Biome



According to Wikipedia, biomes are climatically and geographically defined as similar climatic conditions on the Earth, such as communities of plants, animals, and soil organisms, and are often referred to as ecosystems.

In Minecraft, from the Halloween Update onwards, this means different areas with different heights, temperatures, humidity ratings and foliage colors are created.

Before the Halloween update, when a map was generated it got a theme of either Snowy or Grassy. After this update, a single world includes all themes in a logical fashion determined by the biomes graph.

A demonstration can be viewed here.

Pre-Update Saves
Worlds generated prior to the update remained unchanged save for alterration of the grass color. This "biome" is called Shrubland. However, any new chunks generated (by the player moving outside of the pre-biome world's generated bounds) do generate biomes, just as The Nether is generated when you first enter it using a portal.

Biome Types


Biome types may be easily distinguished by the differentiating grass and leaf colors in conjunction with the kind of blocks present, like cacti in deserts and pine trees in tundras. They are randomly created during the generation of the world and are affected by the seeds.

There were 13 biome types in 1.7; 10 in the overworld, 1 in the nether, and 2 unused ones that are in the code but aren't encountered in normal play.

A fourteenth, unnamed biome, which include the upcoming huge mushrooms, was added to the overworld in 1.8, along with a true swampland biome, mountain biome and ocean biome. Biomes are often separated by a river. Notch has stated that a new rainforest biome (or changes to the current one), snowy biomes, as well as volcanoes (either as a biome or natural feature) are a possibility, but they have probably not been added yet.

Biome Screen-shots
The above screenshots were made by editing code in Minecraft's java files, creating worlds made up of only one Biome. This was done consecutively with each Biome type and their screen-shots are collated here. The original topic is on the Minecraft forum, here.



Difficulty
It can be difficult to play if one starts in the middle of a biome with no trees, such as the desert, ocean, savanna, or tundra.

Trivia

 * Notch has added new biomes in 1.8, including a Swamp Biome, a Mountain Biome (called "Extreme Hills" in the code), an Ocean biome, and a Plains Biome.
 * Biomes have also been expanded in size in the 1.8 update.

Rumors
It appears that desert islands generate in the ocean biome, where animals cannot spawn, sometimes the island spawn with no trees so that players will have to delete the world and start again, or swim. This is not quite as bad of a problem if one starts the map in creative mode so one can fly, make a boat, or plant trees. It is still undetermined whether it is a bug or not (Notch didn't say it was a bug, but the community seems to think it is)