Depletion of natural resources happens when the rate at which resources are used becomes greater than the rate at which they are replaced. That one sentence is the whole topic. Everything that follows is a list of the reasons why that happens.
Look carefully at that definition. It does not say that using a resource destroys it. Nepal has used its forests for as long as there have been villages in Nepal, and the forests were still there. Depletion is not about use. It is about two speeds that have stopped matching. Think back to the tank with a tap. Nothing goes wrong while you draw less than the tap gives. Everything goes wrong the moment you draw more, and the tank does not have to be treated any differently for that to happen.
Seven causes, but really only two
The textbook gives seven causes of depletion. Learning seven separate items is miserable and they fall out of your head within a week. They are far easier to hold if you notice that they are not seven independent things. Depletion needs only two things to go wrong, and each of the seven belongs to one of them.
| What has gone wrong | Which of the seven causes belong here | Why it produces depletion |
|---|---|---|
| We are taking more | Growing population and unbalanced migration; excessive consumption of resources; industrial and technological development | More people, each of them wanting more things, and factories that turn raw material into products faster than ever before. The demand side of the equation keeps rising. |
| The source itself is being damaged | Deforestation and forest fire; unsystematic farming; pollution; natural disaster | These do not just remove a resource, they weaken the thing that makes it. A burnt forest, a poisoned river or a stripped hillside produces less next year than it did this year. |
Now you can see why the two halves are worse together than either would be alone. Rising demand pushing against a weakened source is a much faster collapse than either one on its own. A hillside that has lost its soil cannot grow trees quickly, and it is being asked to supply more firewood than ever.
A forest fire destroys more than the trees
Ask what a fire on a hillside destroys and most people answer with the trees, because those are what you can see burning. The trees are the smallest part of the loss. The fire also takes the birds, insects and small animals that lived in them, together with all the nests and eggs of that season. It takes the dead leaves on the ground, which were about to become soil. It bakes the top layer of the soil itself so that it will not absorb water properly for a long time afterwards. And it fills the air with smoke, which is pollution added to everything else.
Then the first heavy rain arrives on a slope with nothing left to hold it, and the soil goes down into the river. That is the loss that will not be repaired, because soil takes about a hundred years to build one centimetre. The trees might return in thirty years if the ground can still support them. Fires are started both by people, often by a spark left near dry grass, and by nature. Both do the same damage.
The fertiliser loop, which runs downhill
The textbook mentions in one sentence that chemical fertiliser and pesticide are used heavily to get large harvests from small areas of farmland, and that this is reducing the fertility of the soil. That sentence deserves more attention than it usually gets, because it describes a loop, and a loop is a very different thing from a straight line.
| Step | What happens |
|---|---|
| 1 | There is not much farmland, and there are more mouths to feed each year, so more must be grown on the same fields. |
| 2 | Heavy chemical fertiliser and pesticide are used to force a bigger harvest out of the same soil. |
| 3 | The harvest is bigger, and that year the plan works, which is why people go on doing it. |
| 4 | The chemicals kill many of the small living things in the soil that were quietly making it fertile, and the natural fertility of the soil falls. |
| 5 | Weaker soil gives a smaller harvest next year, so even more fertiliser is needed to reach the same amount. Back to step two, but worse. |
A loop like this is dangerous precisely because each single step looks sensible. Nobody in that story makes a foolish decision. A farmer with a small field and a family to feed does exactly what any of us would do, which is to buy fertiliser and grow more food this year. The trap is that solving the problem this year makes the problem slightly worse next year. This is why the answer, when it comes in the next topic, is not to tell farmers to try harder. It is compost, and it is biological pest control, which break the loop instead of tightening it.
A town uses up resources it never sees
Urbanisation is one of the causes on the list, and it works in a way worth thinking about carefully. Look at a busy street. There is no forest on it, no field and no mine. Yet every building on it is made of stone, sand, timber and metal, every shop sells food that was grown somewhere, and every vehicle burns fuel that was pumped out of the ground on another continent.
So a town depletes resources at a distance. The person living there sees none of it, which is the difficult part. A villager who cuts a tree can see the stump. Somebody who buys a wooden window frame in a city shop sees a window frame. Both have used the same tree, but only one of them will ever look at the hillside it came from. This is the same idea as the watershed in the last topic, turned round. Water carries decisions downhill, and trade carries them out of sight.
It is very easy to turn this topic into blame, and blame is both unkind and wrong. The person cutting a tree on a ridge usually needs to cook a meal and has no other fuel. The farmer buying fertiliser needs to feed a family this year, not in twenty years. The family that moved to town moved because there was work there. Not one of those is a foolish or a wicked decision, and telling people to simply stop has never worked anywhere. The honest description of the problem is that the cost of a decision is usually paid later, and usually by somebody else. That is why solving it needs shared rules and better options, and not lectures.
Why depletion is so hard to notice
Here is the part of this topic that is not in the textbook and is worth more than the list of causes. Depletion is difficult to see, not because it is hidden but because of how memory works.
Each of us treats whatever we grew up with as normal. Your grandmother remembers a thick forest on the ridge and a stream that ran all year, and to her that is what a hillside is supposed to look like. Your father grew up with a thinner forest and a stream that went low in Chaitra, and to him that is normal, so he sees nothing alarming. You know a bare ridge and a stream that stops, and unless somebody tells you otherwise, that is simply what a hillside is. Your own children will start from something poorer again and call that normal in their turn.
Nobody in that story is lying and nobody is careless. Each generation is measuring change against a different starting point, so a very large loss can happen across a hundred years while every single person alive feels that not much has changed. This is why the project work in this topic asks you to interview your parents and grandparents. You are not collecting a story. You are collecting the only measurement anybody has of what has been lost, because the change happened too slowly for any one person to see it.
The list includes natural disaster, and that belongs there. A volcano can burn mineral fuel and forest, a landslide can bury a field for good, and a flood can strip a riverbank. Depletion is not only something people do. But there is an important difference between the two kinds. We cannot prevent a volcano and we can plan for it, whereas the causes on the human side can be reduced by decisions we actually control. That is what the next topic is about.
The full lesson is waiting for you
Create a free account to unlock activities, practice tests, presentations and videos - and to track your progress and confidence score for every subject.
The full lesson is waiting for you
Create a free account to unlock activities, practice tests, presentations and videos - and to track your progress and confidence score for every subject.