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, i.e. cacti in desert, etc. Biomes are randomly created during the generation of the world and they are affected by the seeds.

There are 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 will include the upcoming huge mushrooms, will be added to the overworld in 1.8.

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
Starting in a biome with almost no trees, like desert or plains, can prove much more difficult than starting in a biome like a Rain Forest because the player won't have as many trees to create a pick or shelter. Even though one can travel to another biome at the very start of the game if the biome is unpleasant, the player would be wasting precious time that could otherwise be spent preparing for nightfall.

Remaining Work
Remaining work on biomes include variable elevations in certain biomes (flat elevation in desert biomes, etc.) in addition to improving the border between arctic and tropical biomes.

Trivia

 * Notch is going to add new biomes in 1.8, one featuring Huge mushrooms. Others include a Swamp Biome, a Mountain Biome, and Oceans, which are now a biome of their own.
 * Biomes will be expanded in the 1.8 update.