Biodiversity means the variety of living things found on the Earth. It covers the different kinds of plants and animals in a place, the differences between them, and the way they depend on one another. The environment means everything that surrounds a living thing, the air, the water, the soil, the temperature, and every other living thing near it.
These two words are locked together, and the whole of this unit follows from that. Change the environment of a place and the living things in it change too. That is not a warning, it is simply how nature works. A pond that dries up loses its fish, and a hill that loses its trees loses the birds that nested in them.
Start with the question the book asks
Are the yak and the rhododendron found in the Terai, the hills and the high mountains alike? Everybody knows the answer is no. The yak lives high up in the cold, and the lali gurans grows on the hills. Neither of them is found in the flat heat of the Terai. The useful question is not what lives where. It is why the country cannot simply mix them up.
A yak carries a heavy coat, a thick layer of fat, and lungs and blood built for air that holds very little oxygen. Every one of those is a gift in the high pastures and a burden in Jhapa. A yak taken down to the Terai would not die of cold. It would die of heat, wearing a coat it cannot take off. The rhododendron has the same story told in a quieter way. It needs cool air, damp acid hill soil, and mist, and it simply fails where the ground bakes.
So a living thing is not scattered at random. It is found where its body happens to suit the surroundings. Turn that sentence round and you have the idea this whole topic rests on: different surroundings produce different living things. Many different surroundings therefore produce many different living things, and that is exactly what biodiversity is.
Why so much life fits into so small a country
Nepal is a small country. Its land is a little over one hundred and forty seven thousand square kilometres, which is around one thousandth of all the land on the Earth. By any fair share, it ought to hold about one thousandth of the world's plants and animals. It holds a great deal more than that. Nepal has more kinds of bird recorded in it than the whole of Europe.
The reason is one number. From the lowest point in the Terai, about sixty metres above the sea, to the top of Sagarmatha at 8,848 metres, is a rise of nearly nine kilometres straight up. And that rise happens across a country only about two hundred kilometres wide.
Here is why that matters so much. Climbing makes the air colder, at roughly six degrees for every thousand metres you go up. Travelling north also makes the air colder, but you have to go about a thousand kilometres to lose the same six degrees. So climbing one kilometre does the same work as travelling a thousand kilometres towards the pole. Walking from Chitwan to the Khumbu takes you through the same range of climates you would meet walking from the tropics to the edge of the Arctic, except that the whole journey fits inside one small country.
Nepal has stacked its climates upwards instead of spreading them sideways. Sal forest, then oak and pine, then rhododendron and fir, then bare alpine grass, then rock and permanent snow. Each of those bands is a different environment, and each one has filled with the living things that suit it. That is the answer to the question of how so much variety fits into so small a place.
More animals is not the same thing as more biodiversity. A hillside planted with five hundred pine trees, all of one kind, has a great many trees and very little biodiversity. A patch of natural forest half that size with forty different kinds of tree in it has far more. Biodiversity counts how many different kinds there are, not how many individuals. Keep that straight and half the questions on this topic answer themselves.
Variety hides at three different sizes
Most people picture biodiversity as a list of animals. It is wider than that, and it is worth seeing all three sizes it comes in.
| Level | What varies | A Nepali example |
|---|---|---|
| Between kinds | How many different species share a place | A tiger, a rhino, a deer, a peacock and a python all living in the same Terai forest |
| Within one kind | How much difference there is between individuals of the same species | The many local varieties of rice grown in Nepal, some short, some tall, some able to ripen in a cool short Jumla summer |
| Between places | How many different kinds of habitat the country has | Sal forest, grassland, river, wetland, oak forest, alpine meadow and snowfield, all within one country |
The middle row is the one almost nobody thinks about, and for a farming country it is the most valuable of the three. Suppose every field in Nepal were planted with one improved variety of rice because it gives the highest yield. That sounds sensible until a disease arrives that this one variety cannot resist. Then every field fails at once, and there is nothing left to plant instead. The old local varieties are the spare answers. Keeping them is not sentimental, it is sensible.
Why biodiversity matters
It is easy to give this answer as a list and forget it by the next lesson. It is easier to remember if you notice that every item on the list is a job somebody else is doing for us, without being asked and without being paid.
| What we get | Who is actually doing the work |
|---|---|
| Food | Every single thing we eat was once a living thing. There is no third option. |
| Fruit and seed | Bees, butterflies, moths and birds carrying pollen from flower to flower. Without them most crops set no fruit at all. |
| Soil | Earthworms, insects, fungi and bacteria breaking dead material down into something a root can use. You met the earthworms in Unit 3. |
| Clean air and water | Green plants taking in carbon dioxide and giving out oxygen, and forests holding soil in place so that rivers run clear. |
| Medicine | A very large number of medicines began as a plant. Yarsagumba, chiraito and many hill herbs are used and traded in Nepal today. |
| Safety from shocks | Variety itself. A mixed forest survives a disease that would wipe out a plantation of one tree, because not everything in it is vulnerable to the same thing. |
Biodiversity was built slowly. The kinds of living thing in a Nepali forest took millions of years to arrive at their present form. It can be lost quickly. A forest that took a thousand years to grow can be cut in a single season. Everything else in Unit 4 is a version of that same mismatch between two speeds, the speed at which nature makes something and the speed at which we use it up. Watch for it in every topic that follows.
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Biodiversity means the variety of living things in a place, the differences between them, and how they depend on one another.
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