Name real services, not just categories. “Mangroves buffering storm surges” beats “regulating services”.
⚠️ Common mix-up
Swapping capital and income. The forest is capital; the timber is income.
Saying non-renewables are not natural capital. They are — they just yield no sustainable income.
Treating ecosystem services as optional extras. Supporting services are the basis of everything else.
Confusing provisioning (goods taken out) with regulating (processes kept running).
Assuming natural capital always means money. Aesthetic, cultural and intrinsic value all count.
Forgetting that the natural capital framing is itself anthropocentric, which is a valid criticism.
Up next: Putting a Value on Natural Capital — the nine kinds of value, and why the value of a resource keeps shifting.
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