Random Biome Generator

How this random biome generator works

Press Generate and you get a biome. Turn up the Number box for several at once, no repeats. Copy takes them.

Tropical Rainforest. Taiga. Chaparral. Tundra. Mangrove Forest. Coral Reef.

If you have ever been marked wrong on a biology test for saying there are six biomes when the answer sheet said five, this page is for you.

Nobody agrees how many biomes there are

Go and look. One textbook says five. Another says six. A museum poster says nine. A conservation atlas says fourteen.

None of them is wrong, and none of them is being careless. They are answering different questions at different levels of detail, and a biome is exactly the kind of thing where the level of detail is the answer.

Ask how many colours are in a rainbow. Newton said seven. A physicist says the spectrum is continuous. A printer says four. Everybody is right, and the argument is not about the rainbow.

A biome is not a box, it is a point on a graph

This is the idea that makes the whole disagreement dissolve.

Take two numbers for any patch of land: its average annual temperature and its average annual rainfall. Plot the patch as a dot on a graph with temperature along one axis and rainfall along the other. Do this for every patch of land on Earth.

What you get is not fifteen clusters. You get a continuous smear, hot and wet in one corner, cold and dry in another. Rainforest sits where it is warm and it pours. Desert sits where it is dry, at any temperature you like.

The boundaries between them are lines somebody drew across a smear. Draw more lines and you have more biomes. Draw fewer and you have fewer. The ecologist Robert Whittaker made exactly this diagram in the 1970s, and it is still the clearest thing on the subject.

So when a website tells you confidently that there are exactly nine biomes, what it is really telling you is where somebody chose to draw nine lines.

The map that carved the world into 14

If you want the number that working scientists actually use, it comes from a paper published in BioScience in November 2001, by David Olson, Eric Dinerstein and sixteen colleagues, called Terrestrial Ecoregions of the World.

They divided the land surface of the planet into 14 biomes and eight biogeographic realms. Then, nested inside those, they mapped 867 ecoregions, each one a distinct assemblage of species and communities.

Eight hundred and sixty-seven. That is what happens when you stop arguing about how many biomes there are and start drawing the map at the resolution the animals actually live at.

Their 14 are terrestrial only. No oceans, no coral reefs, no freshwater. That work was done separately, because the ocean does not divide the way the land does.

Some biomes are not measured the same way

Look at any biome list and you can see the seams.

Most of the entries are terrestrial. Two rainforests, taiga, deciduous forest, grassland, desert, tundra, chaparral, wetlands, mangrove. Those come from the temperature-and-rainfall graph, and they belong together.

Then there is Freshwater, and Marine, and Coral Reef. These are not land at all, and they are classified by an entirely different set of instruments: water depth, salinity, current, light. Putting them on the same list as chaparral is like putting kilometres and kilograms in the same column. Both are measurements. Neither is the other.

And Alpine is stranger still. Alpine conditions are what you get when you climb a mountain: cold, thin air, treeless above a certain height. That is tundra by another name, produced by altitude rather than latitude. Some ecologists give it its own category. Some refuse.

The school version of the biome list is a perfectly good thing to be. But now you know why your teacher and your textbook disagreed, and it was never about the plants.

Biome, ecosystem, habitat: they are not the same word

These get used interchangeably and they should not be.

• A habitat is where one species lives. The habitat of a barn owl is farmland with old buildings in it.
• An ecosystem is a community of living things plus the physical setting they interact with, at any scale. A rock pool is an ecosystem. So is a forest.
• A biome is the largest of the three: a type of ecosystem that recurs all over the planet wherever the climate repeats. The tropical rainforests of the Amazon, the Congo and Borneo are on three continents and share almost no species, and they are one biome.

That last point is the whole concept. A biome is not a place. It is a shape that life takes when the temperature and the rainfall come out a certain way, and it takes that shape independently, again and again, out of whatever species happen to be nearby.

Ways people actually use this

• Biology homework and revision. Generate one, then write down its temperature range, its rainfall, and two species. That is the whole topic in three lines.
• Teaching. Generate five and ask the class which two are not really in the same category. Somebody will spot Coral Reef.
• Worldbuilding. Pick a biome first and a landscape second. Deciding it is chaparral tells you the weather, the plants, the fire risk and the smell.
• Game and level design. A biome palette of this size is roughly what most open-world games use, and for the same reason: it feels varied without feeling arbitrary.
• Deciding what to read about. Most people can describe three biomes and have opinions about one.

Getting more out of the filters

• Type forest into Contains and watch how much of the world is trees.
• Type biome into Contains. The entries that come back are the ones where somebody felt the need to append the word, and they are, not coincidentally, the ones that sit least comfortably on the list.
• Type Temperate or Tropical to sort by latitude rather than by vegetation.
• This is a short list, so Starts with is a blunt instrument. Use Contains.

Questions people ask

How many biomes are there?

There is no single correct number. The most widely used scientific map divides the land into 14. School curricula commonly teach five or six. The number depends entirely on how finely you choose to cut a continuous gradient.

What is the largest biome on Earth?

If you count the oceans, the marine biome, by an enormous margin. If you restrict yourself to land, the taiga, the belt of coniferous forest that circles the northern hemisphere.

Is Antarctica a desert biome?

Yes. Deserts are defined by how little precipitation falls, not by heat, and Antarctica is the largest desert on the planet. It is also commonly filed under polar ice, which is a good illustration of why these categories leak.

What is the difference between a biome and an ecosystem?

Scale, mostly. An ecosystem can be a pond. A biome is a type of ecosystem that shows up all over the world wherever the climate repeats itself. All tropical rainforests are one biome and thousands of separate ecosystems.

Is alpine a real biome?

It appears in many lists. Some ecologists treat it as tundra caused by altitude rather than latitude. The disagreement is genuine and it is about definitions rather than about mountains.

References

1. Olson and others, Terrestrial Ecoregions of the World, BioScience 51(11)
2. Terrestrial Ecoregions of the World, dataset
3. Desert, National Geographic Education